Polyurethane Laminate Performance and Application III

5.135 °C high temperature cooking sterilization film adhesive

The 135°C high temperature resistant composite film is mainly used in the manufacture of high temperature cooking bags. The high temperature steaming bag was developed in the United States in the 1960s and used for astronauts food packaging. It is placed at room temperature for long life. When it is eaten, it can be eaten cold and can be hot food. It is convenient to use and saves saved energy. Therefore, it is very popular among people. In 1964, Japan's Otsuka Food Co., Ltd. succeeded in using high-temperature cooking bags (transparent) to package curry foods. In 1970, Japan sold 70 million high-temperature cooking bags, but sold 100 million in 1971. Until now, sales of high-temperature cooking bags have continued to grow at an annual rate of 15%.

The characteristics of high-temperature cooking bag are: 1 can kill all bacteria, long shelf life, transparent like more than 1 year application period, opaque aluminum foil (middle) bags have 2 years of food preservation period; 2 oxygen permeability and transparency Very low wetness, no spoilage of the contents; 3 Can use canned food production technology and equipment, so high-temperature cooking bags are also called soft cans; 4 sealing is reliable, easy to operate; 5 bags leave a crack, easy to open, with hand One tear or unsealing; 6 decoration printing beautiful; 7 can be heated within 3min; 8 waste is easy to handle; 9 can be stored at room temperature.

Usually, all pathogenic bacteria will be killed at a temperature of 85°C, but botulinum and spore bacteria with a high risk of toxicity will be killed at 135°C for 10 minutes. Therefore, polyurethane adhesives for forging composite films are required to be cured. Resistant to 135 °C.

Example 1: (Main agent: Poly terephthalic acid - isophthalic acid - azelaic acid - ethylene glycol - epoxy resin)

Dimethyl terephthalate (194.2 g), ethylene glycol (248.3 g), and zinc acetate (0.2 g) were passed through a transesterification reaction at 160-220°C. After methanol was distilled off, 83.1 g of isophthalic acid was added. The esterification reaction is carried out at 200-220° C., the water formed by the reaction is distilled off, and then 282.3 g of sebacic acid is added, and the esterification reaction is carried out at 220-230° C., and the pressure is slowly reduced, and the mixture is condensed at 220-230° C. for 60 min and then reduced. Pressing to 133 Pa and condensing at 220-230°C for 4 hours produced a polyester polyol having a number average molecular weight of 50,000.

The polyester polyol obtained above was dissolved in 67 g of ethyl acetate, 2 g of phthalic anhydride, 0.1 g of phosphoric acid, and 15 g of epoxy resin (Epikote 1002) were added, and the mixture was heated and stirred at 60° C. for 4 hours to obtain a solid content of 50%. Thick liquid (main agent).

The curing agent was an IPDI trimer containing 17.3% NCO% and a solution with a solids content of 50% using ethyl acetate.

According to the main agent: curing agent = 100: 7.5 (parts by mass) formulated into an adhesive.

The composite film was structured as a polyester film (12/um)/adhesive/aluminum foil (9um)/adhesive/unstretched polypropylene (70um), and the bonded film was cured at 50°C for 3 days. The composite film was cut into test pieces of a size of 360 mm*15 mm, and the peel strength was measured on a tensile machine. The peel strength of the aluminum foil and unstretched polypropylene film was 1250 g/15 mm.

The composite film was made into a food bag of 13cm*l7cm in size, and contained vinegar in a concentration of 4.2%. After being sterilized by hot water at 135°C*30min and 0.45 MPa, the composite film was stored at 60°C for 7 days. Separation phenomenon. After the heat and acid resistance test, the peel strength of aluminum foil and polypropylene film is 1000g/15mm.

In the adhesive component, a 1% Y-glycidoxypropyltrimethoxysilane (KH-560) coupling agent is added, which is superior in heat and hydrolysis resistance.

6. Solvent-free composite film adhesive

Domestic and international attention to environmental pollution is very important. The use of solvent-free polyurethane adhesives for composite films can completely solve the problem of solvent-induced pollution. In 1974, German company Henbet first used a solvent-free polyurethane adhesive to make composite packaging materials. In the United States, the solventless adhesive accounted for 10% in 1977, and it accounted for 50% in 1980 and is expected to account for more than 90% in the 1990s. In China, solventless coater equipment is not popular, so there is less use of solvent-free polyurethane adhesives, and future solventless polyurethane adhesives will have a wide range of development prospects.

1. Coating process

Solvent-free polyurethane adhesives are available in two-component and one-component types. The two-component type has a higher viscosity at the room temperature and a curing agent but still has fluidity and is a semi-solid substance. When compounding is required, the main agent and curing agent are mixed in proportions, placed in a plastic tray with a heat-retaining function, and heated to 50-60° C. to reduce the viscosity to 1 Pa·s or lower, and then passed through with heat insulation. A functional gravure roll is applied to the substrate. After being glued, it is not necessary to heat and dry it through a drying tunnel, because it does not contain any solvent itself, and it can be directly compounded with another substrate.

The use of solvent-free adhesives eliminates the need for exhaust emissions. It does not require large and complex heated blasts and exhaust gas treatment devices. The equipment is simple, raw materials are saved, energy consumption is reduced, maintenance costs are low, and production speeds are increased, so the benefits are significant. At present, most common composite film packaging materials can be produced with solvent-free adhesives, and even high-grade composite film packaging materials resistant to high temperature cooking at 121° C. can be manufactured by this method.

2. Features

1 The environment will not cause pollution due to solvent evaporation, safe operation, no explosion-proof measures; 2 glue coating amount 0.8-2.0g/m2 (usually 1.0g/m2), only half of the solvent type; 3 composite The process is simple, the compounding speed is high, and the energy consumption is saved. 4 Because the process of heating and drying the solvent is not required, the coater equipment is simple, compact, economical, and the floor space of the plant is small; 5 there is no problem of contamination of the food caused by solvent residues and migration; 6 The operating temperature is lower than the solvent type, which will not cause deformation of the film at high temperature; 7 The viscosity is large, and it needs to be preheated during use. Generally, the viscosity at the time of coating is 1000 to 3000 mPa·s; and the viscosity at room temperature is 4000 mPa·s. When the two components are mixed together, the viscosity can reach 23 mPa·s within 1 h, so the pot life of the two-component solvent-free adhesive is short, only 1 h.

Comparison of Composite Films Prepared with Solvent-free Polyurethane Adhesives and Other Composite Films