Tear of paper refers to the force required to tear a pre-notched specimen to a certain length, expressed in kilotons (tons). The degree of paper tear has a certain relationship with the folding degree of the paper. The degree of tear depends mainly on the length of the fiber and its internal tissue direction and the strength of the fiber itself, but also on the strength and interweaving of the paper. Generally, the force to tear the paper is much less than the force required to tear the paper. The work done when tearing consists of two parts, the work done by pulling the fiber apart and the work done by breaking the fiber. Paper made from unbeaten pulp has nearly all of its tearing force used to overcome the frictional resistance when pulling the fiber. The actual fiber did not break because of the small contact area between the fibers, the small frictional resistance, and the low tear resistance. After a slight beating, the binding force between the fibers increases, so that the friction resistance to pull the fibers increases, and the tear resistance increases. In the initial stage of beating, the tension increases, which is the typical phenomenon of most papers. However, the dry pulp does not always have the initial phenomenon of tearing force. When the degree of beating is greatly increased, the fibers cannot slide away from each other, and at the same time, the number of fibers whose tensile strength is damaged is greatly increased. The shear effect will be more approximated than the pull effect. Therefore, the work done by breaking the fiber is much less than the work done by pulling the fiber out of the sheet, and the work required to tear the paper is reduced.
Through the determination of tearing degree, we can know the way of fiber treatment and understand the condition of beating. If the counter force is high and the bursting resistance is very low, it is a phenomenon of insufficient pulp. If the counter force is very low, the bursting degree is high. This may be excessive pulping; if the tear resistance and bursting resistance are too low, it may be due to too much cutting during the fiber processing. The tear test is particularly useful for papers that are subject to breakage during use, such as paper bags, strips, construction boards, tissue papers, post seals, and some box-making papers. In this QS certification, manufacturers that produce translucent paper, cellophane, food packaging, and food packaging board must all test this property.
Instrument: SL-1 paper tear tester (please adjust the level before use).
Sampling: Cutting 63±0.5mm×50±2mm, longitudinally and transversely sampling respectively, if the paper is parallel to the short side of the sample, then carry out lateral test, otherwise, perform longitudinal test. Samples were treated with temperature and humidity according to standard conditions (at a temperature of 23±2°C and a relative humidity of 45% to 55% for at least 4 hours).
Measuring method: Lightly pull the tear tester to the left and raise the fan-shaped pendulum body beyond the swing limiter. At this time, slowly release the pendulum body and swing the right edge of the pendulum body to be blocked by the pointer limiter. Place the specimens in groups of four. Place the central part of the specimen in two clamps flat and tighten the jaws. Using a paper cutter attached to the instrument to cut a 20mm gap, the distance from the end of the gap to the end of the specimen should be 43±0.5mm.
Move the pointer to the upright position, ie the left end of the pointer limiter. Immediately press the button of the swing limiter (to prevent contact with the pendulum) and release the pendulum to tear. When the pendulum swings to the left again to the highest point, loosen the button of the swing limiter and grasp the pendulum smoothly by hand to observe the dial for reading. Each time the measured tear value, the number of vertical and horizontal tests should be not less than 5 times, calculate the average value.
The tearing degree shall be calculated according to the formula: F=sp/n, and the result shall retain three significant figures.
Where: F - tearing degree, mN; s - the average scale reading in the test direction; p - conversion factor, which is the scale conversion layer of the scale 16; n - the number of layers tearing the sample at the same time.
The tear index should be calculated according to the formula: X=F/G, and the result is to retain three significant figures.
Among them: X-tearing index, mN•m2/g; F-tearing degree, mN; G-quantitative, g/m2.
(Note: When there are 1~2 specimens, the right and left deflections of the tear line ends and the extension of the knife edge exceed 10mm, they should be discarded. Repeat the test until you get 5 satisfactory results. Deviating conditions are indicated in the report. If tearing occurs in the specimen, rather than tearing in the normal orientation, it should be treated as described above.)
How to measure the bursting strength of paper
The paper and paperboard bursting resistance refers to the uniformly increased maximum pressure that the paper and the paperboard undergo on a unit area. The result is expressed in kPa. Burst resistance represents the total strength and uniformity of the paper, depending on its elongation and some of the characteristics of the paper structure. Its properties are related to its strong mechanical properties, but it is also affected by the elongation of the paper, so it also reflects the strength and toughness of the paper. Tension is the average value of a certain width, vertical and horizontal difference may be very large, and burst strength is the sum of the strength of a certain area. The main factor contributing to these mechanical strengths is the binding force and average length of the fibers. Burst strength is a composite function of tensile strength and elongation. Most of the stress is a tension created by the pressure difference across the web when the paper breaks, resulting in approximately equal deformation in both directions. Uneven stress in the paper, the pattern is generally broken into a vertical crack in the paper. This phenomenon is due to the small elongation in the longitudinal direction of the sheet, which leads to a longitudinal tension when the rubber film bulges. Burst resistance is directly related to the use of paper bags, wrapping paper and carton board. These papers are subjected to similar stresses in the burst test during use, however, for most papers, there is no direct link between shredding and paper use.
In this QS certification, it is required that manufacturers who produce chicken skins, food parchment, translucent paper, food packaging paper, food packaging paperboard, etc., must carry out compulsory self-test burst resistance.
Instrument: NP-1 Electronic Paper Bursting Tester; QD-1 Paper Quantitative Sampler.
