Corrugated boxes are widely used in the outer packaging of goods because of their characteristics and environmental advantages, and play an important role in the transportation, preservation and sale of goods. During use, the carton must be required to achieve a certain degree of firmness and durability.
At present, fierce market competition has enabled various carton manufacturers to continuously improve their production processes and management to maximize profits, which has caused carton users to encounter more or less quality problems in the process of using cartons, such as cartons. After stacking, collapse, rupture, etc. caused many unnecessary losses.
In order to avoid such a situation, in order to produce a qualified carton product, the corrugated carton must be inspected to effectively control the production process of the corrugated carton. Therefore, it is of great significance to correctly understand and understand the detection items and testing methods of corrugated boxes.
Basic test item
Appearance Quality
Qualified carton requires clear printing pattern, clear writing, no broken line and missing condition; the pattern color is consistent, the brightness is bright and the printing position error is small, the large carton error is within 7mm, and the small carton error is within 4mm. The surface quality should be intact, no damage, no smudging, no holes around the box, and no gaps after the lids are closed. For the shape of the carton, the tolerance of the inner diameter of the box and the design dimensions should be kept within ±5mm of the large box and ±3mm within the small box, and the dimensions are basically the same. The corrugated box cover is reciprocated and folded more than 5 times by 180 degrees. The total length of the cracks in the surface layer of the first and second types of cartons and the inner layer and the third type of cartons is not more than 70 mm. In addition, the box joint specification is required, the edges are neat, and the angle is not overlapped.
Moisture content
The so-called water content refers to the moisture content in the corrugated paper or paperboard, expressed as a percentage. The water content has a great influence on the strength of the carton box, and is one of the three heavy defect inspection items of the carton.
Corrugated base paper has certain pressure resistance, tensile strength, puncture resistance and folding resistance. If the moisture content is too high, the paper will be soft, the stiffness is poor, and the quality of compression and bonding is also poor. If the moisture content is too low, the paper is too brittle, it is easily broken when pressed, and the folding resistance is also poor. If the moisture content of corrugated paper and cardboard paper is too large, the corrugated cardboard processed by the single-sided machine is prone to curling, and when it is twisted, it is prone to foaming and degumming. If the molded carton absorbs moisture during storage, the strength of the carton will be significantly reduced, which will affect the use.
The moisture content of corrugated boxes is (12 ± 4)%. For the determination of the moisture content of the carton, the more accurate detection method is the drying method, that is, several pieces are taken from different parts of the cardboard or the box, and about 50g of the sample is weighed by the balance, and then torn into pieces and placed in the oven. , drying to constant weight, you can find the moisture content. The calculation formula for water content is:
Moisture content = (original weight of the sample - weight after drying of the sample) 原来 original weight of the sample × 100%
Cardboard thickness
Corrugated board thickness refers to the vertical distance between the upper and lower sides of the corrugated board under a certain pressure, in millimeters, which is one of the inspection items of the appearance defects of the carton, and directly affects the edge pressure strength, puncture strength and compressive strength of the board. . There are many reasons for affecting the thickness of the cardboard. If the thickness of the corrugated cardboard is thin, the edge strength, puncture strength and compressive strength will be reduced accordingly. Corrugated cardboard has different thicknesses and different thicknesses.
The thickness of the board is usually measured in a laboratory using a corrugated board thickness gauge. The thickness gauge has a circular anvil and a cylindrical measuring head, and the measurement results can be read by the display. The pressure applied by the measuring head is 20 kPa ± 0.5 kPa, and the diameter of the measuring surface is about 35.6 mm.
Carton weight measurement
The measurement of carton weight is also an important task in carton companies. Carton companies need to measure the weight of their containers when exporting customs declarations and in statistical output. In addition, customers sometimes use the box weight as one of the criteria for carton inspection. Although the box weight test method of the carton is extremely simple, it is easily affected by moisture, and the box weight measurement value deviates from the true value.
Measuring tools generally use an electronic balance with an accuracy of 1 gram or more, and the weighing range should be 0~5Kg. Three samples were randomly selected from the same batch of cartons during the measurement, and were equilibrated in the environment of relative humidity (50±2)% and temperature 23±1°C for more than 24 hours according to the GB/T10739 standard, and then three samples were tested separately. The weight of the box is calculated as the average of the three weight values, which is the weight of a single box for this batch of cartons.
It should be noted that the temperature and humidity balance treatment of the sample is very important for obtaining an objective and consistent box weight. For the sample without temperature and humidity balance treatment, the measured box weight error can reach more than 15%.
The moisture content of the carton is an important factor affecting the weight measurement of the bin. However, many carton manufacturers or customers are limited by the delivery time or test conditions, and are weighed without temperature and humidity balance. As a result, the bin weight seriously deviates from the true value. . For this purpose, a quick measurement method can be used to accurately test the weight of the box without temperature and humidity balance.
A large amount of experimental data shows that after the carton is fully balanced in the standard temperature and humidity environment, the moisture content is about 8%, and the dry weight of the carton is constant. Therefore, we only need to measure the weight of the carton before the temperature and humidity balance treatment. And the moisture content, you can calculate the true weight of the carton.
When measuring, it is also necessary to randomly take three cartons from a batch of cartons as test specimens. The box weights of the three samples were weighed separately and averaged. The measured value is the reference weight, expressed by Mc, and the unit is g; the moisture of the three samples is separately measured, and the average value is obtained, and the measured value is expressed by W, and the unit is “%”.
