Flexible packaging bag testing items and reference standards

There are many kinds of bags, such as clothing bags, food bags, cosmetics bags, hardware bags, gift bags and so on. Occupying an important part of the product packaging bag, in the end how to detect, is there a reference standard?

Today, let's share the packaging bag inspection items and reference standards.

I. Basic testing items

1. Appearance inspection

The main purpose of appearance testing is to identify the appearance defects of samples, which generally adopts artificial sensory recognition, so the evaluation of product appearance quality is subjective to a certain extent. In this process, the author suggests that attention should be paid to the following points.

Certain conditions must be set up for the evaluation of appearance quality. For example, the environmental conditions, assessment methods and assessment personnel's vision, touch, practical experience, technical level and other factors should be the same as far as possible when assessing the appearance quality of flexible packaging.

The appearance quality is mostly assessed by the inspection personnel's sensory inspection, so it is necessary to give a clear definition of the evaluation terms of appearance quality. For example, the use of terms such as "must" or "must not", "should" or "should not", "available" or "not allowed", "allowed" or "should not" should be clearly specified to reduce the subjectivity of the evaluation.

GB/T 10004-2008 provides for visual measurement under natural light and measurement with a measuring tool with an accuracy of no less than 0.5mm, mainly to check whether the surface of the sample has wrinkles, bubbles, scratches, perforations, adhesiveness, foreign bodies, stratification, dirt and so on.

2, printing quality inspection

Packaging printing pattern for product publicity, display effect is not negligible. The laboratory uses densitometer, spectrophotometer and other test equipment to objectively evaluate the printing quality of flexible packaging. If necessary, the standard sample can be established as a physical reference for the printing quality, so that the detection personnel have a clear assessment basis.

As for the printing quality, gravure products should be tested according to the provisions of GB/T7707-2008 Gravure Decorative Prints, flexo products should be tested according to the provisions of GB/T 17497-2012 Flexible Decorative Prints. The barcode printing of commodity shall be tested in accordance with the provisions of GB/T 18348-2008 "Inspection of the Printing Quality of Barcode Symbols for Commodity", and the other one-dimensional barcode shall be tested in accordance with the provisions of GB/T 14258-2003 "Inspection of the Printing Quality of Barcode Symbols for Information Technology Automatic Identification and Data Acquisition Technology".

The printing performance of plastic film can be preliminatively judged by the measurement of its surface tension. The large surface tension value indicates that its printing performance is better (generally speaking, the surface tension of the film is greater than 38mN/m, its printing performance is enough to meet the requirements of use).

3. Size deviation detection

The main dimensions of flexible packaging are thickness, length and width. Among them, thickness is the basic guarantee of the performance of flexible packaging, is one of the important factors affecting its mechanical properties, barrier properties, but also the control of product quality and cost needs to be considered. The factors leading to the size deviation of flexible packaging products are multiple and complex, including temperature and humidity of the external environment, equipment conditions, process factors, as well as molecular crystallization, orientation and internal stress changes inside the film. Therefore, the homogeneity of film materials should be considered in the selection of materials, and the effect of shrinkage rate of film materials on the dimensional accuracy of flexible packaging products should be emphasized. In printing and post-press processing, special attention should be paid to the sensitivity of film materials to ambient temperature and humidity.

The length and width deviation of flexible packaging shall be tested in accordance with the provisions of GB/T 6673-2001 "Determination of the Length and Width of Plastic Film and Sheet", and the thickness deviation shall be tested in accordance with the provisions of GB/T 6672-2001 "Mechanical Measurement Method for the determination of the Thickness of Plastic Film and Sheet". The heat sealing width of flexible packaging and the distance between the sealing and the bag edge shall be measured with a measuring tool with a precision of not less than 0.5mm.

