Test method I for properties of plastic film of th

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Test methods for the properties of plastic films of packaging materials (I)

in plastic packaging materials, various plastic films and composite plastic films have different physical, mechanical, heat-resistant and sanitary properties. People choose appropriate materials to use according to different needs of packaging. How to evaluate the performance of packaging materials? There are many test methods at home and abroad. We should give priority to those scientific, simple and small measurement error methods. Give priority to ISO international standards, international advanced organization standards, such as ASTM, TAPPI, etc., and China's national standards and industry standards, such as BB/T standards, QB/T standards, Hb/T standards, etc

the author has used some detection methods in his inspection work. Here is a brief introduction to you

specification and appearance

plastic film is used as packaging material, and its size and specification should meet the needs of the contents. The appearance of some films is closely related to the shelf effect, and the appearance problems directly affect the sales of goods. Thickness is one of the factors that affect the mechanical properties and barrier properties, so we need to find the optimal indicators in terms of quality and cost. Therefore, these indicators will be specified in the requirements of each product standard, and the corresponding requirements and detection methods generally include:

1 Thickness measurement

GB/t6672-2001 "mechanical measurement method for the determination of thickness of plastic films and sheets" this non equivalent adopts iso4593:1993 "plastics - films and sheets - thickness determination - mechanical measurement method". It is applicable to the measurement of the thickness of thin films and thin sheets, which adopts the mechanical method, that is, the contact method. The measurement result refers to the result of the material measured between two measurement planes. The load applied to the test specimen by the measuring face shall be between 0.5N and 1.0N. This method is not applicable to the testing of embossed materials

2. Length and width

GB/T 6673-2001 "determination of length and width of plastic films and sheets" is not equivalent to the international standard ISO 4592:1992 "plastics - films and sheets - Determination of length and width". This standard specifies the reference measurement method for the length and width of coiled materials and sheets

the size of plastic materials is greatly affected by ambient temperature, and the operating tension during unwinding will also cause the size change of materials. Different accuracy of measuring instruments will also lead to different measurement results. Therefore, we must pay attention to every detail in the measurement, so that the measurement result is close to the true value

the standard can use the traditional thermoplastic molding and processing methods such as injection, extrusion and molding, which stipulate that the coil should be opened with the minimum tension before measurement, and the length of the coil should be no more than 5m, and no more than 20 layers should be stacked layer by layer as the tested sample. In this state, it should be maintained for a certain time, and the measurement should be carried out after the size is stable

3. Appearance

the appearance inspection of plastic film is generally carried out by visual inspection under natural light. Appearance defects are specified in GB/T 2035 terms and definitions of plastics. Generally, the size of defects needs to be measured with general measuring tools, such as steel ruler, vernier caliper, etc

physical and mechanical properties

1 Mechanical properties of plastics - Tensile Properties

the tensile property tests of plastics include tensile strength, tensile breaking stress, tensile yield stress, elongation at break and other tests

there are several national standards for plastic tensile property test methods, which are applicable to different plastic tensile property tests

gb/for example, Yamaguchi University in Japan and Tongji University in Shanghai have established corresponding contacts with kostron. T 1040-1992 "test method for tensile properties of plastics" is generally applicable to thermoplastic and thermosetting materials, including filled and fiber-reinforced plastic materials and plastic products. It is applicable to materials with thickness lower than 1mm

GB/t13022-1991 "test method for tensile properties of plastic films" is equivalent to the international standard iso1184-1983 "determination of tensile properties of plastic films". It is applicable to plastic film and sheet with thickness less than 1mm. This method is not applicable to the tensile property test of reinforced film, microporous sheet and microporous film

the above two standards specify several samples with different shapes and tensile speed, which can be selected according to different product conditions. For example, materials with large elongation should not use too wide samples; For hard and semi-hard materials, lower speed can be selected for tensile test, while for soft materials, higher speed can be selected for tensile test, etc

