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Pressure Sensitive Adhesive

Release time:

2016-06-17 11:10

I. Definition

Pressure-sensitive adhesive, often abbreviated as PSA, is a type of adhesive that exhibits sensitivity to pressure. It is primarily used in the manufacture of pressure-sensitive tapes.

II. Classification

1. By compositional structure

It can be divided into two major categories: rubber-type and resin-type.

Rubber types are further divided into natural rubber and synthetic rubber. Natural rubber is produced by processing latex extracted from plants such as rubber trees and rubber grass; synthetic rubber, on the other hand, is obtained through polymerization reactions involving various monomers.

Resins are further categorized into polyurethane, polyacrylate, and silicone types.

2. By shape and dispersing medium

They can be classified into water-soluble pressure-sensitive adhesives, solvent-based pressure-sensitive adhesives, emulsion-type pressure-sensitive adhesives, hot-melt pressure-sensitive adhesives, and calendered pressure-sensitive adhesives.

3. By whether or not they are cross-linked

They can be divided into two major categories: cross-linked and non-cross-linked.

Crosslinkable pressure-sensitive adhesives can be classified according to their crosslinking methods into room-temperature crosslinking types, heat-induced crosslinking types, and light-induced crosslinking types, among others.

III. Key Highlights

1. Acrylic pressure-sensitive adhesive:

Acrylic pressure-sensitive adhesives are currently the most widely used type of pressure-sensitive adhesive. They are copolymers made from acrylic monomers and other vinyl monomers. Compared with other pressure-sensitive adhesives, they have the following characteristics: they exhibit excellent weather resistance and heat resistance without the need for significant amounts of anti-aging agents; they show no phase separation or migration, possess good transparency, and offer superior oil resistance; they are harmless to the skin and are therefore suitable for medical applications. Acrylic pressure-sensitive adhesives are currently the most widely used type of pressure-sensitive adhesive. They are copolymers made from acrylic monomers and other vinyl monomers.

2. Emulsion-type pressure-sensitive adhesive:

Using water as the dispersion medium, these products are non-toxic, non-flammable, safe and environmentally friendly, and low in cost. They have attracted considerable global attention and account for approximately 65% of the total pressure-sensitive adhesive market.

3. Water-soluble pressure-sensitive adhesive:

This pressure-sensitive adhesive uses water as its medium, does not pollute the environment, poses no fire or explosion hazard, and does not require emulsifiers. It exhibits superior adhesion and water resistance compared to emulsion-type pressure-sensitive adhesives, but has poorer storage stability.

4. Hot-melt pressure-sensitive adhesive:

Hot-melt pressure-sensitive adhesives contain no organic solvents, do not pollute the environment, are simple to prepare, convenient to use, and have a wide range of applications. However, these pressure-sensitive adhesives exhibit poor adaptability to temperature changes.

5. Solvent-based pressure-sensitive adhesive:

It is obtained by free-radical polymerization of acrylate monomers and other monomers in an organic solvent. This type of pressure-sensitive adhesive has a relatively low average molecular weight, excellent wettability, rapid drying, strong initial adhesion, and superior water resistance; however, it does present certain challenges in terms of environmental protection, resource utilization, and safety.

6. UV-sensitive adhesive:

It is a new type of light-curable pressure-sensitive adhesive that is solvent-free, pollution-free, energy-efficient, and boasts excellent performance. After being coated onto a substrate and exposed to ultraviolet light or an electron beam, it forms a tape. Once the bonded objects are heated, the adhesive achieves a permanent bond.

Performance Comparison Between UV Pressure-Sensitive Adhesives and Other Pressure-Sensitive Adhesives

Performance	Acrylic emulsion-based pressure-sensitive adhesive	Solvent-based acrylic pressure-sensitive adhesive	Rubber-based hot-melt pressure-sensitive adhesive	UV-curable acrylic pressure-sensitive adhesive
Bonding performance on polar surfaces	+++	+++	+++	+++
Adhesion performance on nonpolar surfaces	++	++	+++	++
Shear strength	++	+++	+	++
Temperature resistance performance	+++	+++	+	+++
Slitting and Die-cutting Performance	+++	+++	+	+++
Water resistance	+	++	+++	++
Water vapor permeability	+++	+++	+	+++
Resistant to polar solvents	+++	+++	+	+++
Resistance to nonpolar solvents	+++	+++	+	+++

IV. Chemical Properties

1. Adhesive performance of pressure-sensitive adhesives

2. Wetting performance of pressure-sensitive adhesives

3. Adhesion strength of pressure-sensitive adhesives

4. Initial adhesion and cohesive strength of pressure-sensitive adhesives

5. Creep-resistant shear performance of pressure-sensitive adhesives

6. Temperature resistance of pressure-sensitive adhesives

7. Flame retardancy of pressure-sensitive adhesives

8. Aging resistance and antioxidant properties of pressure-sensitive adhesives

9. Corrosion resistance of pressure-sensitive adhesives

Key highlights:

1. Initial Adhesion: T (Tack), also known as quick adhesion, refers to the resistance to separation exhibited when a PSA product and the substrate are brought into contact under very light pressure and then immediately separated rapidly.

2. Adhesion: A (Adhesion) refers to the ability of a PSA product to resist interfacial separation from the surface being bonded, achieved by applying appropriate pressure and time during the bonding process.

3. Cohesion: C (cohesion) refers to the strength of the adhesive layer itself;

4. Adhesion: K (keying) refers to the adhesive force between the adhesive and the substrate, or between the adhesive and the primer, as well as between the primer and the substrate.

