The quality of the binder is related to the quality and quantity of the starch. Starch's fineness, protein and fat content all affect its performance. If the content of protein and fat in starch is too high and the fineness is less than 98 mesh (100 mesh pass rate), even if the oxidation degree is high during production, the viscosity at the time of discharge is only 20 seconds (measured with a 4-coat viscometer ) But the adhesive will naturally thicken, lose its fluidity, and become jelly-like after being stored for 5-7 days. When used, the foam is also large, directly affect the quality of the adhesive, and the use of qualified starch, as long as the degree of oxidation and gelatinization is appropriate, the viscosity of the finished adhesive product is 40±10 seconds, and the viscosity will not change much during the storage period. . Only the color is deep, but the viscosity does not change.
The amount of starch used varies according to the specific requirements of the bonded object, such as:
1 Single-faced corrugated board with adhesive cover, lower requirements for adhesive agent, starch dosage: 150-170KG/ton water.
2 High-strength corrugated paper on both sides of the sizing, the adhesive requirements slightly higher, the amount of starch: 170-200KG / ton of water.
3 Ordinary corrugated paper and straw pulp Both sides of the corrugated paper sizing and cardboard and cardboard composite, the adhesive requirements are relatively high, starch dosage: 180-300KG / ton of water.
4 Automatic veneer machine and paper tube glue, with special requirements for adhesives, in addition to fast drying, but also requires good adhesion, high strength. Starch dosage: 200-350KG/ton water.
The following describes in detail the raw materials and recipes used in adhesives (adhesives):
1. Pasting agent: Industrial caustic soda (NAOH) has crystalline, rod-shaped, flake-like and aqueous solution containing 30% of NAOH, as long as the purity of any state of caustic soda can be used, the amount of caustic soda added to the oxidized starch solution, stirring 20 Minute starch liquid is a translucent paste, the amount of caustic soda is too large, the liquidity of the glue is large, transparency is good, and the storage time is long, but the alkali content in the sizing amount of the corrugation peak will also increase, resulting in Corrugated cartons are liable to yellowing, causing discoloration of the surface of the corrugated carton; the amount of caustic soda is small. After adding for 20 minutes, it has been white or milky white paste, opaque and not sticky. This is because the amount of caustic soda is not enough and a part of caustic soda solution should be added as appropriate. It becomes a semi-suitable gelatin solution, with a small amount of alkali, poor adhesive paste, poor adhesion, and thickening. The amount of caustic soda was observed from the actual situation, which is generally about 12% of the starch.
2. Oxidants: Starch binders, commonly used oxidants are hydrogen peroxide (hydrogen peroxide), sodium hypochlorite, potassium permanganate and so on. Potassium permanganate is used as an oxidizing agent, and the amount is easy to grasp. The finished starch binder has a stable quality, but the color of the starch adhesive produced is dark brown or brownish black. The starch binder made with sodium hypochlorite and hydrogen peroxide as the oxidizing agent is yellowish in color. However, the sodium hypochlorite-made starch adhesive has unstable quality during use, and decomposes chlorine gas, which causes the operator to feel eye discomfort; the starch adhesive produced from the double chlorine water often generates a lot of foam during use, and needs to be put into defoaming. Agent. In addition, sodium hypochlorite is easily oxidized and decomposed under sunlight or high temperature, and its secondary chlorine content is reduced. In application, it is necessary to grasp its exact content and moderately increase the dosage. From the use of analysis, the use of hydrogen peroxide as an oxidant starch adhesive, stable quality, small amount, low cost, fast response, is used as an ideal material for oxidants.
When making cold high-strength and quick-drying starch adhesives, the oxidation reaction plays a key role and the oxidation is appropriate (viscosity is 60-80 seconds after caustic soda is added in 20-40 minutes), the starch dissolution performance is improved, the film-forming ability is good, and the adhesion is strong. If the oxidation is not enough, macromolecules are degraded less, and their properties are the same as those of starch. After caustic soda is added, they are not diluted for a long time, and even stirring phenomenon occurs (adding caustic soda reaction for more than 40 minutes, the viscosity is higher than 100 seconds). This requires the addition of an oxidizing agent for secondary oxidation, such as over-oxidation, open chaining of the starch ring structure, low viscosity, and even loss of adhesion (viscosity of less than 40 seconds after the addition of caustic soda for 20 minutes). Therefore, special attention should be paid to the use of oxidant content and ratio.
Oxidation also plays a role in the temperature, the higher the temperature, the faster the oxidation, the summer oxidation reaction generally 10-15 minutes, 15-20 minutes oxidation in spring and autumn, winter oxidation reaction about 30 minutes, oxidation reaction time extension, oxidation is complete, product quality Stable, but too long will affect the production cycle.