2. Tear property

tear property is generally used to evaluate the tear resistance of plastic films, sheets and other similar plastic materials

gb/T 16578-1996 "test method for tear resistance of plastic films and sheets Trouser tear method" is equivalent to the international standard ISO 6383-1:1983 "plastics - films and sheets - Determination of tear resistance part 1; Trouser tear method" which is applicable to soft films or sheets with a thickness of less than 1mm. The test method is to cut a certain length of cut in the middle of the rectangular sample in advance, like a pair of pants. Hence the name of pants tearing method. Then, at a constant tearing speed, the force required to tear the crack down along the notch. The instrument used is the same as the non pendulum testing machine in the tensile tester

qb/t1130 - 1991 test method for right angle tearing properties of plastics is applicable to films, sheets and other similar plastic materials. The test method is to cut the sample into a sample with 900 right angle mouth, clamp the sample on the fixture of the tensile testing machine, and the stress method of the sample is perpendicular to the direction of the sample. Tension is carried out at a certain speed, and the test result takes the maximum force in the tearing process as the right angle tearing load. If the sample is too thin, multiple samples can be stacked for testing. However, the results of monolithic and laminated specimens are not comparable. Laminated specimens are not suitable for foam sheets

gb/t11999-1989 "test method for tear resistance of plastic films and sheets - ellemendorf method" is equivalent to the international standard ISO 6383/2-1983 "determination of tear resistance of plastic films and sheets - Part 2: ellemendorf method". It is applicable to soft plastic films, composite films and sheets, but not to PVC, nylon and other hard materials. The principle is to make the specimen with the specified notch bear the tearing force generated by the energy stored by the pendulum of the specified size, and calculate the tear resistance of the specimen with the energy consumed by tearing the specimen

3. Friction coefficient

static friction coefficient refers to the ratio of the maximum resistance of two contact surfaces at the beginning of relative movement to the normal force vertically applied to the two contact surfaces

dynamic friction coefficient refers to the ratio of the resistance when two contact surfaces move relatively at a certain speed to the normal force vertically applied to the two contact surfaces

the test is composed of a horizontal test bench, a sliding block, a force measuring system and a driving mechanism that moves the two test surfaces on the horizontal test bench relatively

the test passes by placing the two test surfaces flat together, making the two surfaces move relatively under a certain contact pressure, and measuring the force when the specimen starts to move relatively and the force when it moves at a constant speed. The friction coefficient of the sample is calculated

static (dynamic) friction coefficient = at present, the commonly used method standard is GB/t10006-1988 "determination of friction coefficient of plastic film and sheet", which is not equivalent to the international standard ISO 8295-1986 "determination of friction coefficient of plastic film and sheet"

4. Heat sealing strength

plastic film is used as packaging material, and the packaging is often sealed by heat sealing method. The quality of heat sealing is very important to achieve good sealing. At present, the commonly used instrument and equipment in the laboratory is "thermal gradiometer", which is a heat sealing test equipment that can set different temperatures, pressures and times. It can be used to test the best sealing effect of a material under certain conditions, For sealing quality, QB/T 2358-1998 "test method for heat sealing strength of plastic film packaging bags" is a commonly used method standard. This standard is applicable to the determination of heat sealing strength of various plastic film packaging bags

the test is to clamp the two ends of the strip sample on the two clamps of the tensile test, stretch, and destroy the maximum force value of the sealing part of the sample, that is, the force value of heat sealing. The result must be expressed in the force value used by the sample per unit length, that is, the heat sealing strength. The force electronic tensile testing machine used is represented by N/m in addition to the power interface

5. Peeling force

composite films are made of different single films by dry compounding or coextrusion. The good ring of the composite directly affects the strength, barrier property and future service life of the composite film. Therefore, it is important to test the peeling force of the composite layer before selecting packaging materials

GB/t8808-1988 "peeling test method for soft composite plastic materials" is to clamp the two ends of the pre separation layer of the tested film that has been peeled off in advance on the tensile testing machine to test the force required when peeling off the material between layers

6. Impact resistance

GB/t8809-1988 plastic film pendulum impact test method is applicable to all kinds of plastic film pendulum impact test. The test is to measure the energy consumed by the impact of a semicircular pendulum through the plastic film at a certain speed

gb/t9639-1988 "test method for impact resistance of plastic films and sheets free falling standard method" is applicable to plastic films and sheets with a thickness of less than 1mm. The test is to measure the energy when 50% of the plastic film and sheet samples are damaged under the given free falling impact. Expressed by impact damage mass

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