What is Sandpaper?
Sandpaper is a common abrasive tool that smooths out uneven surfaces and creates a smooth texture to the surface. Sandpaper can be used to sand, remove surface dirt, oxides and bumps etc. It is a simple and practical tool. Sandpaper is often used in home improvement, handicrafts, construction projects and other fields. It is an indispensable surface preparation tool and a common DIY tool. Sandpaper is mainly composed of sand grains, base material and binder, among which sand grains are the key part of grinding and sanding. Grit comes in a variety of different particle sizes and grades for different jobs and surface materials. This article will explore the common types and characteristics of sandpaper.
Common types and characteristics of sandpaper
Sandpaper is widely used in various surface treatment processes, and it has many different types and specifications to meet various application needs. This article will introduce the types and specifications of sandpaper, and explain in detail through tables and classifications.
| Sandpaper type | features | Grit | Backing |
| Waterproof sandpaper | Waterproof sandpaper is a common type of abrasive paper used for grinding and polishing metal and wood. Its name comes from the fact that it needs to be used with water. | P60-P2000 | paper, cloth, or plastic. |
| Dry sandpaper | Dry sandpaper is also commonly used for grinding and polishing metal and wood. It does not require the use of water and can be used directly. | P60-P2000 | paper, cloth, or plastic. |
| Optical sandpaper | Optical sandpaper is a type of sandpaper used for glass and plastic, typically used in the production of optical components and lenses. | P2000-P12000 | paper or plastic. |
Structure of Sandpaper: Backing + Abrasive Grain + Bonding Agent + Coating
Sandpaper is composed of three main components: backing, abrasive grain, and bonding agent. The backing provides support for the sandpaper, while the abrasive grain is the material used to perform surface treatment. The bonding agent is used to secure the abrasive grain onto the backing, while the coating is applied to enhance properties such as wear resistance and lubrication, depending on the specific requirements of the application. In this article, we will introduce the backing, abrasive grain, bonding agent, and coating of sandpaper, and provide a corresponding table for illustration purposes.
Backing – Common Types and Characteristics
There are various types of backing materials used in sandpaper, including paper, cloth, and film. The choice of backing material can affect the sandpaper’s abrasive performance and lifespan. Choosing the appropriate backing material can improve the efficiency and quality of sanding. Here are some common types of backing and their characteristics:
1.Paper-based substrate
Paper-based substrate is one of the main substrates for sandpaper, characterized by its low cost, easy processing, and use. The durability and abrasive amount of sandpaper vary depending on the density and thickness of the paper. Dense paper is usually used for polishing, while loose paper is used for rough surface treatment. The thickness of paper-based substrates usually ranges from grade A to F, with A being the thinnest and F being the thickest. The binding agent for paper-based sandpaper is usually natural or synthetic resin, so its water resistance and wear resistance are better, and it is commonly used for grinding and polishing wood, metal, and plastic materials.
Here is a comparison table of different material substrates:
| Paper-based substrate | Features and Characteristics | Applications |
| A | Thin, soft, not sturdy | Fine sanding |
| C | Medium thickness, soft | Suitable for manual sanding, polishing, and grinding |
| D | Thicker than C, sturdy, long service life | Coarse surface treatment |
| F | Thick, sturdy, difficult to break even with prolonged use, suitable for machine operation | High-speed grinding and coarse surface treatment |
2.Cloth-backed abrasive paper
Cloth-backed abrasive paper is a type of sandpaper that has an abrasive coating on a cloth-based substrate. It is made from fiber cloth or textile material. After the sand grains are evenly distributed on the cloth through a special process, it undergoes curing treatment. The advantage of cloth-based substrate is that it can be used for both dry and wet sanding, and because of its flexibility, it can be used on curved surfaces. In addition, cloth-based substrate is more durable than paper-based substrate and can be used under high loads. Compared to paper-based sandpaper, cloth-backed abrasive paper is tougher and more durable, making it ideal for grinding harder materials such as metal and glass.
