Two-component polyurethane adhesive (1)

Two-component polyurethane adhesives overview

Two-component polyurethane adhesives are one of the most important categories of polyurethane adhesives, with a wide range of uses and large amounts. Usually consists of two components, A and B. The two components are packaged separately and can be prepared in a certain proportion before use. The A component (main agent) is a hydroxy component, and the B component (curing agent) is a component containing a free isocyanate group. Some of the main agents are polyurethane NCO-based prepolymers, the curing agent is a low molecular weight polyol or polyamine, and the A component and the B component are mixed at a certain ratio to form a polyurethane resin.

Two-component polyurethane adhesive has the following features.

(1) A reactive adhesive undergoes a cross-linking reaction after the two components are mixed to produce a cured product.
(2) During the preparation, the raw material composition and molecular weight of the two components can be adjusted to have a suitable viscosity at room temperature, and a high solid content or solvent-free two-component adhesive can be prepared.
(3) It can be cured at room temperature, and the curing speed can be set by selecting the raw material for preparing the adhesive or adding the catalyst. In general, two-component polyurethane adhesives have a large initial adhesion, which is called heat curing, and the final adhesive strength is larger than that of single-component adhesives and can meet the requirements of structural adhesives.

(4) The amount of the two components can be adjusted within a certain range, generally there is a certain degree of tolerance. The NCO/OH mole ratio of the two components is generally greater than or equal to 1, and when cured, part of the NCO groups participate in the curing reaction of the glue, resulting in a chemical adhesion force. When the excess NCO group is cured by heating, Produce allophanate, biuret, etc., increase the degree of cross-linking, improve the cohesive strength and heat resistance of the adhesive layer. For solvent-free two-component polyurethane adhesives, because the initial molecular weight of each component is not large, the NCO/OH molar ratio is generally equal to or slightly greater than l, which is conducive to complete curing, especially when bonding seals, pay attention to NCO The components should not be too much. For solvent-based two-component adhesives, the main agent has a larger molecular weight and better initial viscosity. The amount of the two components can be adjusted within a relatively large range, and the NCO/OH molar ratio can be less than 1 or greater than 1. Times. When there is a large excess of NCO component (curing agent), polyisocyanate self-polymerizes to form a tough adhesive layer, suitable for bonding of hard materials; in the case of a small amount of NCO component, the adhesive layer is soft and can be used Bonding of soft materials such as leather and fabrics.

Since the advent of two-component polyurethane adhesives, they have become the most widely used products in polyurethane adhesives because of their advantages of adjustable properties, high adhesive strength, and wide bonding range.

Universal two-component polyurethane adhesive

General-purpose polyurethane adhesive is based on polyethylene adipate as raw material, solvent-based polyurethane resin as the main component (component A), and trimethylolpropane-T1) I adduct as curing agent (component B). ) Two-component polyurethane adhesive. General-purpose two-component polyurethane adhesive, also known as 101-polyurethane adhesive, is the earliest industrialized production of Shanghai Xinguang Chemical Factory, and it is still the largest domestic production of polyurethane adhesives. There are more than 1,000 domestic users, mainly used for insulating materials and packaging materials. Bonding of composite membranes, porous materials, cryogenic protective materials, etc.
1. Product specifications General-purpose two-component polyurethane adhesives are required to formulate national standards and are currently drafting industry standards. The main technical specifications are shown in the table.
Table Universal Specification for Two-Component Polyurethane Adhesive Products\Component A (Main Agent) B Component (Curing Agent)
Exterior
NCO content, %
Solid content,%
Viscosity, 25°C
Light yellow or brown viscous liquid--
30±2, 50±2
30-90
Colorless or light yellow transparent liquid 12±1
60±2
--
Shear strength, MPa 8.0 8.0

2. Storage of adhesives

General-purpose two-component polyurethane adhesive components contain organic solvents (acetone, ethyl acetate, etc.) and are stored and transported in accordance with flammable products regulations. Component B contains active isocyanate groups and should be protected from contact with water and other reactive groups. A component will crystallize or form a flocculent precipitate on a cold day. It is a normal physical change and only needs to be melted in warm water or with a suitable heating device (avoiding open flames). The storage time of components A and B is one year and six months respectively. There are two types of packaging: cans and glass bottles.

3. How to use

The use of two-component polyurethane adhesive directly affects the adhesive properties of the material. Before bonding, it is necessary to pay attention to whether the components of A and B are expired or not. In particular, the B component is deteriorated due to its tendency to undergo polycondensation reaction and should be stored under low-temperature sealing conditions. The application of polyurethane adhesives is generally divided into surface treatment, preparation and coating of adhesives, fixing and curing, and finishing procedures. All steps must strictly comply with the operating procedures, otherwise it will affect the quality of bonding.

1. Instructions

(1) Surface treatment The surface of the adhered material must be decontaminated, rust-removed, degreasing, etc. before the adhesive is applied. Generally, the surface is degreased by sandblasting, grinding wheel, sandpaper, etc., and deoiled with solvents such as toluene, acetone, and ethanol. Go to grease. After treatment, the surface should be dry and flat.

Aluminium-aluminum alloy surface treatment can use zero emery cloth to fight hair and acetone degreasing, put people dipping in 65-70°C sodium dichromate solution for 30min, rinse with water and dry it at 70°C or below. The sodium dichromate solution can be prepared using the following formula: sodium dichromate: water: concentrated sulfuric acid = 7.5:65.2:27.3 or 30:176:50 (parts by mass). The surface of low-carbon steel was sanded with No. 1 emery cloth and then degreased with trichloroethylene to bond. PVC panels and foam are degreased with trichloroethylene, and laminates and fiberglass are trimmed with emery cloth. When the wood, paper and belt are not smooth and clean, they must be surface treated. The effect of the surface treatment method on the bond strength (shear strength) of the aluminum-aluminum material is shown in the table.

Treatment method\Shear strength Shear strength, MPa
-------------------------------------------------- ------------------------------
Sample 1 Sample 2 Sample 3 Average acetone degreaser No. 0 emery cloth Anodizing chemical method
5.32 5.42 5.46 5.40
8.65 9.19 9.67 9.17
9.31 10.91 10.86 10.37
10.96 12.27 13.96 12.40
* Anchor-101 glue, A component: B component = 100:50 (mass fraction).

(2) Glue preparation The formulation of the adhesive depends on the requirements of the material to be adhered. Parts A and B have different ratios, and the adhesive can also be mixed with the adhesive. The proportion of general-purpose two-component polyurethane adhesives A and B is shown in the table.

Table bonding ratio of various materials with plastic

Adhesive material A component (mass fraction) B component (mass fraction)
Paper, Leather, Wood General Materials Metal Materials 100
100
100
10-15
15-30
20-50

To accelerate the curing time and increase the initial adhesion, 0.1% to 0.3% of triethanolamine or diethylaminoethanol may be added to the components.

The adhesive can be used after being formulated according to the ratio of A and B components. With a good adhesive can be stored under closed conditions from half a day to a day time (25 °C), if you press A: B = 100:50 preparation, the storage period will be shortened to 3-4h The higher the box temperature, the shorter the storage period; Group B The more points, the faster the curing speed; the higher the hardness of the glue layer, the better the heat resistance. The effect of the distribution ratio of adhesives A and B on the bond strength is shown in the table.