Corrugated cartons production quality comprehensive test II

Crack test

There are carton and cardboard mills that perform the "cracking" test, sometimes referred to as the Mullen burst strength test. The burst strength test is to pierce a small hole in the test board. Burst testing preceded the Altematice Rule41 standard test of corrugated board material. Rule41 uses ECT as a standard test for corrugated shipping cartons. This change is beneficial to the carton manufacturing industry because ECT better reflects the carton compressive resistance than the rupture test. Use ECT to make carton manufacturers more flexible.

Other tests for corrugated cardboard

Of course, there are some other test methods to test the quality of corrugated board. So far, our discussion of corrugated board testing has focused on compressive strength and stacking strength, and the following tests emphasize board appearance and other properties and durability. These tests include cardboard warping, washboard phenomenon and printability.

Cardboard warping

Cardboard warpage is a very serious quality issue because warping the cardboard can cause crowding on the machine. Warp cardboard can also affect the performance of the carton. The warpage test uses a section of corrugated board to test the warpage of the board. Warpage is acceptable within a certain range, and it is generally accepted that 1/4 inch warpage in a 24-inch cardboard is acceptable. However, the continuous development of technology in the carton industry has gradually reduced the scope of acceptable board warpage. The current standard is that no more than 1/16 inch in 24 inches. Cardboard warp has upturned, downturned, end-to-end warp, warped and S-warped points. Each type of warpage has its origin and its effect on processability.

The cause of warpage is usually related to the different moisture content of the paperboard. If the moisture content or cross-section moisture content of the upper and lower cardboards is not the same, the board warpage may occur due to the shrinkage and expansion of the paperboard fibers. The processing of tile lines varies, such as the paste application process, the temperature of the hot plates and preheating conduits, the use of moisture or steam, and the degree of tension in the web, all of which can cause warpage of the board. The angle of the paper fibers, especially the different fiber angles between the upper sheet cardboard and the lower sheet cardboard, may cause warpage. Different substrates, coating processes, etc. may also affect warpage. To deal with board warpage, it is necessary to supervise and control the characteristics of the paper and the machining process.

"Panboard" phenomenon

Compared with the phenomenon of cardboard warping, the problem of printing that is more likely to bring about printing is the phenomenon of “plates” of cardboard. The phenomenon of "cocooning" occurs due to the slight difference in the thickness of the cardboard. When the paper on the upper layer collapses, it will cause the phenomenon of "coroning board", which will have a great impact on printing, especially when flexo printing. The washboard phenomenon also has a major impact on printing bar codes. Many operators overcome this problem by increasing the flexographic printing plate pressure, but as seen in the cracking test, these increased pressures will severely reduce the strength of the carton.

The phenomenon of the washboard is generated on the corrugated board production line, and the solution is usually related to the amount of glue used. However, paper properties, such as basic weight, number of holes, and fiber orientation can be the culprit in the phenomenon of the washboard.

Printing adaptability/Adhesive receptivity

To make the corrugated paperboard have good printing adaptability, the substrate must cooperate well with the ink, and the ink should be able to stay on the surface of the paperboard stably; the interaction between the ink and the substrate is very important. The next tests are very valuable for carton manufacturers who have printing problems or want to improve the quality of the printing. Since both inks and adhesives are water-soluble, these tests are also important for the adhesive properties of the adhesive. These tests include:

â–  Number of holes â–  Smoothness â–  Number of permeation holes

The number of holes in the substrate is very important for ink application and paste application. If there are too many holes, the ink or adhesive will scatter inside the cardboard. If the number of holes is not enough, the viscosity will not be strong enough, resulting in the sticking problem of the paper and the core paper. The hole number test is an indirect test of board density, hole size, and board openness.

Smoothness test

Insufficient smoothness will reduce the print quality, cause the board surface to be rough, the board to be untidy, and the printing to appear as "hairy" edges. To ensure good bonding of the cardboard on the tile, the paper must have a good surface structure.

The method of testing the smooth surface of the tissue paper mainly includes:

â– EMVICO surface test (mechanical test method)
â– Bendtsen smoothness test â– Parker Print surface test

These are all pretty good standard tests. If the carton factory needs it, this data can be applied to the surface board test.

Permeability

For best printing results, do not allow the ink to penetrate the paperboard, or let the ink flow horizontally, as these will cause the printed image to spread like feathers. It is best to let the ink adhere tightly to the cardboard. In addition, use ink as little as possible to reduce costs and shorten drying time.

Paper test

The next paper test can be used to predict the performance of the carton. No matter what kind of composite board test can understand the performance of corrugated materials or whether there is processing problems. These paper tests were used to pick up cardboard for processing into cartons to meet customer needs. These tests include:

■ Basic weight test ■STFI test (also called “short span stress test”)
â–  Ring pressure test basic weight test

The basic weight test is the most basic test method. It refers to the paper weight per unit area. The weight of the traditional American boxboard (basis weight) is 1000 square feet (lb/msf). Typical linerboard weights are 35, 42, 69, b/msfo typical core paper weights are 26, 33, b/msf. Of course, as the weight increases, the strength of the paper (composite board) increases.

STF, test and ring stress test

Carton manufacturers are interested in the lateral strength of paper because the lateral strength of the paper is the strength of the corrugated board. Paper mills typically use the SVIII1 test or the torquing pressure test to determine the lateral compressive strength of paper.

There are some formulas that can convert STFI and ring tests to ECT. With these formulae, if STFI or annular pressure is known, ECT can be predicted and then BCT can be calculated.

(Author/Matt Coleman Michael Schaepe)

(Translated / Li Xiaolei)