Partial Replacement of TiO2 in Decorative Paint with Mica-Coated CaCO3

Abstract

Paints play a critical role in protecting and decorating various substrates. The formulation of cost-effective and high-quality paints has become increasingly important due to growing demand and the rising cost of TiO2, a key pigment in the paint industry. In this study, we investigate the partial replacement of TiO2 pigment with mica-coated CaCO3, synthesized through controlled co-precipitation of nitrates and carbonates. Various percentages of Mica-CaCO3 filler are incorporated into decorative paint formulations to evaluate their impact on properties such as hiding power, scrub resistance, gloss, adhesion, and weather resistance.

The goal is to determine the optimum percentage of Mica-CaCO3 pigment in paint formulations.

Chapter 1: Introduction

Paints serve the dual purpose of protecting material surfaces from corrosion and enhancing their aesthetic appeal. Within the dry film of paint, the essential components are pigment particles and binder polymer fibers, which work together to create the desired appearance and protective qualities. Titanium dioxide (TiO2) stands out as the primary pigment, prized for its whiteness and widespread use in paints and coatings.

However, its high cost has prompted researchers in the paint industry to seek cost-effective alternatives. In waterborne paints, one approach to cost reduction is the partial substitution of pigment with fillers or extenders.

1.1 Main Components of Paint

Industrial paint formulations, used to protect surfaces made of various materials, exhibit different characteristics that can be tailored to specific applications. These traits are largely determined by the paint's ingredients and the performance requirements of the intended use. Additionally, the method of application can influence paint quality and its adherence to the substrate.

The primary components of paint include pigment, binder, liquid, and additives.

1.1.1 Pigment

A paint's pigment is a crucial factor in determining its color and appearance. Some pigments also contribute to the paint's thickness when needed. Pigments can be categorized into two main types: prime pigments and extender pigments.

Prime Pigments

Prime pigments primarily impart color or whiteness to a paint, as well as the ability to conceal surface imperfections. In paints with a white hue, titanium dioxide (TiO2) is the dominant prime pigment. For paints in other colors, pigments are chosen to selectively absorb specific wavelengths of light, resulting in the desired color. Organic pigments produce vibrant colors, while inorganic pigments offer durability over brightness.

Extender Pigments

Extender pigments are designed to increase bulk but are less effective at concealing surface flaws compared to prime pigments. Nevertheless, they influence the overall sheen, color retention, and abrasion resistance of the paint. Examples of extender pigments include silica, silicates, and zinc oxide, each contributing specific properties to the paint, such as durability and resistance to mildew and corrosion, particularly in outdoor applications.

1.1.2 Binder

The binder in a paint formulation plays a critical role in adhesion, pigment binding, and providing durability to the final coating. The binder is transparent and glossy, but the presence of pigment affects its visual properties. The ratio of pigment to binder, known as the pigment volume concentration (PVC), determines the level of gloss in the paint. Paints with high gloss typically have a PVC of around 15 percent, while matte paints have a PVC ranging from 40 to 80 percent. Lower gloss paints have a higher proportion of binder per unit of pigment, resulting in increased durability.

1.1.3 Solvent

The liquid component of paint is responsible for transporting the binder and pigment to the surface of the substrate. The choice of liquid depends on the composition of the paint. Oil-based paints, for instance, use paint thinners as the primary liquid, while latex-based paints typically employ water.

1.1.4 Additives

Additives are incorporated into paint formulations to manipulate or enhance specific properties. These include thickeners, which increase viscosity for easier application, surfactants to disperse pigments evenly within the paint, and co-solvents that aid in binder film formation and prevent paint damage when exposed to freezing temperatures. Co-solvents also extend the open time of the paint, allowing for more straightforward application.

Chapter 2: Raw Material

2.1 Calcium Carbonate (CaCO₃)

Calcium carbonates are extensively utilized in paint and coating systems due to their cost-effective nature and their ability to enhance both rheological and mechanical properties of coatings. These materials are employed to reduce the overall formulation cost while improving the paint's performance characteristics. In non-aqueous systems, ground limestone products are commonly used in exterior house paints and interior flats and semi-gloss enamels. However, the high demand for the vehicle in precipitated calcium carbonates restricts their use in non-aqueous systems, although they are still employed as flow control agents.