Sampling: Cut the 100cm2 standard sample to be tested, and treat the sample under temperature and humidity according to standard conditions (at a temperature of 23±2°C and a relative humidity of 45% to 55% for at least 4 hours).
Detection process: open the burst tester, etc. After the instrument shows stability, input layer values ​​and quantitative values. The sample is mounted on the fixture, press the "automatic" button, the pressure ring on the instrument slowly press down, the pressure reaches a certain level, stop the pressure. The hydraulic piston begins to move. The pressure is applied to the center of the specimen through the film and gradually increases until the specimen breaks. The upper pressure ring and piston return to their initial positions. The display window shows the resistance to breakage and the number of tests. By pressing the corresponding button, you can display the average value of burst resistance, burst resistance index and coefficient of variation.
Sizing
The degree of paper sizing refers to the degree of water absorption of the paper, that is, the degree of penetration and diffusion of water on the paper surface. The degree of sizing is expressed by the maximum width mm of the line that does not spread or penetrate when it is scribed with standard ink. This is often the ink marking method.
LD Sizing Kit (including duckbill pen, standard ink, transparent standard width sheet), glass plate.
According to the requirements of GB/T450, 150mm x 150mm specimens shall be taken and the positive and negative sides shall be marked. At least 3 specimens are required for each paper. It is best to wear gloves to avoid direct contact with the test surface. Adjust the width of the tip pen to correspond to the paper to be tested. For example, 40g-50g paper is 0.50mm and 60g paper is 0.75mm. Filled with standard ink.
Lay the sample on a glass plate, place the scriber at a 45° angle to the glass plate, and quickly draw a straight line ((in a second, it should be more than 10cm). If the ink does not spread or penetrate, the width of the pen must be constantly adjusted (increased) until diffusion or penetration occurs. If diffusion or penetration occurs, the width of the pen must be continuously adjusted (decreased) until diffusion or penetration does not occur.
The sample was allowed to air dry and then compared with a transparent standard width sheet (not 1.5 cm at the head and tail of the sample). The maximum width of the line that did not diffuse or permeate on each side was the degree of sizing of the paper.
Fluorescent substance detection
In the production of paper packaging, in order to increase whiteness or aesthetics, fluorescent brighteners are often added. Excess fluorescent brighteners in packages will migrate into foods. Long-term human consumption can lead to a series of diseases such as cancer. Therefore, it is necessary to control the addition of brighteners. According to the relevant regulations, the standard sample is required to be irradiated with two ultraviolet rays at 254 nm and 365 nm, and the area of ​​the fluorescent part cannot exceed 5 cm2.
A standard circular sample with a diameter of 112.8 mm was cut out and placed on the observation table of the ZW-III triple-purpose UV analyzer. The shade was lowered, and the 254 nm and 365 nm ultraviolet switches were turned on, and the 254 nm and 365 nm ultraviolet were turned on at the same time. Switch observations were compared using the attached standard transparent scale. Any of the above three cases had a fluorescence area of ​​more than 5 cm2 and were judged to be unacceptable.
Dust detection
Degree of dust refers to the hygienic condition of the paper packaging, that is, dust or foreign materials that are visible to the naked eye on the paper. It is usually observed with the CA-1 Dust Observer.
According to GB/T450, cut 250 specimens of 250mm 250mm respectively. Each sample was placed on the observatory and the observation light was turned on. Observations were made at distances of 250 mm to 300 mm. Different areas of dust were circled with different marks. Use the attached standard dust image to identify the size of the dust area. It is also possible to record the number of dust in the same area by the size of different areas. The specimen is then rotated 90 degrees and new dust is found and marked for each revolution, until it rotates back to its original position. The other three sheets were similarly tested, and only the surface dust was generally measured. The results were expressed as the number of dust per square meter (ND, per square meter) or square millimeter per square meter of paper dust (SD, mm2/m2).
Whiteness detection
The BD-1 reflectance meter is mainly used for whiteness measurement of white and near-white objects or powder surfaces. The whiteness value that is consistent with the visual acuity can be accurately obtained. For papers treated with fluorescent whitening agents, the whiteness after fluorescent whitening can be quantitatively reflected. The paper's opacity can be accurately measured.
150 x 75mm specimens of 10 or more (total thickness should be opaque), according to standard conditions for temperature and humidity treatment samples (temperature 23 ± 2 °C, relative humidity of 45% to 55% of the environment placed at least 4h).
Turn on the reflective photometer switch, the display should have a digital display, preheat 30min.
Zero calibration: press the sample holder slide tube to place the black tube on the sample holder, and then let the slider rise to the measurement port. After the display value is stable, adjust the zero adjustment knob on the panel so that the display shows 00.0.
Worksheet whiteness value: remove the black tube, put on the working standard whiteboard, adjust the correction knob on the panel after the digital display value is stable, make the display value consistent with the whiteness value of the target, remove the working standard whiteboard , Put on the reference standard whiteboard, and record the whiteness value after the display value is stable. Later, it is calibrated as a standard value for sample measurement, and then the working standard whiteboard is stored in a desiccator containing silica gel.
Calibration: Zero calibration and calibration are required for each sample measurement using a black tube and a reference standard whiteboard that has passed the standard values.
R457 whiteness measurement: For non-fluorescent paper whiteness measurement, after the instrument is pre-adjusted, the sample to be tested can be placed on the sample holder, and the whiteness value can be displayed automatically after the displayed value is stable.
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