Pearlescents

Metallic pigments, especially for automobile applications such as bumpers, door panels, grips, buttons, hub covers, and scooter panels and wings, are a focal point of current development by Clariant Masterbatches Division. The company also claims it has the first colour masterbatch series for HDPE packaging with an anodized aluminium appearance, giving high reflectivity, chrome, and lustre. 

These are pigments based on thin platelets of transparent mica, coated with titanium dioxide or iron oxide, producing interference patterns. Titanium dioxide (Ti()2)-coated mica pigments have a 2-10 pm particle size, for incrca.sed lustre, whiteness, and coverage there are also silver sparkle effects. A two-tone effect can be obtained with absorption colours deposited directly on interference pigments of TiOj-coated mica (such as Mearlin Dynacolor). 

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Colorability is another reason IDs select plastics for many products. Molding color into a product eliminates finishing and painting operations, thus reducing costs. Beyond cost, integral color also masks the nicks, chips and scratches that impair appearance during the life of the product. Color effects are almost limitless. Transparent, translucent, pearlescent, fluorescent, or marbleized colors are readily available for use in plastics. 

Waxes are used in water-resistant coating on cars and furniture. They are also used in lipsticks and eyebrow pencils and in liquid soaps and shampoos to give a pearlescent effect (the tiny flakes of the wax glycol distearate reflect the light). 

The wax glycol distearate is added to make shampoos opaque and pearlescent. It has tiny flakes that mix well with surfactants, and stay in solution. They also add shear-thinning qualities, making liquid hand soaps pump out of the bottle more easily. 

New applications (e.g. demand for fluorescent, pearlescent and other brilliant pigments introduction of photoconductive elements in polymer-based electro-optical devices)... 

Metallic, pearlescent and fluorescent pigments are grouped together in this section as three types of pigment used for their ability to produce unusual optical effects. 

Pearlescent pigments give rise to a white pearl effect often accompanied by a coloured iridescence. The most important pearlescent pigments consist of thin platelets of mica coated with titanium dioxide which partly reflect and partly transmit incident light. Simultaneous reflection from many layers of oriented platelets creates the sense of depth which is characteristic of pearlescent lustre and, where the particles are of an appropriate thickness, colours are produced by interference phenomena. Pearlescent pigments are used in automotive finishes, plastics and cosmetics. 

The brittle, silvery, shiny metal was long considered the last stable element of the Periodic Table. In 2003 it was unmasked as an extremely weak alpha emitter (half-life 20 billion years). Like thulium, there is only one isotope. Bismuth alloys have low melting points (fuses, fire sprinklers). As an additive in tiny amounts, it imparts special properties on a range of metals. Applied in electronics and optoelectronics. The oxichloride (BiOCl) gives rise to pearlescent pigments (cosmetics). As bismuth is practically nontoxic, its compounds have medical applications. The basic oxide neutralizes stomach acids. A multitalented element. Crystallizes with an impressive layering effect (see right). 

Colorants have been developed for special effects. Pearlescent or iridescent give an attractive appearance. They are often used for coating paper (e.g., cosmetic packaging). The pigment consists of thin platelets, less than 1 pm thickness, which have a high refractive index, e.g., mica coated with Ti02. 

What causes the pearlescent appearance of some paints See p. 147. 

Question 12.4 What Causes the Pearlescent Appearance of Some Paints ... 

Pearlescent lusters are commonly seen in many paints, inks, and cosmetics. The pearlescent pigment technology that brings us these unusual effects relies on a common mineral to achieve these opalescent qualities. 

Pearlescent pigments contain small flakes or platelets of the mineral mica that are additionally coated with a very thin layer of titanium dioxide. The simultaneous reflection of light from many layers of small platelets creates an impression of luster and sheen. By varying the thickness of the coating on the surface of the mica particles, pigment manufacturers can achieve a range of colors for the pearlescent effect. 

The presence of mica in pearlescent pigments only partly accounts for the appearance of the pigment. A very thin layer of the inorganic oxide titanium dioxide (TiC>2) or iron oxide (Fe2C>3) or both is coated on the mica platelets. The various colors and pearlescent effects are created as light is both refracted and reflected from the titanium dioxide layers. The very thin platelets are highly reflective and transparent. With their plate-like shape, the platelets are easily oriented into parallel layers as the paint medium is applied. Some of the incident light is reflected... 

Microscopic photo of pearlescent paint, http //www.standox.de/standote/englisch/color/3schicht.htm... 

Application Multifunctional care additive for clear and pearlescent cleansing preparations... 

The pearlescent effect in natural pearls arises because of the interaction of incident light with alternating layers of high refractive index (CaCOj) and low refractive index (protein), reflected and diffracted light from which leads to the observed iridescent colours. 

There are four main manufacturers of pearlescent or colour variable pigments with properties of the types discussed in this section, namely Merck, Engelhard, BASF and Flex Products. Some of the current ranges from these manufacturers are given in... 

Lustre/pearlescent pigments have found wide application in automotive coatings, coloured plastics, synthetic leather, printing inks, ceramic products and cosmetics, e.g. nail polish, lipstick and mascara. 

The majority of pearlescent coatings in the automotive industry are based on a two-stage process, in which pearlescent pigments with good opacity are included in... 

Pearlescence is the iridescence produced by refracted and reflected light from a surface (pearl-like colour). 

Synthetic or natural pigments used to achieve lustrous, brilliant, or iridescent color effects by interference on thin optical films are called nacreous or pearlescent pigments [5.190]—[5.194]. They were originally used to simulate the appearance of... 

Nacreous and Interference Pigments. The optical principles of nacreous (interference) pigments are shown in Figure 72 for a simplified case of nearly normal incidence without multiple reflection and absorption. At the interface P, between two materials with refractive indices n t and n2, part of the beam of light L, is reflected (L,) and partially transmitted (i.e., refracted) (L2). The intensity ratios depend on n, and n2. In a multilayer arrangement, as found in pearl or pearlescent and iridescent materials (Fig. 71 C), each interface produces partial reflection. After penetration through several layers, depending on the size and difference between n1 and n2,... 

The development of the mica-based pigments started with pearlescent colors (Fig. 76 A, TiOz - mica). It was followed by brilliant, mass-tone-colored combination pigments (i.e., mica, Ti02, and another metal oxide) with one color (interference color same as mass tone) or two colors (interference and mass tone different) that depend on composition and viewing angle (Fig. 76 B). In the 1980s further development was made by coating mica particles with transparent layers of iron(III) oxide (Fig. 76 C) [5.222]. 

Pearlescent pigment Advantages Disadvantages Main application field... 

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