Finally, by substituting the measured value of Mc and W into the formula, the standard box weight after the temperature and humidity balance can be derived and expressed by M. The formula for calculating the standard box weight is:
M=Mc×(1-w)
Strength measurement project
Side pressure strength
For a sample of a certain width, the amount of pressure that can be withstood per unit length is called the edge pressure strength, and the edge pressure strength of the corrugated box refers to the ability to withstand the pressure parallel to the corrugation direction. According to the relevant standards, when testing the edge pressure strength, three pieces of mechanically indented, no printing marks and damaged samples are cut out from each of the three cartons. The corrugation direction of the sample should be short side, the sample size It is 25mmx100mm with an error of ±0.5mm. The edge of the sampler should be kept sharp and the blade should be installed in the correct position. The angle between the edge and the sipe can be adjusted to 45 degrees. In addition, the tip of the knife must not be rubbed against the bottom of the sipe to prevent the blade from being bent and deformed, so as to avoid corrugation and fluffing of the edge of the cut sample and affect the accuracy of the detection.
The conversion formula for the side pressure strength is:
R=F×1000/L
Where: R is the side pressure strength of corrugated board, expressed by N/m: F is the force value read when the sample is crushed; L is the dimension of the long side of the sample, and the unit is mm. The ring pressure strength of the base paper and the bond strength of the paperboard largely determine the edge strength of the paperboard. The results are expressed as an average.
Compressive strength
The compressive strength of the corrugated box refers to the maximum load and deformation that can be withstood until the box is damaged under the condition that the pressure tester uniformly applies dynamic pressure.
Bond strength
The peak adhesion of corrugated paper, paper, core paper and corrugated paper, the maximum peeling force that can be withstood within a certain unit length, called the bond strength of corrugated board, indicating the corrugated board firmness.
For the detection of type A corrugated board, the pin of the stripping frame should be Φ3mm, and the pin of the stripping frame of type B and C corrugated board should be Φ2mm. Each pin on the stripping frame should be aligned with the center of the corrugated notch, and after the spacing adjustment is equal, tighten each screw. For the test specimen of adhesive strength, 4 pieces can be taken from each of the three sample boxes, and the corrugation direction is the short side direction. The material should be intact, no degumming, no blistering. The sample size is 25mmx80mm, and the error is within ±1.0mm, which can better ensure the accuracy of the test results.
The conversion formula of the bond strength is: P = F / L. Where: P is the bond strength of the corrugated board sample, expressed as N/m; F is the force value read when the sample is separated, the unit is N; L is the dimension of the long side of the sample, and the unit is m. The quality of the adhesive, the formulation and the suitability of the equipment, operation process and other factors determine the bond strength of the paperboard. The bond strength of the paperboard affects the pressure resistance and resistance of the carton to a large extent. Performance such as breaking strength and puncture strength.
Puncture strength
The work performed by a certain shape of the pyramid through the corrugated board is called the puncture strength of the corrugated board, and the unit is J, which can be inspected by a puncture strength tester.
During the test, select 3 samples with better appearance, and take 4 pieces of cardboard without damage, no watermark, no crease and no other appearance defects from the wall of each sample box. The test sample with the specification of 175mmx175mm 12 Piece. When slitting the sample, it should be noted that the starting line should be parallel to the corrugated. Before each test, the instrument should be zero-calibrated. According to the general strength of the sample, select the appropriate weight so that the measured value is between 20% and 80% of the measurement range. After the sample is fixed, turn the pointer to the highest scale. Value, put the friction ring behind the pyramid, lock the pendulum to the starting position of the test and press the release device, so that the swing arm pushes the pyramid to penetrate the sample, and then reads the detection value; the front, back, and portrait The value of the detection, the horizontal direction, etc., find the arithmetic mean, and retain the three significant digits as the measurement result.
When testing, it should be noted that the sample should be clamped. If slip occurs, the test value should be considered invalid. The puncture strength of corrugated board is closely related to the fiber toughness, hardness, tightness, moisture content of the base paper, and the bond strength of the board and the thickness of the board.
Burst resistance
The burst strength of corrugated board refers to the maximum pressure per unit area that can withstand a uniform increase perpendicular to the surface of the specimen under certain test conditions, and the unit is Kpa.
The determination of the bursting resistance is usually carried out by a sample chuck system. When the test is performed, the sample is placed on the film and clamped with the sample holder, and then the pressure is uniformly applied. To prevent the sample from slipping during the measurement, the sample chuck should have No less than 690 kPa of clamping force. Under pressure, the sample and the film are free to bulge until the sample is broken, and the burst strength of the sample is the maximum value of the force applied at this time.
When sampling, it is necessary to cut 12 samples without watermark, fold, wrinkles and damage, and the specifications are 140mmx140mm, that is, 4 pieces from each of the 3 sample boxes, and one side of the sample should be parallel to the corrugation direction. In the burst strength test, the samples are divided into two groups, one group is attached to the rubber film on the front side, and the other side is attached to the rubber film for detection. When the sample is crushed, the detection value is read. To ensure the accuracy of the results, the arithmetic mean of all measured values can be used to indicate the magnitude of the burst. The degree of precision of the results depends on the uniformity of the sample and other factors, such as the error of the pressure gauge, the clamping force, the rate of pressurization, the presence or absence of air in the system, and the condition of the film.
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