Pigment White 4, a chemical compound, known as zinc oxide, is chemically classified as an inorganic colorant. This pigment is widely used in various industrial and cosmetic applications due to its excellent properties, including high stability, opacity, and non-reactivity.

Chemical Composition and Structure

Pigment White 4 is an inorganic compound with the chemical formula ZnO. It consists of zinc (Zn) and oxygen (O), forming zinc oxide. This composition gives the pigment its characteristic white color and other valuable properties.

Physical Properties

This pigment typically appears as a fine white powder. It has a high density and excellent covering power. Pigment White 4 is known for its chemical stability, resistance to light and heat, and inert nature, making it suitable for long-lasting applications. Its opacity and strong tinting strength make it a versatile pigment for various uses.

Chemical Industrial Synthesis Process

• Preparation of reagents. The main raw materials include metallic zinc (Zn) and air or oxygen.
• Melting of zinc. The production of Pigment White 4 begins with the melting of zinc metal in a high-temperature furnace.
• Oxidation. The molten zinc is vaporized and then oxidized in the presence of air or oxygen at high temperatures. This process transforms the zinc vapor into zinc oxide (ZnO).
• Cooling. The zinc oxide fume is rapidly cooled and collected in a cooling chamber to form fine zinc oxide particles.
• Collection. The zinc oxide particles are collected using filters or electrostatic precipitators.
• Washing. The collected zinc oxide is washed with deionized water to remove any soluble impurities.
• Drying. The washed zinc oxide is dried at controlled temperatures to remove residual moisture and obtain a dry powder.
• Grinding. The dried zinc oxide is ground to obtain a fine and uniform powder. This step may involve the use of ball mills or other grinding machinery.
• Classification. The dried powder is classified to ensure a uniform particle size. This step may involve sieving or the use of air classifiers.
• Stabilization. The Pigment White 4 powder is stabilized to ensure its stability during transportation and storage, preventing aggregation and degradation.
• Quality control. The Pigment White 4 undergoes rigorous quality testing to ensure it meets standards for purity, color intensity, and safety. These tests include chemical analysis, spectroscopy, and physical tests to determine particle size and rheological properties.

What it is used for and where

Cosmetics

Restricted cosmetic ingredient as IV/144 a Relevant Item in the Annexes of the European Cosmetics Regulation 1223/2009. Substance or ingredient reported:

• Zinc oxide. Wording of conditions of use and warnings:  Not to be used in applications that may lead to exposure of the end-user's lungs by inhalation.

Cosmetics - INCI Functions

• Colorant. This ingredient has the function of colouring the solution in which it is inserted in a temporary, semi-permanent or permanent manner, either alone or in the presence of the complementary components added for colouring.

Pigment White 4 is used in cosmetic products such as sunscreens, foundations, face powders, and creams due to its high opacity, UV protection, and skin-soothing properties. 

Medical

Chemical compound with an antiseptic action. It is also used as an astringent and topical in bandages, creams, ointments, dental cements, and as UV protection.

Pharmaceuticals: Zinc oxide is widely used in pharmaceutical products, such as ointments and creams, for its antiseptic and skin-protective properties.

Industrial Applications

Paints and Coatings: In the paint industry, zinc oxide is used to achieve white shades and enhance UV resistance. Its stability and strong tinting properties make it ideal for both decorative and protective coatings.

Plastics and Polymers: This pigment is employed in the production of plastics and polymers to improve color uniformity, opacity, and UV protection. It is commonly used in products like packaging materials, consumer goods, and outdoor applications.

Ceramics and Glass: Pigment White 4 is used in the production of ceramics and glass to achieve stable white colors and improve the materials' overall properties. It is particularly valued for its resistance to high-temperature processes.

Inks: The pigment is also used in printing inks to produce bright white colors, ensuring high-quality and durable prints.