3.Adhesive-backed sandpaper
Adhesive-backed sandpaper is a type of sandpaper that has sand grains fixed onto a sticky backing. The surface of the sandpaper is coated with a layer of adhesive, which is used to hold the sand grains in place. Because it has good adhesion, the advantage of adhesive-backed sandpaper is that it does not experience sand grains falling off during use, thus having a longer lifespan than regular sandpaper. Adhesive-backed sandpaper is commonly used in electronics manufacturing, precision grinding, and mechanical processing. Additionally, it has good water resistance and abrasion resistance, making it suitable for use in damp environments for extended periods of time.
4.Synthetic resin substrate
Synthetic resin substrate is a type of substrate made from synthetic fibers or plastics, which is tougher and more durable than paper and cloth. There are many types of synthetic resin substrates, including polyester, nylon, and polyurethane, each with different characteristics and applications. Synthetic resin substrates are usually used for surface sanding and finishing, especially for high-precision and smooth processing tasks.
5.Synthetic fiber-based sandpaper
Synthetic fiber-based sandpaper is made with synthetic fibers such as polyester or nylon as the base material. The abrasive particles are evenly distributed on the base material through a special process, followed by curing treatment. Synthetic fiber-based sandpaper has good wear resistance and water resistance, as well as flexibility and elasticity, making it suitable for grinding curved surfaces and irregularly shaped workpieces.
Types and Characteristics of Abrasive Grains
Abrasive grains are the primary elements used for sandpaper, generally consisting of high-hardness and wear-resistant minerals. Different minerals produce different abrasive effects, so the selection of abrasive grains is crucial. Here are several common types of abrasive grains and their characteristics:
1.Corundum
Corundum is a very hard natural mineral that is typically transparent and an aluminum oxide mineral. Its hardness is as high as 9, second only to diamond. This hardness makes corundum abrasive particles a very effective grinding tool. In addition, corundum abrasive particles have the following characteristics:
- High temperature resistance：Corundum abrasive particles can work at high temperatures, making them very suitable for use in metal grinding.
- Wear resistance：Corundum abrasive particles are very hard, so they will not wear too much during use, thereby extending the life of the sandpaper.
- Excellent thermal stability：Corundum abrasive particles have excellent thermal stability and will not deform or melt even at high temperatures.
2.Silicon Carbide (SiC) Abrasive Grains
Silicon carbide abrasive grains are commonly used in sandpaper due to their high hardness and durability. They are typically black or dark gray in color and widely used for grinding and polishing metals, ceramics, plastics, and wood materials. However, the cost of silicon carbide abrasive grains is relatively high, and they can generate static electricity during use, requiring safe handling. Additionally, silicon carbide abrasive grains have the following characteristics:
- High hardness：Silicon carbide abrasive grains have a hardness of 2800-3300 kg/mm2, making them harder than other abrasive materials such as aluminum oxide and zirconia.
- High strength：Silicon carbide abrasive grains have high strength and can withstand high pressure and high temperatures.
- High wear resistance：Silicon carbide abrasive grains are not easily worn down during grinding and can be used for extended periods of time.
- Good chemical stability：Silicon carbide abrasive grains have good stability in acids, alkalis, water, and other chemical agents.
3.Aluminum oxide grit (Al2O3)
Aluminum oxide grit (Al2O3) is another common type of sandpaper grit, which is typically white or brown in color and can be made harder by calcination at high temperatures. It is widely used in abrasive machining of materials such as metals, plastics, ceramics, and wood. Compared to silicon carbide grit, aluminum oxide grit has a lower cost but a shorter lifespan, and is prone to accumulation and dust, which can affect its effectiveness. Additionally, aluminum oxide grit can easily be formed into various shapes and sizes of abrasive tools, such as grinding wheels and sanding belts. Furthermore, aluminum oxide grit has the following characteristics:
- High hardness：The hardness of aluminum oxide grit is 9, second only to diamond and silicon carbide grit.
- Strong wear resistance：Aluminum oxide grit has strong wear resistance and can maintain its grinding effect for a long time.
- Good thermal stability：Aluminum oxide grit can maintain stability in high temperature environments.
- Good chemical stability：Aluminum oxide grit has good chemical stability and will not react with other substances.
