Important factors of corrugated cardboard's quality of punching resistence.

Jurecic, Denis ; Babic, Darko ; Lajic, Branka 等

1. INTRODUCTION

Corrugated cardboard is defined as cardboard made of one or more layers of paper used for a wave and glued between two or more single--or multi-layered flat areas (Stricevic, 1983). Corrugated cardboard used for packaging in the food industry must be glued with gluten, not with siliceous glue. Packaging used for overseas transport must be waterproof and corrugated cardboard packaging for frozen products must be resistant to low temperatures (those below 0[degrees]C) and humidity and must not be slippery (Rodin, 1991). In other words, the choice of the type of paper used in corrugated cardboard manufacturing will largely depend on the packaging type (transport or commercial). High-grammage paper types are used for making transport packaging, while low-grammage ones fit commercial packaging better.

2. EKSPERIMENTAL

Dynamic punch test is used to determine mechanical resistance of corrugated cardboard to direct mechanical hits: the test tells us how strong those hits can be before a specific corrugated cardboard type breaks (Hanlon, 1989). Four types of five-layered corrugated cardboard were tested: 2BT, BST, 2TS and T2S. The material tested is specified in Table 1.

A Franck dynamic punching device was used to test the dynamic punching resistance of corrugated cardboard and its relation to humidity (www.techlabsystems.com, 2007). The samples were cut into 175x175mm pieces, as required by the standard. The cut samples were then exposed to different levels of humidity: 97%, 85%, 75%, 55% and 35%. Five large bags containing solution of varying humidity levels (35%, 55%, 75%, 85% and 97%) were used in the process. A container of liquid was placed in a bag and so were 20 samples of each corrugated cardboard type. The bag was then sealed and the samples were exposed to a particular humidity level for 5 days.

After the samples had been exposed to humidity for 5 days, 10 punches were made on the obverse and 10 on the reverse for each humidity level and each corrugated cardboard type. After punching all the samples, the average was calculated. The total reached 400 punches (200 on the obverse and 200 on the reverse).

2.1 Determining humidity in laboratories

Humidity can be extracted from corrugated cardboard by putting it in kilns for a longer period of time at 105-120[degrees]C. Corrugated cardboard dries until it reaches a constant weight. The cardboard is then taken out of the kiln and weighted. The difference in weight before and after the drying process tells us how much water it contained. A round corrugated cardboard sample of 10 cm in diameter is placed under a 2.5 cm column of distilled water of temperature around 20[degrees]C for 30 minutes. The difference in weight between the wet and the dry corrugated cardboard must not exceed 1.25 g for the outer layer of paper or 2 g for the inner one. Absorption of corrugated cardboard is tested in the following way: a sample of 15x15 cm is immersed completely in a water container for 10 minutes. The quantity of water absorbed can be determined by weighing the sample before and after the immersion. The test results are called immersion numbers and they express grams of absorbed water after the immersion in standard room conditions.

2.2. Testing the dynamic punching resistance of corrugated cardboard--Puncture Test

The test is used to determine the behaviour of corrugated cardboard when exposed to direct mechanical hits. Toughness of corrugated cardboard and its resistance to tearing is determined on the basis of that test: the test tells us how strong those direct mechanical hits can be before a specific corrugated cardboard type breaks, which is very important if a corrugated cardboard packaging contains fragile objects (Talbi, N., Batti, A., Ayad, R., Guo, Y. O., 2008),. Three different samples of corrugated cardboard were tested: 2K, 2K/3 and 2K/e. Each cardboard sample was tested 10 times on the obverse and 10 times on the reverse.

3. RESULTS AND DISCUSSION

3.1. Results

The results show that the maximum work required for a punch-through on the obverse is 7.58 J when the humidity level is 75%. The minimum work required is 7.33 J when the humidity level is 35%. The maximum work required for a punch-through on the reverse is 7.82 J when the humidity level is 55%. The minimum work required is 7.58 J when the humidity level is 97%. It is, therefore, to be concluded that the optimum humidity levels for a punch-through on the obverse are between 97% and 75%, while the optimum humidity levels for a punch-through on the reverse are between 85% and 55%.

The results show that the maximum work required for a punch-through on the obverse is 7.25 J when the humidity level is 85%. The minimum work required is 7.11 J when the humidity level is 35%. The maximum work required for a punch-through on the reverse is 7.44 J when the humidity level is 55%. The minimum work required is 7.11 J when the humidity level is 97%. It is, therefore, to be concluded that the optimum humidity levels for a punch-through on the obverse, as well as on the reverse, are between 85% and 55%. When the humidity level is 97%, a larger amount of work is required for a punch-through on the obverse.

The results show that the maximum work required for a punch-through on the obverse is 7.18 J when the humidity level is 55%. The minimum work required is 6.82 J when the humidity level is 97%. The maximum work required for a punch-through on the reverse is 7.25 J when the humidity level is 85%. The minimum work required is 7.13 J when the humidity level is 75%. It is, therefore, to be concluded that the optimum humidity levels for a punch-through on the obverse are between 55% and 35%, while those for a punch-through on the reverse are between 85% and 35%.

