The hardness and strength of the solid surface of acrylic acid are influenced by multiple factors such as the glass transition temperature (Tg value) of the resin, curing conditions, formula composition, and testing methods. The following is an analysis from several aspects including the relationship between hardness and Tg value, strength testing methods, and factors affecting hardness and strength:
The relationship between hardness and Tg value
The higher the Tg value of acrylic resin is, the greater the hardness of the resin will be, and the two are directly proportional. When the Tg value increases, the hardness of the coating film increases and the scratch resistance enhances. Conversely, the lower the Tg value, the lower the hardness of the coating film and the worse the scratch resistance. For instance, the Tg value of KDD®MR7313 functional acrylic resin is 97℃, and its product characteristics are characterized by high hardness, high wear resistance and fast drying.
Strength testing method
Tensile test: The cured acrylic resin sample is cut into standard-sized specimens, and then tensile force is applied on a tensile testing machine to measure the tensile strength and elongation at break of the material, in order to evaluate the tensile strength and ductility of the acrylic resin.
Compression test: The cured acrylic resin sample is cut into standard-sized specimens and a pressure perpendicular to the material surface is applied on a universal testing machine. The compressive strength and elastic modulus of the material are measured to evaluate the compressive resistance performance of the acrylic resin.
Bending test: The cured acrylic resin sample is cut into standard-sized specimens and a bending force is applied on a bending testing machine. The bending strength and modulus of the material are measured to evaluate the bending resistance of the acrylic resin.
Hardness testing: Tools such as Rockwell hardness testers or Brinell hardness testers are used to measure the hardness of acrylic resin samples. The hardness value can be used to evaluate the surface hardness and compressive strength of acrylic resin.
Factors affecting hardness and strength
Resin type and dosage: According to the final coating purpose and requirements, select acrylic resin with suitable molecular weight and molecular structure to ensure the balance of hardness and toughness of the coating.
Type and dosage of curing agent: The curing agent reacts with the functional groups in the acrylic resin to form a network structure, which affects the crosslinking density and hardness of the coating. Generally speaking, the more types and amounts of curing agents there are, the higher the crosslinking density and hardness of the coating will be, but at the same time, the flexibility and impact resistance of the coating may decrease.
Types and dosages of matting agents: Matting agents can disrupt the continuity of the coating surface, creating a micro-rough surface and reducing gloss. The more types and amounts of matting agents there are, the lower the gloss of the coating will be, but the hardness and impact resistance of the coating may also decrease.
Types and quantities of fillers: Fillers can improve the performance of coatings and reduce costs. Commonly used fillers include barium sulfate, calcium carbonate, talcum powder, kaolin, sericite, wollastonite, etc. The type and amount of fillers will affect the fluidity, hardness, wear resistance, scratch resistance and other properties of the coating, and further influence the gloss and impact resistance of the coating.
Coating process: According to the characteristics of acrylic coatings and coating conditions, optimize the parameters of the coating process, such as coating temperature, coating thickness, curing time, and curing temperature, to ensure the uniform application and full curing of acrylic coatings, and improve the quality and performance of the coating.
