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The strength of corrugated cartons is an important technical indicator for the quality inspection of packaging containers. The level of these indicators reflects the quality of raw materials on the one hand and the quality of processing techniques on the other. The production process shows that to improve the strength of corrugated cartons, it is not enough to rely on purchased raw materials. The quality control of the production process is also an important part of improving the strength of corrugated cartons. Therefore, correctly understanding and understanding the relevant factors that affect the strength of corrugated boxes is of great significance for better production and product quality improvement.
Raw Paper Technical Index and Its Relation to Corrugated Box Strength
Quantitative quantification, also known as grammage, is the weight per square meter of paper, expressed in g/m2. The quantitative calculation formula is: the weight of the sample/area of ​​the sample. Quantitative is an important index to measure the physical properties of paper. In general, the paper has a high basis weight, and its tensile strength, ring pressure strength, tear strength, stiffness and thickness are relatively high. Making corrugated boxes with high-quantitative paper materials has relatively higher compressive strength. Therefore, to make a high-strength corrugated carton, selecting a high-quantity paper material is often one of the basic requirements of the customer.
Tightness It refers to the weight per cubic centimeter of paper, expressed in g/cm3. Its calculation formula is:
The tightness of the paper reflects the degree of densification of its fibrous tissue structure. Boxboard and corrugated paper have high tightness values, and their burst strength, ring pressure strength, puncture resistance, and tensile properties are relatively good. Then, the overall strength of the carton is relatively high. However, if the tightness is too large, the paper material is likely to be brittle, especially for whiteboard paper. If the tightness value is significantly larger than the standard, the folding endurance performance will be reduced. Therefore, the use of white paper for the surface layer of corrugated cardboard, should not use the high degree of tightness of the white paper, so as not to affect the folding box carton folding degree.
Ring compression strength The standard sample length (longitudinal) 152 ± 0.2mm, width 12.7 ± 0.1mm, take 10 tablets for testing, 5 of which were tested outwards facing outwards. The other five sheets were tested with the reverse side facing out into the circular tray. After that, the ring pressure strength of the base paper can be obtained by formula conversion. In general, cartons made from paper with good crush strength are relatively high in strength. The formula for calculating the crush strength is: RF/152. In the formula, R denotes the ring crush strength in kN/m; F denotes the force value read in crushing the sample, unit N; and 152 denotes the length of the sample in mm. The standard value of the ring pressure index in the national standard is an important index to measure the compressive performance of the base paper. It refers to the ratio of the ring pressure strength and the basis weight of the base paper and the unit is N·m/g. The calculation formula for this indicator is: Rd=1000R/W. In the formula, Rd denotes the ring pressure index, R denotes the ring pressure strength, and W denotes the basis weight of the sample, and the unit is g/m2. How the ring pressure index of the base paper affects the overall strength of the carton to a great extent, especially the impact on the compressive strength of the carton.
Sizing When paper or cardboard is produced, apply a certain amount of colloidal material such as rosin gum to increase the water resistance of the paper. This production and processing process is called sizing. The degree of sizing is a measure of the quality of the glue. According to the national standard, the ink scribe method and the surface absorption weight method can be used for detection. The factory can also use the “drip method†to detect the degree of sizing on paper. The practice is: a little water on the paper surface, if the speed of water droplets infiltration, indicating that the degree of sizing is not good; if the water droplets are not prone to seepage phenomenon, water droplets floating on the paper, indicating the degree of sizing is good. The base paper for making corrugated boxes requires a good degree of sizing, so that it is not easy to absorb moisture, the moisture content of the carton is stable, and the strength of the carton can be better ensured.
Moisture content The so-called moisture content refers to the content of water in paper or paperboard, expressed as a percentage, and its calculation formula is:
The moisture content has a great influence on the strength of the carton box, so this is also the main reason why the moisture content has become one of the three important defects inspection items of the carton. When the moisture content of the carton is high, its resistance to puncture compressive strength and burst strength will be relatively reduced. Corrugated paper has a certain degree of pressure resistance, tensile resistance, puncture resistance, and folding endurance. If the moisture content is too high, the paper will appear soft, poor in stiffness, and poor in pressure and adhesion. If the moisture is significantly lower than the lower limit of the standard value, the cracking phenomenon will occur easily when pressing. If the moisture content of corrugated paper and linerboard is too large, the corrugated board machined by one-sided machine is prone to curl. When the next process is combined, foaming and degumming are likely to occur, and the strength of the carton will be significantly reduced.
