Formulation of Nail Lacquers

FORMULATION OF NAIL LACQUERS

The formation of an efficient nail polish may be based on the selection of a proper and an essential ingredient. The ingredients involved in the formation of a good variety of nail polish could be as follows:

S.N.      Ingredients Example

1  Film forming agents:    Nitro cellulose, ethyl cellulose, vinyl polymers

2  Resinous substances:     Aryl sulphonamide-formaldehyde

3  Dissolving solvent :  Ether, ethyl acetate, amyl acetate, butyl acetate

4  Dissolving solvent/co-solvent: Ethyl alcohol, butyl alcohol

5  Plasticizing agents:        d-butyl phthalate, n-butyl stearate

6  Coloring agent:   5% titanium dioxide (TiQ2)

7  Nacreous/pearly pigments:     Guanine crystal

8  Miscellaneous substances:      (1) suspending agent

                                                       (2) perfumeries

1.          Film Forming Agents:

The selection of a film forming agent is an important step in the formation of a relevant type of nail lacquer. The most commonly used film forming substance is nitrocellulose, due to the following properties.

·                               The films formed using nitrocellulose pigment stay flexible for a sufficient period of time.

·                               It has good adherent property and hence does not allow any chipping and peeling.

·                               Its solvent retaining capacity is very low.

·                               The films formed by nitrocellulose are impermeable to water and air and hence fungal infections can be eliminated.

·                               It imparts relevant transparency to the nail enamel.

·                               When compared to other film forming agents it is quite hard, tough and has good abrasion resistance ability.

Other Film Forming Substances: Several grades of nitrocellulose are available with varying viscosities but only low viscosity grades are used for the preparation of nail polishes. The degree of polymerization determines the viscosity which is necessary in order to prepare a nail polish of required consistency.

Two types of grades of nitrocellulose are readily used for nail polish preparation. They may be 'RS' and ‘SS’ type. The most common used type is 'RS' grade with viscosity range 0.25 to0.5 cps. When nitrocellulose is used alone it produces a poor gloss and hence in order to avoid this resins are added.

2.          Resinous Substances:

Resins enhance the glossy nature of the nail polish and also impart adhesive property.

·                               Natural resins such as benzoin, shellac, damar, sandarac and ester gums were used initially but have been replaced' by synthetic resins as they provide good gloss, better adhesion and also increased water resistance capacity.

·                               The most commonly used synthetic resin is sulphonamides-formaldehyde resin. it is a polymer made by mixing equimolar proportions of formaldehyde and para toluene sulphonamide.

·                               The two commercial types of aryl-sulphonamide-formaldehyde forms are santolite MHP and santolite MS 80 percent.

·                               The santolite MHP forms a harder film and the santolite MS 80% provides good gloss, flexibility and now property. But the resin combination is known to cause certain allergic reactions and hence it has now been replaced by other synthetic resins such as polystyrene, polyvinyl polyacrylic ester.

·                               Acrylic esters are compatible with nitrocellulose and they provide excellent gloss, adhesion, durability, good flexibility etc.

3.           Solvent System:

The solvents normally used for preparation of nail polishes may be volatile organic liquids that can dissolve all the ingredients and make a homogenous and uniform preparation. The solvent should be volatile enough in order to leave a continuous, impermeable and hard film but the evaporation should not be too rapid. The selection of a solvent plays an important role in order to provide a balanced rate of evaporation.

Generally a mixture of solvents is preferred rather than a single solvent. The solvents used for the formation of nail polishes are of the following types.

(a)            Low Boiling Solvents: They include the solvents having boiling point below 100°C. They take more time to evaporate. Examples for low boiling solvents with their respective boiling points are as follows:

Solvent Boiling point       

    Acetone      55°c 

    Butyl formate      96°c 

    Carbon disulphide        46°c 

    Carbon tetra chloride   77°c 

    Ethyl acetate        68°c 

    Methyl acetate     56°c 

    Isopropyl alcohol 80°c 

    Isopropyl acetate 92°c 

(b)           Medium Boiling Solvents: these are solvents that have a boiling point ranging between 100°C to 150°C.The example of medium boiling solven ts with their boiling point are as follows:

    Solvent       Boiling point

Amyl formate 110°c

Butyl alcohol  113°c

Diethyl carbonate    126°c

Ethylene glycol Monoethyl ether 135°c

Ethyl lactate   135°c

Butyl propionate     145°c

(c)           High Boiling Solvents: Liquids with boiling points more than 150°C are r egarded as high boiling solvents. Examples with their boiling points are as follows:

