Link: nvestigating Baked Eye Shadow Production Process | PCM
By: Timea Sulenta – Pam, Austria

Pressed eye shadows have, so far, been the largest segment of the eye shadow product group available on the market. However, there are other, smaller product ranges with different textures like jelly, liquid or stick form.

At the moment, on the shop shelves we can observe new products with different shapes, stamps, in innovative containers. Most often these products are multicoloured with some additional effect like a glittery, marbled or metallic look. What is the secret of this product? How they were made?

Some of them were made with liquid powder technology but there are also a lot of them which belong to the baked product group. Baked product process technology and the most common problems connected to this technology are the main subjects of this article. Below all the stages of production process are presented and the main problems which occur during formula creation and production process.

Baked technology production process

The baked technology production process consists of several steps:

• Powder bulk preparation
• Liquid powder preparation
• Solvent selection and powder bulk wetting
• Process of dosing
• Drying operation

The first stage of powder bulk preparation is the easiest stage of whole process. It is very similar to pressed product technology whereby fillers such as mica, talc, pigments and pearls are mixed in the vessel, and then the binder is added and the bulk is mixed again. For pigment, loaded bulk time of the mixing is longer than for the pearl one. Mixing for too long a period of time for pearl loaded bulk may destroy its structure and the product may be not as shiny and glittery as it should be. One of the biggest advantages of baked products is the potential to add in the formulation a high level of pearl pigments. In pressed products there are constraints imposed by the technology process and pearl content with its particle size is limited. The powdered components can be pre-contacted with a liquid binder and thoroughly mixed and pulverised before introduction of the solvent. Solvent changes the rheology of the bulk into a semi-liquid texture. The volume of the solvent depends on bulk type and it is carefully selected for each mixture. Some of the fillers like talc adsorb a higher quantity of solvent than the others. So to get the right consistency you need to add a higher volume of the solvent.

When the proportion of solvent and powder bulk are at an optimal level the process of dosing can start. Godet needs to be made from material resistant to high temperature, because at the end of production process it needs to be dried in the oven. It is very important to match the best size and shape of godet at the beginning of the project; these traits determine the appearance of the finished product. With the choice of right godet we also need to evaluate our production possibilities and available equipment.

Powder bulk preparation

Talc or mica as the main filler in the composition? This is the first question that we should consider. The absorption capacity and after-feel in application of these two raw materials are very different. Selection of the right proportion in the composition is the most important factor.

Specialists with experience in pressed product technology are able to handle this area very easily. The physical-chemical parameters of the raw materials directly affect the features of the finished product. When one creates a new formulation based on this information we can assume the right proportion of each ingredient has been included in the mixture.

Heavy, oily or light after-feel application is the next issue to consider. Mica as a raw material has a smaller density than talc. It forms ‘fluffy’ bulks which are difficult to aggregate. In combination with pearl pigments it is not as easy to achieve a homogenous, smooth bulk. With the addition of pigment or talc load to the bulk and it becomes more compact and easier to process with dosing. Talc-based formulations are the opposite. They are smooth and become too well-knit, though we can loosen it with pearl or mica addition. Mixtures that contain only talc and pigments without any filler, with low density result in products that are very hard and impossible to apply. It is recommended to use the combination of talc and mica in proper proportions in order to eliminate all the problems mentioned above. Depending on what kind of effect we want to achieve in the finished product – matt, pearly, metallic, or glittery – the proportions of the mixture can change, or even one of these fillers can be eliminated.

Solvent selection and powder bulk wetting

The biggest challenge is to find the right liquid binder. In pressed products it determines the quality of the product. In baked products it is more complicated because besides the binder, we also need to select the right solvent and its content in the composition. The solvent must be a volatile substance and easily removable from the finished product. It should be neutral in order to avoid a reaction between the mixture components. The most unpredictable are reactions between pigments or pearls with the rest of the mixture. The solvent needs to guarantee product stability over time, and it should not change the properties of the product after a period of time. And what is most important is that it cannot increase the cost of the production. The most common used solvent is water.