A good PSA must strike a balance among its four key adhesive properties, namely T < A < C < K. This is because A must be greater than T; otherwise, the PSA would lack pressure-sensitivity. Similarly, C must exceed A; otherwise, when removing the tape, the adhesive layer could be damaged, leading to issues such as adhesive contamination of the adhered surface and stringing. Moreover, C must be less than K; otherwise, the adhesive layer might peel away from the substrate. In other words, the peel force of the pressure-sensitive adhesive (the force required to remove the adhesive tape from the adhered surface after it has been pressed firmly onto the surface) must be less than the cohesive strength of the adhesive itself (the intermolecular forces within the pressure-sensitive adhesive), which in turn must be less than the adhesive's adhesion to the substrate (the bond strength between the adhesive and the substrate). Only under these conditions will the pressure-sensitive adhesive avoid problems such as debonding during use.

V. Scope of Application

1. Packaging products: DPP tape, sealing carton tape, battery label shrink film;

2. Self-adhesive tapes: cloth-based tapes, high-strength double-sided tapes (used for attaching carpets, hooks, etc.);

3. Magnetic tape: Magnetic cards and debit cards—currently used less frequently;

4. Trademark signs: anti-counterfeiting marks, decorative laser signs, gap-type recording signs;

5. Textile Industry: Back-coating adhesives for automotive carpets, composite fabrics for automotive seat cushions, non-woven fabrics, and automotive interior headliners (composed of PU films and multiple textiles). Hot-melt polyamide adhesives are widely used in textiles for bonding applications such as non-woven fabrics, back-coating adhesives for carpets, garment linings, zippers, and more.

6. Medical and health supplies.

VI. Quality Measurement Standards

1. Solid content

Solid content is also one of the important factors affecting the quality of pressure-sensitive adhesives. The higher the solid content, the stronger the adhesive force and the faster the drying speed.

2. pH value

Synthetic resin adhesives are generally weakly acidic and do not negatively affect bonding processes. However, waterglass and starch-based adhesives have relatively high alkalinity. Excessive alkalinity can not only corrode operators and equipment but sometimes also corrode the materials being bonded, leaving unsightly stains. Therefore, when purchasing adhesives, it’s important to consider the impact of pH on the product’s performance.

3. Adhesive strength

First and foremost, a pressure-sensitive adhesive must possess sufficient adhesive strength to ensure the proper functioning of bonded objects after adhesion. To determine whether the adhesive’s bonding strength is adequate, simply pull apart the two adhered materials along the bonding interface. If you find that the adhered materials themselves are damaged upon separation, it indicates that the adhesive strength is sufficient. However, if only the bonding interface separates without any damage to the adhered materials, it suggests that the adhesive’s strength is insufficient.

4. Viscosity

Viscosity is the most important factor affecting the quality of adhesives. If the viscosity is too high, the coating will be thicker, adhesive consumption will increase, drying will slow down, and the adhesive’s ability to wet and penetrate the surface of the substrate will be impaired, directly affecting the bond strength. On the other hand, if the viscosity is too low, the coating will be thinner, drying will be too rapid, and problems such as poor adhesion are likely to occur.

5. Drying speed

When selecting pressure-sensitive adhesives, it’s essential to ensure that the drying speed is compatible with the bonding process. Generally, manual bonding processes are relatively slow and require a longer initial drying time; in contrast, machine bonding processes are fast-paced and demand a shorter initial drying time. As for the final curing time, in most cases, the faster the better, so that the next production step can be initiated as soon as possible.

VII. Future Development

For a long time, the pressure-sensitive adhesive industry was monopolized by international giants and multinational corporations, leaving domestic industries heavily reliant on imports or joint-venture products for their high-end pressure-sensitive adhesives. Starting in the 1990s, Chinese enterprises and research institutes gradually began to engage in independent research and development of products in this field. After years of technological accumulation, they have progressively obtained independent intellectual property rights in high-performance products such as silicone adhesives, acrylate adhesives, anaerobic adhesives, epoxy resin adhesives, and polyurethane adhesives—many of which are aimed at replacing imported alternatives. Today, there are roughly over 30 domestic enterprises in the pressure-sensitive adhesive industry that possess independent R&D capabilities, have reached a certain production scale, own their own brands, and focus primarily on pressure-sensitive adhesive products. As a result, the domestic pressure-sensitive adhesive industry features a competitive landscape characterized by multinational corporations with comprehensive product portfolios and advanced technology, while domestically-funded enterprises specialize in niche segments, exhibit rapid growth, closely follow their foreign competitors, and collectively maintain a highly fragmented market structure. Pressure-sensitive adhesives represent a high-end segment within the adhesive industry, placing stringent demands on companies in terms of R&D capabilities, product technology levels, and distribution channels. After experiencing a decade of rapid growth, the industry’s expansion has slowed somewhat in recent years, leading to overcapacity and intense market competition. Nevertheless, new application areas continue to be explored, driving double-digit annual growth. Over the past five years, pressure-sensitive adhesive production has steadily increased. With the development and application of various novel synthesis and curing methods, the performance of pressure-sensitive adhesives has significantly improved. Meanwhile, to meet diverse application requirements and further expand their scope of use, many pressure-sensitive adhesives with specialized functions and applications have been developed. The continually growing demand for pressure-sensitive adhesives across numerous industries has deepened research efforts in this field, and the study and development of new types of pressure-sensitive adhesives will increasingly attract attention. Looking ahead, pressure-sensitive adhesives will evolve toward greater environmental friendliness, enhanced convenience, and even higher performance.

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