Polyurethane Adhesive Bonding Principle and Classification

Polyurethane adhesive bonding principle and classification
The polyisocyanate molecular chain contains isocyano groups (-NCO) and urethane groups (-NH-COO-), so polyurethane adhesives exhibit a high degree of activity and polarity. It has excellent chemical adhesion with substrates containing active hydrogen, such as foam, plastic, wood, leather, fabric, paper, ceramics and other porous materials, as well as metals, glass, rubber, plastics and other materials with smooth surfaces. Regardless of the polyurethane adhesive, the isocyanate is chemically reacted and cured.

Polyurethane adhesives have excellent shear strength and impact resistance, are suitable for various structural bonding fields, and have excellent flexibility properties.

1. Universal two-component polyurethane adhesive

The universal two-component polyurethane adhesive is made of polyethylene adipate as the raw material, solvent polyurethane resin as the main component (component A), and trimethylolpropane—T1) adduct as the curing agent (B Component) two-component polyurethane adhesive. The universal two-component polyurethane adhesive, also known as 101-polyurethane adhesive, is the first polyurethane adhesive that was put into industrial production in Shanghai Xinguang Chemical Plant and is still the largest domestic production volume. There are more than 1,000 domestic users. It is mainly used for insulation materials, packaging materials, Bonding of composite membranes, porous materials, cryogenic protection materials, etc.

Two-component polyurethane adhesives have the following characteristics:

(1) After the two components are mixed, the reactive adhesive will undergo a cross-linking reaction to produce a cured product.

(2) During preparation, the raw material composition and molecular weight of the two components can be adjusted to make it have a suitable viscosity at room temperature, and it can be made into a high solid content or solvent-free two-component adhesive.

(3) Usually it can be cured at room temperature, and the curing speed can be reduced by selecting the raw materials for preparing the adhesive or adding a catalyst. Generally, two-component polyurethane adhesives have a greater initial adhesion, called heating curing, and their final adhesive strength is greater than that of single-component adhesives, which can meet the requirements of structural adhesives.

(4) The dosage of the two components can be adjusted within a certain range, and there is generally a certain tolerance. The NCO/OH molar ratio of the two components is generally greater than or equal to 1. When curing, part of the NCO groups participate in the curing reaction of the glue to produce chemical adhesion. The excess NCO groups can also be cured by heating. Produce allophanate, biuret, etc., increase the degree of crosslinking, and 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, generally the NCO/OH molar ratio is equal to or slightly greater than 1, which is conducive to complete curing, especially when bonding seals, pay attention to NCO The components should not be excessive. For solvent-based two-component adhesives, the molecular weight of the main agent is larger, and the initial adhesion performance is better. The amount of the two components can be adjusted in a larger range, and the NCO/OH molar ratio can be less than 1 or greater than 1. Times. When the NCO component (curing agent) is excessively large, the polyisocyanate self-polymerizes to form a tough adhesive layer, which is suitable for bonding hard materials; when the amount of NCO component is small, 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, it has become the product with the most variety and the largest output in polyurethane adhesives due to its performance adjustability, high bonding strength, and wide bonding range.
General purpose two-component polyurethane adhesive

General-purpose two-component polyurethane adhesives can be used to bond metals (such as aluminum, iron, steel, etc.), non-metals (such as ceramics, wood, leather, plastics, etc.) and bonding between different materials. General-purpose two-component polyurethane adhesives are widely used in the manufacture of insulating paper (polyester film-blue shell paper composite), paper-plastic composite (color printing paper-polypropylene film), iron plate-polyurethane foam composite and bristle brushes used in motors. The manufacturing and other uses penetrate into various fields of the national economy.

(1) Maintenance of machine tool rails

Adopt inlaid and bonded plastic plate method to glue thin plastic plate on cast iron guide rail to make plastic guide rail, which can solve the abrasion of machine tool guide rail. Use iron anchor-10l polyurethane glue, prepare glue liquid according to component A: component B=100:50 (mass parts), stir in the glue liquid a thin copper wire with a diameter of 0.1mm and a length of 20mm to make There is enough space between the guide rail and the plastic plate to prevent all the glue from squeezing out. The two bonding surfaces of the plastic plate and the cast iron rail need to be coated with glue twice. The first time is 5 minutes and then the second time. After 15-20 minutes, the glue layer is sticky and there is a wire drawing phenomenon, and then the plastic The plate and the guide rail are superimposed and pressurized by its own weight. Due to the large temperature difference between winter and summer, the plastic will expand or contract, resulting in internal stress and cracking. Therefore, the curing temperature should be kept between 20-25°C. The curing time is 1-2 days.

