Development of High-speed Application of Casein Adhesive

Abstract: A high-speed labeling adhesive that can be used in beer production lines with a capacity of more than 36,000 bottles/hour has been described using casein, polyacrylamide, urea, and starch as raw materials. The influence of various factors on the properties of the adhesive was studied. The results showed that the adhesive viscosity, drying speed and refrigeration stability increased with the increase of casein content; the storage stability increased with the increase of PH value; the viscosity also increased when the polyacrylamide content increased.
Key words: casein; labeling adhesives; performance introduction At present, in addition to the beer bottle labels made of starch and modified starch in the beer production industry in China, there are polyvinyl formal, modified polyvinyl formal, etc. Type of labeling adhesive. They have their own characteristics and have played a positive role in the development of China's beer manufacturing industry. However, these adhesives are only suitable for labeling beer lines with a speed of around 20,000 bottles/hour. Due to the rapid development of the beer manufacturing industry, the production rate has been greatly improved and the production speed has been accelerated. The current speed has risen to 30,000-40,000 bottles/hour, and the demand for labeling adhesives has become higher and higher, resulting in some manufacturers. More dependent on foreign imported labeling adhesives. This not only increases the production cost, but also restricts the development of the beer industry in China to some extent. In order to meet actual production needs, the authors used casein as the main raw material, dissolved in polyacrylamide water-soluble polymer materials, and starch as a filler to make high-speed labeling suitable for beer production lines with a speed of 36,000 bottles/hour or more. adhesive.
1 Experimental section 1.1 Names, specifications and proportions of major raw materials Table 1 Names, specifications and proportions of major raw materials

1.2 Preparation method A certain amount of casein, water, and borax are placed in a reaction vessel and heated and stirred to dissolve the casein into a uniform solution. The urea and polyacrylamide were added to the solution to continue dissolution. After being stirred for about half an hour, the starch was added and stirred and heated at 80° C. to be gelatinized into a homogeneous viscous solution. Cooling, adding ammonia to adjust the pH value of about 8 can be discharged.
1.3 Performance test Non-volatile content: determined according to GB/T2793-1995. Viscosity: MDJ-1 rotary viscometer, measured according to GB/2794. pH: Determined using a PHS-3 acidity meter. Refrigeration stability: A certain amount of adhesive is placed in the refrigerator freezer (0-5°C). After 72 hours, it is taken out. It is left at room temperature for about 4 hours, and the viscosity is measured at 25°C. The viscosity does not change. Drying speed: Different adhesives are used for the labeling machine to measure the drying speed. Storage stability: The casein adhesive was observed at room temperature to see if it had stratified and gelled.
2 Results and Analysis 2.1 Labeling Adhesive Performance Indicators The performance indicators of adhesives produced through repeated experiments and production practice tests are shown in Table 2.
Table 2 Adhesive performance indicators

2.2 Factors Affecting Adhesive Viscosity 2.2.1 Effect of Casein on Viscosity The amount of casein has a great influence on the adhesive viscosity. Figure 1 (illustration omitted) shows the relationship between the amount of casein and the viscosity. As can be seen from Figure 1 (abbreviated in the figure), the viscosity increases with increasing amounts of casein, because casein is a phosphorus-containing protein derived from animal emulsions and has a large relative molecular mass (approximately 75,000-375,000). Protein molecules contain amino (-NH2) and carboxyl (-COOH). When dry, the protein is curled in powdery particles. Under acidic or basic conditions, -NH2 is converted into -NH2+ in combination with H+, or -COOH is converted into -COO-Na+ in water by alkali neutralization. At this point, the crimped protein rapidly expands in size and forms micelles. The hydrophilic end points to the aqueous phase, the lipophilic end points to the micelles, and is suspended in water. The amount of casein increases, micelles increase, viscosity increases. The amount of casein cannot be too large. Different labeling machines require different adhesive viscosity requirements. In general, the amount of casein is controlled at 14%-25%. If the amount is too large, the viscosity of the casein adhesive is large at normal temperature and the flowability is poor, which affects the coating.
2.2.2 Influence of Polyacrylamide on Viscosity Polyacrylamide has a linear structure and good water solubility. When it is soluble in water, it forms a coil structure in water. The amide group strongly interacts with water to form a bulky kinetic volume that increases the viscosity as shown in Figure 2 (abbreviated in the figure). As the amount of polyacrylamide increases, the viscosity increases more and more significantly. However, the amount of polyacrylamide cannot be too large. In addition, the relative molecular mass of the polyacrylamide can not be too large. If the relative molecular mass is large, the polyacrylamide has poor dispersion performance in the casein glue solution, and it is easy to hold the rod during the stirring process and affect the production.
2.3 Effect of casein on drying speed Drying speed is a very important indicator of beer label adhesives. In the high-speed beer production line, if the drying speed is small, the label cannot be affixed to the beer bottle, which makes the dropping of the mark and the flying mark very serious. The relationship between the amount of casein and the drying speed is shown in Figure 3 (abbreviated in the figure).
From Figure 3 (abbreviated in the figure), it can be seen that the amount of casein is small, the drying speed is slow, the amount of casein is 4%, the drying time is about 13 seconds, and when the amount is 8%, the drying time is 12 seconds. As the amount of casein increases, the drying time becomes shorter. When the amount of casein is 16%, the drying time is about 9 seconds, which is more in line with the labeling requirements for a beer production speed of 36,000 bottles/hour.
2.4 Effect of casein on the refrigerating stability of adhesives People are accustomed to drinking frozen beer. Therefore, the ability of beer label adhesives to withstand low temperatures is a very important indicator of the quality of adhesives. If the labeling adhesive has poor low temperature stability, the label attached to the beer bottle will wrinkle and drop at low temperature. The study found that casein plays an important role in the cold storage stability of adhesives. First, casein is insoluble in cold water, so at low temperatures, the casein film is not destroyed by cold water; second, casein has good initial tack strength; and the addition of polyacrylamide improves the casein retention better. Viscous, so that the casein adhesive has better refrigeration stability.
2.5 Effect of pH on storage stability Aqueous ammonia was added in the final stage of preparation of casein adhesives to adjust the pH to around 8 to make the adhesive alkaline and increase the stability of the adhesive. The effect of pH on the stability is shown in Figure 4. As the pH value increases, the stability increases; but the pH value is less than 4 and the stability also increases. This is because the isoelectric point of casein is 4.6, greater than or less than 4.6 is conducive to the dissolution of casein in water systems.
3 Conclusions Experiments and practical tests prove that casein is high