Study On Dispersion And Related Mechanism Of Zao Lake Pigments In Aqueous Medium

With the increasing development of the makeup market,consumers have higher requirements for the coloring power,covering power,and skin adhesion of makeup products.As one of the raw materials for cosmetics,colorants mainly play a beautifying and modifying role in cosmetics [1-3].Eye shadow,lipstick,powder blusher,etc.use organic pigments to make them have bright and beautiful colors,so then achieve the effect of modifying facial makeup and increasing color.However,organic pigments with high surface energy are prone to sedimentation,aggregation,and other phenomena when used in formula systems,ultimately leading to problems such as poor stability,poor spreadability,weak skin affinity,and poor covering power of the product.Therefore,in order to produce high-quality makeup,the dispersion of pigments in the medium is particularly important.One of the largest pigments in terms of production and usage among azo lake pigments is pigment red 57:1,which has strong coloring power and is widely used in cosmetics.Therefore,for pigment red 57:1,this study first explores the effects of different physical dispersion methods on its particle size and determines the optimal dispersion process;Then,the properties of pigment red 57:1 were studied,and the effects of different pH values on the chemical structure of pigment red 57:1 were investigated;Finally,a systematic investigation was conducted on the effects of different non-ionic surfactants,anionic surfactants,cationic surfactants,and cationic polymers on the dispersion of pigment red 57:1.The dispersion process of pigment red 57:1 was analyzed from four aspects: Zeta potential,wetting angle,centrifugal stability,and suspension.The trends in the dispersion of pigment red 57:1 in aqueous media under different factors were summarized and summarized.The chemical structure of pigment red 57:2 is similar to that of pigment red 57:1,with only the difference in the metal ion portion(pigment red 57:1 is a calcium salt,and pigment red 57:2 is a barium salt).To investigate the effect of different counter ions on the dispersion of pigments in aqueous media,the same research method as pigment red 57:1 was used to investigate the dispersion behavior of pigment red 57:2 in aqueous media,and finally,the law of the influence of different application conditions on the dispersion performance of pigments was obtained,to improve the application performance of organic pigments.The main results of the experiment are as follows:(1)The optimal preparation process for reducing the particle size of pigment particles was successfully investigated using pigment red 57:1 as the dispersion phase.Based on the physical dispersion method,the optimal mass ratio of pigment to ethanol,the optimal magnetic stirring time for pigment dispersion in aqueous medium,ultrasonic cleaning time,and ultrasonic probe ultrasonic time were investigated.a.Ethanol fully permeates the surface of the pigment particles,and under external stirring conditions,the pigment particles are fully dispersed.The original aggregate size of the pigment particles is significantly reduced.When the pigment/ethanol mass ratio is 1:50,the pigment particle size is reduced to 143 nm,greatly enhancing the dispersibility of the pigment in the medium.b.The optimal preparation process obtained through single factor experiments is: magnetic stirring for 30 minutes,ultrasonic cleaning for 60 minutes,and ultrasonic probe(probe model:Φ 6.With a power of 35%,ultrasound for 2 seconds,pause for 2 seconds)for 15 minutes,the particle size of the pigment can be reduced to 122 nm under this condition.(2)For pigment 57:1,the effect of pH on its molecular structure was mainly studied,and the improvement of its dispersion stability in water medium by non-ionic surfactant,anionic surfactant,cationic surfactant and cationic polymer was systematically investigated.a.When pH<7,the azo group in the molecule of pigment red 57:1 transforms into hydrazone,the conjugated structure increases,the redshift phenomenon is obvious,and the dispersion is enhanced.If added to cosmetic products,the optimal dispersion pH is 6.5.b.Under weak acid conditions(pH=6.5),nonionic surfactants adsorb on the surface of pigment red 57:1 particles to form a hydration layer,increasing spatial hindrance and slowing down aggregation between particles.Anionic surfactants,due to their negative charge after dissociation,enhance the electrostatic repulsion force between pigment powder particles,thereby hindering their collision with each other.The addition of cationic polymers can provide strong positive electrostatic repulsion for particles and a certain spatial hindrance,effectively improving the dispersion stability of pigment red 57:1 in aqueous media from two aspects.c.Under weak acid conditions(pH=6.5),when a cationic surfactant is added to an aqueous medium,it will combine with pigment red 57:1 through electrostatic attraction to form a flocculent precipitate.The longer the hydrophobic chain of the cationic surfactant,the weaker the hydrophobicity of the conjugate,and the more severe the precipitate.(3)For pigment red 57:2,the effect of pH on its molecular structure was mainly studied,and the improvement of its dispersion stability in water medium by non-ionic surfactant,anionic surfactant,cationic surfactant and cationic polymer was systematically investigated.a.When pH<6,the azo group in the molecule of pigment red 57:2 transforms into hydrazone,the conjugated structure increases,the redshift phenomenon is obvious,and the dispersion is enhanced.If added to cosmetic products,the optimal dispersion pH is 5.5.b.The dispersibility and suspension of pigment red 57:2 in water are stronger than that of pigment red 57:2.c.When pH=5.5,nonionic surfactants slow down the aggregation between particles by increasing the surface steric hindrance of the particles.Anionic surfactants enhance the electrostatic repulsion force between pigment powder particles,thereby hindering their collision with each other.Cationic polymers provide strong positive electrostatic repulsion and certain spatial hindrance to particles,effectively improving the dispersion stability of pigment red 57:2 in aqueous media from two aspects.However,due to the strong dispersibility of pigment red 57:2 itself,the addition of dispersants has a less effective improvement effect than pigment red 57:1.d.When pH=5.5,when cationic surfactants are added to the aqueous medium,they will combine with pigment red 57:2 through electrostatic attraction to form flocculent precipitates,exacerbating the settling rate of pigment particles.