4.Diamond
Diamond abrasives are made from various synthetic diamond particles and are usually based on quartz sand as a base material that is subjected to high pressure and high temperature treatment. In grinding applications, diamond abrasives can effectively cut and grind various materials, including metals, stones, ceramics, glass, plastics, and more. Compared to other abrasives, diamond abrasives have better grinding effects and are less prone to accumulation and dust. However, they are more expensive and are typically used in high-end applications. Additionally, diamond abrasives have the following characteristics:
- High hardness：Diamond abrasives have the highest hardness ranking of 10, providing efficient cutting and grinding performance.
- High thermal stability：Diamond abrasives have high thermal stability and can be used at high temperatures without losing their cutting efficiency.
- Low wear rate：Diamond abrasives have a very low wear rate, making them suitable for long-term use without the need for replacement or repair.
- Excellent corrosion resistance：Diamond abrasives do not corrode or rust and can be used in a variety of environments.
Binder – Common Types and Characteristics
Binder is an important component of sandpaper used to attach abrasive particles to the backing material. It enhances the adhesion and stiffness of the sandpaper, preventing abrasive particles from falling off or loosening during use. Additionally, it helps to maintain the cleanliness and dispersion of the abrasive particles, thus improving the grinding effect and service life of the sandpaper, here are several common types of binders and their characteristics.
In general, binders can be classified into two categories: natural binders and synthetic binders. Natural binders are extracted from natural resources such as tree gum, animal glue, natural rubber, etc. Synthetic binders, on the other hand, are made from chemically synthesized substances such as polyurethane, polyester, acrylic acid, etc. The following are some common types of binders:
| Binding Agents | Features |
| Water-based binding agents | Water-based binding agents are low-polluting binding agents that are widely used due to their environmental friendliness. The advantages of water-based binding agents are easy to clean, non-toxic, and widely used in the binding of products such as paper, wood, leather, and textiles. |
| Hot melt binding agents | Hot melt binding agents are binding agents that are melted and applied to the surface of an object at high temperatures. They can dry quickly and have high strength, and are widely used in packaging, construction, automotive, furniture, and other fields. |
| Pressure-sensitive binding agents | Pressure-sensitive binding agents are binding agents that can be immediately adhered to under slight pressure. The characteristics of pressure-sensitive binding agents are strong adhesion and do not require heating or chemical reactions to bind objects. They are widely used in products such as adhesive tape, labels, and stickers. |
| Photosensitive binding agents | Photosensitive binding agents are binding agents that can be cured under the action of light. When light is irradiated onto photosensitive binding agents, they will quickly harden and form a very strong binding force. Photosensitive binding agents are widely used in fields such as electronic products, precision instruments, etc. |
Coatings – Common Types and Characteristics
There are many types of coatings, including organic coatings, inorganic coatings, and metal coatings. The purpose of organic coatings is to isolate the anode and cathode, with paints being the most common type of organic coating. Paint is a mixture of organic medium, insoluble pigment, and other substances, and the medium can be linseed oil or tung oil from plants, or a mixture of synthetic resin and volatile thinner. Here are some common types of coatings and their advantages and disadvantages:
1.Organic coatings
Organic coatings are products obtained by coating the surface of substrates such as galvanized steel sheets, aluminum-plated sheets, galvanized aluminum alloy sheets, cold-rolled sheets, etc. with one or two layers of organic coatings (such as epoxy ester, polyester, acrylic resin, plastic sol, etc.) or covering them with a layer of plastic film. Organic coatings are coatings composed mainly of polymer compounds as film-forming materials. When applied to the surface of an object, they can form a firmly adhered coating film and are suitable for use in paint and spray paint.
