Applications of Shellac

 Applications of Shellac

Shellac  resin boasts unique and excellent properties. Its films, formed from alcohol or  alkaline solutions, are hard, glossy, and tough. It exhibits strong adhesion to  various materials such as wood, glass, metal, paper, and mica, and is resistant  to acids and hydrocarbon solvents; it also offers moisture resistance, rust  prevention, oil resistance, electrical insulation, and good thermoplastic  properties, without being toxic or irritating to humans. Therefore, it is a  versatile natural resin used across a broad range of industries, including  defense, electronics, food, coatings, pharmaceuticals, machinery, rubber,  plastics, leather manufacturing, papermaking, and printing. However, shellac  resin also has some inherent drawbacks, such as brittleness, low softening  point, and poor resistance to water, heat, and chemicals, which limit its  applications in certain areas. To expand the range of uses for shellac resin and  to meet the special requirements of different industrial sectors, numerous  experiments and studies have been conducted both domestically and  internationally in recent years. These efforts have involved testing various  formulations and adding different substances to chemically modify shellac resin,  producing a wide array of modified shellac resin products with special  functions, achieving significant success.

1. Fruit Preservation

Fruit  preservation and storage is an extension of agricultural production. Utilizing  shellac's colorless, odorless, non-toxic properties, and its excellent  film-forming capabilities with good water resistance, moisture resistance, acid  resistance, and oil resistance, the introduction of nano SiOx powder materials  improves the gas barrier properties of bleached shellac films. By incorporating  natural fungicides, antioxidants, and growth regulators, a bleached shellac  fruit preservative is created. When applied to the surface of citrus fruits,  pears, apples, and melons, it not only enhances the gloss and appearance of the  fruit but also retains moisture, preserves freshness, reduces rot, maintains the  original flavor, and extends the storage period, shelf life, and increases the  rate of marketable products and selling points. Under ambient temperature  conditions: apples can be stored for 90 days, pears for 80 days, citrus for 50  days, melons for 25 days, and crisp plums for 15 days. The appearance of the  fruit remains plump, the skin color pure, with a commercial rate of 90%, and a  moisture loss rate of ≤12%.

2. Military Industry

The  direct use of shellac resin products in military technology and formulations is  often classified as military secrets and rarely published. Indirect uses include  insulation materials for military electrical equipment (electron tubes,  detonators, instruments, and radio equipment), protective varnishes for military  hardware (guns, shell casings, wings, hulls, etc.), and as moisture-proof  agents. It is applied inside and outside the shell casings and at the junction  of the bullet and casing to prevent ammunition from becoming damp and  ineffective during storage. It is also used to manufacture moisture-proof paper  and cloth for packaging ammunition and as an adhesive for powder  granulation.

3. Ink

Inks  made from shellac resin as the main ingredient are durable, smooth, bright,  quick-drying, and wear-resistant, with strong adhesion to glossy surfaces like  glassine paper and aluminum foil. Shellac-based inks have been widely adopted in  the ink industry abroad.

Shellac  inks are divided into alcohol-soluble and water-soluble types. The former is  mainly used for printing on glassine paper, celluloid, packaging paper, lampwick  paper, holiday paper, and printed products; the latter is mainly used for black  waterproof drafting ink, colored waterproof drafting, and advertising  inks.

4. Fertilizers

Due  to its excellent waterproof, moisture-proof, and sealing properties, shellac  resin is used to manufacture and improve the packaging materials for  fertilizers. Fertilizers like ammonium chloride, calcium superphosphate, and  dipotassium phosphate often deteriorate during storage and transportation due to  moisture absorption or dehydration. Applying modified shellac varnish to  packaging materials makes them heat-resistant (≤100°C), waterproof, leak-proof,  dust-proof, and also resistant to chemical corrosion.

5. Electronics

Shellac  resin, with its excellent electrical insulation properties, adhesiveness,  anti-carbonization, and thermoplasticity, is widely used in the electronics  industry for insulating varnishes, laminated insulators, and molded  insulators.

Due  to its superior insulation and non-conductivity after exposure to electric arcs,  shellac resin can be directly used in the electrical industry to manufacture  high-voltage resistant laminated mica sheets and other insulating materials'  adhesives. It can also be esterified and modified with ethylene glycol, tartaric  acid, etc., to prepare laminated mica sheet adhesives with improved strength and  flexibility. Additionally, by blending with semi-drying oils such as castor oil,  linseed oil, fatty acids, and glycerin, modified shellac can be used to produce  black insulating adhesives.

There  is a wide variety of insulating varnishes, including those used for impregnating  or coating instruments, small motor coils, and bare wires, or for bonding paper  strips and fibrous strips on enameled conductors, thereby improving the  dielectric properties and mechanical strength of the conductors. Some are used  for protective varnishes for electrical equipment to resist heat, water, and  cold; others are used for insulating coatings on enameled steel wire, providing  flexibility, heat resistance, and corrosion resistance.