A liquid binder is then sprayed onto the mixed powder. The mixed powder with binder is then blended and pulverised again. In a second stage, the mixed powder with binder is combined with a solvent and mixed to form a slurry. The slurry needs to display good consistency while the product is formed. The liquid binder ingredients may be individually added, if one of them needs to be liquefied by heating, or in a single mixture.

The liquid binder used in compounding the composition needs to be selected individually according to the final effect of the product. Oils with vegetable origin work well in baked product formulations, especially if we want to achieve a metallic or high pearly effect. This range of oils is able to readily bind a high content of pearl pigments. In this case, finished goods are creamy and easily applicable on the skin. By increasing the pearl level in formulations the formulator is required to also increase the level of binder. If we want to use pearl with a larger particle size like glitter it is necessary to add an ingredient which improves skin adhesion properties. Silicones are the second most commonly used group of emollients in the case of baked eye shadow binders. They give unique soft touch application and ensure long wear on the eyelid. Silicones like dimethicone are suitable for matte and also pearl effect formulations. To get the best result it is recommended to use a mixture with a different viscosity value to this raw material. This solution protects products from quick drying.

If we decide to use vegetable origin oils it is necessary to prevent them from the oxidation process. The product is heattreated so the oxidation is accelerated. The popular antioxidant, tocopherol, or its derivatives is one of the options. Also ascorbyl palmitate, or its mixture with tocopherol, is a good choice.

Of course formulations also need to contain ingredients that protect from colour fading. A standard UV filter like ethylhexyl methoxycinnamate may be used. A mixture of diethylhexyl syringylidene malonate (and) caprylic/capric triglyceride is also a good choice.

Of course formulations also need to contain ingredients that protect from colour fading. A standard UV filter like ethylhexyl methoxycinnamate may be used. A mixture of diethylhexyl syringylidene malonate (and) caprylic/capric triglyceride is also a good choice.

During the process of producing a cosmetic, they are exposed to microbiological contamination, which originates from the environment of the production process. Depending on type of selected solvent, addition of a preservative system may be required, especially if it is a water based system.

During the process of forming a powder into a slurry, thixotropy of the bulk change and unexpected problems may occur. One of the problems is when the bulk seems to be liquid but is in fact still very tight and difficult to dose. This observed effect is explained by the Newtonian Fluid theory. In non-Newtonian shear thickening fluids, viscosity appears to increase when the shear rate increases. This means that if the bulk is mixed with a higher shear speed or the pressure is increased during the dosing process, the bulk becomes impossible to dispense. It is logical that the higher the content of the disperse phase in a solvent, the higher the viscosity of the mixture. These shear thickening fluids are also known as dilatant materials and this type of flow behaviour is encountered in concentrated suspensions and can be qualitatively explained as follows: When a suspension is at rest, the voidage is minimum and the liquid present is just sufficient to fill the void space. At low shear rates, the liquid lubricates the motion of one particle past another and resulting stresses are consequently low. At high shear rates the dense packing of solids breaks down and the material expands or dilates slightly causing an increase in the voidage. Thus, the amount of liquid available is no longer sufficient to lubricate the solid motion ofone particle past another and the resulting solid-solid friction causes the stresses to increase rapidly, which, in turn, causes an increase in the apparent viscosity.1

The severity of the shear thickening depends on the concentration, in proportion to some maximum packing fraction which is itself partly controlled by the form of the particle size distribution. The particle shape is also important. The extent of the phenomenon can be greatly reduced by either reducing the particle size, thus delaying the onset to higher shear rate, or by using a mixture of particle sizes. The latter procedure changes the onset condition, and reduces the severity by increasing the maximum packing fraction of the suspended material.2 If dilatation is observed during bulk production, there is a low probability of eliminating it. Addition of water or dilution in another solvent will most likely not have the desired result. The real problem lies in formula content. It is vital to change the powder bulk composition. A raw material particularly vulnerable to this occurrence is titanium dioxide with its big particle size. In combination with fillers like mica, bulk loaded with titanium dioxide may result in dilatation fluid but rheology change of the bulk is not the only problem that can occur during the production process.