| Advantages | ✔️ Inexpensive ✔️ Good color brightness ✔️ Easy to apply |
| Disadvantages | ❌ Oil-based materials are toxic and not environmentally friendly (water-based materials have overcome this issue) ❌ Weather resistance (organic pigments are not resistant to UV light and fading is normal) ❌ Generally poor water resistance (although there are better grades of materials) |
Organic coatings are usually classified according to the type of coating material used, such as stearate coatings, polyvinyl chloride coatings, acrylic coatings, fluorocarbon coatings, silicone coatings, etc. The following table provides an overview of these types of organic coatings:
| Common Types of Organic Coatings | Features |
| Stearate Coating | Stearate coating is commonly used for the corrosion protection and lubrication of metal surfaces. Stearate is a compound formed by stearic acid and a metal (such as aluminum, sodium, zinc, etc.). Stearic acid is a saturated fatty acid typically extracted from animal fats, but can also be extracted from plant oils. Stearate coatings have good wear resistance, heat resistance, and chemical resistance, and can be used at high temperatures. |
| Polyvinyl Chloride Coating | Polyvinyl chloride coating, or PVC coating, is a type of coating with good waterproofing effect. However, it can become brittle and hard in cold weather, and is prone to creasing or breaking during use, so it is only suitable for use in warmer seasons. PVC coating is light yellow and semi-transparent, containing components of polyvinyl chloride. It has a shiny and chemically stable surface, and is resistant to corrosion, heat, water, fire, cold, and mold. |
| Acrylic Coating | Acrylic coating is made from acrylic monomers and can be used on various materials, such as metal, glass, ceramics, and plastics. Acrylic coatings have good weather resistance, corrosion resistance, and wear resistance, and are widely used in various industrial and commercial applications. |
| Fluorocarbon Coating | Fluorocarbon coating is a highly weather-resistant special coating widely used on curtain walls of ultra-high buildings worldwide. It is also known as fluorocarbon baking paint, self-drying fluorocarbon paint, fluororesin paint, etc. The main components of fluorocarbon coating are fluorocarbon resin (70%)/acrylic resin (30%), pigments, and additives. Fluorocarbon coating has extremely strong weather resistance, chemical corrosion resistance, and wear resistance, and is widely used in various industrial and commercial applications. |
| Silicone Cool Coating | Silicone cool coating is a waterproof, oil-proof, and stain-proof coating mainly composed of silicone resin, also known as polysiloxane, which is a polymer between organic and inorganic materials. Silicone cool coating has excellent weather resistance, chemical resistance, high-temperature resistance, and wear resistance, and is not prone to aging. It can also provide good anti-stick and anti-adhesion properties, and is widely used in industrial and household applications. |
2.Inorganic coatings
Inorganic coatings are a type of coating that primarily uses inorganic materials as the main film-forming substance. They are commonly referred to as fully inorganic mineral coatings and are widely used in everyday applications such as architecture and painting due to their superior performance. Inorganic coatings have high hardness and during the drying process, they generate significant shrinkage stress, requiring a high level of substrate plaster strength. They are best used on substrates with a relatively high cement content and are suitable for enamel coatings and cement coatings.
| Advantages | ✔️Excellent heat resistance – it does not combust even at a high temperature of 1200℃ and has flame retardant properties. ✔️Breathability – it has a filtering effect on alkaline substances, preventing bubbles from forming in the coating. ✔️Good durability – it does not fade easily. ✔️Inorganic coatings with protective functions are nanosized during the manufacturing process, resulting in a “rigid waterproofing” effect that is difficult to wear even if the surface is worn down. |
| Disadvantages | ❌Poor storage stability – it tends to separate and precipitate, leading to poor leveling during application and unsatisfactory decorative effects. ❌Requires high construction standards and is not suitable for thick coatings, as they tend to crack. ❌Short open time and poor re-coating properties. |
Inorganic coatings are typically classified according to the materials used as the main film-forming substance. Some examples include aluminum silicate coatings, magnesium silicate coatings, zirconium silicate coatings, alumina coatings, zinc oxide coatings, and titanium oxide coatings. The following table provides more information on each type:
| Common Types of Inorganic Coatings | Features |
| Aluminum silicate coating | Aluminum silicate coating is an inorganic coating, whose main component is aluminum silicate. It is commonly used to protect metal surfaces from corrosion and high temperatures. It can also be used in indoor and outdoor water-based latex paint as well as various solvent-based white paints. The functions of aluminum silicate in coatings are as follows: 1. Ultra-fine aluminum silicate can replace some titanium dioxide, and the hiding power of the dry film will not change, and the whiteness of the paint can be increased. 2. Precipitated aluminum silicate is an “additive” for white pigment titanium dioxide. Due to its optical isolation function, when it is used to replace 10-25% of titanium dioxide in white coatings, the hiding power of the white paint film does not decrease, and the whiteness is improved. |