Mica  is one of the best insulators in the electrical industry. By peeling mica sheets  and bonding them with shellac resin, different additives (such as tartaric acid,  oxalic acid, zinc oxide, chlorinated biphenyl, ethylene glycol, naphthenate,  etc.) can be incorporated into the shellac to prepare adhesives with varying  properties. This process produces laminated mica sheets, rigid laminated  insulators, laminated insulating tubes, and flexible laminated insulating  materials with various characteristics.

Shellac  is also a commonly used thermoplastic adhesive for molding insulators. These  molded insulators are characterized by their non-conductivity after exposure to  electric arcs (i.e., they do not cause surface carbonization and significantly  weaken insulation performance due to short-term electric arcs or sparks passing  over the surface). Typically, shellac is mixed with asbestos powder, mica  powder, rubber, rosin, ethanol, talc, sulfur, and fibers, among others, using  various formulations to produce acid-resistant insulating materials,  flame-retardant molding materials, fire-resistant and heat-resistant insulating  materials, and waterproof insulating materials. These materials are then molded  into various electrical insulating parts, such as knobs, buttons, switch bases,  switch plates, switch handles, and arc shields.

A  putty made by adding marble powder and phenolic resin to a shellac resin alcohol  solution can be used for bonding light bulbs, fluorescent lamps, and vacuum  tubes.

6. Pharmaceuticals

In  the pharmaceutical industry, shellac can be used to coat tablet or sugar-coated  tablet surfaces, providing an attractive gloss while protecting against moisture  and quality degradation. Utilizing the acid resistance and lack of alkali  resistance of shellac resin, enteric coatings that do not dissolve in the  stomach but dissolve in the intestines can be prepared. This regulates the drug  release rate and timing, enhancing the stability and effectiveness of the  medication while reducing gastrointestinal irritation. Coating medications not  only helps mask unpleasant odors, making them easier to swallow, but also  facilitates transportation, storage, and use through improved handling  properties.

Shellac  is also used in health supplements. Applying a shellac ethanol solution to the  exterior of health supplement capsules can prevent royal jelly capsules from  dissolving in the stomach and protect the capsules from oxidation, degradation,  and discoloration during storage and transport.

When  combined with other drugs, shellac exhibits strong antibacterial activity,  showing effectiveness in preventing and treating dental caries. A mixture of  shellac with anhydrous ethanol, formic acid esters, and lavender oil, in  specific proportions, can be uniformly applied to the tooth surface to form an  antibacterial film. This film is effective in preventing and treating dental  caries and periodontal caries.

A  mouthwash with high antibacterial activity can be produced by mixing shellac  with ethanol, glycerin, licorice-salt acid, sodium hydroxide, etc. Shellac can  also be used to make tooth powder, which prevents periodontal caries and absorbs  bacteria on the surface of the tooth. For teeth whitening, shellac can be mixed  with methyl polysiloxane solution in proportion to create a teeth whitening  agent. When applied to teeth, this whitening agent can maintain its effect for  24 hours, providing a cosmetic whitening benefit. Additionally, the excellent  film-forming properties of shellac can be utilized in formulations for treating  athlete's foot and tinea corporis.

7. Food Industry

In  the food industry, shellac resin products are used to enhance the appearance and  gloss of candies and pastries, preventing them from becoming moist and sticky.  This application leverages shellac's easy film formation as a coating material  and its derivation from natural products, which facilitates approval for food  use. Additionally, when combined with other ingredients, shellac can improve the  texture and appearance of food. Generally, only shellac that has been dewaxed,  carbon-black filtered for decolorization, and not chemically modified is  suitable for food applications. If necessary, it can also be modified with  edible acids, phenols, or extracts from natural berries containing these  substances before use. For example, mixing sugar, starch, eggs, water, and  shellac-coated chocolate in certain proportions, then rolling, cutting, and  baking at 200°C for a few minutes, produces beautifully finished, tasty  biscuits. Shellac and starch can also be used as base materials to produce  edible internal packaging films through modification, offering good water  resistance, oil resistance, and moisture barrier properties, high mechanical  strength, non-toxicity, harmlessness, absorbability by the human body, and  natural degradability. Coating bread with shellac can effectively prevent mold  and extend its shelf life.