Process of dosing

The process is divided in two stages:

• Applying the desired product dosage
• Correct shape forming

In baked products, the technology available enables a possibility to achieve a variety of shape and colour combinations. Colour arrangement depends on the technique of dosing and it is easy changeable. By deciding for a marble effect product it is necessary to know that none of the products will be identical.

Another problem resulting from an incorrect formula combination which appears just after dosing process is cracking. It occurs with small gaps on the product surface. This problem is the result of drying the bulk too quickly. To eliminate this defect, addition of a wetting agent is desired. It should be added to the powder bulk or directly to the binder system. Lack of wetting agent results in shrinkage of the bulk and cracking.

Drying operation

Drying is the last step in the production process. It is ideally achieved by heating, but other methods of drying, such as ambient temperature air drying, can also be used. The semi-finished product is placed in an oven, while parameters like time and temperature of drying depend on the type and quantity of the solvent. The size of the godet also needs to be considered. A large size of godet or high stamp products require a longer period in the oven. In most cases the temperature of drying should not exceed 50°C. After the drying operation, the humidity of the semi-finished product needs to be measured. Humid or wet products, especially with water added to the mixture, are extremely vulnerable to microbiological contamination. It may also evaporate in the container which causes a lot of trouble and additional work. These mistakes reduce production capacity and the quality of the finished goods.

Temperature and the amount of drying time need to be selected at the right level. A drying time that is too long or a temperature that is too high may totally change the features of the product. It can be very hard and impossible to apply. To choose the right parameters a lot of trials need to be done.

Quality control

To release the semi-finished product to the assembling process, first it is checked by the quality control department. Just as for pressed products, control tests like the drop test and crash test are conducted. In the case of baked products, limits and test standards may change, especially when the shape of the product is easy to break or with a very high stamp. Sometimes when the test results are not acceptable, the bulk needs to be hardened. One of the ways is with the addition of a rheology modifier. Most often it increases the viscosity of the solvent. The rheology modifier can be mixed with the solvent, or incorporated onto the powdered components. The simplest way is also to increase the liquid binder content to build a stronger structure. The same solution is used when the product is too soft during application or it is crumbling. On the raw material market there are a lot of fillers available to use as a powder binder, but to make them effective they need to be selected individually to each formulation.

Conclusion

Baked eye shadow is an easy recognisable product and it stands out on the market with unique form, colour, and overall appearance. It has a creamy texture, and a soft and velvety after-feel.

The unquestionable advantage of this product is the ability to get amazing metallic, glittery or pearly effects. This product is also interesting with regard to its application. Baked formulas compared to pressed formulas make an ultra-smooth application. Baked also allows the product to be used wet or dry; when using dry, it provides traditional eye shadow colour to eyelids. When using wet, it increases the colour payoff for a more dramatic look and it also increases its staying power. It can be used as a multifunctional product ‘2 in 1’ like an eye shadow and eyeliner in one, using only two different applicators. With the shadow end of a double ended brush the colour may be applied over the entire lid. As an eye liner using the liner end of a double ended brush, it can be applied along the top and bottom lash lines.

Baked products are still a mystery for development chemists. It is a challenge to formulate decorative products which meet with market and end consumer expectation. This article is mostly based on experience and I am sure that many of the issues connected with this topic have not been mentioned yet. Considering all the production steps, it takes a lot of time and hard work to get the right formulation and process description.

References

1 Chhabra RP. Bubbles, drops and particles in non-Newtonian fluids, 2nd Edn. Taylor & Francis Group 2007, 26-27.
2 Barnes HA. Shearthickening (‘dilatancy’) in suspensions of nonaggregating solid particles dispersed in Newtonian liquids. J Rheol 1989; 33: 329.

Copyright of this article by Personal Care Magazine. We are sharing and promoting the market innovation.
If you like this article, kindly to visit www.personalcaremagazine.com