Second, physical and chemical performance detection

Flexible packaging made of pure resin film has good hygiene and can be directly used in food packaging without causing any harm to consumers. However, in order to improve the physical and mechanical properties, chemical stability and processing properties of the film, a certain amount of plasticizer, stabilizer, antioxidant, filler, colorant, lubricant, foaming agent and other additives are often needed in the process of blowing film in the resin. In addition, a large number of organic solvents, such as toluene, xylene, ethyl acetate, butanone, butyl acetate, ethanol and isopropyl alcohol, are used in the printing, composite and coating processes during the production of flexible packaging. These solvents will be more or less residual in the packaging materials. When the residual solvent contained in them is higher than the safe value, it will cause harm to the human body or the environment. Therefore, in order to meet the basic requirements of food packaging, it is particularly important to test the following physical and chemical properties of flexible packaging.

1. Outgoing object detection

According to the sanitary performance analysis method of plastic film, the expulsions of samples were detected by simulating different environments. The specific test operation was as follows: multiple groups of samples were immersed in ethanol aqueous solution, acetic acid aqueous solution, n-hexane and water at a certain proportion and temperature for a certain period of time to obtain the soaking solution. These detection solutions simulated the liquid environment of alcohol, acid, oil and water in contact with food flexible packaging, and finally assessed the sanitary performance of flexible packaging by testing the leaching solution, potassium permanganate consumption, heavy metal content and so on.

2. Detection of sensory indicators

There are two methods to detect the sensory indicators of the flexible packaging film. The relatively simple and intuitive method is to open the packing box containing the flexible packaging film and smell whether there is an odor. The objective method is to take a film with the size of 10cm×10cm, cut it into strips, put it into a conical bottle, add 150ml distilled water, cover the bottle and seal the conical bottle, put it in the oven or water bath at 60℃ for 30min, take it out, open the bottle cap, smell the smell of water vapor, and judge whether there is a bad smell.

3. Detection of residual solvent

Residual solvent refers to volatile organic compounds used in flexible packaging production but not completely removed during the process. The detection of residual solvent by gas chromatograph can not only help flexible packaging enterprises to have an overall understanding of the safety of various additives and solvents used in printing and compounding (whether they contain components that do not meet the requirements of use or whether the content of a certain component exceeds the standard). It can also effectively solve the problem of odor caused by residual solvent in some packaging materials (can be detected by sensory index detection), so as to better control the health and safety of flexible packaging.

The size of residual solvent in flexible packaging composite film is related to the type of solvent used, water content, properties of film substrate, properties of adhesive, printing area of ink, drying temperature, air volume, production speed and other factors. At present, more toxic organic solvents (such as benzene) do great harm to the human body, so at present printing ink and paint are in benzene-free, water-based and solvent-free transformation, and most adhesives have changed from fat soluble (with lipid solvent) to alcohol soluble, water-soluble and solvent-free.

Three, food packaging bag inspection items

The main indicators for the detection and control of food packaging include: barrier performance, physical and mechanical performance, health performance, thickness, solvent residue, cooking resistance, sealing performance, bottle cap torque, headspace analysis, printing quality, roll sealing performance, etc.

1, the barrier of food packaging materials

The main cause of food spoilage is the growth and reproduction of microorganisms. Oxygen and water vapor in the environment can affect the quality of food through packaging materials. Therefore, the transmittance of oxygen and water vapor of packaging materials has a very close relationship with its shelf life. Another major cause of food spoilage is oxidation of oil and other components. Therefore, food packaging should have a good barrier effect.

Oxygen permeability test standards are: ASTM D3985, ASTM F2622, ASTM F1927, ASTM F1307, ISO 15105-2, GB/T 19789.

The moisture permeability test standards are: ISO 15106-3, DIN 53122-2, GB/T 21529.

2. Physical and mechanical properties of food packaging materials

1. Tensile strength and breaking elongation

The most basic function of food packaging is to serve as a container for carrying food, which requires the material to have a certain strength to prevent accidental breakage. The tensile strength and elongation at break of packaging materials are the most basic performance requirements. We can use universal material testing machine to carry out constant speed tensile test to get the tensile strength and elongation at break.