(2) Bonding of speakers

The loudspeaker vibration system, namely the paper box, voice coil and positioning bracket, need to be glued together. Especially when the high-power loudspeaker vibrates, the amplitude is large, so it must be firmly bonded, because it is directly related to the service life of the loudspeaker. Especially loudspeakers above 100mm are glued with polyurethane adhesive. Adopt iron anchor-101 polyurethane adhesive according to component A: component B=100:30-35 (mass parts), and the expected effect can be achieved after use. For the bonding of the speaker voice coil, the glue is prepared with component A: component B=100:25 (mass parts).

(3) Application in bristle brush products

General-purpose two-component polyurethane adhesive is an ideal adhesive for bristles. The bonding of the bristle brush is to bond the bristles (bristles or nylon bristles, etc.), wood chips (wood) and brush shells (tinplate). The surface is required to be closed by 1-2mm, and it is required to penetrate 6-9mm. Commonly used glue formulations are: 100 parts of component A, 35 parts of component B, and 30 parts of talc (≥160 mesh). Pour the prepared adhesive into the brush shell or use a bristle brush glue filling machine for potting. After potting, shake the brush head to make the adhesive even, and place it until it has dried (turned into the hair for no less than 24h). The adhesive strength of the brush bristles after potting with the adhesive is greater than 130N, which meets the SG236-8l bristles paint brush standard (98N). If the bristles do not come off or loose after being soaked in acetone for 24 hours, the glue meets the requirements.

2. Performance of polyurethane for shoes

Polyurethane adhesives for shoes, like other polyurethane adhesives, have excellent low temperature performance, low curing temperature, excellent flexibility, impact resistance, wettability and adhesion to many materials. Therefore, it is often used in occasions that require room temperature, fast curing and flexibility, and is especially suitable for bonding dissimilar materials with different expansion coefficients. The performance requirements of shoe-making adhesives vary with shoe materials, shoe shapes and bonding processes, but as a whole, shoe adhesives should have the following properties:

(1) It has sufficient bonding strength for dissimilar materials and different crystalline materials, and the peeling strength is high;

(2) The initial adhesion is high, which is suitable for the requirements of the shoe production line; especially the peeling strength is high;

(3) The sizing process is simple, easy to operate, and the service life is adjustable to meet the needs of the shoe production line; (4) It has moderate heat resistance, sufficient water resistance and bonding durability. Polyurethane adhesives for shoes can meet the above requirements, and their initial adhesion performance is worse than that of neoprene adhesives. However, at present, researchers at home and abroad have proposed methods to improve initial adhesion, which have basically been solved.

3. Waterborne polyurethane adhesive

Waterborne polyurethane adhesives have the characteristics of low VOC content, low or no environmental pollution, non-combustibility, etc., which is the key development direction of polyurethane adhesives. The diversity of polyurethane adhesives has prepared solutions for many bonding problems, and is especially suitable for places where other types of adhesives cannot be bonded or where bonding is difficult.
In addition, polyurethane adhesives also have the characteristics of adjustable toughness, simple bonding process, excellent low temperature resistance and excellent stability. It is precisely because of the excellent adhesion performance and adaptability of polyurethane adhesives to a variety of substrates that its application fields have been continuously expanded, and it has become the fastest growing adhesive at home and abroad in recent years.
Uses of polyurethane adhesives
Polyurethane adhesive is an important part of the polyurethane resin that is currently developing rapidly. It has excellent properties and has been widely used in many aspects. It is one of the eight important types of synthetic adhesives.
Polyurethane adhesives have excellent shear strength and impact resistance, are suitable for various structural bonding fields, and have excellent flexibility properties. Polyurethane adhesive has excellent rubber properties and can adapt to the adhesion of substrates with different thermal expansion coefficients. It forms a soft-hard transition layer between the substrates, which not only has strong adhesion, but also has excellent cushioning and shock absorption. Function. The low and ultra-low temperature properties of polyurethane adhesives exceed all other types of adhesives. The diversity of polyurethane adhesives has prepared solutions for many bonding problems, and is especially suitable for places where other types of adhesives cannot be bonded or where bonding is difficult.