The results show that the maximum work required for a punch-through on the obverse is 7.04 J when the humidity level is 55%. The minimum work required is 6.69 J when the humidity level is 35%. The maximum work required for a punch-through on the reverse is 7.38 J when the humidity level is 55%. The minimum work required is 7.03 J when the humidity level is 35%. It is, therefore, to be concluded that the optimum humidity levels for a punch-through on the obverse, as well as on the reverse, are between 97% and 55%.

3.2. Discussion

The results for the BST type are good when compared to those for 2BT, i.e. the average values of work required at all humidity levels on the obverse and the reverse are higher than 7.1 J. The two other types of material tested (2TS and T2S) gave almost the same results for a punch-through on the obverse (less than 7 J at all humidity levels), while their results for a punch-through on the reverse are slightly better, ranging between 7 J and 7.4 J. However, when compared to 2TS, T2S yields better results when the humidity levels are higher than 55%. The amount of work required for a punch-through on the 2BT type is the largest of all, on the obverse and on the reverse alike. BST comes second and 2TS and T2S could both hold the third place, since the results are very similar. At all humidity levels, 2BT and T2S are more resistant to punching on the reverse, while BST is more resistant to punching on the obverse only when the humidity level is 97%. 2TS is more resistant to punching on the obverse only when the humidity level is 55%. The punching resistance of the 2BT, BST and T2S types on the obverse is proportionate with the humidity level, but for the 2TS type it varies inversely with humidity. The punching resistance on the reverse varies inversely with humidity for 2BT, BST and 2TS, while it is proportionate with the humidity level for T2S. The test shows that the results obtained for the obverse of the 2BT type are the best when the humidity level is between 97% and 75%. The best values for the work done on the reverse are obtained when the humidity levels are between 85% and 55%. The greatest difference between the values obtained for a punch-through on the obverse and that on the reverse of 2BT is 3.7% at the humidity level of 55%, and the smallest difference is 1.3% with the humidity level of 75%. The results obtained for the obverse and the reverse of the BST type are the best when the humidity level is between 85% and 55%. The values obtained for a punch-through on the reverse exceed those on the obverse only when the humidity level is between 85% and 35%. When the humidity level is 97%, a larger amount of work is required for a punch-through on the obverse. The greatest difference between the values obtained for a punch-through on the obverse and that on the reverse of BTS is 3.76% at the humidity level of 55%, and the smallest difference is 0.14% with the humidity level of 35%. The test shows that the results obtained for the obverse of the 2TS type are the best when the humidity level is between 55% and 35%. The best values for the work done on the reverse are obtained when the humidity levels are between 85% and 35%. The values required for a punch-through on the reverse exceed those on the obverse at all humidity levels except that of 55%, in which case a slightly larger amount of work is required for a punch-through on the obverse. The greatest difference between the values obtained for a punch-through on the obverse and that on the reverse of 2TS is 4.74% with the humidity level of 97%, and the smallest difference is 0.13% with the humidity level of 55%. The results obtained for the obverse and the reverse of the T2S type are the best when the humidity level is between 97% and 55%. The values obtained for a punch-through on the reverse exceed those on the obverse at all humidity levels. The greatest difference between the values obtained for a punch-through on the obverse and that on the reverse of T2S is 5.97% with the humidity level of 85%, and the smallest difference is 4.6% with the humidity level of 55%. The 2BT type yielded the best results in the test and could, therefore, be said to stand out from other tested cardboard types. The second best type would be BST, while 2TS and T2S yielded very similar results and are considered to be of the same quality.

4. CONCLUSION

However, the research done on the material and the analysis of the results obtained did not result in any linear or square function that could illustrate the trend of increasing or decreasing amount of work required for dynamic punching. The results remain unpredictable. Nevertheless, it could be concluded that the best results for all the types tested were obtained at the humidity levels between 85% and 55%, as the practice has clearly confirmed.

5. REFERENCES

Hanlon, J. F., (1989). Handbook of Package Engineering, McGraw Hill Book Company, pp. 1-6, New York

http://www.techlabsystems.com/en/datasheets/corrugated/punct ure-testers-web.pdf, Accessed: 2007-03-25.

Rodin A., (1991). Packaging of cardboard, pp. 265-266, Progres, Zagreb

Stricevic N. (1983). Modern Packaging 2, pp. 31-32, Skolska knjiga, Zagreb

Talbi, Nr, Batti, A., Ayad, R., Guo, Y. O. (2008), An analytical homogenization model for finite element modelling of corrugated cardboard Composite Structures, Available online 11 April 2008 Tab. 1. Specification of the material tested Corrugated cardboard type 2BT BST Flat layer type-- white white obverse testliner testliner grammage [g/[m.sup.2]] 130 130 Flat layer type-- white testliner reverse testliner grammage [g/[m.sup.2]] 130 115 Mid-layer type testliner srenc grammage [g/[m.sup.2]] 115 100 Wavy layer type fluting fluting grammage [g/[m.sup.2]] 105 105 Corrugated cardboard type 2TS T2S Flat layer type-- testliner testliner obverse grammage [g/[m.sup.2]] 132 132 Flat layer type-- testliner srenc reverse grammage [g/[m.sup.2]] 115 100 Mid-layer type srenc srenc grammage [g/[m.sup.2]] 100 100 Wavy layer type fluting fluting grammage [g/[m.sup.2]] 105 105