The commonly used test standard is GB/T 13022.

Step 2: Thickness

The thickness and width of packing materials must meet certain requirements. The thickness of the film or sheet can be measured within a certain standard pressure range using a precision thickness gauge.

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

3. Heat sealing performance

Heat sealing performance directly affects the overall physical performance of food packaging. Select appropriate heat sealing parameters (temperature, pressure, time) for heat sealing of packaging materials to achieve the best heat sealing strength. The heat sealing effect can be used to test the heat sealing strength of the seal using the universal material testing machine.

Test standards are ASTM F2029, QB/T 2358.

4. Friction coefficient

Friction coefficient is a physical quantity used to characterize the resistance of flexible plastic packaging materials when they contact with the material itself or other objects such as packaging machinery and have relative motion. If the friction coefficient of packaging materials is too large or too small, it will have an adverse effect on the production process. For example, if the friction coefficient is too large and the packaging materials are uncomfortable, it will require a larger pulling force to make the reel rotate to pull and reel the bags, which not only increases energy consumption and reduces production efficiency, but also may cause the stretching deformation of packaging materials. It affects its barrier properties, impact resistance, puncture resistance and other physical and mechanical properties. The friction coefficient is small, it is easy to lead to the material in the process of use, skid, deviation, stacking instability, wrong edge and other problems. Therefore, it is of great significance to control the friction coefficient of flexible plastic packaging film in the appropriate range to improve its convenience of use.

The common test standard is GB/T 10006.

5. Tear degree

The test to measure tear strength actually mainly measures the energy required for tear proliferation. The main measurement methods include trouser method and Elemendorf tear method, and the Elemendorf tear method is preferred for samples with constant radius. For consumers, the tear resistance of the material is a major indicator of whether the packaging is easy to open.

Commonly used test standards are ASTM D1922, ISO 6383/2.

6. Roughness of printing surface

In the packaging of finished products, will be printed with a clear pattern and logo. But we will also find in some materials (especially paper or paper film) packaging printing blur, some is related to the quality of ink, color process, but a large part is related to the roughness of the printing surface. Because the general printing ink layer is only dozens of microns thick, if the printing surface roughness is too large, then the printing ink layer will be embedded into the deep layer of the material, so that the surface of the ink layer thickness is not uniform, will produce paste white phenomenon. We should test the roughness of the printing surface, and measure the surface roughness by simulating the conditions of the printing press. We can investigate the influence of the smoothness of the material on the printability from the microscopic point of view. According to the results of the roughness, we can adjust the thickness of the ink layer according to 2~2.5 times.

Commonly used test standards are ISO 8791/4, TAPPI T555.

7. Ink friction

Food packaging uses a lot of ink in the printing process. Sometimes when we are in contact with food packaging, we will encounter the situation of ink dirty hands, or find the phenomenon of ink shedding, which will seriously affect consumers' desire to buy. This requires the ink friction resistance test, the use of standard ballast to make two kinds of materials according to the set speed friction, to check the solid performance of printing ink. According to the different conditions of actual use, it can be divided into dry friction, wet friction, wet transfer, wet smearing and thermal friction.

3. Sealing and air-adjusting packaging of food packaging materials

The sealing performance refers to the reliability of the packaging seal. Through this test, the integrity of the packaging seal of the entire product can be ensured to prevent leakage, pollution, deterioration and other problems caused by poor product sealing performance. There are two test methods: positive pressure and negative pressure.

More and more packaging is using air-conditioned packaging to increase shelf life, such as milk powder, coffee, crisps and cheese are packed with nitrogen and carbon dioxide. In order to test the actual inflation effect, the headspace analyzer is used to analyze the actual gas composition in the package.

Related instruments: oxygen permeability meter, moisture permeability meter, heat sealing meter, thickness meter, peel strength meter, universal material testing machine, friction coefficient meter, tear meter, peel tester, printed surface roughness meter, leak detector, sealing tester, headspace analyzer.