Views: 263 Author: Site Editor Publish Time: 2023-07-24 Origin: Site
Polyvinyl alcohol is widely used in paper industry for its outstanding adhesive force and film-forming property, and its dosage is getting bigger and bigger. As there are more grades of polyvinyl alcohol, Chinese and foreign grades are not the same, and different grades, their properties and uses are also different, which causes some trouble for enterprises. This paper introduces the domestic and foreign grades of polyvinyl alcohol and its properties and uses, so as to provide reference for enterprises to choose.
1, the appearance of polyvinyl alcohol: generally white or yellowish, flocculent, granular, powdery 3 shapes.
2, polyvinyl alcohol preparation: polyvinyl alcohol monomer vinyl alcohol is extremely unstable, there can be no free vinyl alcohol monomer, so can not be obtained directly from the polymerisation of vinyl alcohol monomer, but first through the polymerisation of vinyl acetate polymerisation of vinyl acetate, and then hydrolysis of vinyl acetate prepared by polyvinyl acetate. The hydrolysis reaction is generally carried out in ethanol or methanol solution, so it is also called alcoholysis.
1、According to different indicators can be divided into types
(1) According to the degree of hydrolysis can be divided into super hydrolysis, full hydrolysis, partial hydrolysis of three types.
Super hydrolysis type of hydrolysis degree of 99% to 100%, full hydrolysis type of hydrolysis degree of 92% to 98%, part of the hydrolysis type of hydrolysis degree of 86% to 89% and 73% to 78% (used in papermaking), and 66% below (not used in papermaking).
(2) According to the degree of polymerisation can be divided into high, medium and low 3 types. Polymerisation degree of 2400～2500 is high polymerisation degree, polymerisation degree of 1700～1800 is medium polymerisation degree, and polymerisation degree of less than 600 is low polymerisation degree.
(3) According to the viscosity can be divided into high, medium and low 3 types. Viscosity of 55 to 67 (10-3Pa.S) is high viscosity, 25 to 32 (10-3Pa.S) is medium viscosity, and 6.0 (10-3Pa.S) or less is low viscosity. (This viscosity value was measured at 4% concentration). In the case of the same degree of hydrolysis, the three types of high, medium and low viscosity correspond to the three types of high, medium and low degree of polymerisation.
2. Foreign type grades. Foreign type grade mainly has 1×× and 2××, 1 and 2 for the degree of hydrolysis, 1 on behalf of the whole hydrolysis, 2 on behalf of the partial hydrolysis, × × on behalf of the degree of polymerisation.
3. Chinese type grades. Domestic type grades have a polymerisation degree of 500 and 1700, and hydrolysis degrees of 99%, 88% and 78%, mainly 17××.
1、Sizing agent for paper and cardboard. Due to the good film-forming properties of polyvinyl alcohol, film strength, toughness, abrasion resistance, strong adhesion, oil resistance, so it can be used for internal sizing, can also be used for surface sizing
(1) Internal sizing. In the securities paper, index paper, map paper and other high-grade paper, with a small amount of polyvinyl alcohol as a sizing agent, can effectively increase its paper strength and toughness. In cellophane, with polyvinyl alcohol as a sizing agent, can improve its strength, transparency, gloss and dimensional stability. Sizing agent preparation concentration of 5% or less, often using Chinese brand PVA1799.
(2) Surface sizing. For high-grade cultural paper surface sizing, polyvinyl alcohol can be used alone, can also be used in conjunction with oxidised starch. Especially in the production of high-quality paper, often polyvinyl alcohol and oxidised starch and use. This can make the pulp has thixotropic properties, can reduce the pulp to the paper internal penetration, greatly improving the surface strength of the paper and printing adaptability. Often use Chinese brand PVA1799.
2, coated processed paper pigment binder. Due to the strong bonding force of polyvinyl alcohol, can reduce the amount of adhesive in the coating, so that the coating leaves more pores, you can get a better opacity, brightness, smoothness and good ink absorption.
Because of the poor fluidity of polyvinyl alcohol, not suitable for the preparation of high solid content coatings, often used in conjunction with the latex and modified starch, generally use the Chinese brand PVA1788. its ratio, for example, 100 parts of china clay pigment, 17-88 polyvinyl alcohol 5 parts, 7 parts of modified starch, 9 parts of styrene-butadiene latex.
3, paper and cardboard processing adhesives. Polyvinyl alcohol is widely used in paper and cardboard industrial adhesives to bond paper, cardboard. It is the current domestic and foreign paper bags, paper boxes and cartons in the adhesive with the best performance. General selection of Chinese brand PVA1799.
4, stamp paper, wallpaper rewetting adhesive. Polyvinyl alcohol for stamp paper, wallpaper, label paper, tape paper and other back coating, with re-wetting adhesive force, quality and stability, less affected by humidity, not easy to rot and deterioration, film flexibility, products are not easy to wrinkle and other characteristics. Generally use Chinese brand PVA0588.