The folding-resistant carton is a kind of packaging container, and the flap needs to be frequently opened. This requires that the paper should have a certain folding-resistant ability. The paper's transverse folding resistance measures the paper's 1350 angle reciprocating folding test for 150 × 15mm specimens under a certain tension, speed, and angle conditions. When the paper is broken, it is the number of inspections of the folding resistance. . The pulp properties of the linerboard and folded paper, the moisture content of the paper, the tightness, the fiber length and the fastness of the binding force, and the influence of factors such as the storage time and temperature of the base paper largely determine the resistance of the base paper. Discounts. Therefore, to improve the folding performance of the carton, it is an important part to ensure the quality of raw materials.
Relationship between production design, corrugated board characteristics and corrugated box strength
The shape of the box and the structure of the carton are different, and their compressive strength will be very different. The maximum supporting force of the carton should be: the four corners of the box and the sides next to the corners. It can be seen that the supporting force of the square carton is relatively larger. In addition, the longer the perimeter of the box, the higher the height, the lower the corresponding compressive strength; the larger the area of ​​the opening, the closer the compression resistance of the box closer to the corner is, so the design should pay attention to these conditions .
Corrugated type definition, characteristics in accordance with the provisions of GBT6544-1999 standard, UV-shaped corrugated cardboard is divided into A, C, B and E type four. The enthalpy height of A type is 4.5 to 5mm, the number of turns in units of 300mm is 32 to 36, the height of C type is 3.5 to 4mm, the number of turns in units of 300mm is 36 to 40, and the height of B is The number of turns is 2.5 to 3mm and 300mm in length, and the number of turns is 48 to 52. The height of an E-shape is 1.1 to 2mm, and the length of a 300mm length is 92 to 100. The A-type corrugated corrugation is high and wide, so it is called a large-scale type. The A-type carton bears poorer planar pressure performance than the B and C-types, but it has higher vertical pressure resistance, so it is more suitable for the production of cartons containing non-pressure-resistant items, and is more commonly used. The crucible height and the number of turns per unit length of the C-type carton, and its performance, are between the A and B types, and it is also known as the "fine" type, which is suitable for containing general items. B-type corrugated medium is low and dense, so its vertical pressure resistance is poor, but its flat pressure resistance is high. Therefore, B-type paper is suitable for bottled foods. E-type paperboard corrugated low and fine, it is also known as a small rake. E-type cardboard has the characteristics of light weight, good cushioning performance, good flat compressive strength, etc., which facilitates direct printing. The three types of corrugated paperboards A, C, and B can also be combined into double corrugated paperboards and three-watt corrugated paperboards to greatly increase the strength of the carton. Most non-pressure-resistant products such as cigarettes and glass containers are packaged in corrugated boxes with multi-layered structures that are resistant to pressure and impact.
Characteristics of corrugated waveforms Corrugated waveforms refer to the shape of the top and bottom of the corrugations and the edges of the corrugations. The corrugated board waveform has a certain influence on the compressive strength of the carton. Corrugated waveforms are U-shaped, V-shaped, and UV-shaped. The U-shaped ridges are arc-shaped. This type of corrugated cardboard has good cushioning and elasticity. The slight deformation of the corrugated ridges can be quickly restored and the cul-de-sac does not break easily. However, the pressure it receives is worse than that of V-shaped cardboard, and the amount of core paper and adhesive is large. The V-shaped ridges are triangular in shape, and the 楞-shape is composed of straight lines. The intersection of two straight lines constitutes 600. The V-shaped crucible carton has a small amount of core paper and adhesive, and has strong and durable good characteristics. Its plane compressive strength is significantly higher than that of a U-shaped crucible, but once it has been deformed under pressure, it cannot be easily restored to its original shape. UV-shaped helium is compatible with the advantages of V and U shape, making up for their own defects, able to withstand higher pressures, and greatly improving the strength of the carton.
The relationship between cardboard production process, equipment failure and corrugated box strength
The quality of corrugated board produced by single-sided machine has great influence on the strength of corrugated box. The quality of single-sided machine is mainly reflected in the hardness, flatness, adhesive strength and corrugating forming effect of the board. The production process shows that the strength of corrugated paperboard, and the quality of linerboard and corrugated paper are certainly influential factors, but if the production process is not properly controlled, even the best paper quality cannot produce high-strength corrugated cardboard. Comparing and analyzing experimental results, it was found that, sometimes with paper materials with high index values ​​such as quantitative and ring crush strength, the hardness of the corrugated paperboard produced was not as good as the corrugated paperboard made from paper with low quantitative and ring pressure index. ,There are:
Incorrect selection of paper and paper corrugated cardboard are made of cardboard and corrugated paper. If the moisture content between them is too large, then after the glue is absorbed and heated, the paper's expansion and contraction will also change. Obvious differences, it is easy to cause the cardboard curl, so that the strength of the carton. Therefore, before the paper roll on the machine, it is best to test the moisture content of the base paper, try to choose the box paper and corrugated paper with similar moisture content to match the production, in order to prevent the paper board from curling.
