The use of high-temperature cooking plastic points (a)

In two-component polyurethane adhesives, the main agent is usually a hydroxyl terminated polyester polyol, and the curing agent is often an adduct of a polyol and an isocyanate. A 0H of the main agent after mixing in proportion is further reacted with a NCO group of the curing agent to produce a block copolymer between the soft segment and the hard segment. Because the curing agent is generally a ternary adduct, this chain extension reaction produces a network-like polymer structure that can form a strong adhesive layer.

The use of aromatic diacids in the molecular chain of the main plasticizer, such as isophthalic acid and terephthalic acid, can increase the antioxidant capacity and rigidity, and improve the hydrolysis resistance due to steric hindrance. Distilled diols have also been introduced into main components of cooking gels. Since the presence of side chains hinder the association between molecules, a space protection effect is applied to ester bonds, thus improving heat resistance, oxidation resistance, and hydrolysis resistance. , And have good solvent resistance.

Aromatic curing agents are widely used in domestic cooking plastics. Products using aromatic isocyanates are not only controversial in terms of sanitary properties, but also in terms of heat resistance, stability of composite fastness, internal stress, and aliphatic isocyanates.

The earliest cooking gel is 50% solids, and generally 90-line coating rollers are used. Due to the high viscosity of the glue, the concentration of the working fluid can only be low. A mass of about 4 grams leads to a large amount of wet glue, and there is a certain requirement for the ability of the drying system. Coating rollers for cooking bags in China are basically embossing rollers. In addition to the new rollers, the application of 50-inch high-viscosity cooking glue can rarely exceed 4 grams, and the quality of cooking bags is hidden. Early retort pouches were mainly made of aluminum/plastic structure. There was no requirement for the transparency of the pouches. Now they have developed into various types of transparent packaging retort pouches. There is a higher requirement for the leveling properties of cooking gums. There are more than 60 cooking gums in the market, and the ability to withstand 135C1: cooking. The viscosity of the high solid cooking gel is relatively low, the working fluid concentration can be increased to about 30%, and it is easy to reach a coating amount of 4 grams or more.

The national standard and industry standards for the performance of cooking bags are shown in Table 1. At present, the domestic status quo is that the national standard is not applicable to situations in which the contract does not specifically stipulate the peel strength data, and most of them are used for quality disputes. Most of the companies can only adapt to the needs of users, so there is no need to study the national standard carefully. In fact, the conditions under which users use packaging bags are ever-changing, and the properties of adhesives are not even the majority of adhesive manufacturers. For example, we often measure the peel strength before and after cooking, but the data measured at room temperature does not necessarily indicate the situation during high-temperature cooking. After the packaging bag is cooked for a specified time, the maximum stress is exerted when the insulation is returned to the pressure. The requirements for the bags during the storage and transportation process are easily met.

The degree of curing in various factors affecting the peel strength of the adhesive is very important. It can be clearly seen from the peel strength test curve of the glue in the figure that the strength is the highest when the ratio of the main agent to the hardener 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 in different places are also inconsistent and cannot be unified. The ratio.

Polyurethane adhesive composite film will have a decrease in peel strength with longer storage time, but different glues are still very different. Look at Figure 1 # plastic curve, the ratio l 0:1.6, stored to the fifth day peel strength and 2 # plastic, with the increase in the number of storage days 1 # plastic strength decreased more. The peel strength is generally stable after 60 days, and the peel strength curve is not much different from the 130 days storage time and can be used as the final strength. The composite strength of the adhesive was evaluated as: 2# glue was 5N/l5mm, l# glue was only 2.5N/l5mm. Although the aging was completed, the strength of l# glue was higher than that of 2# glue.