Calcium carbonates are typically used in combination with other fillers and titanium dioxide to improve the dry hiding power and rheological properties of the paint system. The optimal particle size range for ground natural filler grades of calcium carbonate in coatings is 3 to 7μm. High-brightness ultrafine ground and precipitated calcium carbonates are utilized as TiO₂ extenders and opacifiers in water-based paints. Although they require a higher binder content than filler grades, they offer superior dry hide and gloss retention.

Types

There are two main types of calcium carbonate fillers: ground calcium carbonate and precipitated calcium carbonate.

1) Ground Calcium Carbonate

Ground calcium carbonate is produced by wet or dry grinding of natural calcium carbonate ores, which are high in chemical and mineralogical purity. Dry-ground calcium carbonates, ranging from nominal 200 to 325 mesh products, are cost-effective white fillers. They are obtained by grinding ores and may also undergo beneficiation through air separation. Wet-ground products are finer and may undergo beneficiation through washing or flotation.

2) Precipitated Calcium Carbonate

Precipitated calcium carbonate (PCC) is manufactured to meet specific requirements for higher brightness, smaller particle size, greater surface area, lower abrasiveness, and higher purity compared to ground natural products. PCC is produced through the lime-soda process, involving the reaction of milk of lime with sodium carbonate to form calcium carbonate precipitate and sodium hydroxide solution. Commercial alkali manufacturers use this process to produce relatively coarse PCC as a byproduct of sodium hydroxide recovery.

Uses

Ground natural calcium carbonate is the most widely used white pigment in paints, offering cost-effectiveness, high brightness for TiO₂ extension, purity, low abrasiveness, and weather resistance. Fine and ultrafine grades, including PCC, find applications in various decorative and protective coatings. PCC products, with their higher brightness, excel as TiO₂ extenders. Both PCC and ultrafine wet-ground grades enhance rheology, stability, dry hide, and gloss retention.

2.2 Mica (Al₂K₂SiO₆)

Mica minerals are characterized by their platy or flake-shaped particles, typically with talc or pyrophyllite structures. Micas are known for their ready delamination, high electrical and thermal insulating properties, resistance to chemical attack, transparency in the form of flat films, and the ability to be cut or stamped into various shapes.

Types

Mica comes in two main types: wet-ground mica and dry-ground mica.

1) Wet-ground Mica

Flake mica concentrates obtained from flotation are ground wet to delaminate and grind. Such mills provide products with a higher aspect ratio, sheen, and slip compared to dry-ground mica. Trimmings from high-quality sheet mica are also used as feed for wet grinding plants.

2) Dry-ground Mica

Flake mica flotation concentrates are partially dried and then ground to achieve the desired particle size. Coarse milled products (>100 mesh) are processed using hammer mills and screens or air separators. Fine-ground products, with particle sizes ranging from -100 mesh to -325 mesh, are processed in fluid energy mills, often with superheated air.

Uses

In paint applications, fine-ground, mesh, and micronized mica grades serve as pigment extenders and reinforcement for dry films. Mica's inert, platy nature improves suspension stability, controls issues like film checking, chalking, shrinkage, and blistering, enhances resistance to weathering, chemicals, and water penetration, and improves adhesion to most surfaces. Coarser mica grinds are employed in textured paints, while wet-ground mica is utilized in high-quality exterior house paints. Automotive paints make use of high aspect ratio mica for achieving metallic effects, either in its natural form or after conversion into pearlescent pigments through surface coating with metal oxides.

2.3 Calcium Nitrate Tetrahydrate (Ca(NO₃)₂.4H₂O)

Calcium nitrate tetrahydrate is a hydrate and the tetrahydrate form of cadmium nitrate. It is an inorganic nitrate salt and a calcium salt. This colorless salt readily absorbs moisture from the air and is commonly found as a tetrahydrate. While its primary application is as a component in fertilizers, it has various other uses.

2.4 Sodium Carbonate (Na₂CO₃)

Sodium carbonate, also known as washing soda, soda ash, and soda crystals, is an inorganic compound with the formula Na₂CO₃ and its various hydrates. All forms of sodium carbonate are white, water-soluble salts. They possess a strongly alkaline taste and yield moderately alkaline solutions when dissolved in water. Sodium carbonate is produced in large quantities through the Solvay process, which involves sodium chloride and limestone.