Solvent Boiling point

Cyclohexanone        154°c

Methyl Cyclohexanone     160°c

Diacetone alcohol    164°c

Methyl hexalin        165°c

Ethyl hexalin 185°c

Butyl lactate   185°c

Cyclohexanone pthalate   190°c

Generally, a combination of two or more solvents is preferred over a single solvent. The solvent system used in the preparation of nail polish influences the ease of its application. It also influences its drying rate and hardening ability and other characteristic properties of the film such as gloss shine etc,. The solvent combinations should not have either too high or too low evaporation rates. Solvents that evaporate very quickly may cause intense cooling. This may cause precipitation of moisture from surrounding atmosphere making the film dull with unattractive finish blushing. The phenomenon of blushing and blooming can be prevented during the preparation of a nail polish by selecting a suitable solvent.

The viscosity of a nail lacquer is also influenced by the boiling point of the solvent. Lower the boiling point of the solvent, lower will be the viscosity of the resultant null lacquer and hence better flow property. The rate of evaporation of solvents depends on many factors such as specific heat, latent heat of evaporation, molecular weight, degree of association etc, The solvent, with high boiling points generally provide at brighter film than low boiling point solvent.

4.            Diluting Solvents/ Co-solvents:

They are not the actual solvents for the dissolution of nitrocellulose but are the co-solvents which increase the strength of the normal solvents. The various reasons for the addition of diluents are to:

·                               Maintain the viscosity of the lacquer to form a stable film.

·                               Increase the solubility of the incorporated resins, thus working as a co-solvent.

·                               Abate the effect of freshly applied polish or a recently applied lacquer.

·                               Reduce overall cost of the product since the solvents used might he costly.

·                               The most commonly used diluents are alcohols such as ethyl alcohol, butyl alcohol etc., they may also be used in combination with their esters. Example: Ethyl alcohol with ethyl acetate etc,.

The quantity of diluent used may also influence the formation of a good film. The limit for use of diluent may he expressed in terms of tolerance ratio or dilution ratio. The dilution may he defined as the maximum ratio of the diluent to the solvent (diluents/solvent) that can be tolerated by nitrocellulose solution without causing precipitation of nitrocellulose pigment.

Thus, selection of a proper combination of diluent and the solvent system is necessary. The combination should be such that the diluent should have a faster evaporation rate than the solvent system which would prevent the precipitation of nitrocellulose due to reduction in diluent solvent ratio. Thus, a clear, smooth and continuous film may be formed rather than a rough and cloudy film. The other examples of diluents beside alcohol are benzene, Xylene, toluene etc.

5.             Plasticizing Agents:

The plasticizing agent constitutes an important part in the formulation of nail polish preparation. Plasticizers are used for the following purposes.

·                               In order to improve the flexibility of the nail lacquer and minimize its tendency to shrink in order to form a uniform film.

·                               The nitrocellulose fibres alone make a dull and brittle film, but the addition of a plasticizer increases the gloss and adhesive property. Example: Castor Oil.

Functionally plasticizers may be divided into two types:

(a)          Solvent Plasticizers

(b)                      Non-solvent Plasticizers

(a)          Solvent Plasticizers: Solvent plasticizers, besides imparting flexibility to the nail polish, may also act as solvents for the dissolution of nitrocellulose. Many of them are the high molecular weight esters that have low volatility and relatively high boiling point. Example: butyl acetyl ricinoleate.

(b)          Non-solvent plasticizer: These are not compatible with nitrocellulose and hence can’t be used alone. They cannot act as solvents but only act as plasticizer.

·                               The ideal properties for the choice of a good plasticizer could be as follows:

·                               It should be compatible with other ingredients of the preparation.

·                               It should be able to impart flexibility and enhance the glossiness and adhesive property of the nail polish.

·                               It should not evaporate quickly.

·                               It should not affect the stability of the preparation.

·                               It should not affect colour of the product.

·                               It should be non-irritating and non-toxic to the skin.

·                               It should be odourless and colourless.

·                               It should not cause any change in viscosity of the preparation.

The most commonly used plasticizers are dibutyl phthalate, n-butyl stearate, butyl glycolate, tributyl phosphate, resorcinol diacetate, castor triethyl citrate, dibutyl tartrate, dibutoxy ethyl pthalate, butyl acetyl ricinoleate.