 8. Furniture

Shellac  varnish, as a protective and decorative coating, is widely applied in the  furniture industry for furniture, tables, chairs, cabinets, doors, windows,  floors, musical instruments, vehicles, and various industrial wood products  (countertops, radio casings, cultural goods, etc.). Shellac coatings are simple  to prepare, easy to use, have strong adhesion, dry quickly, and produce a  smooth, hard, transparent, elastic, and uniformly glossy film. Common types  include ordinary varnish, colored shellac varnish, colored shellac enamel, and  shellac nitrocellulose lacquer. They can be used for transparent finishes (to  highlight wood grain) or opaque finishes (to cover the grain), and serve as an  excellent sealer for knots and aniline dyes. Resin from wood knots can erode the  surface coating of wood, causing peeling, discoloration, and the appearance of  dark spots or even sticky droplets. Shellac paint provides good sealing  properties. Additionally, when general varnish or paint is applied over a dye,  it may redissolve aniline dyes, whereas a shellac varnish layer can seal or  prevent oil-based dyes from diffusing into the top layer of varnish or  paint.

9. Adhesives

Due  to its exceptional adhesiveness, especially on smooth surfaces such as glass,  mica, glazed ceramics, and polished metals, shellac resin has long been used as  an ingredient in adhesives and bonding materials.

Shellac  resin products can also be used to bond abrasive particles (such as aluminum  oxide, silicon carbide, and corundum) to form grinding wheels of specific  shapes. Grinding wheels are essential equipment in the mechanical industry for  grinding various tools and cutlery. Shellac-based grinding wheels are highly  wear-resistant, offer excellent cutting quality, do not deform, generate minimal  heat on the object being cut, and can produce a high gloss on the material being  ground. They are commonly used for grinding bearings, rollers, cutlery,  camshafts, races for bearing balls, cutting high-speed tool steel, and for the  precision processing of stainless steel strips, brass strips, and non-ferrous  metal strips. They are also used for cutting and polishing agate, marble, and  granite.

Shellac  is also used in the manufacture of water sandpaper. The paper is first soaked in  light mineral oil, then coated with a shellac-based mixture, after which the  abrasive is uniformly adhered to the surface and gently baked.

Furthermore,  shellac is used in the production of laminated paperboard. Paper is impregnated  in a shellac mixture (shellac reacted with urea and formaldehyde in an alcohol  solution), dried, and then hot-pressed into boards.

Hydrolyzed  shellac reacting with maleic anhydride, followed by esterification with allyl  alcohol, can produce a strong water-resistant adhesive suitable for bonding  glass to glass and metal to metal.

10. Coatings

Shellac  resin is commonly applied to various metal sheets, foils, wires, and their  products to prevent corrosion and rust, preserving the original appearance and  luster of the metals and extending their lifespan.

Acrylic  and Acrylonitrile-Butadiene-Styrene (ABS) Modified Shellac  Varnish: Enhances  adhesion to metal surfaces, producing a tough coating that is heat and solvent  resistant.

Melamine  Modified Shellac Varnish (40%): When  sprayed on metals like copper, brass, and silver, it forms a hard, smooth, and  shiny film with excellent heat and water resistance.

Water-Soluble  Resin and Drying Oil Modified Shellac Varnish: Offers  good adhesion to metals. After baking, the film can resist 10% solutions of  lactic acid, acetic acid, oxalic acid, hydrochloric acid, acetone, and  lubricating oil.

Butylated  Urea-Formaldehyde Resin Modified Dewaxed Shellac Varnish  (20%): The  film is water-resistant, chemical-resistant, and weather-resistant.

Another  major use of shellac resin products in metal coatings is as a primer. Phosphoric  acid and chromium trioxide modified shellac phosphating primers significantly  improve adhesion and water spotting resistance on stainless steel, cold-rolled  steel, galvanized steel, and aluminum sheets. Urea and dibutyl phthalate  modified shellac phosphating primers are effective on any metal surface,  especially on aluminum, zinc, magnesium, copper, and other light metals and  alloys that are generally difficult to paint. The characteristics of phosphating  primers include quick drying, metal surface passivation, strong adhesion, and  providing an excellent adhesive base for subsequent painting.

Modified  shellac resin with olefin-branched phenolic compounds, added with dioctyl  phthalate and glycerol for plasticization, and polyethylene glycol to reduce  stickiness, can be made into a sealing glue. This sealant exhibits excellent  resistance to oil, acid, water, and organic solvents other than alcohols, with a  short curing time, easy film formation, non-stickiness to sealing surfaces, good  elasticity, and shape adaptability to the sealed surfaces, making it convenient  for disassembly and assembly of sealed parts. Thus, it is used in mechanical  manufacturing, construction windows and doors, petrochemical, and electronics  industries. Shellac and shellac polymers combined with hydroxy esters, hydroxy  acids, hydroxy ketones, phosphate esters, and acidic phosphate esters can be  made into sealing agents for glass containers, allowing treated glass bottles to  be reused.

Shellac  can also be used with ethanol, realgar resin, n-amyl acetate, benzaldehyde, and  acid-resistant bituminous materials to make letter correction fluid; combined  with pigments, adhesives, pearl essence, surfactants, and wetting agents, it can  produce smooth, glossy, and even nail coatings.