The paper folding tester can be used to measure the strength of folding paper, paperboard, and other sheet materials with a thickness of less than 1 mm, such as copper foil used in the electronics industry, etc. It is mostly used by carton factories, quality inspection institutes, and college and university papermaking testing departments to test how well paper and paperboard can be folded.

Why test the folding resistance of paper?

During the production process, things like temperature, humidity, the quality of the paper, the strength of the adhesive, and the quality of the testing tools all affect the paper. When printing and making other things, paper that is hard to fold can cause a number of problems, so measuring how hard it is to fold is a very important test index.

Folding resistance is a very important measure of how well paper bag paper and carton lining paper will work. Most of the time, paper that needs to be folded a lot has to meet pretty strict requirements for how well it can be folded. For example, carton board needs to be hard to fold, or else it can be easily damaged while being shipped. There are also rules about how well cultural printing papers, like tracing paper, writing paper, letterpress printing paper, book cover paper, and packaging paper, can be folded. If you don’t, it’s easy for the words and pictures to get blurry and change how people see them.

1) Relative humidity. When changing from low humidity to high humidity, the folding resistance increases, reaches its maximum value after a certain humidity, and then decreases with the increase in humidity.

2) Temperature. As the temperature rises, the fiber strength inside the paper folding area decreases, resulting in a sharp decline in folding resistance, sometimes down to 1/3 of the original. Most of the folding resistance instruments currently used are equipped with a small fan to blow into the folding area, which limits the temperature rise in the folding area, so as to ensure the stability of the test results.

3) The paper folding tester‘s tension. The paper folding resistance test is actually a periodic measurement of the knife edge tension of the sample gradually damaged by folding under the condition of changing tension. The greater the tension, the smaller the number of paper-folding resistances.

4) Paper folding resistance tester’s folding blade and clamping opening. If the paper-folding resistance tester’s folding blade isn’t very smooth or wears out quickly, the folding times will be longer.

5) The initial viscosity and adhesive force of the adhesive are the most important factors influencing the bonding surface’s flexibility and folding resistance after drying.

What makes the MIT folding tester different from the Schopper folding tester?

The folding tester is the tool used to test how well paper and paperboard fold. The folding tester is divided into MIT folding testers and Schopper folding testers.

What makes one different from the other?

When the Schopper folding tester works, it folds the sample back and forth for almost 180 degrees. The other type, called the m1t type, folds the sample vertically. During use, the sample folds back and forth at an angle of 135 degrees.

The Schopper folding tester can be used with paper that is less than 0.25 mm thick and has a tensile strength of more than 1.33 kN/m. It can also be used with paperboard that is between 0.25 mm and 1.4 mm thick. The MIT folding tester works with paper and paperboard that is no thicker than 1.25 mm. So, the MIT folding tester can be used in a wider range of situations.

The functions of a Schopper type and MIT type folding tester are basically the same. What users purchase can be compared with each other.

1) According to different structures, the MIT folding tester can replace the collet. At the same time, many MIT folding testers are mostly LCD with printers, so it is more convenient to use.

2) Schopper type folding testers are made by a few companies of the enterprises in use are MIT-type folding testers.

A folding tester’s testing principle

Under a certain amount of tension, the paper or paperboard can handle being folded twice at 135°. It is shown by the number of times it folds in half and then back again, or by the logarithm of the number of times it folds in half and back again, with 10 at the bottom. Write down the times you used to break.

A box, a transmission system, upper and lower clamps, and counters make up a paperboard folding tester. The motor drives the connecting rod through the crank at 130 RPM, which sends the transmission system to the swing gear. Then, the swing gear meshes with the swing head gear to drive the swing head back and forth, which makes the upper fixture swing back and forth within a range of 135° swing angle.

The upper clamp has one splint that doesn’t move and one that does. The sample is bent back and forth 270° by moving the upper clamp left and right. The lower clamp is attached to the load rod and has a variety of weights on it so that the load can reach 3500g. During the test, the tension depends on the sample, and a liquid crystal display is used for the counter.

How to use the folding tester

Operation steps

1: Sample collection and processing, sampling according to the standard, and cutting 140 mm along the paper web. There are 10 40mm samples with a dimensional error of 1mm. The long side is parallel to the corrugation direction, and the short side is perpendicular to the corrugation direction.

2: Vertically clamp the corrugated board sample with an indentation between the folding tester‘s upper and lower clamps. For the single corrugated board sample, the edge of the upper clamp is clamped at a position 3mm away from the center line of the indentation. For the double corrugated board sample, the edge of the upper clamp is clamped at a position 5mm away from the center line of the indentation.

3: Apply a weight of 1500–2500g to the lower fixture’s load rod, lift the bottom support of the lower fixture, and relax after clamping the sample to tension the sample.

