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The present Invention Patent refers to the color and hard anodizing for application in metal plates of manual equipment generally used for hair straightening and modeling, also traditionally known as “hair straightener”, “board” or “strengthening plate” and can be optionally be introduced in other equipment types of the same function, used to make curly hair.
As common knowledge, these manual equipment types employ heat to produce hair straightening and/or hair modeling. In order to the equipment be efficient, it is necessary that the surface of the metal plates, which are embodied as the components that gets into direct contact with hair, to have the following characteristics: be flat, sliding, resistant to scratches, have a good surface hardness, good resistance to abrasion and resistance to high temperature. For this reason the anodized aluminum is employed, which has all these characteristics.
The incorporation of a layer on the metallic surface, precisely on the contact face of the metal plates with hair, in case of hair straighteners as well as in case of modelers is obtained from the hard anodizing process, which confers to material a protective layer with high resistance to abrasion, resistance to high temperatures and high surface hardness.
Anodization is an electrolytic or electrochemical process that promotes the formation of a uniform layer of oxide on the aluminum surface. Aluminum oxide is a ceramic material. Hard anodizing is a process where considerably harder layers than the common ones are obtained. For this process, energetic agitation and efficient cooling are necessary, could resulting in very thick layers at a speed of 50 micrometers/hour. The hardness of these layers is comparable to hard-chrome, having a high resistance to abrasion. The thickness of layer in the hard anodization starts with 45 microns, and it can reach up to 100 microns of layer, according to necessity and the product characteristics desired.
Due to its greater thickness, the hard layers of aluminum oxide vary from light gray to dark gray, ranging the coloration according to aluminum alloy employed. The hard anodizing grants to the aluminum an increased superficial hardness, higher resistance to wear and good sliding capability. As greater is the layer thickness more difficult is the traditional tinting processes.
The color anodizing is commonly used only for decorative effects, being employed only in low anodizing layers, or in other words, in common anodizing processes. The color hard anodizing is an innovative technology where the properties desired of hard anodized layer and the benefits of layer coloring are obtained by absorption, by means of organic dyes. The color anodizing of aluminum known in market does not resist to heating of devices called “straightening plates” or “modelers”. The present invention embodies to the mentioned devices a coloration resistant to high temperatures (250° C.) and also confers to the material a surface with high resistance to risk, abrasion, as the surface has an aluminum oxide layer, ceramic material, which resistance is comparable to steel.
In the anodizing, an anodic film is formed, which is highly porous and has a very lengthy inner surface. This surface is highly polar and acquires charge from the water itself. Due to its high absorption power, it is capable to absorb large amounts of different kinds of solutes. Inside the film, the absorption power is determined, mainly by the rate of dye diffusion, through the pores filled with water. When the film or any highly porous solid is colored, this rate causes an effect which modifies the layer by means of slower diffusion in the pores.
The control factor in the coloring is the depth of penetration of the dye in the pores of the aluminum oxide film formed. The rates follow the usual pattern of absorption by the highly porous substrates and increase with the temperature, initially, and the quantity absorbed increases linearly with the square root of time. This behavior implies one more light internal diffusion of a dye film, of constant concentration, quickly absorbed by the more external surface of the anodic layer.
To apply color to anodized aluminum, a coloration substance must contain groupings which are capable to form chemical bindings stable with the aluminum oxide of the anodic layer. Also, it refers to the fact, verified by real chemical doctors, in which the coloration rate is proportional to square root of the immersion time.
The dyes used in the anodic layers are of acid type or solvent dyes and for the employment in these types of manual equipment they must have high resistance to temperature and resistance to photo-oxidation, prolonging the service life time of equipment in relation to the color of metal plates, since all organic substance is subjected to discoloring of its coloring, which does not interfere in the aluminum oxide layer formed by hard anodizing, neither jeopardizes the properties conferred by it.
After the traditional methodology of hard anodization, the parts are submerged into acid dye highly resistant to temperature in the chosen color such as blue, red, green, among other colors, and the parts are left in rest for 30 minutes, under constant agitation and neutral pH of solution.
The coloration of hard anodized aluminum, for a consistency of the color and definition of performance standards, requires preliminary cares of operation. The dye properties regarding to solidity against light, heat and its usage capacity in coloration process must be observed. The dye bath concentration should vary from 3 to 15 grams/liter.
The effects in the pH value coloration used in the initial tests can suffer alterations during the process. If a variation of ±0.5 in its value does not produces visible difference in the obtained color and in the range of ±1.0 shows a slight difference, then the dye will not cause major problems. For this application, it was defined the pH of the solution which must vary from pH acid=1 up to maximum for neutral pH, or in other words, pH=7. The pH of bath with caustic soda, acetic acid or sodium acetate must be controlled because some organic dyes contain sulfates or chlorides, as the sodium sulphate or sodium chloride, which can cause galvanic corrosion or retard the coloration during the process.
As the organic coloration is an absorption phenomenon, the temperature significantly affects the coloration rate. If the bath temperature is too low, the coloration will be slow, which will help in color maintenance, but however, probably, it will prejudice the solidity against light. High temperatures produce partial sealing and promote disarrangement and decomposition of the dye. Temperatures around 60° C. are optimal for the majority of organic dyes. Therefore, it was concluded that the dye bath temperature must be at 65° C. Being possible to work with acceptable results between 40° C. to 100° C., depending on the usage.
The combination of colors is easier with longer coloration times, especially because little variations of temperature, pH, and agitation can cause an unequal effect on the absorption rate, when shorter times are used.
An important prerequisite for a good coloration is that the anodizing is performed under strict conditions of control and the washing is adequate. The prolonged washing is not necessary, as the free acids diffuse from the layer and from cavities in few minutes when the washing is made with agitation. Although neutral washes with sodium or ammonia bicarbonate are recommended, they can cause changes in coloration tonality.
Precautions must be taken for not accumulating aluminum dissolved in the coloration reactions once that some dyes are affected by this accumulation of aluminum, producing a change of color. The contamination of coloration bath with heavy metals such as iron can have deleterious effects, like color changing or wear acceleration of the dye.
After the immersion of the colorant bath, the parts go to a sealing bath where they remain by a hour and a half, under constant agitation, sealing bath temperature ranges from 40° C. to 120° C., in order to fixing the dye in the interior of pores of aluminum oxide layer formed in the hard anodization. The quality of sealing is related to the temperature, in order that a good sealing requires a temperature near to the boiling point. If the sealing temperature significantly raises above the established range, it will no longer provide an effective sealing, while lower temperatures will result in a slower and unsatisfactory quality sealing.
The pH of sealing varies from 5 to 7. The sealing bath concentration varies from 3 to 20 g/liter and it is used only deionized water. The sealing of anodic layers makes the surface to stop being highly absorbent.
By using an organic dye available in the market for common anodizing and as per this work routine described above, we obtained the hard anodizing of the color correspondent to the dye used. While the decorative anodizing (common) has superficial hardness and easily risks, the results obtained in the prototypes made based on the matter described in the present invention patent accomplished the hardness of 50RC, being highly resistant to risk with infinite durability and coloration resistant up to 250° C., that is, grater than the temperature used in the straightening plates and/or modelers available in the market.