Machine Speed ​​Discomfort The speed of a single-sided machine is too fast or too slow, which will affect the stiffness and bond strength of the board. Especially when the moisture of the base paper is high, if the production speed of the machine is too fast, the warm-up time is short, and the time for “eating glue†on the corrugation peak is short, so that the bonding effect and forming hardness of the cardboard are reduced. If the speed of the machine is too slow, the heating time of the board is relatively long, the board will easily become brittle, and the overheated temperature will cause premature curing of the adhesive, affecting the adhesive effect, all of which will reduce the strength of the board. Therefore, the production speed of the machine should be based on the situation of the moisture content of the base paper, the preheating area and the temperature, comprehensive consideration, and reasonable control, in order to ensure the quality of corrugated board production. According to the experience of the production process, the machine speed can be mastered by referring to the following Table:
Poor Adhesion The quality of paperboard bonding directly affects the compressive strength of the carton. The bonding quality depends mainly on the properties of the binder and the operating process, such as the physical and chemical properties of the viscosity, pH, solid content, and gelatinization temperature of the binder, and the blending operation of the binder. In order to ensure the bonding strength of the cardboard, good raw and auxiliary materials must be used. According to the actual production conditions, adjust the ratio of the binder, control the mixing time, stir the binder evenly, and use good water quality as much as possible. In the production process, it is necessary to control the amount of rubber properly, grasp the relationship between the speed of the machine and steam pressure, temperature, and the amount of adhesive applied to prevent the occurrence of blistering, pseudoplastic, and degumming. Improve the strength of the cartons.
The machine parts are in bad condition When corrugated roller shaft heads and bearings are worn or damaged, causing corrugated roller looseness, poor parallelism, and damage to crucibles, etc., it is prone to flat boring, collapse, high and low blemishes, degumming, foaming And corrugated board thickness and other quality issues. In addition, the old single-sided machine, the guide sheet wear and dirt, and the gap with the corrugated roll is too large, it is easy to cause the corrugated paper to jump, resulting in poor adhesion and high and low defects. all of these
Raw Paper Technical Index and Its Relation to Corrugated Box Strength
Quantitative quantification, also known as grammage, is the weight per square meter of paper, expressed in g/m2. The quantitative calculation formula is: the weight of the sample/area of ​​the sample. Quantitative is an important index to measure the physical properties of paper. In general, the paper has a high basis weight, and its tensile strength, ring pressure strength, tear strength, stiffness and thickness are relatively high. Making corrugated boxes with high-quantitative paper materials has relatively higher compressive strength. Therefore, to make a high-strength corrugated carton, selecting a high-quantity paper material is often one of the basic requirements of the customer.
Tightness It refers to the weight per cubic centimeter of paper, expressed in g/cm3. Its calculation formula is:
The tightness of the paper reflects the degree of densification of its fibrous tissue structure. Boxboard and corrugated paper have high tightness values, and their burst strength, ring pressure strength, puncture resistance, and tensile properties are relatively good. Then, the overall strength of the carton is relatively high. However, if the tightness is too large, the paper material is likely to be brittle, especially for whiteboard paper. If the tightness value is significantly larger than the standard, the folding endurance performance will be reduced. Therefore, the use of white paper for the surface layer of corrugated cardboard, should not use the high degree of tightness of the white paper, so as not to affect the folding box carton folding degree.
Ring compression strength The standard sample length (longitudinal) 152 ± 0.2mm, width 12.7 ± 0.1mm, take 10 tablets for testing, 5 of which were tested outwards facing outwards. The other five sheets were tested with the reverse side facing out into the circular tray. After that, the ring pressure strength of the base paper can be obtained by formula conversion. In general, cartons made from paper with good crush strength are relatively high in strength. The formula for calculating the crush strength is: RF/152. In the formula, R denotes the ring crush strength in kN/m; F denotes the force value read in crushing the sample, unit N; and 152 denotes the length of the sample in mm. The standard value of the ring pressure index in the national standard is an important index to measure the compressive performance of the base paper. It refers to the ratio of the ring pressure strength and the basis weight of the base paper and the unit is N·m/g. The calculation formula for this indicator is: Rd=1000R/W. In the formula, Rd denotes the ring pressure index, R denotes the ring pressure strength, and W denotes the basis weight of the sample, and the unit is g/m2. How the ring pressure index of the base paper affects the overall strength of the carton to a great extent, especially the impact on the compressive strength of the carton.
