Application of cooking resistant adhesives

Resistance to cooking adhesive performance

In the production of retort pouches, ordinary adhesives cannot be used in the compounding process and cooking-resistant adhesives must be used. At present, there are many domestic manufacturers that can produce retort-resistant polyurethane adhesives, and the temperature resistance and compound performance of the products have basically reached the level of similar imported adhesives.

The indexes for assessing the quality of cooking-resistant adhesives are as follows.

(1) The initial viscosity requirement is generally higher.
(2) The reaction speed is faster and the curing time is shorter (less than 48 hours for plastic-plastic composite products and less than 72 hours for aluminum-plastic composite products).
(3) The coating amount is small, the adhesive strength is high, the heat seal strength is high, and the temperature resistance is better.
(4) Low dilution viscosity, high solid state operation, and good coating property.
(5) Wide range of applications for various films.
(6) Has good resistance (heat, cold, etc.).
(7) Conforms to the health index, non-toxic, no odor. Acid resistance

In general, adhesive products with high solids content, low viscosity, high initial tack, high peel strength before and after cooking, and high food hygiene safety and quality stability are selected.

Anti-cooking adhesive application process

1. Preparation of glue

First of all, we must master the ratio of the main agent and curing agent of polyurethane adhesive. The ratio between the main agent and curing agent of some polyurethane adhesives is adjustable within a certain range, and there is an optimal mixing ratio. However, some adhesives must strictly comply with certain main agent and curing agent ratio requirements when used, and cannot be easily modified when not specifically required. Otherwise, the excessive amount of curing agent will make the composite film hard: too little amount of curing agent will lead to insufficient crosslinking reaction, resulting in viscosity and other issues.

Secondly, the use of ethyl acetate to dilute the solvent requires that its water content (including alcohols) not exceed 0.2%, and is preferably below 0.15%. If the water content is too high, the adhesive layer will not dry or be brittle, and the peel strength of the composite film will be significantly reduced.

2. Adhesive coating amount control

Under the conditions permitting the viscosity of the adhesive to work, the high concentration of work should be selected as much as possible, which can save the solvent and reduce the amount of residual solvent in the composite film. In addition, in the production of retort pouch products, the amount of glue applied is generally higher than that of ordinary products, so as to ensure the peel strength of the composite products after cooking.

Due to the high working concentration of the adhesive, in order to ensure a suitable amount of adhesive coating, an application roller with a lower number of screens should be used. In general, when producing retort pouch products, a coating roller with a mesh number of 80 to 100 lines/inch is selected, and the dry coating amount of the binder is controlled at 4.0 to 5.0 g/m 2 .

3. Drying temperature

Due to the large amount of glue applied, it is necessary to control the drying tunnel temperature and exhaust conditions to ensure that the adhesive is fully dried. If the drying temperature is too low, the solvent will not evaporate sufficiently and the odor of the composite product will easily occur, and at the same time, the composite strength will be directly affected. However, the drying temperature should not be too high, otherwise the adhesion of the adhesive coating to the skin will occur, affecting the volatilization of the solvent in the coating and causing the solvent residue. In general, the drying temperature is controlled within the range of three gradients from 60°C to 70°C to 80°C.

4. Compound temperature and compound pressure

In the dry compounding, the composite roll needs to be heated in order to soften the adhesive, increase the viscosity, and evenly distribute it on the film; meanwhile, the hot melt reaction state of the adhesive is maintained, and it is easy to bond with other substrates. In general, the composite temperature is controlled at 50-60°C.

There are two main effects of composite pressure on composite products: one is the effect on composite fastness, and the other is the effect on the transparency of the composite film. The best composite pressure is 2.5-5.0kg/cm2.

5. surroundings

When operating in combination, the ambient air must be kept dry at no more than 85%, otherwise it will affect the composite fastness.

6. Aging

Due to the large amount of rubber compounded, the aging temperature of the composite film can be appropriately increased, and the aging time can be appropriately extended. In general, the production of composite film to cook bag should be placed at 50 ~ 60 ~ C for 48 hours, preferably more than 72 hours, so that the adhesive is fully cross-linked and cured to ensure the composite strength, and help to reduce the composite film The residual amount of solvent prevents the cooking bag from appearing differently.

Zhejiang New Oriental Ink Group Co., Ltd. Xiao Haiyi

Source: Printing Technology