Safety

Pigment White 4 is generally considered safe for use in consumer products when handled following proper safety procedures. It is important to avoid inhalation of the powder and to minimize direct contact with skin and eyes.  Recommendations mostly concern inhalation, which is to be avoided, of this substance, but most studies find it to be safe when included in creams and formulated according to established guidelines for cosmetic and pharmaceutical safety (2).

Zinc oxide studies

Molecular Formula  ZnO

Molecular Weight 

CAS   1314-13-2

EC number   215-222-5

DTXSID7035016

UNII SOI2LOH54Z

Synonyms:

Zinc oxide

CI 77947

References__________________________________________________________________________

(1) Kim KB, Kim YW, Lim SK, Roh TH, Bang DY, Choi SM, Lim DS, Kim YJ, Baek SH, Kim MK, Seo HS, Kim MH, Kim HS, Lee JY, Kacew S, Lee BM. Risk assessment of zinc oxide, a cosmetic ingredient used as a UV filter of sunscreens. J Toxicol Environ Health B Crit Rev. 2017;20(3):155-182. doi: 10.1080/10937404.2017.1290516. 

Abstract. Zinc oxide (ZnO), an inorganic compound that appears as a white powder, is used frequently as an ingredient in sunscreens. The aim of this review was to examine the toxicology and risk assessment of ZnO based upon available published data. Recent studies on acute, sub-acute, and chronic toxicities of ZnO indicated that this compound is virtually non-toxic in animal models. However, it was reported that ZnO nanoparticles (NP) (particle size, 40 nm) induced significant changes in anemia-related hematologic parameters and mild to moderate pancreatitis in male and female Sprague-Dawley rats at 536.8 mg/kg/day in a 13-week oral toxicity study. ZnO displayed no carcinogenic potential, and skin penetration is low. No-observed-adverse-effect level (NOAEL) ZnO was determined to be 268.4 mg/kg/day in a 13-week oral toxicity study, and a maximum systemic exposure dose (SED) of ZnO was estimated to be 0.6 mg/kg/day based on topical application of sunscreen containing ZnO. Subsequently, the lowest margin of safety (MOS) was estimated to be 448.2, which indicates that the use of ZnO in sunscreen is safe. A risk assessment was undertaken considering other routes of exposure (inhalation or oral) and major product types (cream, lotion, spray, and propellant). Human data revealed that MOS values (7.37 for skin exposure from cream and lotion type; 8.64 for skin exposure of spray type; 12.87 for inhalation exposure of propellant type; 3.32 for oral exposure of sunscreen) are all within the safe range (MOS > 1). Risk assessment of ZnO indicates that this compound may be used safely in cosmetic products within the current regulatory limits of 25% in Korea.

(2) Keerthana S, Kumar A. Potential risks and benefits of zinc oxide nanoparticles: a systematic review. Crit Rev Toxicol. 2020 Jan;50(1):47-71. doi: 10.1080/10408444.2020.1726282. Epub 2020 Mar 18. PMID: 32186437.

Abstract. Zinc oxide nanoparticles are well-known metal oxide nanoparticles having numbers of applications in the field of cosmetology, medicine, and chemistry. However, the number of reports has indicated its toxicity also such as hepatotoxicity, pulmonary toxicity, neurotoxicity, and immunotoxicity. Thus, in this article, we have analyzed the potential risks and benefits of zinc oxide nanoparticles. The data related to risks and benefits of zinc oxide nanoparticles have been extracted from PubMed (from January 2007 to August 2019). A total of 3,892 studies have been published during this period regarding zinc oxide nanoparticles. On the basis of inclusion and exclusion criteria, 277 studies have been included for the analysis of risks and benefits. Emerging reports have indicated both risks and benefits of zinc oxide nanoparticles in concentration- and time-dependent manner under in vitro and in vivo conditions through different mechanism of action. In conclusion, zinc oxide nanoparticles could play a beneficial role in the treatment of various diseases but safety of these particles at particular effective concentration should be thoroughly evaluated.