Key points for the use of the hottest high tempera

2022-08-10
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Key points of high temperature cooking adhesive (I)

in the two-component polyurethane adhesive, the main agent is usually hydroxyl terminated polyester polyol, and the curing agent is often the adduct of polyol and isocyanate. After mixing in proportion, the - 0h of the main agent further reacts with the - nc0 base of the curing agent to produce a block copolymer with soft and hard segments alternating. Because the curing agent is generally a ternary adduct, this chain expansion reaction generates a like polymer structure, which can form a solid bonding layer

aromatic diacids in the molecular chain of the main agent of cooking gum, such as isophthalic acid and terephthalic acid, can increase the antioxidant capacity and rigidity, and improve the hydrolysis resistance due to steric hindrance. Branched diols are also introduced into the main agent of cooking gum. Because the existence of side chains hinders the association between molecules and plays a spatial protective role in the ester bond, it improves the properties of heat resistance, oxidation resistance and hydrolysis resistance, and has better solvent resistance

aromatic curing agents are also widely used in domestic cooking adhesives. In addition to controversial hygienic properties, products using aromatic isocyanates also differ from aliphatic isocyanates in heat resistance, stability of composite fastness, internal stress, etc

the first thing you can expect is that the cooking glue is solid plastic packaging, which has taken up an increasing proportion in the packaging industry, including 50%, and generally uses 90 thread coating rollers. Due to the high viscosity of the glue, the concentration of the working fluid can only be low. About 4 grams of 1000 base leads to a large amount of wet glue coating, which has certain requirements for the capacity of the drying system. Although the rock blocks and rock masses in China have the same geological prehistory environment, the coating rollers of cooking bags are basically embossing rollers. Except for the new rollers, the coating of 50 Ming high viscosity cooking glue can rarely really exceed 4 grams. The quality of cooking bags is hidden, and then compared with the force value points on the dial of the tensile testing machine that are the same as the standard tensile samples. In the early days, cooking bags were mainly made of aluminum/plastic structure, and there was no requirement for the transparency of packaging bags. Now they have developed into all kinds of transparent packaging cooking bags. There are high requirements for the leveling property of cooking glue. There are more than 60 cooking glue on the market, with capacity of 135c1: cooking. The viscosity of cooking gum with high solid content is relatively low, and the working fluid concentration can be increased to about 30%. It is easy to reach the coating amount of more than 4 grams

the regulations of national and industrial standards on the performance of cooking bags are shown in Table 1. The current domestic situation is that the national standard is applicable only when there is no specific agreement on peel strength data in the contract. Most of them are used for quality disputes, while most enterprises can only meet the needs of users, so there is no need to study the national standard carefully. In fact, the conditions for users to use packaging bags are ever-changing, and the various properties of adhesives are not well understood even by most adhesive manufacturers. For example, we often measure the peel strength before and after cooking, but the data measured at room temperature does not necessarily explain the situation during high-temperature cooking. After the packaging bag is cooked to the specified time, the stress is the largest during insulation and back pressure, which can survive this level, and the requirements for bags in the future storage and transportation process are easy to meet

among the various factors affecting the peel strength of the adhesive, the degree of curing is very important. It can be clearly seen from the peel strength test curve of the adhesive in the attached figure that the strength is the highest when the ratio of the main agent to the curing agent is 10:2. When the peel strength is not high, we often subconsciously increase the amount of curing agent. In fact, each kind of glue has the best ratio, but the quality of ethyl acetate used by customers is different, and the climatic conditions around are not consistent, so it is impossible to determine a unified ratio

the peel strength of polyurethane adhesive composite film will decrease with the extension of storage time, but different adhesives still have great differences. Looking at the curve of 1# glue in the above figure, when the ratio is 10:1.6, the peel strength of 1# glue is the same as that of 2# glue after storage until the fifth day, and the strength of 1# glue decreases more with the increase of storage days. Generally, the peel strength enters a stable stage after 60 days, and the peel strength curve has little difference from that stored for 130 days, which can be used as the final strength. The composite strength of the adhesive is evaluated as follows: 2# adhesive is 5N/l5mm, and l# adhesive is only 2.5n/l5mm. Although it has just been matured, the strength of l# adhesive is higher than that of 2# adhesive

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