Special sealant for steel barrels containing food
In recent years, with the development of the economy, China's food import and export volume has gradually increased, and a large number of steel drums have been used for food export packaging, among which steel drums for honey, ketchup, applesauce, edible oil, etc. are the most. Because foreigners have higher requirements on food hygiene, in addition to the application of food coatings on the inner wall of steel drums, the sealant of steel drums must also use fillers that are harmless to the human body and the food itself. However, as far as the author's investigation is concerned, most of the manufacturers that produce domestic food barrels do not use edible sealant. Since the sealant is filled in the crimping edge for sealing, whether the food sealant is used in the finished product bucket There is no good way to check, only to observe during use. Most manufacturers are unscientific and irresponsible, and should be corrected as soon as possible.
Since most of the steel drums previously produced are used in the chemical industry, there are not many requirements for the sealant, but the seal is the principle, so the barrel manufacturers have formed a habit. The sealant provided for the barrel manufacturers is also used for general purposes. So far, the supplier of sealant for the steel drum for food has not been used. This is also the case that there is no universal use of food sealant for food drums. One of the main reasons. This article gives a general introduction to the requirements and preparation of sealants for food steel drums, and hopes to attract the attention of the industry, in order to improve the domestic situation.
First, the use of steel barrel sealant for food
The steel barrel sealant for food is solidified into a film as a sealing filler for the steel drum packaging container, and is filled in the middle of the bottom of the barrel (item) and the seam of the barrel body, and after being crimped, the film and the curling are The compaction combines the bottom of the bucket (item) with the barrel; It is important for ensuring the sealing performance of the steel drum container, preventing the intrusion of external microorganisms and air, and allowing the barreled food to be stored for a long time without deterioration.
Second, the quality requirements of food for steel barrel sealant
In addition to sealing, food drum sealants must also meet a range of mechanical, chemical and physical process requirements for steel drum production and food containment, so other special conditions must be available. The general requirements are as follows:
(1) It is required to be non-toxic and harmless, and the film cannot contain substances harmful to the human body and must meet the food hygiene requirements.
(2) The requirement is that it does not contain impurities, and should have good plasticity, which is convenient for the gap between the bottom of the barrel (item) and the seam of the barrel to ensure the sealing performance of the steel drum.
(3) It should have good adhesion and wear resistance when combined with the surface of the barrel board.
(4) The film should have good resistance to heat, water, oil and oxidation, ensuring insolubilization and non-shedding under the condition of hot food, and still maintain good sealing performance, especially thermal stability. Good, otherwise it will melt under high temperature, causing glue in the barrel to contaminate food.
3. Types and composition characteristics of sealants for food packaging containers
The steel barrel sealant for food is generally liquid rubber, which is formed into a film in a pre-rolling groove on the edge of the bottom (top) of the barrel. The liquid rubber used as the steel barrel sealant is divided into water-based glue and solvent glue according to different dilution conditions. Aqueous glue of water-based glue is easy to prepare, the price is also cheap, and can meet various requirements. Sulfurized latex is generally used in China, and alginate latex is also used in some places. The use of solvent gels is rare and is not recommended due to its toxicity.
The main component of ammonia glue is natural latex. It is a colloid consisting of a suspension of rubber particles in an aqueous medium. The chemical structure of the latex is isoprene C5H8 or isoprene polymer C10H16. The latex acts as a sealant in the steel drum sealing filler.
In addition, in the composition of the steel barrel sealant, a variety of other auxiliary materials are also required as a compounding agent, such as sulfur cross, kaolin, casein, accelerator TMTD, and the like. The compounding agent can improve the performance of the liquid glue. With the addition of various compounding agents, the sealant can meet the requirements of the manufacturing process of the steel drum. At the same time, due to the addition of a large amount of filler, it is beneficial to reduce the surface tension of the latex, so that the glue can be evenly distributed according to the requirements during the injection. Coated in the pre-rolling groove at the bottom of the barrel.
4. Preparation technology of steel barrel sealant for food
Sulfurized latex is an ammonia glue, which is prepared by using natural latex, sulfur, vulcanization accelerator, filler and other materials. After spraying, it is dried and vulcanized by I to obtain good plasticity, wear resistance and oil resistance. The preparation operation is safe and harmless to the human body, and the preparation method of the steel sealant for food is as follows.
1. Liquid glue preparation process
As shown in Figure 1, "red pigment" is edible amaranth, "flat" is a condensate of ethylene oxide and fatty alcohol, and the accelerator "TMTD" is tetramethylthiuram disulfide, accelerator "D "Diphenyl hydrazine, accelerator "PX" is phenylethyl disulfide carbamate, and "CMS" is carboxymethyl starch.
