How to choose and correctly use starch adhesive 0

2022-09-30
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How to choose and use starch adhesive correctly plays an important role in carton production process. How to choose adhesives to bond cartons to improve the quality of cartons has become a hot topic in the carton production industry. With the continuous progress of science and technology in breaking the foreign monopoly, many large carton production enterprises have more advanced cardboard production lines, while the vast majority of small and medium-sized enterprises still follow the traditional single-sided machine or even single machine to produce corrugated cardboard, and most of the adhesives they use are still sodium silicate (sodium silicate). For these production enterprises, it is more important to correctly select starch adhesives

at present, the production process of starch adhesive used by domestic carton manufacturers is still based on the process formula in the 1980s and 1990s. The breakthrough is nothing more than adding desiccant to the adhesive to shorten the drying time. As we all know, more than 80% of starch adhesive is water. After the adhesive is coated on corrugated paper, the water in the adhesive must penetrate into the paperboard to make the paperboard wet and soft. Adding desiccant to the adhesive can solve the problem of wet and soft paperboard, but the desiccant is easy to precipitate. Once the desiccant precipitates, it will not play a drying role. Moreover, it is troublesome to use and store. In order to not only ensure the bonding strength, but also make a qualitative leap in shortening the drying time, the problems that must be solved are: 1. Effectively prevent the water in the adhesive from penetrating into the cardboard too quickly, so as to reduce the moisture content of the cardboard. 2. Increasing the amount of desiccant can reach 60% or even higher of the amount of starch, which not only shortens the drying time, but also enhances the stiffness of the paperboard. 3. Do not let the desiccant precipitate in the adhesive to extend the effective service life. In order to solve the above problems, Jiangxi Chuangxin color printing and packaging Co., Ltd. has successfully produced a starch adhesive - 2000 type quick drying rubber powder, which has the advantages of firm bonding, fast drying, high cardboard strength and low bonding cost through several years of repeated experiments. The moisture content of this product is 16%-18% when the glue (ordinary glue machine) such as engine nacelle, aileron and aircraft wing beam is off the machine for 20 minutes, which can completely enter the cutting process

the specific methods adopted are:

1. When an additive is added to the gelatinized oxidized starch glue solution, it can combine with the oxygen-containing groups in the oxidized starch molecules to form a complex with like structure, which improves the initial adhesion and water holding capacity of the glue solution. When mounting glue, the water in the glue liquid is not easy to penetrate into the cardboard

2. Add an auxiliary oxidant before the oxidation of the adhesive. Under alkaline conditions, it can reduce the oxidized starch to tetravalent MnO2 and Mn (OH) 2 at the same time. Under alkaline conditions, MnO2 can combine with water to form H2 MnO3, and its reaction formula is: mno2+h2o=h2mno3. Mn (OH) 2 is a kind of white sediment insoluble in water. It has the activity of absorbing oxygen and combining water. When mounting the glue, the glue is in full contact with the air. Mn (OH) 2 will absorb oxygen in the air and water in the glue to form dark brown Mn (oh) 4, which accelerates the drying effect of the glue. Its chemical reaction formula is as follows:

2mn (OH) 22+o+2h2o=2mn (OH) 4

3 A powdery mineral with 65% starch (which can also be replaced by white clay and clay, with a fineness of more than 200 mesh) is added to the adhesive as a desiccant and reinforcement agent, creating a successful history of safe and accident free use of aluminum alloy cables for nearly 50 years. At the same time, a suspension agent is added, which can fully mix and dissolve the powdered desiccant and starch glue. At the same time, under the action of the suspension agent, the powdered desiccant will expand and become a suspended slurry, which will be completely mixed with starch glue, so that the adhesive will not precipitate after being stored for more than 6 months

the company also boldly improved the raw rubber formula for single-sided machine and paperboard production line, adding reinforcing powder and suspending agent on the basis of traditional formula. The hardness of the paperboard bonded with the glue made with this formula is significantly increased, and the technical problem that the raw glue is easy to precipitate is also solved. The key technologies to be noticed are:

1. Control of the dosage of additives and suspending agents. As additives and suspensions are added, the glue will thicken. If too much is added, the adhesive concentration is too high to be used. It is too little to play its due role. With the change of temperature in four seasons, the dosage of suspending agent and additive should be adjusted at the same time, otherwise, the adhesive produced will be unsatisfactory

2. There should be strict requirements on the fineness and sand content of the powdered desiccant for drying and strengthening. The fineness is less than 200 mesh and is not easy to dissolve. Excessive sand content will precipitate in the adhesive

3. After the surfactant produced by the reaction in the adhesive contacts with the air, it absorbs the water in the glue and accelerates the drying effect. Therefore, the adhesive will be skinned on the open storage surface, and the longer it is placed, the adhesive will slowly thicken and cannot be used. It must be covered and sealed during storage. The glue in the glue tray under the glue machine should be released after one week without use and poured into the covered container for storage. The adhesive produced is unqualified or the adhesive produced is qualified but used improperly will cause poor adhesion. There are many factors causing poor adhesion of paperboard. The author puts forward the following points for colleagues' reference: first, the reason of the adhesive itself, starch molecules change in two aspects after oxidation: (1) some functional groups are oxidized from --ch2o to --cho and - COOH; (2) The molecular chain is degraded and the molecular weight is reduced. The change of functional groups improves the water solubility and permeability of starch, and the degradation of molecular chains reduces the viscosity after gelatinization and improves the fluidity. When the oxidation is excessive, the starch molecular chain is degraded too much, the viscosity of the combined adhesive is too low (less than 20 seconds), and the adhesion decreases. When mounting, there will be run edges, and the adhesive may penetrate the surface of the tissue paper. When the oxidation is insufficient, the viscosity of the adhesive is too high. When mounting the adhesive, there will be glue throwing and wire drawing, which can also not be used. Therefore, the main factor affecting the quality of the adhesive is the viscosity of the adhesive, and the main reason affecting the viscosity is the degree of oxidation

the analysis of various factors affecting the degree of oxidation is as follows:

1. The influence of starch quality

the same formula, the same reaction conditions, different starch varieties, the viscosity of the adhesive is also different. For starch with high viscosity, increase the amount of oxidant. Some starch contains reducing impurities, such as low molecular weight organics,...

