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Comparison and application of testing methods and results of corrugated board adhesion strength

the adhesion strength of corrugated board is one of the important indexes to evaluate the physical properties of corrugated boxes. For a long time, in the field of corrugated box production and inspection, there has been no consensus on the standards, test methods and results of corrugated board bonding strength. This paper intends to compare and discuss some understandings and practices in current practice in combination with the newly revised and implemented gb6548-98 "method for determining the bonding strength of corrugated board" (implemented on February 1st, 1999), in order to unify the understanding, implement the new national standard as soon as possible, and correctly understand and evaluate the bonding quality of corrugated board

I. test principle and test method of corrugated board adhesion strength

corrugated board adhesion strength refers to the firmness of the combination between corrugated paper and face paper, lining paper and core paper. The test principle is to insert the needle shaped stripping frame between the corrugated paper and the face paper or between the corrugated paper, the lining paper and the core paper of the sample, and then use a special compression instrument to press the needle shaped stripping frame with the sample to make it move relatively until the separated parts are separated. At this time, the maximum separation force between the ridge peak and the face paper or the joint surface between the ridge peak and the lining paper and the core paper is the bonding strength value

at present, there are two methods used to test the adhesive strength in the test experiment, one side method and two side method; The single side method adopts three kinds of rigid pins with different diameters according to different corrugation types. During the test, the pins are inserted into the same side space of the single corrugation in turn and stripped together with the support frame. This method can accurately measure the adhesion between the corrugation peak and the face paper or between the corrugation peak and the lining paper and core paper on any joint surface. The disadvantage is that the operation is cumbersome, so it is rarely used in practice. The double side method adopts 14 comb shaped pins with different diameters and spacing according to different ridge types. During the test, the upper and lower comb pins are inserted from both sides of the sample to peel off the two joint surfaces of the same ridge layer at the same time, and the force value of the joint surface with poor bonding strength. This method is widely used by corrugated box production and inspection units because of its simple operation and fast speed

it should be pointed out that the double-sided stripping method is a non-standard method, and there is no such provision in the new and old gb6548 standards for vigorously implementing the catch-up strategy for high molecular materials. From the perspective of testing practice, the comb shaped pins used in the double-sided method will produce different degrees of artificial cracking at the bonding place of the sample when inserting corrugated because the pins are too thick and arranged too closely when measuring the sample of type B corrugated, At the same time, due to the lack of support for this pin, after using for a period of time, the pin will produce bending deformation, which is not parallel to the pressure plate surface (the standard requires that the parallelism deviation of the pressure plate shall not be greater than 1%, so that the specimen has uneven peeling on one side in the width direction, which seriously affects the test results. On the contrary, the single side method is equipped with separate pins with different diameters, and there is a corrugated space between the pins; The end face of the pin is equipped with supporting accessories, which makes the pin difficult to deform after being stressed, and better overcomes the defects of the former. This method is the standard method specified in gb6548 new and old standards. In the test practice, it is also found that the test data of double-sided method and single-sided method for the same sample under the same conditions are 5% - 10% lower than that of the latter. If some other factors analyzed above are taken into account, the difference is even greater

II. Calculation formula and result expression of corrugated board adhesive strength

calculation formula and result expression of corrugated board adhesive strength indicate that the previous national standards are different from the industrial standards, and the concept is relatively confused. At present, the standards involved in the actual inspection mainly include gb6548 "determination of the adhesive strength of corrugated boards", GB "inspection procedures for corrugated boxes for transportation and packaging of export commodities", and the "detailed rules for the quality inspection of corrugated box production license" (hereinafter referred to as the "detailed rules") approved and implemented by the State Bureau of Technical Supervision in June 1992

it is specified that the calculation formula of bonding strength is:

p=f/s (1)

where p - bonding strength, n/m; F - the maximum force required for the specimen to be completely separated, N; S - sample area, cm2

it is not difficult to see that (1) the units on both sides of the equation in the formula are inconsistent, that is, n/m ≠ n/cm2, and the concept is not tenable. Obviously, the standard is wrong. This result of bonding strength in practice indicates that it is not adopted

2. In the detailed rules, the result of bonding strength is expressed as n/m2, so it is concluded that the unit of s in formula (1) is m2. At present, the understanding of this result of bonding strength is relatively unified, and it is widely used in the quality spot check of technical supervision system. This expression essentially refers to the maximum separation force required to peel the corrugated board per unit area