The specific amount of oxidizing agent changes with starch, the amount of starch is small, the amount of oxidizing agent is also small, the amount of sodium hypochlorite (10%) is about 28% of starch, the content of hydrogen peroxide (27.5%) is about 4% of starch, potassium permanganate The dosage is about 2% of starch. The method of determining whether the oxidation is appropriate is: after adding caustic soda, the reaction is stirred for 20-40 minutes and the viscosity is measured to be about 60 seconds (summer). In this way, the finished product is stored for about 50 hours in about two hours, and is stable for 40 seconds ± 10 days after one day. In addition, the winter temperature is low, the amount of oxidant should be increased appropriately, the summer air temperature is high, the reaction is fast, and the dosage is appropriately reduced.
3. Strong catalyst (abbreviation as desiccant): The main factor that distinguishes the cold, high-strength and quick-drying series of starch adhesives from other adhesives is the selection of a strong catalyst. The strong catalyst is formed by the polymerization reaction of several salts and organic and inorganic compounds. In the production process of adhesive, as long as the dosage is suitable, it not only accelerates the reaction speed, but also reacts with the oxygen in the air through the polymer after sizing. It quickly flocculated and crystallized, accelerated the speed of adhesive conjunctiva, shortened the carton drying time, and improved the cardboard strength. Therefore, the adhesion speed of the adhesive (first-viscosity, full-stick, and fiber-breaking) is several times higher than that of the conventional starch glue. And cardboard high hardness, good stiffness, strong catalyst dosage in the binder per ton of water below 5KG will not work, per ton of water than 15KG, adhesive film is too fast, easy to produce cardboard degumming phenomenon. So we must strictly control the proportion of placement. The normal usage standard is 6 12KG/ton water.
4. Cross-linking agent: A binder is added after the paste is gelatinized to add borax or boric acid, which can make the short-chain oxidized starch form a complex with its hydroxyl group and boron atom. Through these irregular cross-links, a network structure is formed. , With cross-linked thickening effect, help to improve the initial viscosity and speed up the drying, in addition to play a role in anti-corrosion, anti-seepage and termination. However, the amount is not as good as possible. Too much will cause the binder to have poor flowability, be jelly-like, difficult to be glued, and have a brittle gum. Under-complexation is not enough, poor adhesion, causing degumming and run-in phenomenon of corrugated board.
Oxidized starch paste after adding alkali and stirring 20-40 minutes, such as the viscosity of 60 seconds or so, you can further add borax solution, such as the viscosity is too high for more than 100 seconds can be added to the oxidant for secondary oxidation, the viscosity after stabilization is 50 seconds ( Usually 2-3 hours), plus borax solution, such as less than 100 seconds, can be stabilized after 2 hours, add water, as appropriate, dilute to about 60 seconds add borax solution.
The effective boron content of borax is 11.32%, and the effective boron content of boric acid is 17.48%. In application, the amount of boric acid can be reduced by nearly 1/3 compared to borax. The amount of borax is generally 3-3.5% of starch, and the amount of boric acid is generally 2-3 for starch. %.
5. Defoamer: During production and use, due to the improper quality and reaction of starch, many foams will be generated, affecting the glue machine's normal sizing, especially the use of hydrogen peroxide as oxidant, it is easier to produce foam, so it is necessary to add appropriate amount of foam Antifoaming agent, defoamer can choose silicone oil or tributyl phosphate, n-decanol and so on. Sodium hypochlorite and potassium permanganate are used as oxidizing agents, and tributyl phosphate is used in an amount of 0.1-0.3 胶 for the amount of gum, and hydrogen peroxide is used as the oxidizing agent. The amount of tributyl phosphate used is 0.3-0.5 胶 for the amount of gum.
Pay special attention to the amount of defoamer should not be too much, excessive pressure will reduce the adhesive surface tension, loss of viscosity, adhesive strength can not meet the requirements, in the production, such as glue machine foam too much, it is best to stop to the plastic tank Riga defoamer a little stir, start the trial, such as bubble more, plus a little, until the normal operation, but one thing, do not add anti-foaming agent to the top roller, so as to avoid the phenomenon of rejection. Observe whether the defoamer is suitable for the starch glue in a glass bottle with high transparency. Shake vigorously for about 2 minutes and stop immediately. Observe the foam on the glue in the bottle, such as the foam on the glue liquid within 20-30 seconds. Disappearing, that is, the amount of defoamer can be, can be used on the glue, such as 20-30 seconds, the small bubble in the glue solution also disappeared, then the amount of slightly larger, can be reduced appropriately. (Chen Baoyuan)
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