2.5 Surfactants

Surfactants play a crucial role in paint formulations, particularly when dispersants have limited surface activity. Surfactants reduce surface tension, enabling the liquid vehicle to effectively wet pigment and mineral surfaces, facilitating dispersant-particulate association. This is particularly important for hydrophobic solids like talc. Surfactants function as wetting agents, enhancing paint wetting and spreading on the substrate.

Types

Two main types of surfactants are used in paint formulations: anionic surfactants and nonionic surfactants.

1) Anionic Surfactants

Anionic surfactants are typically sodium salts of alkyl sulfates, alkyl sulfonates, alkyl aryl sulfonates, and sulfosuccinates. These surfactants are often employed as dispersants, and it is not uncommon for a paint to contain both surfactants and dispersants for optimum performance. Sodium Laureth Sulfate (SLS) is an example of an anionic surfactant.

2) Nonionic Surfactants

Nonionic surfactants used in aqueous systems contain a lipophilic or pigment/mineral-compatible group, often a long-chain alkyl or alkyl aryl group, and a hydrophilic group, typically polyethylene oxide. These surfactants bond loosely to pigment and mineral surfaces, creating a film of hydrophilic groups to ensure wetting by the aqueous vehicle. Nonionic surfactants can also provide a dispersant effect by offering steric hindrance to particle flocculation. Tween 80 is an example of a nonionic surfactant.

Chapter 3: Methodology

3.1 Synthesis of Mica-Coated CaCO₃ Using Nonionic Surfactants (Tween 80)

Materials

• Calcium nitrate tetrahydrate (Ca(NO₃)₂.4H₂O)
• Tween-80 (Surfactant)
• Sodium carbonate (Na₂CO₃)
• Titanium dioxide (TiO₂)
• Mica
• Pine Oil
• Styrene Acrylic Emulsion (46%)
• Double distilled water (used as a medium for the preparation of Mica-CaCO₃ Pigment)

Procedure:

1. The co-precipitation process was initiated using a (1M) solution of Calcium nitrate tetrahydrate Ca(NO₃)₂.4H₂O as the precursor.
2. A suspension was prepared by mixing 100 mL of water and 5.05 g of mica with Tween-80 surfactant.
3. After completing the addition, the suspension was stirred for 30 minutes, and then the supernatant liquid was decanted.
4. The precipitate was washed with distilled water and dried at 60°C. Characterization was performed based on FTIR, density, oil absorption, and tinting strength analysis.

3.2 Synthesis of Mica-Coated CaCO₃ Using Anionic Surfactants (SLS - Sodium Laureth Sulfate)

Materials

Chemical Name	Chemical Formula	Molecular Weight	Grams/Moles Taken in Actual Practical
Calcium nitrate tetrahydrate	Ca(NO3)2.4H2O	236.15 g/mol	16.52 g
SLS (Sodium Laureth Sulfate)	NaC12H25SO4	288.372 g/mol	0.57 g
Mica	Al2K2O6Si	256.239 g/mol	3.53 g
Sodium carbonate	Na2CO3	105.9888 g/mol	7.41 g

Procedure:

1. The co-precipitation process was initiated using a (0.7 M) solution of Calcium nitrate tetrahydrate Ca(NO₃)₂.4H₂O as the precursor.
2. A suspension was prepared by mixing 100 mL of water and 3.53 g of mica with SLS surfactant.
3. After completing the addition, the suspension was stirred for 30 minutes, and then the supernatant liquid was decanted.
4. The precipitate was washed with distilled water and dried at 60°C. Characterization was performed based on FTIR, density, oil absorption, and tinting strength analysis.

3.3 Synthesis of Mica-Coated CaCO₃ Using Octadecylamine

Materials

Chemical Name	Chemical Formula	Molecular Weight	Grams/Moles Taken in Actual Practical
Calcium nitrate tetrahydrate	Ca(NO3)2.4H2O	236.15 g/mol	47.218 g
Octadecylamine	C18H39N	269.517 g/mol	3.14 g
Mica	Al2K2O6Si	256.239 g/mol	10.1 g
Sodium carbonate	Na2CO3	105.9888 g/mol	21.18 g

Procedure:

1. The co-precipitation process was initiated using a (2 M) solution of Calcium nitrate tetrahydrate Ca(NO₃)₂.4H₂O as the precursor.
2. A suspension was prepared by mixing 100 mL of water and 10.1 g of mica with Octadecylamine surfactant.
3. After completing the addition, the suspension was stirred for 30 minutes, and then the supernatant liquid was decanted.
4. The precipitate was washed with distilled water and dried at 60°C. Characterization was performed based on FTIR, density, oil absorption, and tinting strength analysis.

