For plastic film printing inks, there are some special requirements, but because the standardization of the determination methods of these contents is relatively poor, we can only briefly describe the situation here. Admittedly, judging from the current reality, these methods are also sufficient to solve some practical problems.
1. Determination of adhesion (sex) fastness
Use a certain length of scotch tape (or adhesive plaster) to paste on the printed matter, flatten it with your fingers and make it fit tightly with the printed matter. Then, slowly uncover half of its full length, and then quickly uncover the other half.
Observe the situation where the printed matter is stuck by the tape and the amount of ink stuck on the tape. In this measurement, it is necessary to pay attention to the fact that the coating on the film (some films are coated with a layer of coating) is peeled off, because this will give completely incorrect results.
Adhesion fastness is an inspection item required for film printing.
2. Kneading (soft)
The determination of this application performance is to pinch (hold) the printed matter with the thumb and forefinger of both hands, rub it 10 times, and then judge the shedding of the ink to determine the total mass.
3. Finger resistance
Swipe the printed matter repeatedly (for example, 5 times) with your nails, and then judge the ink shedding on the printed matter.
According to the current situation in our country, the evaluation of the above three determinations is generally divided into five grades, that is, excellent, good, fair, poor, and poor.
4. Slippery
In order to make the packaged products pass through the automatic packaging machine smoothly, and for the convenience of control and mastery, the slipperiness of the printed matter is also very important.
Before measuring the slipperiness, if the printed matter is just printed, it needs to be left for more than two hours before measuring. Because some slippery materials (additives) used in the ink can only migrate to the surface of the printed matter after being stored for a certain period of time.
Determining the degree of slipperiness of printed matter is to measure the electrostatic coefficient of friction on an inclined plane.
The method of measurement is to tighten a piece of printing sample on a flat plate (ink film facing upwards), and then tighten the second printing sample on a relatively small slider (pry) (ink film facing outwards), and then place the wrapped sample Put the slider with the printed sample on one end of the flat surface, make the ink surfaces of the two printed samples contact each other, and then slowly lift up the end of the flat surface with the slider until the slider just starts to stabilize slide down the plane. The tangent angle of the inclination when the flat surface is raised to the sliding block is equal to the coefficient of static friction.
5. Adhesion into blocks
After printing and drying, the printed matter should be rolled up quickly and in contact with the same film, it will be subjected to a pressure of 340-1360 kg/hour. Therefore, it is very important whether the printed matter is sticky, which can slowly pull (separate) the printed matter, observe the transfer of the ink to the plastic (back side)... (comparable with standard printed matter) and identify it .
Another situation is that when the printed product is used to package hot food (such as biscuits, etc.), the printed product will be bumped and contacted by this on the packaging line, so the adhesion should also be measured.
For the measurement, two pieces of printed samples can be stacked face to face, and then clamped with two pieces of glass (so that some parts of the printed matter are in contact with the ink, and some places are in contact with the plastic), and placed in a temperature of 50 ℃. In the oven, press a weight (for example, 500 grams) on the glass sheet, take it out from the baking after one hour, uncover the printed matter, and observe and judge the ink on the printed matter sticking to each other.
In addition to the above items, the following items can also be determined according to the type of oil and the final application.
6. Heat resistance
It is mainly considered to be used in the heat sealing process to prevent the ink from being pulled (pulled) up by the pressure in the heat sealing process.
Method: Contact a piece of printed matter with a piece of clean aluminum foil (stacked together), and then check it with the heat sealing process during actual production (usually heat pressing for one second), separate the printed matter from the aluminum foil after cooling, and observe the ink Pulling (pulling) off and ink transfer to aluminum foil.
7. Freezing resistance
Because some packaged products are stored in deep freeze. It seems that since these products are not really used under cryogenic conditions, but during the period of (ice) melting after removal from the refrigerator, the determination can be carried out by water immersion.
The method of determination is to immerse the printed matter in cold water for 1-5 hours and take it out. Folded 10 times, the ink film must not lose 5% of its weight, then wipe it dry with a water-absorbing substance, and then use scotch tape to carry out the sticking test according to the method in item 1 and item 1 of this section, and the result should not lose 5% of its weight ( fall off).
8. Smell
Since there are many liquid inks used for food packaging, they (mainly inks) should have minimal odor and should not cause any foul smell to the packaged items.
Put the tested printing sample, the standard printing sample and the clean empty table film (the same as the film used to print the tested printing sample) in sealed jars, put them in a baking foil at 50°C for one hour, and then take them out, containing Open the can and sniff its smell, compare the difference. Then put it in a sealed jar, cool to room temperature, take it out and smell its smell for comparison. Then judge and evaluate it.
Nine, fat resistance
Many plastic products are used to package oily food, therefore, it is necessary to measure the oil resistance of printed matter. The measurement method can be used to dip a ball of cotton wool with appropriate oil (depending on the need), rub it on the printed matter 20 times (the pressure should be as uniform as possible), and then observe to judge the dyeing situation on the cotton wool ball.