2. The influence of the amount of oxidant

the amount of oxidant is insufficient, The viscosity will be high due to insufficient oxidation degree. For example, if sodium hypochlorite is used as oxidant, its actual content is difficult to master due to continuous volatilization

3. Influence of catalyst

during the oxidation reaction, the high concentration of alkali can accelerate the completion of the oxidation reaction, but with the increase of alkali concentration, starch will produce gelatinization, which will increase the viscosity of the reaction slurry, and even stick into a ball, which will affect the progress of the oxidation reaction. Therefore, the amount of alkali added in the initial stage of oxidation reaction should not be too large, and it should be added in several times with the deepening of oxidation reaction

4. Effect of oxidation time and temperature

when starch is sticky or the temperature is low, the oxidation reaction time must be extended. Otherwise, the viscosity of the adhesive will be high. When the temperature is high, the oxidation reaction time must be shortened. Otherwise, the viscosity of the adhesive will be low. The best reaction temperature is 30 ℃ -35 ℃. When the temperature is lower than this temperature, hot water can be added to the bottom water to raise the temperature

5. The influence of caustic soda dosage and the speed of adding caustic soda. The amount of caustic soda is insufficient, the adhesive viscosity is poor, it is thin, and even there will be the phenomenon of starch retrogradation and whitening, and the glue liquid will freeze. The amount of caustic soda is calculated according to the actual concentration, which will inject new impetus into the development of the real economy and the construction of a modern economic system in the new area. If solid alkali is used, it is necessary to measure its actual content, and then calculate the amount of solid alkali, otherwise, the amount of added alkali will be insufficient. If too much alkali is added, one is prone to alkali pollution, and the other is easy to absorb moisture

6. Influence of borax addition amount borax addition can increase the viscosity of the adhesive, but if the addition amount exceeds the limit, the adhesive will appear wiredrawing phenomenon, and even make the adhesive become rubber like and lose bonding force

7. Influence of water quality on adhesives

(1) reducing substances contained in water, such as reducing organic ferrous ions, can react with oxidants, consume some oxidants, and reduce the effective amount of oxidants

(2) calcium ions and magnesium ions contained in water react with sodium hydroxide during preparation to produce calcium hydroxide that is difficult to dissolve in water, and magnesium hydroxide precipitates, consuming part of caustic soda, reducing the effective amount of alkali, and producing poor gelatinization

(3) the calcium ion in the water has a complexation effect with the gelatinized oxidized starch, which thickens the prepared glue. When the calcium ion content in the water is high, this phenomenon is obvious, and the glue gradually produces gel, which is frozen and cannot be used

II. Reasons for use

1. Whether it is single-sided paperboard compounding or corrugated paper double-sided gluing, the current production process is basically: (1) corrugated paper is rolled out into corrugated corrugation through the heat setting effect of the corrugating machine (2) glue is mounted on the corrugated tip through the glue machine (3) the face (inner core) paper is compounded on the front and back sides of the corrugated paper by manual compounding (single-sided paperboard is compounded only on one side), It requires operators to have good operating skills. The amount of glue coated on the corrugated tip is generally controlled at grams per m2 (adjusted according to the paper sizing degree). The glue evenly distributed on each corrugated tip is about 1 5mm wide, forming a linear adhesive film. This requires that when the operator catches the corrugated paper after gluing, he must put it in place in one step and accurately on the surface (inner core) paper. After putting it on, he cannot move. Once it is moved, it will produce friction, which will wipe off the glue on the corrugated tip, destroy the linear adhesive film formed on the corrugated tip and fail to play a bonding role. As long as the surface (inner core) paper is opened for observation, irregular flake glue marks can be seen on the paperboard with large area of degumming. This is caused by the movement. On the other hand, the adhesive itself dries for about 3 minutes. If the adhesive itself is dry or close to dry (not sticky to hands), then it will not be stuck if it sticks to the surface (inner core) paper. After the adhesive contacts the surface (inner core) paper, it is pressed by the increasing weight of the paper. In this way, the operation speed should be faster, otherwise, For example, the adhesive cannot be fully bonded with the surface (inner core) paper during the initial bonding period (sometimes the surface and inner paper will float locally on the corrugated paper to form a gap). After the glue itself is dry, how to use the press plate machine to press will also cause blistering or degumming

2. The lamination of corrugated paper on the glue machine is carried out by applying glue on the upper and lower glue rollers. The thickness of the glue applied on the upper and lower glue rollers is adjusted by applying glue evenly on the upper and lower glue rollers. It requires that the four roller surfaces are free of impurities and residual dry glue, so as not to affect the uniformity of glue coating. However, when the glue machine is not used for more than an hour, the glue on the glue roller will adhere to the roller after solidification, and the thickness is seriously uneven, This requires the operator to clean the glue roller at work, or scrape the solidified dry glue with a scraper before work, so as to keep the roller smooth without affecting the uniformity of glue coating. The gap between the upper and lower rollers is generally slightly larger than the corrugated height, so that the corrugated paper can be evenly coated with a glue film line on the corrugated tip after gluing, such as the gap

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