Both sugar coating and film coating are the most common coating techniques for solid dosage forms. However, they differ in processes, materials, functions, and other aspects. A thorough understanding of the differences between them will help you choose a more suitable coating method for your product. This article provides a detailed introduction.
What Is Sugar Coating and Film Coating?
Sugar Coating Definition
The sugar coating refers to a layer of sugar substance (such as sucrose, glucose, or syrup) used as the main coating material. Through multiple spraying and drying processes, a thick, smooth, and shiny sugar layer is formed on the surface of the tablet core.
Film Coating Definition
Film coating is the most commonly used coating method in the modern pharmaceutical industry. The process involves spraying a polymer-containing coating solution onto the surface of a tablet, which is then dried with hot air to form a uniform, continuous, and extremely thin polymer film.
A Comparison of Sugar Coating and Film Coating
Procedure
Sugar Coating
The sugar coating process involves five distinct stages. First, a sealing layer is applied to prevent moisture absorption. Next, sugar syrup is sprayed, and powdered sugar is sprinkled alternately to smooth out sharp edges and thicken the tablet. The surface is then repeatedly coated with high-concentration sugar syrup to level it out, followed by the addition of colorants for coloring, and finally polished with wax.
The entire process typically requires 20 to 50 layers of coating, takes 6 to 16 hours, and demands a high level of operational experience. The weight of the tablet is typically 30–80%, and in some cases may approach 100%. And it has a low degree of automation.
Film Coating
The film coating process completes the three core actions of spraying, drying, and film formation simultaneously in a closed system. The coating solution is atomized by a spray gun and evenly applied to the tumbling tablet cores. The hot air quickly evaporates the solvent, and the high molecular polymer solidifies into a dense, thin layer.
If you are highly focused on productivity and quality, you can adopt modern efficient equipment. It can be controlled automatically by PLC, with a single batch taking 1 to 3 hours. It has little batch difference and can be designed to comply with GMP requirements.
Appearance
Sugar Coating
Sugar-coated tablets have a smooth and shiny surface. After coating, the tablets will significantly thicken, and the weight of the tablet will generally increase by 50% to 100%. You should notice that the original shape of the tablet core and the engraved characters may be obscured because of the thick coat.
Film Coating
Film coatings typically have a semi-gloss to matte finish. You can also use a polymer wax to enhance the gloss. The film coating is extremely thin, typically adding only 2–5% to the weight. While functional coatings may require higher weight gains. It can clearly preserve the core’s shape and engravings. Moreover, film coatings provide better uniformity than sugar coatings. And it can be made in transparent or multicolored finishes.
Functions
Sugar coating
The sugar coatings are sweet and thick, so they can effectively mask unpleasant odors. The effect is better than that of film coatings. Sugar coatings can provide light protection when combined with pigments and opacifiers such as titanium dioxide. Additionally, the thick coating layer provides physical protection against abrasion during handling. But its texture is brittle, and it is prone to chipping easily upon impact.
Film Coating
The film coating can achieve various functions by adding different polymers or other components. The film coating containing specific polymers, such as Eudragit E, has good taste-masking properties. It can also achieve functions such as blocking light and preventing moisture. Due to its good toughness, its impact resistance is better than that of the sugar coating.
The functions of film-coated tablets are more diverse than those of sugar-coated tablets. They can also achieve enteric-coating and controlled-release functions.
Materials
Here is a table regarding the common raw materials of sugar coatings and film coatings for your reference.
| Sugar Coating Materials | Effect | Film Coating Materials | Effect |
| Sucrose, glucose, Syrup | Main coating material | HPMC | Water-soluble film-forming |
| Talcum powder | Anti-stick powder coating | PVA | Film-forming polymer with good mechanical strength |
| Gelatin, arabic gum | Isolation layer, plasticizer | Acrylic resins (Eudragit series) | Enteric-coated/sustained-release |
| Titanium dioxide | Light blocking | PEG | Plasticizer |
| Wax | Polishing | Titanium dioxide, color lakes | Coloring, light blocking |
| Food colouring | Coloring | Triethyl citrate | Plasticizer |
Advantages
Sugar coating
The sugar coating can effectively mask the bitter and unpleasant flavors of drugs. It offers an excellent sweet taste and is highly acceptable to patients, especially for pediatric medications. In traditional markets such as the Middle East, Africa, and Southeast Asia, some customers prefer sugar-coated drugs. If your product is mainly sold in these regions, this is a good choice.
Sugar coatings often have a good appearance. Additionally, sugar coating is often made using traditional coating pots, with relatively low equipment investment.
