With the progress of science and technology and the improvement of people’s living standards, the consumption of coated paper is increasing, and the application scope and purpose of coated paper are more and more extensive, such as packaging, calendar, exquisite printed matter, trademark, gift, etc. This is mainly because coated paper has incomparable advantages and characteristics of other paper products. Classification And Application Of Coating Adhesives.
The performance of coated paper mainly depends on the coating. The main components of the coating are pigment and adhesive. Due to different requirements for coating properties and coating equipment, the matching proportion is also different. The proportion of these two components generally accounts for 75% – 90% of pigment and 10% – 25% of adhesive. The following is a brief introduction to the classification, function, properties and preparation of adhesives.Classification And Application Of Coating Adhesives.
1 Classification of adhesives
Adhesives are generally divided into two categories: one is natural products, such as modified starch, casein, soy casein, animal glue, etc. Among the natural adhesives, modified starch is the most widely used. It has the characteristics of stable quality and low price. The other is synthetic rubber, commonly used are styrene butadiene latex, carboxyl styrene butadiene latex, polyvinyl alcohol, polyacrylate, etc. The most widely used synthetic adhesives are carboxylated styrene butadiene latex and polyacrylate emulsion. The former emulsion is slightly stable and easy to yellow, and the latter has relatively stable quality, but the relative price is relatively high.Classification And Application Of Coating Adhesives
Generally speaking, an adhesive is difficult to achieve the required coating viscosity and concentration. Therefore, it is generally mixed with two or more adhesives. Pay attention to the interaction between adhesives when mixed. General adhesives are divided into protein system adhesives and starch (carbohydrate) system adhesives, which are used in the system and have good adaptability to each other.Classification And Application Of Coating Adhesives
For synthetic resin latex, casein generally has better adaptability than starch, but latex with good adaptability to starch has also appeared in recent years. In the common coating formulation, two kinds of adhesives are used together, that is, the so-called “two-component” system binder, in order to give full play to their respective advantages, so as to obtain a good coating that can meet the requirements of printing and use.Classification And Application Of Coating Adhesives
properties and functions of adhesive and conditions to be met
The nature of the adhesive should have strong adhesion ability to the pigment, otherwise it will reduce the whiteness and opacity. Secondly, it has better adaptability to the pigment, and ensure that the coating has appropriate ink absorption and appropriate plasticity, so as to improve the calendering effect.Classification And Application Of Coating Adhesives.
1) As the carrier of pigment, the pigment has appropriate fluidity.
2) As a colloidal protective agent for pigments.
3) As a binder of pigment and pigment and pigment and base paper.
4) When printing on coated paper, control the absorption of printing ink.
3 properties of several commonly used adhesives
A kind of white powder, which is mainly extracted from corn, sweet potato, Maling potato and wheat. It has no adhesive property. In order to play an adhesive role, starch must be dispersed in water to form a granular suspension for boiling colloidal dispersion. After boiling, the form is usually called paste starch. The solid content of starch used as adhesive paste is required to be 25% – 35%.Classification And Application Of Coating Adhesives
The high molecular polymer prepared by hydrolyzing polyethylene acetate with alkali or acid, referred to as PVA, is called the degree of hydrolysis. The higher the degree of hydrolysis, the lower its water solubility. According to the degree of hydrolysis, polyvinyl alcohol is divided into cold-soluble and hot-soluble polyvinyl alcohol. Hot soluble products with a degree of hydrolysis of 98% are often used in coating. It is white to light colored debris with a specific gravity of 1. １９——１。 ２７。Classification And Application Of Coating Adhesives
1) Easy to form film, good ink luster.
2) It has strong adhesion with pigment and is used as adhesive
3) High whiteness, not easy to fade.
4) It is not easy to mold and can resist grease
Its disadvantage is poor water resistance and coating fluidity.
The utility model has the advantages that the viscosity of the coating can be reduced, the stiffness of the coated paper can be appropriately reduced, which is conducive to further processing and has good printability. It is the most widely used adhesive for coated printing paper.Classification And Application Of Coating Adhesives.
Agent, generally used in combination with modified starch, casein and other auxiliary adhesives, can obtain coatings with satisfactory fluidity, sizing and excellent paper performance.Classification And Application Of Coating Adhesives.
Acrylate latex is basically similar to styrene butadiene latex and polyvinyl polyester latex in appearance and latex properties. It has good shear stability, low viscosity, membrane folding resistance, flexibility and so on. Its printability is hardly affected by the coating amount, and shows superior printability under each coating, that is, it improves the surface smoothness of the coated paper and the compressibility of the coated paper. It can be seen that the use of acrylate latex can improve the printing quality, ink absorption and brush gloss.Classification And Application Of Coating Adhesives.
Dissolving casein is carried out in a dissolving pot with stirrer and steam pipe heating or jacket heating. In order to reduce the amount of alkali acid, the casein can be impregnated with cold water to expand the particles, and the water can be changed for 1-2 times to remove the residual acid. Classification And Application Of Coating Adhesives.
Put the soaked casein into the dissolving pot, add a certain amount of water and ventilate slowly to make the temperature reach 45-50 ℃, add the required alkali one by one, and further raise the temperature to 60-65 ℃ until the particles are completely dissolved. The whole process dissolution time is 40-60min.Classification And Application Of Coating Adhesives.
When dissolving, polyvinyl alcohol is added into cold water with water consumption of 5-10 times its weight. After mixing evenly, stir and heat it. The temperature is controlled at 80-90 ℃. After it is completely dissolved, it is cooled. If the degree of polymerization is too high, a small amount of sodium hypochlorite solution can be added to chlorinate and degrade it.Classification And Application Of Coating Adhesives.