The results of adhesive strength given inand sn/t are kgf/Leng · 10cm and n/m · Leng, respectively. These two units are the same in meaning, and they are only a coefficient conversion relationship. The test method specified in the two standards is gb6548, and no calculation formula is given. According to the meaning of the unit expressed, the calculation formula should be:

p=f/l · n (2)

where l - the longitudinal length of the sample, m; N - the sample contains the number of corrugations that you hope will be helpful, corrugation

the adhesive strength value (n/m · corrugated) thus obtained essentially refers to the maximum separation force required to peel off a single corrugated strip per unit length in the paperboard. At present, the application of this formula and result expression is relatively common in the inspection of export corrugated boxes in the commodity inspection system. However, due to the limitation of test methods, the number of corrugated edges peeled off in the actual test is at most n-1. Therefore, there are two views and practices on the value of the number of corrugated edges. One is to take all (complete) edges contained in the sample, and the other is to take only the number of edges actually peeled off by the pin on the sample, that is, at most n-1. These are related to the effectiveness of the experiment. According to this understanding, equation (2) becomes p=f/l · (n-1) or in equation (2), n takes the actual number of peeled edges. Therefore, the adhesive strength value of the same sample will vary greatly due to the different values of the number of ridges taken by the inspectors, which is an urgent problem in practice

4. According to the revised GB, the result of adhesive strength is expressed as n/m, and the calculation formula is:

p=f/l (3)

where l - sample length, m

the adhesive strength value obtained from formula (3) essentially refers to the maximum separation required to peel the corrugated board per unit length when the width, that is, the length of the corrugated board, is certain (25mm). This concept of bonding strength is closer to formula (1), that is, n/m2, and there is a mathematical conversion relationship between the two, that is, 1n/m2=0.024n/m

the new standard has made new provisions on the expression of the result of corrugated board bonding strength, and clarified some wrong concepts in the old standard. However, since the revision of the current corrugated box production standard is not synchronized with the method standard, the changes in the expression of the bonding strength results in the new standard have created a vacuum in the evaluation basis of the bonding quality of corrugated boxes. At present, there are mainly two product standards based on. The standard value of bonding strength in the detailed rules is not less than 58800n/m2, and that in sn/t is not less than 588n/m · Leng. In addition, in testing practice, if the same sample is calculated with formula (1) and formula (2) respectively under the same conditions and judged according to the above two standards, sometimes two completely different judgment conclusions will be obtained. For example, for the B-type corrugated sample (the number of corrugated samples is 12), the maximum peeling force tested is f=120n, and p=60000n/m2 is calculated according to formula (1); Then the sample is judged to be qualified, and p=400n/m · Leng is calculated according to formula (2); The sample is judged as unqualified. From this point of view, the revision of corrugated box product standards and the unification of units between standards are imperative

III. conclusion

gb equivalently adopts the Japanese standard jzs "test method of corrugated board adhesion", which is also adopted by many developed countries in the world. In order to implement this standard in our country, we need the joint efforts of insiders and relevant departments

1. Relevant departments should speed up the revision of the detailed rules and GB corrugated board, GB, sn/t and other product standards, so that the standard value, calculation formula and result expression of the bonding strength of corrugated board can be unified to GB as soon as possible

2. Unified testing method, completely eliminate non-standard tools, namely, double-sided comb stripping frame, and adopt standard single-sided rigid pins and support frames in testing practice

3. Before the relevant standards were revised, with regard to the value of the number of corrugations in formula (2), the author believes that in the actual test, the number of corrugations that were not peeled off at the end of the sample is an uncertain value, that is, it shows irregularity, so it is inappropriate to take (n-1) as the corrugation data in formula (2). If calculated according to the actual number of peeled edges, many human factors will be added, resulting in inconsistent data processing and even wrong judgment. In addition, from the meaning of F, f refers to the maximum separation force required for the specimen to be completely separated. At this time, even if there is still corrugated in the specimen connected with the face paper or core paper, if the specimen is continuously pressed, the force value will not increase. Therefore, from the perspective of the correct understanding of the standard and the unification of the method, it is correct to adopt the first view and Practice for the value of the corrugation number in formula (2), that is, to take all (complete) corrugation numbers contained in the sample

4. Under the current situation, inspectors should be familiar with and master the relevant national standards and industrial standards, especially deeply understand that the above problems still cannot be eliminated, understand GB, be aware of the differences between standards and test methods, and try to eliminate the impact of objective and human factors on the adhesive strength test of corrugated board. This is particularly important for quality inspection institutions that have the power to judge product quality. (author: liguoming, China packaging industry product quality supervision and Testing Center (HUAIFANG)

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