Film Coating
The film coating production time is shorter than that of sugar coating. Its weight and volume increase very little, which helps you reduce transportation costs. It also clearly maintains the shape and engraving of the tablet core, which improves product identification and brand identification. The film coating process is gentler than the sugar coating process, making the tablet core less prone to breaking.
Film coating offers more functions than sugar coating and can meet a wide range of needs. Film coating avoids the use of large amounts of sugar and may be preferred for products intended for diabetic patients. Moreover, film coating equipment can be equipped with a continuous coating system. It can offer higher production efficiency with minimal batch-to-batch variation.
Drawbacks
Sugar coating
The sugar coating process is time-consuming and energy-intensive. Furthermore, there is significant variation between batches, requiring experienced operators. The thicker sugar coating and increased weight may obscure the original shape and engraving of the tablet core, and could also increase your shipping costs.
Additionally, sugar coatings are prone to absorbing moisture, which may lead them to stick together, turn yellow, or peel off. If your products are primarily sold in high-humidity regions, you had better avoid using a sugar coating.
Film Coating
For medications that need effective masking, such as some extremely bitter active ingredients, a single film coating may not be effective as a sugar coating. And some polymer films may soften in high-humidity environments.
If you want to use high-efficiency coating machines, the initial investment will be higher. In addition, organic solvent film-coating lines need to be equipped with explosion-proof equipment.
Applications
Sugar coating
Today, sugar coating is primarily used in the production of traditional vitamin tablets and for coating certain bitter-tasting tablets. This method is also commonly used for placebo pills or candy-like products.
Film Coating
Film coating is primarily used in the production of many enteric-coated tablets, such as aspirin enteric-coated tablets. It is also used to protect vitamin C and probiotic tablets from moisture. Sustained-release tablets are also a major application of film coating.
Moreover, film coating can be used for multifunctional combined coatings that simultaneously provide an attractive appearance, moisture and light protection, and masking of off-flavors.
FAQ
Can a Film Coating Provide the Same Texture as a Sugar Coating?
They can be similar but not the same. Film coatings themselves have no sweetness. The taste can be improved by adding sweeteners such as aspartame or sucralose to the coating or adding sweeteners to the tablet core. However, film coatings do not provide the same rich, sweet, and cloying sensation as sugar coatings do.
Can the Same Equipment Be Used for Both Sugar Coating and Film Coating?
No. Traditional sugar-coating pans (non-perforated, with open ventilation) are not suitable for high-efficiency film coating. This is because film coating requires high-efficiency atomizing spray guns, a hot-air system, precise ventilation, and temperature control.
However, some high-end equipment, such as high-efficiency film coaters, can support both film coating and sugar coating processes through parameter tuning. But traditional sugar coating pans remain used because they are more suited to the multiple syrup application and polishing required in sugar coating.
Which Is More Environmentally Friendly? Sugar Coating or Film Coating?
Film coating. Traditional sugar coating may generate more dust due to the use of powdered ingredients (such as talcum powder and powdered sugar) during processing.
While the water-based film coating technology uses water as a solvent, avoiding the flammability and toxicity of organic solvents. Moreover, its preparation process is simple, which supports environmentally friendly and workplace safety. Water-based film coatings are now widely used in Europe, the United States, and Japan for many immediate-release applications.
What Are the Advantages and Drawbacks of Water-Based Film Coating and Organic Solvent-Based Film Coating?
Water-based film coating is more environmentally friendly, poses no explosion or volatility risks, and has lower production costs. However, its drying efficiency is relatively low, and it requires stricter control of process parameters. Organic solvent film coating offers fast drying speeds and excellent film formation, but it requires explosion-proof facilities and presents safety hazards and environmental concerns.
What Are the Common Failures in Sugar Coating and Film Coating Equipment?
Equipment failures in sugar coating primarily include poor dust control, uneven tablet tumbling, and clogged syrup nozzles in traditional coating pans. Common failures in high-efficiency film coating machines include poor atomization of the spray gun, mismatched spray rates and drying capacity, and unstable temperatures in the hot air system.
High-efficiency film coating equipment requires periodic calibration of spray guns, maintenance of the hot air system, and cleaning of exhaust ducts to ensure process stability.
Final Thoughts
Are you looking for the right tablet coating machine? Pilotech is a tablet coater manufacturer in China. We integrate R&D, design, manufacturing, sales, and service under one roof, enabling us to provide you with professional, customized solutions. If you have any questions, please feel free to contact us.