3.4 Paint Formulation

Following the synthesis of mica-coated calcium carbonate, paint formulations were prepared to evaluate the partial replacement of TiO₂ by mica-coated calcium carbonate. The initial formulation involved replacing 5% of TiO₂ with the mica-coated calcium carbonate.

Materials

Chemical Name	Total Formulation (Kg)	Mill Base Formulation (Kg)	Let Down (Kg)
TiO2	1.87	1.87	-
Mica coated CaCO3	0.089	0.087	-
Alkyd Resin	3.3421	0.4212	2.9209
Toluene	0.8515	0.3637	0.4878
Dipentane	0.1344	0.0574	0.077
MEK (Methyl Ethyl Ketone)	0.0064	-	0.0064
Drier	0.1024	-	0.1024

Procedure:

1. Initially, 20% of the formulation in grams was taken and added to a 500 mL beaker.
2. Solvent and resin were added to the beaker, and the mixture was stirred continuously for 15 minutes.
3. The mill base was then prepared by transferring the mixture to a ball mill and revolving it at around 86 RPM until the desired fineness of grind was achieved.
4. After achieving a fineness of +7 grind, the remaining amount of resin and solvent, referred to as the "let down," was added.

These steps were followed to prepare the paint formulation for further evaluation.

3.5 Evaluation of Paint Formulations

After the paint formulations were prepared, they underwent evaluation to determine their properties and performance. Key parameters such as hiding power, scrub resistance, gloss, adhesion, and weather resistance were assessed to establish the effectiveness of the partial replacement of TiO₂ with mica-coated calcium carbonate.

Key Evaluation Parameters

1. Hiding Power: The ability of the paint to cover and hide the underlying substrate.
2. Scrub Resistance: The paint's ability to withstand scrubbing without deterioration.
3. Gloss: The level of shine or sheen exhibited by the painted surface.
4. Adhesion: The strength of the bond between the paint and the substrate.
5. Weather Resistance: The paint's ability to withstand environmental conditions over time.

These evaluations were conducted to determine the optimum percentage of mica-coated calcium carbonate pigment in the paint formulation, considering cost-effectiveness and quality requirements.

3.6 Characterization of Mica-Coated CaCO₃ Pigment

The mica-coated calcium carbonate pigment obtained through the synthesis processes described in Section 3.1, 3.2, and 3.3 was characterized to assess its properties.

Characterization Techniques

1. FTIR (Fourier Transform Infrared Spectroscopy): Used to analyze the chemical composition and functional groups present in the pigment.
2. Density: Measured to determine the density of the pigment, which can affect its dispersion in paint formulations.
3. Oil Absorption: Determined to understand how much oil the pigment can absorb, influencing its behavior in paints.
4. Tinting Strength Analysis: Evaluated to assess the pigment's ability to tint a paint and influence its color.

These characterization techniques provided valuable insights into the properties of the mica-coated calcium carbonate pigment, which, in turn, contributed to the optimization of the paint formulation.

Chapter 4: Results and Discussion

In this chapter, we will present the results of the evaluations conducted on the paint formulations with varying percentages of mica-coated calcium carbonate. The discussion will focus on the impact of partial TiO₂ replacement on paint properties and the optimal percentage of mica-coated calcium carbonate in achieving cost-effective and high-quality decorative paint formulations.

Chapter 4: Application

4.1 Application on Wall

After making the paint, the first step was to check its particle size using a Hegman gauge. For the undercoat paint, the particle size should be in between 6+ to 7+, and we achieved the desired particle size.

Once we obtained our desired particle size, we initiated the application on walls. The process started as follows:

1. Application on a Small Area: Initially, we applied the paint to a small area on the wall and allowed it to dry for several hours.

4.2 Application on Metal

After applying on walls, we applied our paint to a metal plate and placed it outdoors when direct sunlight was shining on the plate.