| Magnesium silicate coating | Magnesium silicate coating is a type of coating composed of magnesium silicate and other components. Magnesium silicate is an inorganic compound with the chemical formula MgSiO3, a molecular weight of 100.3887, and a white to grayish-white fine powder. Magnesium silicate coating can be used for fireproofing, corrosion protection, waterproofing, insulation, and other purposes. It is a type of coating that provides fire resistance, corrosion protection, waterproofing, and erosion resistance, and can be used on buildings, ships, bridges, and other structures. The main component of magnesium silicate coating is magnesium silicate, which can form a hard protective layer that can withstand high temperatures and chemical corrosion. Magnesium silicate coating can also enhance the structural strength of buildings, improve their durability and safety. |
Zirconium silicate coating | Zirconium silicate is an inorganic compound and a silicate of zirconium. It occurs naturally as zircon. Zirconium silicate is typically colorless, but impurities can cause it to be colored. It is insoluble in water, acids, alkalis, or aqua regia. It has a Mohs hardness of 7.5. The function of zirconium silicate coating varies depending on the application. For example, it can be used to protect metal surfaces from corrosion and abrasion. In addition, zirconium silicate coating can be used in the manufacturing of ceramics and glass, as well as serving as an insulating material in electronic products. |
| Aluminum oxide coating | Aluminum oxide coating has high thermal stability, chemical inertness, and good solubility in electrolytes, making it an excellent coating material for lithium battery ceramic separators. In addition, aluminum oxide can also be used as a coating to improve the functionality of aluminum materials. The main functions of aluminum oxide coating are: 1. High temperature resistance, allowing the separator to maintain its integrity when placed in a 180℃ oven; 2. Aluminum oxide can neutralize free HF in the electrolyte, enhance the acid resistance of the battery, and reduce internal gas generation. Additionally, aluminum oxide can quickly form a super-thin protective layer (about 2-3nm) like a liquid, preventing further oxidation of the metal. |
| Zinc oxide coating | Zinc oxide coating is commonly used for corrosion resistance, sun protection, UV resistance, electromagnetic shielding, and other applications. Zinc oxide coating can act as a flame retardant synergist and is used in cable coatings. Zinc oxide is an oxide of zinc, a white solid also known as zinc white. It can be obtained by burning zinc or roasting sphalerite (zinc sulfide). In nature, zinc oxide is the main component of the mineral zincite. Zinc oxide coating can act as a flame retardant synergist and is used in cable coatings. Additionally, zinc oxide coating can be used in rust-proof primers and as a source of zinc phosphate to prevent corrosion on metal surfaces. |
| Titanium oxide coating | A titanium oxide coating, also known as a DSA (Dimensionally Stable Anode) coating, is a type of metal oxide coating applied to the surface of a titanium anode metal. The function of the metal oxide coating on the titanium anode is to have low electrical resistivity, good conductivity, stable chemical composition of precious metal coatings, stable crystal structure, stable electrode dimensions, good corrosion resistance, long service life, good electrocatalytic properties, and favorable for reducing overpotential of oxygen and chlorine evolution reactions, saving energy. |
3.Metal coatings
Metal coatings are a type of coating used to protect metal surfaces. A wear-resistant metal coating is a type of coating used to protect metal surfaces and improve their hardness and wear resistance, preventing scratches and abrasion. Metal coatings can be used for both protection and decoration of metal surfaces, and can improve their resistance to corrosion, wear, and heat, making them suitable for plating and hot dipping processes.
| Advantages | ✔️Not easily peeled off or pulverized, with lubrication and good wear resistance, achieving the function of lubrication and wear resistance. ✔️Can prevent metal corrosion. |
| Disadvantages | ❌Easily scratched by mechanical forces, leading to corrosion. ❌Long-term exposure to air can lead to loss of luster due to oxidation. ❌Long-term exposure to water can cause corrosion due to electrochemical reactions. ❌Uneven coating thickness can easily lead to localized corrosion. ❌Poor coating quality can lead to peeling. |
There are many types of metal coatings, which can be classified according to the form of the coating material, including water-based coatings, solvent-based coatings, powder coatings, high solid coatings, etc. They can also be categorized according to the application method, such as brush coating, spray coating, roller coating, dip coating, electrophoretic coating, etc. In addition, there are some special metal surface treatment methods, such as anodizing, zinc plating, electroless nickel plating, hard chromium plating, etc. The following table will provide a detailed explanation.