4: Start the machine and bend the sample by moving the upper fixture back and forth at a rate of 130 R/min. The upper clamp bends 135° to the concave surface of the indentation, then bends 270° in the opposite direction, and then bends 135° to the concave surface of the indentation to return to the vertical position. This is called a 270° reciprocating bend. The sample is bent back and forth over and over again until the sample breaks. Take the counter’s value, which is the sample’s folding time. For the next test, the counter has been reset.

The test results are shown as the arithmetic mean of all the values that were measured, and the highest and lowest values are shown.

How to calibrate the paper folding tester?


1) Tension spring verification: place the weight on the disc, observe whether the indicated value of the pointer equals the weight, and verify three points: 4.9, 9.8, and 14.7n three times each. If there is a deviation, move the pointer position to make it reach the correct value. If the deviation is small, it can be adjusted by the fine-tuning screw.

2) Checking for the change in the tension indication: Press the tension rod until the pointer is at 9.8N, clamp a strong sample between the upper and lower collets, start the machine and fold it 100 times, stop the machine, and then slowly turn the knob by hand to make the folding head fold back and forth once. At the same time, pay attention to the fact that the change in the pointer should not be more than 0.34n.

3) Tension rod friction test: place the weight on the weight plate, gently lift the tension rod with your hand, and then slowly lower it to the equilibrium position. The reading on the scale is F1. Then pull the tension rod down, and then slowly relax to restore it to the equilibrium position. The position reading value is F2, and the tension rod friction must not exceed 0.25N.The calculation formula is as follows: F = (F1-F2)/2 0.25N.


What is the folding resistance of paper?

Folding resistance is one of the most basic mechanical properties of paper. It shows how well paper can resist being folded and unfolded over and over again. The folding resistance of paper is the time it takes to break after being stretched with a certain amount of force and then folded back and forth. It is measured in time, and the unit is the number of times it takes to fold twice. For the longitudinal folding resistance, the longitudinal cutting sample is used, and for the transverse folding resistance, the transverse cutting sample is used.

Which has the greater transverse and longitudinal folding resistance?

In general, it is harder to fold something in the long direction than in the short direction. This is because of how the fibers are set up and how well the long fibers stick together.

What factors influence how well paper resists folding?

  1. The weight, thickness, tightness, and amount of moisture in the paper also affect how well it can be folded. When the thickness and amount of the same kind of paper made from the same kind of slurry increase within a certain range, the resistance to folding goes down by a lot. This is because the thicker paper surface will cause more tensile stress when it twists and turns.
  2. Folding resistance depends on how long, strong, flexible, and stuck together the fibers are. High folding resistance comes from paper made of long, strong, and tightly bound fibers. Adding hardwood pulp or grass pulp to chemical pulp made from coniferous wood will make it easier to fold computer paper.
  3. When the amount of water in paper goes up, the fibers stick together less, but both the fibers and the paper get softer. The result has two opposite effects on how well paper can be folded. When the humidity goes up, paper with a high tear strength will be harder to fold, while paper with a low tear strength will be easier to fold.
  4. The process of putting mineral fillers into fiber materials to make them stronger. This will make it much easier for the paper to fold. Mineral filler hurts the folding resistance because it weakens the fibers’ ability to stick together and because the hard filler particles make it easy to break the fibers when folding.
  5. Beating makes the paper tighter, which has two different effects on how well it holds its shape when folded. At the start of a beating, the resistance to folding goes up as the amount and tightness of the beating get better. As the beating degree and tightness get better, the folding resistance will go down when the tightness is above a certain point.

What are the requirements for how well printed paper doesn’t bend?

Folding resistance is a good way to measure how strong and flexible a piece of paper is. This index is more important when printing on paper and paperboard, especially when the ink needs to dry and set at a certain temperature. When the paper sheet goes through the drying part, it quickly loses water and becomes brittle. This makes it easy to break the paper sheet when folding it. Many types of paper, such as security paper, account book paper, map paper, book cover paper, and packaging board, need to be folded many times before they can be used. This means that these papers need to have high folding resistance.

What’s the difference between paper tearing and folding resistance?

The tearing degree of paper is a technical index to evaluate the shear resistance of paper. The force needed to tear a certain length of pre-cut paper is measured in Mn. It is easier to tear the paper along the long side than along the short side. For web printing, the degree to which paper can be torn is an important measure of its mechanical strength.

Folding resistance is the number of times a 15 mm wide sample is folded back and forth at 135 degrees until it breaks. There is also longitudinal folding resistance and transverse folding resistance when it comes to folding paper. In general, the index of folding resistance needs to be high for drawings and book covers.