If the joint strength of the box is poor, carton cracking occurs at the interface of the carton during handling, stacking and transportation. This requires adjustment of the production process to increase the joint strength of the box; if the joint strength of the box is strong, The problem will appear far away from the junction. Therefore, the joint strength of the box is also an important factor affecting the strength of the carton. In the design of the carton, the joint strength of the carton must be taken into consideration, and an appropriate joint method is selected according to the actual situation.
The general box joint includes three ways: adhesive joint, tape joint and box joint joint. In foreign countries, adhesive bonding and tape bonding are mainly used for single corrugated cardboard, and the box is mainly used for double corrugated cardboard and three corrugated cardboard; domestic adhesive bonding and box bonding are most commonly used in China.
Adhesive Bonding Adhesive bonding has high strength, is suitable for automated mass production, does not affect printing, and does not generate scratches. It is the most economical joining method.
However, its biggest drawback is that the adhesive is easily affected by temperature and humidity.
The bonding strength of the tape-adhesive tape bonding method is not affected by the strength of the corrugated cardboard, and there is no damage to the joint portion of the carton. Moreover, the adhesive tape joining method does not need to overlap the tongue structure, and the appearance of the adhesive and stapled jointed carton is neat, and the cardboard material is saved, the internal dimensions of the carton are easily ensured, and the commodity loading is facilitated.
However, the bonding process imposes high requirements on the strength of the adhesive tape, resulting in additional costs. Therefore, this method is currently used less frequently.
The engagement of the box and the binding box is not affected by environmental factors. The nailing method is simple and the equipment cost is low. Is a more common way of carton joining, but it is not the best way. The stapled carton nails are exposed at the interface. The appearance is poor, and the interior is easy to scratch the contents. The stapled carton interface is only partly overlapped by staples. The strength is not high and the sealing performance is poor. If the container is not processed and dampened Easy to rust, affecting the structural strength of the carton.
In addition, from the perspective of environmental protection, box-making methods are not conducive to recycling, and are subject to export restrictions in the United States and other European Union countries.
At present, there are few standard methods for the jointing of corrugated boxes in China. The joint methods and testing standards are described in GB/T 6543-2008 "Standard Single Corrugated Boxes and Double Corrugated Boxes for Transport Packaging":
(1) The cartons can be joined by an order or adhesive.
(2) The corrugated box staples the overlap requirements for the tab width, top line spacing, staple angle, and head and tail staple distance.
a) The width of the tongue: 30mm for single corrugated cardboard boxes and 35mm for double corrugated cardboard boxes.
b) Nail line spacing: single nails not more than 80mm and double nails not more than 110mm.
c) Stapling angle: nailed along the midline of the overlapping part, using inclined nails (approx. 45° with the standing edge of the carton) or horizontal nails, the box should be arranged neatly and evenly.
d) Head-to-tail distance: The distance between the tail-tail distance and the centerline of the bottom indentation is 13mm±7mm. Nail joints should be nailed and nailed, and there must be no defects such as stacked nails, dowels, and corners.
(3) The width of the adhesive lap joints of corrugated box joints should not be less than 30mm, and the adhesive for the joints should be uniform and sufficient so that there is no excess adhesive overflow. Bonding should be firm and at least 70% of the adhesive surface is destroyed when peeled.
Problems encountered in the actual testing process However, in the actual production process, the detection of the box joint according to the GB/T 6543-2008 standard is relatively easy, and the quality of the test results is not much different from the actual ones. However, for the joints with adhesive joints, the quality of the box joints is only assessed in accordance with the standards for the detection of the width of the joint tongues and the destruction ratio of the adhesive surface at the time of peeling. As a result, the test results are usually acceptable, but the joint burst occurs during use. Happening.