Sizing When paper or cardboard is produced, apply a certain amount of colloidal material such as rosin gum to increase the water resistance of the paper. This production and processing process is called sizing. The degree of sizing is a measure of the quality of the glue. According to the national standard, the ink scribe method and the surface absorption weight method can be used for detection. The factory can also use the “drip method†to detect the degree of sizing on paper. The practice is: a little water on the paper surface, if the speed of water droplets infiltration, indicating that the degree of sizing is not good; if the water droplets are not prone to seepage phenomenon, water droplets floating on the paper, indicating the degree of sizing is good. The base paper for making corrugated boxes requires a good degree of sizing, so that it is not easy to absorb moisture, the moisture content of the carton is stable, and the strength of the carton can be better ensured.
Moisture content The so-called moisture content refers to the content of water in paper or paperboard, expressed as a percentage, and its calculation formula is:
The moisture content has a great influence on the strength of the carton box, so this is also the main reason why the moisture content has become one of the three important defects inspection items of the carton. When the moisture content of the carton is high, its resistance to puncture compressive strength and burst strength will be relatively reduced. Corrugated paper has a certain degree of pressure resistance, tensile resistance, puncture resistance, and folding endurance. If the moisture content is too high, the paper will appear soft, poor in stiffness, and poor in pressure and adhesion. If the moisture is significantly lower than the lower limit of the standard value, the cracking phenomenon will occur easily when pressing. If the moisture content of corrugated paper and linerboard is too large, the corrugated board machined by one-sided machine is prone to curl. When the next process is combined, foaming and degumming are likely to occur, and the strength of the carton will be significantly reduced.
The folding-resistant carton is a kind of packaging container, and the flap needs to be frequently opened. This requires that the paper should have a certain folding-resistant ability. The paper's transverse folding resistance measures the paper's 1350 angle reciprocating folding test for 150 × 15mm specimens under a certain tension, speed, and angle conditions. When the paper is broken, it is the number of inspections of the folding resistance. . The pulp properties of the linerboard and folded paper, the moisture content of the paper, the tightness, the fiber length and the fastness of the binding force, and the influence of factors such as the storage time and temperature of the base paper largely determine the resistance of the base paper. Discounts. Therefore, to improve the folding performance of the carton, it is an important part to ensure the quality of raw materials.
Relationship between production design, corrugated board characteristics and corrugated box strength
The shape of the box and the structure of the carton are different, and their compressive strength will be very different. The maximum supporting force of the carton should be: the four corners of the box and the sides next to the corners. It can be seen that the supporting force of the square carton is relatively larger. In addition, the longer the perimeter of the box, the higher the height, the lower the corresponding compressive strength; the larger the area of ​​the opening, the closer the compression resistance of the box closer to the corner is, so the design should pay attention to these conditions .
Corrugated type definition, characteristics in accordance with the provisions of GBT6544-1999 standard, UV-shaped corrugated cardboard is divided into A, C, B and E type four. The enthalpy height of A type is 4.5 to 5mm, the number of turns in units of 300mm is 32 to 36, the height of C type is 3.5 to 4mm, the number of turns in units of 300mm is 36 to 40, and the height of B is The number of turns is 2.5 to 3mm and 300mm in length, and the number of turns is 48 to 52. The height of an E-shape is 1.1 to 2mm, and the length of a 300mm length is 92 to 100. The A-type corrugated corrugation is high and wide, so it is called a large-scale type. The A-type carton bears poorer planar pressure performance than the B and C-types, but it has higher vertical pressure resistance, so it is more suitable for the production of cartons containing non-pressure-resistant items, and is more commonly used. The crucible height and the number of turns per unit length of the C-type carton, and its performance, are between the A and B types, and it is also known as the "fine" type, which is suitable for containing general items. B-type corrugated medium is low and dense, so its vertical pressure resistance is poor, but its flat pressure resistance is high. Therefore, B-type paper is suitable for bottled foods. E-type paperboard corrugated low and fine, it is also known as a small rake. E-type cardboard has the characteristics of light weight, good cushioning performance, good flat compressive strength, etc., which facilitates direct printing. The three types of corrugated paperboards A, C, and B can also be combined into double corrugated paperboards and three-watt corrugated paperboards to greatly increase the strength of the carton. Most non-pressure-resistant products such as cigarettes and glass containers are packaged in corrugated boxes with multi-layered structures that are resistant to pressure and impact.
