Overview of two-component solvent-free polyurethane adhesive

Solvent-free polyurethane adhesive does not have solvent volatilization The problem is environmentally friendly adhesives, which is also a development direction of adhesives.

Broadly speaking, two-component polyurethane sealants belong to a field of solvent-free polyurethane adhesives, similar to polyurethane potting adhesives, two-component foaming polyurethane adhesives, polyurethane structural adhesives, etc.

From an application perspective, solvent-free two-component polyurethane adhesives are used for composite films, for bonding or sealing transportation vehicles such as cars, trains, and ships, and for bonding or sealing mechanical equipment. It is used for bonding and sealing of building materials, potting for sealing electrical components, and adhesives. Two-component polyurethane sealant will be introduced in a special section and will not be discussed here.

Oligomer polyol raw materials used in solvent-free two-component polyurethane adhesives, including polyether polyols, polyester polyols, polyolefin polyols, castor oil, etc. Among them, polyether polyols based on propylene oxide are due to viscosity Low, the prepared adhesive has a viscosity suitable for construction, and is the preferred oligomer polyol raw material.

Polyisocyanate raw materials are generally used as TDI, PAPI, and MDI. Aliphatic diisocyanates such as HDI and IPDI are used in special polyurethane adhesives that require transparency and non-yellowing, such as sign pouring glue, safety glass glue, etc.

Crosslinking/chain extender is used to formulate the hydroxyl (active hydrogen) component. In particular, room temperature curing adhesives often contain aromatic diamines such as MOCA, or other diamine chain extenders.

When preparing or using solvent-free adhesives, fillers are sometimes needed. Fillers not only reduce the cost of the adhesive, but also improve the initial viscosity of the adhesive and increase the hardness and heat resistance of the adhesive. Fillers include calcium carbonate, titanium dioxide, carbon black, talc powder, kaolin (porcelain clay), clay, mica powder, diatomaceous earth, alumina, etc. Sometimes add an appropriate amount of pigments, such as rust red, phthalocyanine green, etc.

For adhesives that require no bubbles after curing, it is recommended to add a foam suppressor. According to the foaming inhibition mechanism, foaming inhibitors are divided into two types: dehydrating agents (zeolite molecular sieves, anhydrous gypsum, diatomaceous earth, etc.) andCO2 absorbers (fine CaO, special carbon black, etc.).

Thixotropic agent is an additive for sealants and solvent-free adhesives used on vertical surfaces. Generally, fumed silica (white carbon black) is used. In addition, surface-treated ultrafine calcium carbonate and acetylene carbon black are used. Fillers such as organic bentonite and organic bentonite are also thixotropic.

Catalyst is a commonly used additive. Generally, it is an organometallic catalyst such as dibutyltin dilaurate. Some special catalysts are also used to accelerate the preparation or curing process.

The preparation of two-component solvent-free polyurethane adhesive is relatively simple. Usually one of the components is an isocyanate component, which can be an NCO-terminated polyurethane prepolymer, or It is a polyisocyanate such as PAPI, or a mixture of several prepolymers and polyisocyanates. The isocyanate component generally does not have fillers added. The other component is the hydroxyl component, which is usually a mixture of polyether polyol (or polyester polyol) and fillers, chain extenders, foam suppressors, catalysts, etc. Room temperature curing adhesives require slightly more catalyst.

For two-component solvent-free polyurethane adhesives, there is no convention as to which of the isocyanate component and hydroxyl component is called component A (component A) or the main agent. . The main agent refers to the adhesive component that is used in greater amounts when dispensing glue. Many two-component solvent-free polyurethane adhesives do not have a main agent and a curing agent. For the convenience of glue preparation, the ratio of the two components of the adhesive is designed to be 1/1 or other integer multiples.

The differences between two-component solvent-free polyurethane adhesive and two-component solvent-based adhesive are as follows.

①The molecular weight of each component resin of solvent-based adhesive is higher, and in order to It has good fluidity and operability, and the molecular weight of each component of the solvent-free glue is lower.

② Solvent-based adhesives obtain better initial viscosity after the solvent evaporates. The initial viscosity of solvent-free adhesives is generally Not high.

③ The hydroxyl component of conventional solvent-based adhesives is a higher molecular weight polyester polyol or polyurethane polyol, the latter is an oligomer polyol prepared through a chain extension reaction; while the hydroxyl component of solvent-free adhesives is Value components are generally formulated from a mixture of oligomer polyols without chain extension reaction.

④ When designing the ratio of the two components of a solvent-based adhesive, the NCO/OH ratio of the adhesive is the R index It can be around 1.0, which has a large tolerance; for solvent-free adhesives, the R index is generally between 1.0 and 1.1, otherwise it will not cure well. Solvent-free adhesives generally require a catalyst.