Corrugated cartons are playing an increasingly important role in modern production.As one of the effective measurement standards of corrugated carton quality, compressive strength is not only influenced by molding process and printing design, but also closely related to environmental factors.Therefore, in daily production, it is necessary to strengthen the carton compressive strength testing, carton bursting strength tester through grasping the change curve of force value and deformation quantity, combined with various influencing factors, to further evaluate and improve the quality of corrugated carton.

Corrugated carton is one of the most widely used packaging containers in modern packaging, because of its light weight, easy to fold, cheap price, reusable and other advantages, so that its consumption has been significantly increased.With the expansion of corrugated carton application market, carton users on its quality and performance more demanding, corrugated carton in a variety of environments, should have enough to withstand the external load of mechanical strength.Among them, the compressive performance comprehensively reflects the basic characteristics of the carton, while playing a protective role in the circulation of goods, therefore is the primary indicator of corrugated carton quality control.

The compressive performance of corrugated carton refers to the compressive strength of corrugated carton under pressure and the ability to protect the contents, usually expressed by compressive strength.In order to calculate the compressive strength of corrugated boxes, many empirical formulas such as kelly carter formula and markey formula were put forward.Among them, the kelly carter formula is recognized as the formula with the smallest relative error in the calculation results: PK=PX(4aXZ/Z) 2/3zj

Where, PK is the calculated compressive strength, N;PX is the comprehensive ring compression strength of the corrugated base paper, N/cm;Z is the circumference of the carton (cm);AXZ is the corrugated constant;J is the carton constant;

Through the formula, we can see that the composite ring strength of the original paper, as well as the circumference of the carton and corrugated carton compressive strength has a direct relationship.In addition, forming process and external environmental factors will also interact, resulting in different degrees of decline in the compressive performance of corrugated boxes.

First, the quality of the paper

1. the quantitative basis paper

Quantitative, that is, paper grams.Quantitative sampler is used to test the quantitative of the original paper.For the same fiber structure and manufacturing process of the raw paper, the strength of the ring is equal to the quantity of the raw paper multiplied by the ring pressure index.The cyclic pressure index of different types of corrugated paper is listed in table 1.Therefore, the same material of corrugated raw paper ring compression strength, depends on the actual application of the raw paper quantitative, the larger the quantitative, the more the carton compression strength.On this basis, the quantitative stability of the original paper, that is, whether the thickness of the paper is uniform throughout is also an important factor affecting the compressive stability of the finished carton.

2.the tightness of the paper

Tightness, refers to the weight of each cubic centimeter of the paper, is a measure of the paper structure of the index of tightness, determines the rigidity, strength, permeability and absorption of the paper and other characteristics.When a variety of raw paper using adhesive after bonding, the high tightness of the raw paper due to its own fiber has a strong mutual pulling pull force, so as to combine with the adhesive effect is good, the overall bonding strength is high.On the contrary, the adhesive is easy to be absorbed and dispersed by the original paper, the same sizing dose, the amount of glue per unit area, reduce the adhesive strength between the original paper, indirectly affect the compressive strength of the finished corrugated carton.

3.the moisture and sizing of the paper

Corrugated carton used by the original paper is generally composed of plant fibers, after a series of processing, will contain a certain amount of water, normal should be controlled in 9%~12%, conducive to corrugated molding.If the water content of the original paper is less than 9%, after sizing the original paper will absorb moisture and produce bubbles, reducing the bonding area between corrugated and tissue/paper.If the water content of the paper is too high, the sizing is easy to diffuse, reducing the bonding strength.

At the same time, sizing will also have a certain effect on the moisture content of the paper.In general, in the production of raw paper, a certain amount of water-resistant colloids are applied to improve the process of water-resistant raw paper for sizing.This process requires a reasonable sizing, in order to make the original paper is not easy to absorb moisture, to maintain the stability of its water content, and to ensure the compressive strength of the finished carton.However, if the sizing is too high, that is, low moisture content, the raw paper fiber will become brittle, affecting the compressive strength of the box.If the sizing of the paper is too low, it can not block the absorption of moisture, resulting in increased water content of the paper, fiber expansion, ring compression strength greatly reduced.

Two, the impact of corrugated box molding process

1. Edges and waveforms of corrugated boxes

Corrugated boxes are generally divided into A, B, C, E, K five types, the first four of which are most widely used.The a-type coil is A kind of corrugated shape first invented, which has the largest corrugated spacing and height, and the smallest number of coils per unit length. This shape has A certain degree of elasticity, which can play A good buffering performance and bear A large impact force.B type and A type of the opposite, the lowest corrugated height, unit length of the corrugated density, the surface of the paperboard flat, with high flat strength, in the external pressure is not easy to deform, good stability.Both the length and the number of corrugations per unit length of c-type coil are between type A and type B, and their performance is also between them.E - type coil is thin and dense, its rigidity and strength, feel hardness is better.Based on the above characteristics, the compressive strength after packing is A, C, B and E from high to low.In practice, in order to obtain higher compressive strength, usually use two or three kinds of corrugated corrugated board of three, five or seven layers.

In addition to the shape of corrugated, corrugated board waveform will also affect the strength of corrugated board and boxes.V-shape, u-shape and UV shape are the three main waveforms with different characteristics, as shown in table 2.As can be seen from the table, UV is an ideal waveform, producers can also choose the right waveform according to the actual demand.

2. Length, width and height of corrugated cartons

Under the condition that the material of corrugated paper is consistent with the shape and waveform, the length, width and height of finished cartons are closely related to their compressive strength.As a rule of thumb, the ratio of length to width of corrugated cartons is between 1 and 1.8, which has the least impact on the compressive strength, only ±5%. When the ratio of the two is about 1.5, the compressive strength of cartons is the highest.In addition, the height of the carton should not be too high, should be controlled in 350~650mm, when the height increases, instability suddenly increase, compressive strength will also decline.Therefore, when designing the size of the carton, it is advisable to consider the three-party ratio comprehensively, so as to ensure that the carton has good compressive strength and reduce the waste of cost.

3. Printing technology

In the attention to brand publicity today, corrugated box printing design is more and more attention, but, printing technology in a certain extent will also cause the decline in the compressive strength of finished cartons.Mainly reflected in two aspects:

(1) influence of printing pressure.The traditional printing process will impose a certain amount of pressure on the corrugated board, if the pressure is too large will be easy to collapse the corrugated, so that it lost the original compression function;

(2) ink infiltration effect.Ink is an indispensable part of the printing process, but it will be on the surface of corrugated board infiltration, seriously reduce the compressive strength of the carton.When the printing area is large and overprint times, it will make the infiltration more obvious.

Three, environmental factors - humidity

According to the above introduction, corrugated cartons because of the use of highly absorbent fiber materials, easy to absorb water, resulting in a decline in compressive strength.In addition to the control of material moisture content during processing, factors such as production environment, storage environment, use environment, weather and so on May cause the high humidity environment of corrugated boxes.According to the analysis of the research data, the relative humidity increased from 40% to 60%, and the compressive strength decreased the most, reaching 17%.Second, relative humidity 80% to 90% range, compressive strength decreased by 10%;The smallest drop was between 60 and 80 per cent, at 7 per cent.Therefore, it can be seen that the greater the humidity around the corrugated box, the greater the loss of compressive strength.

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