Chapter 5: Results and Discussion

5.1 Oil Absorption Value

Oil absorption value is a crucial parameter to assess the behavior of the pigment in the paint formulation. Here are the results for two different batches:

Analysis	Batch 1	Batch 2
Oil absorption value	63 gm/100 gm of pigment	70 gm/100 gm of pigment

5.2 Bleeding Tendency

Bleeding tendency is an important consideration for paint stability and performance. We observed the behavior of the paint with different solvents in three different batches:

Solvent	Batch 1	Batch 2	Batch 3
Toluene	Slight	Slight	Slight
Methanol	Non bleeding	Non bleeding	Non bleeding
Ethyl acetate	Non bleeding	Non bleeding	Non bleeding

5.3 Specific Gravity

Specific gravity is an indicator of the density of the paint. Here are the specific gravity values for three different batches:

Batch 1	Batch 2	Batch 3
2.3	2.8	2.7

5.4 Colour Matching Spectrometry

Color matching spectrometry was performed to compare the color of the paint batches with the standard (TiO₂). The following color difference parameters were analyzed:

Parameter	Standard (TiO2)	Batch (Mica coated CaCO3)	Color Difference
L*	89.897	89.974	ΔL* = 0.077 (Lighter)
a*	-0.387	-0.501	Δa* = -0.114 (Greener)
b*	-6.906	-6.884	Δb* = 0.022 (Less Blue)
C*	6.917	6.902	ΔC* = -0.015 (Duller)
H*	266.758	265.803	ΔH* = -0.115
K/S	0.855	0.975	ΔK/S = 0.139
Reflectance	54.829	53.146	Strength: 114.011%

These results indicate the color differences between the paint batches using Mica coated CaCO₃ pigment and the standard TiO₂, with specific values and comparisons in terms of color attributes.

Chapter 6: Conclusion

1. Successful Preparation: The preparation of mica-CaCO3 was successfully carried out using the co-precipitation reaction and utilized in the formulation of durable decorative coatings.
2. Improved Properties: The decorative coatings formulated using mica-CaCO3 exhibit better properties as per required standards. The results of paint formulation indicate that we can easily replace 5 to 10% of TiO2 with Mica coated CaCO3, thus reducing the cost of paint.
3. Strength Enhancement: By using octadecylamine as a surfactant, we can enhance the strength and other properties of our product. Therefore, Mica-CaCO3 was found to be an acceptable substitution for TiO2.

References

1. McGonigle, F. et al., (1996), McGonigle, F., Ciullo, P.A., (edited by Ciullo P.A.), Paints & Coatings, Chapter 4 in Industrial Minerals and Their Uses, A Handbook & Formulary, Noyes Publication, Westwood New Jersey, P.125-136.
2. 289504810_Synthesis_of_Mica_Doped_Calcium_Carbonate_Filler_for_Partial_Replacement_of_TiO2_in_Decorative_Paint
3. 258048460_Substitution_of_TiO2_With_PCC_Precipitated_Calcium_Carbonate_in_Waterborne_Paints
4. 258048345_Interaction_Between_TiO2_and_Calcite Calcined_Kaolin_Mixture_During_Grinding_of_Pigment_in_Water_Based_Paints
5. Karakas, F. et al., (2010), Karakas, F.; Hassas, B. V.; Ozhan, K.; Boylu, F.; and Celik, M. S.; “Calcined kaolin and calcite as a pigment and substitute for tio2 in water based paints”, XIV Balkan Mineral Processing Congress (BMPC 2012), Tuzla, Bosnia and Herzegovina; 06/2011
6. Laura, L. (2009), Laura, L., “combinations of titanium dioxide and fillers in paints”, Degree Thesis, Satakunta University of Applied Sciences.
7. Maisch, R. et al., (1996), Maisch, R.; Stahlecker, O.; Kieser M.; “Mica pigments in solvent-free coatings systems”, Progress in Organic Coatings, vol. 27, Issue 1–4, pp. 145-152
8. Bayat N. et al., (2008), Bayat, N.; Baghshahi, S.; Alizadeh, P.; “Synthesis of white pearlescent pigments using the surface response method of statistical analysis”, Ceram Int, Vol. 34, Issue 8, pp. 2029-2035.

Figure References

1. Fig.1.1
2. Fig.1.2
3. Fig.1.3
4. Fig.1.4
5. Fig.2.1
6. Fig.2.4
7. Fig.2.5
8. Fig.2.6