On the moisture content and pH of paper

Dissect paper and explore the water content and pH of paper

the basic raw material of paper is plant fiber, which is generally subdivided into wood and non wood. Most of the paper is made of wood fiber, because each part of wood has a large amount of fiber, and its cost is relatively cheap. However, in addition to using wood, there are also papers made of non wood fibers, such as bagasse, reed, rags, etc. Different raw materials will affect the chemical properties of paper. The following will discuss with you about the water content and acid gluten of paper

water content of paper

generally, the water content of paper is expressed as a percentage of the weight of water contained in the paper and the weight of the paper. Generally, the water content of printing paper is about 4 ~ 8%. According to this ratio, about 40 ~ 80kg of water is in a ton of paper

it is a very important question how much Baxian in the paper is water. Whether the water content of the paper is too much or too little, it will affect the printing effect. With too little moisture, the paper is easy to become brittle, and it is also easy to generate too much static electricity on the printing machine; But too much moisture in the paper is not a good thing, because it will make the printing ink difficult to dry. However, relatively speaking, the amount of moisture has a small impact on printing. It has a greater impact on the paper itself. The tension resistance, flexibility, folding resistance, etc. of the paper will change due to the change of water content

as mentioned earlier, the basic raw material of papermaking is plant fiber. Plant fibers are hydrophilic and belong to hydrophilic substances. It turns out that all hydrophilic substances have a characteristic, which is to combine with water as the medium. That is to say, if the paper fibers are squeezed by pressure alone, and water is lost for blending, the fibers cannot be bound together, resulting in paper. However, this does not mean that the more water there is, the tighter the fiber will knot. The so-called extreme will change. The relationship between the bonding strength between fibers and the amount of water is a bell curve. Assuming that the water content increases to a certain amount, the structure of the paper will become loose, and the bonding strength of the fiber will begin to decline, affecting the tensile strength of the paper

conversely, too little moisture will also affect the paper. Due to too little water content, the paper becomes too rigid, so it is easy to be brittle, and the fibers are also easy to slip, which greatly reduces the flexibility and folding resistance of the paper. Therefore, in order to give full play to its best performance, it is necessary to properly control the moisture content in the paper

however, we also need to consider the humidity in the air. When the fiber in the paper is exposed to the air, it will naturally absorb the moisture in the air. The speed of absorption depends on the humidity and temperature at that time; If the air was very dry at that time, the water in the paper would be lost in the air in turn. Whether paper will absorb water or lose water depends on the relative humidity of paper and air. If the moisture content of the paper is equal to that in the air, the equilibrium moisture will be reached, and the structure of the paper will not change again due to the humidity of the air. Different papers have corresponding equilibrium moisture under different relative humidity, and different papers will have different equilibrium moisture even under the same humidity. The more hydrophilic the paper is, the higher the equilibrium moisture of the paper is, and vice versa

the method of measuring moisture is not complicated. Simply explain, put the tested sample into an oven at 100 ~ 105 ° C and supply it to [constant weight] (Huan weight refers to the weight of two consecutive times, and the weight difference of the sample is less than two tenths of a million), and then calculate according to the following formula:

x = (m1-m2)/m1 × 100%

X: moisture content in the sample (%)

M1: mass of the sample before drying (g)

M2: mass of the sample after drying (g)

pH of paper

pH is expressed in pH value. When pH value is 7, it means that the pH of the paper is neutral. If pH value is lower than 7, it means that the paper is acidic, and if pH value is higher than 7, it means that the paper is alkaline. Of all these values, the best one is neutral 7, of course, but in fact, there are not many papers with a pH value of exactly 7. The pH of many non coated paper is between 4.5 and 7.0, with weak acidity; The pH value of coated paper is between 7 and 9, with weak alkalinity

but even if the pH value of the paper is measured, it does not mean that the paper will always be 9. The fasteners of the electro-hydraulic servo universal experimental machine should be locked regularly: the vibration after the sample is broken will often make some fasteners loose. At this pH value, the pH value will change due to the surrounding environment.  the air contains carbon dioxide, which will react chemically with the water in the paper, gradually reducing the pH value and generating weak acidity. The paper with alkali may gradually become sour, and the paper with acid will become more sour

why do we have to know the pH value of paper? Because the pH of paper will directly affect the life of paper. The more the pH value of a piece of paper is, the more straight the size is. The characteristics of nanoparticles can be analyzed from two aspects: the surface characteristics and the internal characteristic diameter are 150 ± 50nm low, and the fading phenomenon and tension resistance of the paper will be more and more poor, which means that this paper will not live long. Under the influence of acidity, the cellulose and hemicellulose of paper will accelerate the decomposition, making the molecular structure of paper become loose. However, increasing the pH value does not necessarily prolong the life of the paper, because in an alkaline environment, the fiber will also accelerate the decomposition

what problems will occur when printing with paper with low pH value? During printing, the acidic substances of the paper will react chemically with the drying agent added to the ink to produce substances insoluble in oil, which will hinder the drying process of the oxidized conjunctiva and slow down the drying speed of the ink; In addition, due to the weak acidity of the printing lubricant itself, and the continuous exudation of acidic substances from the paper during the printing process, the acidity of the lubricant is aggravated, and the drying time is further prolonged, resulting in poor dryness and dirty back of the print

paper with high pH has another problem. Like paper with too high acidity, paper with too high alkalinity will also decompose substances in printing, but this time it will decompose alkali. These alkaline substances will neutralize the fountain solution and improve the pH value of the fountain solution, thus affecting the proper transfer of ink. What's more, they will reduce the gloss of prints and make the ink look less bright

therefore, as long as we first understand the pH of the paper before printing, we can adjust the pH value of the fountain solution according to this, and use compatible inks to print, so as to effectively maintain the printing quality