Characteristics of corrugated waveforms Corrugated waveforms refer to the shape of the top and bottom of the corrugations and the edges of the corrugations. The corrugated board waveform has a certain influence on the compressive strength of the carton. Corrugated waveforms are U-shaped, V-shaped, and UV-shaped. The U-shaped ridges are arc-shaped. This type of corrugated cardboard has good cushioning and elasticity. The slight deformation of the corrugated ridges can be quickly restored and the cul-de-sac does not break easily. However, the pressure it receives is worse than that of V-shaped cardboard, and the amount of core paper and adhesive is large. The V-shaped ridges are triangular in shape, and the 楞-shape is composed of straight lines. The intersection of two straight lines constitutes 600. The V-shaped crucible carton has a small amount of core paper and adhesive, and has strong and durable good characteristics. Its plane compressive strength is significantly higher than that of a U-shaped crucible, but once it has been deformed under pressure, it cannot be easily restored to its original shape. UV-shaped helium is compatible with the advantages of V and U shape, making up for their own defects, able to withstand higher pressures, and greatly improving the strength of the carton.
The relationship between cardboard production process, equipment failure and corrugated box strength
The quality of corrugated board produced by single-sided machine has great influence on the strength of corrugated box. The quality of single-sided machine is mainly reflected in the hardness, flatness, adhesive strength and corrugating forming effect of the board. The production process shows that the strength of corrugated paperboard, and the quality of linerboard and corrugated paper are certainly influential factors, but if the production process is not properly controlled, even the best paper quality cannot produce high-strength corrugated cardboard. Comparing and analyzing experimental results, it was found that, sometimes with paper materials with high index values ​​such as quantitative and ring crush strength, the hardness of the corrugated paperboard produced was not as good as the corrugated paperboard made from paper with low quantitative and ring pressure index. ,There are:
Incorrect selection of paper and paper corrugated cardboard are made of cardboard and corrugated paper. If the moisture content between them is too large, then after the glue is absorbed and heated, the paper's expansion and contraction will also change. Obvious differences, it is easy to cause the cardboard curl, so that the strength of the carton. Therefore, before the paper roll on the machine, it is best to test the moisture content of the base paper, try to choose the box paper and corrugated paper with similar moisture content to match the production, in order to prevent the paper board from curling.
Machine Speed ​​Discomfort The speed of a single-sided machine is too fast or too slow, which will affect the stiffness and bond strength of the board. Especially when the moisture of the base paper is high, if the production speed of the machine is too fast, the warm-up time is short, and the time for “eating glue†on the corrugation peak is short, so that the bonding effect and forming hardness of the cardboard are reduced. If the speed of the machine is too slow, the heating time of the board is relatively long, the board will easily become brittle, and the overheated temperature will cause premature curing of the adhesive, affecting the adhesive effect, all of which will reduce the strength of the board. Therefore, the production speed of the machine should be based on the situation of the moisture content of the base paper, the preheating area and the temperature, comprehensive consideration, and reasonable control, in order to ensure the quality of corrugated board production. According to the experience of the production process, the machine speed can be mastered by referring to the following Table:
Poor Adhesion The quality of paperboard bonding directly affects the compressive strength of the carton. The bonding quality depends mainly on the properties of the binder and the operating process, such as the physical and chemical properties of the viscosity, pH, solid content, and gelatinization temperature of the binder, and the blending operation of the binder. In order to ensure the bonding strength of the cardboard, good raw and auxiliary materials must be used. According to the actual production conditions, adjust the ratio of the binder, control the mixing time, stir the binder evenly, and use good water quality as much as possible. In the production process, it is necessary to control the amount of rubber properly, grasp the relationship between the speed of the machine and steam pressure, temperature, and the amount of adhesive applied to prevent the occurrence of blistering, pseudoplastic, and degumming. Improve the strength of the cartons.
The machine parts are in bad condition When corrugated roller shaft heads and bearings are worn or damaged, causing corrugated roller looseness, poor parallelism, and damage to crucibles, etc., it is prone to flat boring, collapse, high and low blemishes, degumming, foaming And corrugated board thickness and other quality issues. In addition, the old single-sided machine, the guide sheet wear and dirt, and the gap with the corrugated roll is too large, it is easy to cause the corrugated paper to jump, resulting in poor adhesion and high and low defects. all of these
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