According to domestic and international conditions, the detection methods of domestic bonding strength can be summarized as follows:
a) Tensile testing machine test method
b) Compression tester test method
c) Practical Tests in Circulation
d) Drop test method
Among them, the practical test and drop test in circulation have certain practicality, but only qualitative analysis can be performed, and their strength values ​​cannot be determined. If you need to determine the specific strength data, you must use the tension and compression test method. This is also a more experimental method used by domestic users. The specimens were tested on a pressure tester and a tensile tester after constant temperature and humidity treatment. The test diagram is shown in the figure:
At present, there is no ISO international standard for the detection method of the box joint strength. There are mainly two methods: the compression tester test method and the tensile tester test method. The compression test method adopts ASTM D642, and the tensile tester test method adopts the standard TAPPI T813. Here, the pulldown tester test method is mainly introduced.
This method uses a constant speed drawing method to detect the strength of the box joint and is suitable for adhesive bonding, tape bonding and box bonding.
The sample corrugated carton shall be placed in a standard atmosphere at a temperature of 23°C and a relative humidity of 50% for 24 hours. Then take 5 intact corrugated cartons, one for each corrugated box. The sampling position is shown in Figure 6. Take five test samples, each sample length at least 200mm, the length direction to include the joints, the joint is preferably in the middle of the length direction, the general adhesive bonding and tape bonding sampling width of 25mm, box binding shall include 1 nail, nails at least 6mm from the sample edge.
Test equipment optional products enjoy PN-JT500 computer tensile testing machine, the distance between the two clips is (180 ± 5) mm, the test speed is (25 ± 5) mm / min, the time of the sample fracture is 15 to 30 Completed in seconds. The maximum force at which each sample breaks is recorded and then divided by the width of the sample, which is the bond strength of the box, expressed in kN/m. If more than 30 seconds, change the test speed so that it can break within 30 seconds and indicate in the report.
Foreign joint strength detection methods At present, there is no ISO international standard for the detection method of the box joint strength. There are mainly two methods: the compression tester test method and the tensile tester test method. The compression test method adopts ASTM D642, and the tensile tester test method adopts the standard TAPPI T813. Here, the pulldown tester test method is mainly introduced. This method uses a constant speed drawing method to detect the strength of the box joint and is suitable for adhesive bonding, tape bonding and box bonding.
The sample corrugated carton shall be placed in a standard atmosphere at a temperature of 23°C and a relative humidity of 50% for 24 hours. Then take 5 intact corrugated cartons, one for each corrugated box. The sampling position is shown in Figure 6. Take five test samples, each sample length at least 200mm, the length direction to include the joints, the joint is preferably in the middle of the length direction, the general adhesive bonding and tape bonding sampling width of 25mm, box binding shall include 1 nail, nails at least 6mm from the sample edge.
The test equipment can use computer tensile tester. The distance between the two chucks should be (180±5)mm, the test speed should be (25±5)mm/min, and the time for the sample to break should be within 15 to 30 seconds. The maximum force at which each sample breaks is recorded and then divided by the width of the sample, which is the bond strength of the box, expressed in kN/m. If more than 30 seconds, change the test speed so that it can break within 30 seconds and indicate in the report.
Box joint strength calculation formula:
,
In the formula, the maximum force at break of Pmax specimen is represented by N; W is the width of the specimen and expressed in mm.
Comparison of the strengths of the three bonding methods Among the three bonding methods of the carton box, the bonding strength of the adhesive bonding is the best, the bonding strength of the bonding tape is the second, and the bonding strength of the metal nailing is the lowest. Figure 7 shows. It's not the best way to get the best bond strength. The three bonding methods of the carton are not the best and the worst. The three can complement each other and replace each other. When the corrugated box joining method is selected, it should be reasonable according to the characteristics of the contents, the type of corrugated cardboard and the corrugated box production volume. Choose.
Conclusion In the normal detection process, the strength of the box joint is often easily overlooked, but problems such as breakage or breakage of the joint, or poor adhesion will occur in batches, and the consequences will be disastrous. The production process of corrugated cartons and the factors affecting the quality of corrugated cartons are numerous and complex. Quality problems at all stages will ultimately affect the quality of cartons. Therefore, during the production process of corrugated cartons, from the beginning of design to the selection of raw materials and equipment operations And maintenance to the various processes of the production process, each link can not be ignored, the only way to ensure the quality of the carton.
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