How to choose the appropriate valve for aerosol?
There are currently over 200 types of aerosol products used in personal, household, industrial, agricultural, construction, fire protection, safety, medical and other fields.
The aerosol valve may not seem eye-catching, but it is of utmost importance compared to the entire aerosol product. It not only affects the sealing performance of the product, but also the spraying effect, and of course, the stability of the entire aerosol product. Therefore, how to choose the appropriate valve is worth everyone's attention in the development process of aerosol products.
If we look at the types of valves, aerosols are mainly divided into two categories: one-component packaging and two-component packaging (BOV system). The main structure of one yuan aerosol includes: aerosol can body, aerosol valve, outer cover, actuator, propellant, and raw materials. The main results of binary aerosols include: aerosol can body, aerosol spray valve, extra layer of aluminum bag, outer cover, actuator, raw materials, and compressed gas.
Valves usually consist of seven parts: sealing cup, outer gasket, inner gasket, valve stem, spring, valve chamber, suction tube, etc. Considering different materials, sizes, and structures, theoretically, valves can exhibit billions of different variations.
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Therefore, how to choose the appropriate spray valve requires comprehensive consideration of the following factors:
Firstly, is it a one-component valve or a BOV valve?
The compatibility issue needs to be considered when mixing the material and propellant in a one-component aerosol formulation. When both the propellant and the contents are sprayed out simultaneously, it is easy to produce a situation where the propellant has already been sprayed out while the material remains, which affects the consumer experience. Cannot be used 360 degrees, can only be used upright or upside down. Volatile propellants (such as butane or dimethyl ether) have a geometric fold increase in pressure with temperature, and are classified as hazardous materials with strict requirements for transportation and storage conditions.
Without considering cost factors, BOV valves have many advantages, such as:
The contents do not directly come into contact with the aerosol can, providing protection for the raw materials;
Spray out in all directions to adapt to diverse consumption scenarios;
Before filling, the valve bag can be vacuumed or disinfected by cobalt 60 irradiation. The formula can reduce preservatives and allergens;
The pressure inside the tank is constant, the spraying is stable, and the residual material is low;
Using compressed air or nitrogen, the pressure remains almost constant with increasing temperature, and the requirements for transportation and storage are relatively low.
Secondly, the choice of material for the sealing cup?
The thickness of tinplate cups is usually 0.27mm, and the thickness of aluminum cups is usually 0.42mm. The application in the field of personal care products usually uses aluminum cups, which are more stable and less prone to rusting. The size stability of the tinplate cup is better, and it is not easily affected by the aerosol can body or sealing process;
Thirdly, the material of the gasket
Gaskets are usually divided into inner gaskets and outer gaskets, with various materials including butyl, chloroprene, butyl, chlorobutyl, nitrile, chloroprene, polyurethane, and so on. Shrinkage of the gasket will affect the fit between the valve stem and gasket, sometimes leading to leakage. If the gasket expands excessively, the valve stem hole of the gasket cannot be exposed when pressing the nozzle, which will affect the spraying efficiency. After repeated experiments, a mixture of 75% ethanol and 25% isopentane was used for gold testing, and the best choices were chloroprene rubber (NEOPRENE) and butadiene sodium rubber (BUNA), which were relatively stable.
Fourth: Valve stem orifice
Common sizes include 0.35, 0.4, 0.46, 0.51, and 0.61mm, and the number of valve stem holes is one of the determining factors for the ejection rate. There are also different series of valve stem air holes, including 1, 2, 4, 6, and even 8 holes.
Fifth: Valve side hole
The gas phase side hole is located on the valve housing and is located inside after the valve is sealed. It is mainly used to increase atomization effect, increase the stability of content spraying for some powder products, and increase the spraying of high viscosity products. There are both single hole and double hole designs.
Sixth: Dip tube length
At the initial setting, the valve length can be calculated as the total height of the aerosol can minus the set value. Then, through compatibility testing, confirm the degree of shrinkage of the dip tube in the product, and the final valve length should be such that the bottom of the dip tube is at the lower one-third of the half circle at the bottom of the can after soaking and stabilizing.
Considering that dip tube have a 3-6% expansion rate, it is crucial to confirm the length after compatibility testing. Of course, a straw design with oblique cuts can also be slightly helpful.
Paired with appropriate buttons, the selected aerosol valve can convey the characteristics of the aerosol to consumers. As a packaging solution for complex products, compatibility and stability testing are required to design stunning products!
