Ester resin viscosity measurement

01 Introduction to Waterborne Acrylate Resin

The rapid development of the automotive industry since the 20th century has pushed automotive coatings to a new level in quality, output and variety. Along with people's understanding of environmental issues, a series of strict environmental regulations and industry regulations have been formulated. In the field of coatings, environmentally friendly coatings, including waterborne coatings, high solids coatings and powder coatings, have gradually replaced solventborne coatings in order to reduce emissions of volatile organic compounds. In environmentally friendly coatings, water-based coatings are water-based solvents or dispersion media, which are low in pollution, cheap in price, and convenient in construction. They are an important class of three types of environmentally friendly coatings.

Waterborne automotive coatings are prepared by mixing aqueous resin matrix, curing agent and other additives and deionized water in a certain proportion. Acrylate resin is a high molecular polymer obtained by homopolymerization or copolymerization of acrylates and vinyl-based unsaturated monomers. The main chain structure is stable and does not contain groups susceptible to oxidation and hydrolysis. The prepared coating film has the characteristics of light color, gloss retention, color retention, brightness, weather resistance and corrosion resistance, and is therefore particularly suitable for preparing automotive coatings.

02 Significance of viscosity measurement and control

As an important component of water-based automotive coatings, the viscosity of water-based acrylate resin has a great influence on the storage stability, construction performance and film-forming properties of coatings, and is an important technical index for measuring the quality and performance of coatings. The viscosity is too high, which is not conducive to the spraying construction of the coating, affecting the performance of the cured film of the coating, resulting in poor leveling of the coating film, and the coating film is easy to form orange peel; if the viscosity is small, on the one hand, it is made in the process of dilution with water. Less water can dilute the resin coating to the construction viscosity. On the other hand, the decrease of the viscosity of the resin is favorable for the uniform dispersion of the resin in water and the smaller the dispersion size, thereby facilitating the contact reaction between the curing agent and the resin aggregate, and the performance of the paint film is more it is good. The suitable viscosity helps to improve the stability of the coating film, improve the leveling and construction properties of the coating film, and obtain a good appearance of the paint film.

Numerous studies have shown that increasing the amount of acrylic monomer in the development and production of aqueous acrylate resin will increase the water solubility and viscosity of the acrylic resin; increase the amount of monomers containing aromatic ester groups, initiators and chain transfer agents. Increasing the polymerization temperature lowers the viscosity of the resin. In addition, the use of a co-solvent in automotive coatings can effectively improve the water solubility of the resin, adjust the viscosity of the coating, thereby improving the performance and film forming properties of automotive coatings.

03 Waterborne acrylate resin viscosity measurement

This article uses the DV2T standard viscometer with a small sample adapter SSA (shown in Figure 1) to measure the viscosity of an aqueous acrylate resin, designed to help users establish a viscosity test method for product quality control during production and preparation of the product. .

Figure 1 SSA+TC Series Water Bath Circulation System

The TC-650 AP water bath cycle system is used to control the sample temperature (test temperature is 25 ° C), use Rheocalc T software to connect to the host, program editing and data acquisition, and draw viscosity curve. Measure a certain amount of the formulated aqueous acrylate resin in the sample cup of the SSA, slowly immerse the rotor into the sample, and connect the viscometer main unit to the TC-650 AP water bath circulation system. Edit the corresponding test program on the RheocalcT software and start measuring after the sample temperature has stabilized. Select “MultiPoint” mode for data acquisition, the test time is 120s, the data acquisition interval is 10s, and a total of 12 data points are collected to observe the viscosity change data and the stability of temperature control during the test.

Data is collected using the “Multi Point” function, and the “Test Averaging” function calculates the viscosity average and observes and analyzes instrument stability and data fluctuations during the test. According to Fig. 2, the average value of the viscosity of the aqueous acrylic resin measured at 5 RPM was 23018 cP. During the test, the data fluctuation was small and the relative standard deviation was only 0.04%. The Brookfield Digital Viscometer's unique continuous sensor ensures real-time and accurate test data output. In addition, the temperature was very stable during the test and was always maintained at 25 ± 0.01 °C.

The sample volume required for SSA testing is only 2-16mL (the specific sample size is related to the rotor type used), which can effectively save test cost and improve test efficiency. SSA can be calculated using coaxial cylindrical rotor and matching sample cup. Shear rate and shear stress give absolute viscosity; TC series circulating water bath system has a temperature control accuracy of up to 0.01 °C, which provides accurate and stable temperature conditions for viscosity testing.

04 Application Overview

As one of the well-known viscometer/rheometer manufacturers in Zui, AMETEK Brookfield has been committed to providing customers with stable and reliable quality, high measurement accuracy and good measurement repeatability. The Brookfield viscometer measures up to ±1% of the full-scale measurement range with repeatability of ±0.2%. For individual viscosity testing needs, we offer a personalized solution that is perfectly adapted to the analytical needs of users in a variety of industries.

The RST rheometer offers comprehensive rheology testing for perfect rheological analysis in both quality control and R&D. The RST Series rheometers have two modes of controlling shear rate and shear stress, and are especially suitable for measuring the viscosity and rheological curves of non-Newtonian fluids under steady flow. In addition, it can measure rheological properties such as viscoelasticity, yield stress and thixotropic properties in unsteady shear flow and creep conditions.