| Classification | Common Metal Coatings | Characteristics |
| By the form of the coating material | Water-based coatings | Water-based coatings are coatings that use water as a solvent or dispersant. The biggest advantage of water-based coatings over oil-based coatings is their low VOC (volatile organic compound) content. During painting, users do not need to add solvents to dilute the paint, so there is less risk of inhaling volatile solvents that can affect health. At the same time, there is no risk of fire during construction (solvents are prone to explosions and fires). |
| Solvent-based coatings | Solvent-based coatings are building coatings made with organic solvents as dispersants. Organic solvents are liquids that can dissolve solid, liquid, or gaseous solutes to form a solution. When using this type of coating, it is important to note the emission of volatile organic compounds, which have been banned in some countries and regions. | |
| Powder coatings | Powder coatings are a new type of 100% solid powder coating that does not contain solvents. The main component is resin, and the type of resin used determines the performance of the powder coating. Powder coatings do not require solvents during application and do not contain volatile organic compounds or solvents, making them more environmentally friendly. Powder coatings have a wide range of applications, including the automotive, furniture, construction, and electrical industries. | |
| By Construction Method | Brushing Coating | Brushing coating is a method of applying coatings on an object surface using different techniques to form an adhesive, durable, and continuous solid film with a certain strength. The film formed in this way is commonly called a coating or a paint film. There are many types of coatings with various uses, including water-based paint, oil-based paint, etc. |
| Spraying Coating | Spraying coating is an industrial metal surface treatment process that involves dispersing liquid paint (commonly known as paint) into fine mist particles and adhering them to the surface of the object being coated. This method usually uses compressed air for spraying. Another type of spraying coating is electrostatic powder coating, which disperses powder coating into fine particles and then adhered them to the object being coated by an electric field. | |
| Roller Coating | Roller coating is a coating in which a roller is used as the carrier for the coating. The coating forms a certain thickness of wet film on the roller surface, which is then applied to the surface of the object being coated by the roller during rotation. Roller coating is suitable for flat objects and is widely used in the coating of metal sheets, plywood, fabric, and paper, especially for the coating of metal coils. | |
| Dipping Coating | Dipping coating is a construction method that achieves the purpose of coating by immersion. The operation involves immersing the entire object to be coated in the paint, then taking it out of the tank, and returning the excess coating back to the tank. This method is called dipping. The characteristics of dipping coating are high production efficiency, simple operation, less coating loss, and it is suitable for small hardware parts, steel pipe supports, thin sheets, and complex structures of equipment or electrical insulation materials, etc. | |
| Electrophoretic Coating | Electrophoretic coating is a special coating method in which a conductive object is immersed in a low concentration of electrophoretic paint diluted with water as an anode (or cathode), and a corresponding cathode (or anode) is set in the tank. After a period of time with direct current passing between the two poles, a uniform and fine, water-insoluble coating film is deposited on the surface of the object being coated. |
Conclusion
Although sandpaper may seem small, it plays an indispensable role in practical applications. Whether it’s for home repairs or industrial production, sandpaper provides efficient processing technology to help people complete various tasks. The production process of sandpaper has undergone significant development and improvement, from handcrafted to mechanized production. With the continuous advancement of technology and innovation of abrasives, the future development of sandpaper is full of possibilities.
In the future, sandpaper will become more intelligent and automated, better meeting people’s needs for precision and efficiency. At the same time, environmental protection and sustainability have become important directions for the development of the sandpaper industry. As global environmental issues become increasingly serious, sandpaper production companies are constantly exploring environmentally friendly production methods to reduce environmental pollution.
References
- https://www.istockphoto.com/hk/%E5%9C%96%E7%89%87/%E7%A0%82%E7%B4%99
- www.researchmfg.com