Dibutyl pthalate and glycolate plasticizers are considered to be the best as They provide better hardness, feel and adhesion to the nail. They generally contribute 5% of the total mixture or as 25% to 30% in combination with the film forming agents.

The use of acetylated monoglycosides along with other plasticizers may increase the stability and flexibility of the Product thus improving the long lasting ability.

6.           Colouring Substances:

The colouring substances also form an important component of the nail lacquer as they are required to impart a desirable shade.

·                               It should also be able to opacify the nail lacquer so that the most delicate shade may be able to cover the nail.

·                               More than 10 basic colours are required to produce large variety of sheds used in polishes.

·                               All the colours must conform to the terms and conditions of the Drugs and Cosmetics Act.

·                               The coloured substances are available as colouring agents and are incorporated with the pigments and lakes.

·                               They are mostly available in the form of dispersion. The usual concentration is between 3 to 5%. Examples: Lithopone or 5% titanium dioxide is incorporated along with lakes to produce pastel shades. Iron oxides are used to produce brown or tan shades. The dinitrobenzene pigments are used to produce brilliant brown colours.

7.          Nacreous/ Pearlescent Substances:

They are used in order to produce an iridescent or a nacreous appearance. They have high refractive index and hence produce a glow when light falls on then. The can be obtained either from nun-al or synthetic origin.

(a)          Natural Pigment: The example for the substance from natural origin is guanine crystals. Chemically they are 2-amino, 6-oxypurine crystals. They are obtained from the skin and the scales of fish. They are marketed mostly in the form of suspensions or pastes.

(b)           Synthetic Pigments: Synthetic pigments can be obtained from the coating of bismuth oxychloride or titanium dioxide or the flakes or platelets of mica. They are less expensive than natural pigments.

8. Miscellaneous Agent:

(a)           Suspending Agents: Suspending agents such as Bentone - 27 and Bentone-34 are most commonly used in nail polishes in order to prevent settling of the pearlescent pigments, thus avoiding sedimentation. The concentration of these substances varies between 0.5 to 2%.

(b)           Perfumes: Perfumes are basically used to cover the odour of other ingredients and to provide a pleasant smell. Mostly synthetic perfumes are used in an optimum quantity of about 1% concentration. The formulae for the preparation of nail lacquer are as follows:

Formula-1   Quantity for 100 g

Nitrocellulose (film former)        7 g

Dibutyl phthalate (plasticizer)    5 g

Polyvinyl acetate (resin)    8 g

Methylene chloride  29.4 g

Ethylene glycol monomethyl ether       28 g

(solvent)        

Diethyl glycol monomethyl ether (solvent)    2 g

Ethyl alcohol (diluents)     14 g

Perfume oil    6 g

Color    0.6 g

Formula-2   Quantity for 100 g

Nitrocellulose (film former)        10 g

Sentolite MHP (resin)        10 g

Dibutyl phthalate (plasticizer)    3 g

Ethyl alcohol (diluents)     6 g

Ethyl acetate  (solvent)     20 g

Butyl acetate  (solvent)     15 g

Toluene  (solvent)    36 g

Formula-3   Quantity for 100 g

Nitrocellulose (film former)        4 g

Dibutyl phthalate (plasticizer)    4 g

Polypropyl methacrylate (resin) 18.6 g

Ethyl alcohol (diluents)     25.6 g

Butyl acetate  (solvent)      23.9 g

Toluene  (solvent)    23.4  g

Color    0.5 g

The Preparation Of Nail Lacquers

The preparation of nail polishes can be carried out as follows:

The film forming substance i.e., nitrocellulose is dissolved in a suitable solvent. Resins plasticizers can be added directly or after dissolving them in small amouts of solvent.

The finely divided pigments are added by forming dispersion of the pigment as they form aggregates. The dispersion can be formed by milling the pigments in a ball null or a or triple roller mill.

The dispersion of the pigments, nitrocellulose and plasticizer are ground together in a solvent in order to form a plastic mass.

The final mixing of the ingredients for the manufacture of nail polishes is carried out in stainless steel tanks with a stirrer.

Initially, the tank is charged with the diluent and nitrocellulose (suitably wetted the diluent) is added to it.

The plasticizer and the resin are added next and the mixing process continues.

The mixing process is carried out till sufficiently uniform solution is formed. The clear lacquer is then subjected to filtration and centrifugation in order to remove any particles.