Figure 1 Flow chart of liquid glue preparation process
2, the preparation of various additives
(1) Preparation of 16% casein solution: 2240 g of casein and 112 g of Î²-naphthol were ground into a fine powder, mixed with 1094 g of water in an enamel bucket, and heated in a water bath to soften the water of the casein (temperature about 70-80) Â°C, time 1-2h), using stainless steel or glass rod to continuously stir without precipitation, then add ammonia, continue to stir until all dissolves into a clear clear solution, and stir it in paraffin oil for two hours.
(2) Preparation of 50% emulsified paraffin oil: In an enamel bucket, 5000 g of paraffin oil and 200 g of oleic acid were mixed, and 4600 g of water and 20 g of triethanolammonium were mixed. If it is room temperature, it can be heated to about 30 Â° C with water to make a transparent liquid. The two liquids were then mixed and stirred in a blender to form a milky white emulsion.
(3) Preparation of 46.45% sulfur dispersion: 1800g sulfur, 50g CMC, 2025g water was poured into the porcelain jar of the roller mill (the speed was 48~50r/min, the size was 230Ã—275mm), and the ceramic ball was closed. ~50h.
(4) Preparation of 30% accelerator TMTD dispersion: 9000g CMC accelerator TMTD, 10g CMC, 2085g water was poured into the porcelain jar of the roller ball mill, and the ceramic ball was added and sealed for about 20h.
(5) Preparation of 30% accelerator D dispersion: 900 g of accelerator D, 45 g of CMC and 2055 g of water were poured into a porcelain bowl of a rotary ball mill, and a ceramic ball was placed and sealed for about 20 hours.
(6) Preparation of 35% accelerator PX dispersion: 1400 g of accelerator PX, 33 g CMC, and 2567 g of water were poured into a porcelain ball of a roller ball mill, and ceramic balls were placed and sealed for about 20 hours.
(7) Preparation of 43.27% zinc oxide dispersion: 2460 g of zinc oxide, 61.5 g of CMC, and 3163.5 g of water were poured into a porcelain bowl of a roller mill, and ceramic balls were sealed and ground for about 20 hours.
(8) Preparation of 9% CMC solution: Put 30kg water in the enamel bucket, first add 150ml ammonia water, add CMC slowly, stir while adding, add 3.3kg and continue stirring for 0.5~lh, then add ammonia water, stir To the solution into a completely transparent liquid. The liquid should be covered and stored to prevent ammonia gas, and the storage period should not be too long, otherwise the viscosity will drop.
3, the formula of liquid glue
The liquid glue formula is shown in Table I.
The water and 10% CMC solution in the formula can be increased or decreased according to the production needs and room temperature changes. For example, on hot days, I0% CMC solution increases, water decreases; in winter, 10% CMC solution decreases, and water increases. However, the total amount of adjustment after adjustment of 32.5kg remains unchanged.
4. Liquid glue preparation steps and methods
(1) Mixing ball milling with compounding agent: Put the porcelain ball into a large stainless steel ball mill (Î¦560X650mm, rotating speed 31~34r/min), accounting for about 1/10 of its total volume. According to the formula, the kaolin is poured into the ball mill; the flattening is first dissolved by heating with 5 times of water, and then the water is kept together, and then the pigment is added to dissolve the pigment in the water and poured into the ball mill. Care should be taken to leave a small amount of water and prepare the raw materials to be added in the next step. Stir-mixed and emulsified according to the formula amount of 16% casein solution and 50% emulsified paraffin oil, and 46.45% sulfur dispersion, 30% accelerator TMTD dispersion, 30% accelerator TMTD dispersion, 35% accelerator PX dispersion, 43. The 27% zinc oxide dispersion was poured together into the above stainless steel ball mill. After washing their containers with the remaining water, they were also poured into a ball mill, sealed in a stainless steel ball mill, and ground for 4 to 8 hours.
(2) Mixing with natural latex, adjusting viscosity: Take out the mixed dispersion after ball milling, pour into the enamel bucket, add natural latex according to the formula, and gently stir to make it evenly mixed. It has a high viscosity and is not easily precipitated during storage. Therefore, before the barrel lid is sprayed, water and 10% CMC solution must be added to adjust the viscosity to 20-66 s. If the viscosity is affected by changes in room temperature, etc., the ratio of water to 10% CMC solution can be appropriately adjusted according to the formulation requirements.
The formulated liquid glue is sieved by a 60-80 mesh nylon sieve or a sieve to obtain 53% liquid glue.
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