From the point of view of performance, silicone leveling agent can mainly provide the following nine aspects of performance: leveling, leveling speed, wetting ability, recoating, compatibility, smoothness, low stability bubble, anti-shrinkage porosity and anti-adhesion, etc. These properties are related to the chemical structure of organosilicon leveling agent. The most important indicators are silicon content and molecular weight.

1、 compatibility

The compatibility of organosilicon leveling agent mainly depends on the type and number of modified groups. Thus, the smaller the value of m/n (that is, the lower the content of incompatible chain segments), the better the compatibility. When the m/n value is fixed, the larger the x/y value is, the better the compatibility will be. This is because the compatibility of polyethylene oxide exceeds that of polypropylene oxide.

2、stable foam

Silicone additives, especially polyether modified silicone oil, when the silicon content reaches a certain range, its surface activity reaches a relatively high level, usually showing obvious foam stability, this range as a benchmark, and when the silicon content to the low direction change, due to the gradual increase of compatibility with the system, foam stability gradually weakened. When the silicon content gradually changes to the higher direction, due to the incompatibility with the system, the foam stability is also gradually weakened, and finally it even begins to have the ability of defoaming.

For polyether modified silicone oil, under the usual x and y values, when m/n> 3 or m/n< 0.25, the effect of basically unstable bubble can be obtained. Colloquially, when the silicon content is very high or very low, the leveling agent is unstable bubble, and if made of silicon content is very high, you can get excellent hand feel, unstable bubble, but slightly poor compatibility of leveling agent, if made of silicon content is very low variety, The performance of the leveling agent obtained is a silicone leveling agent with good compatibility, unstable bubbles but insufficient hand feel.

3、 feel

Generally, the feel of organosilicon leveling agent is closely related to its silicon content, and in the case of similar silicon content, it is also related to the specific structure of the leveling agent (such as the linking way of polyether and organosilicon chain segment, etc.). According to the principle of modern physics and chemistry, the feel of paint film comes from the low friction coefficient on its surface, so in terms of molecular structure, the feel comes from the distribution of CH3 groups on the surface of paint film.

Under the condition of fixed xy value, the larger m/n value (equivalent to the higher content of pure silicone chain segment), the better the hand feel; When m/n is a constant value, the greater the absolute value of m, the better the feel. You can see from this. For silicone leveling agent, the pursuit of good compatibility and good feel is often a pair of contradictions, in order to get both, usually m/n can only be selected in a small range.

4、 shrinkage cavity prevention performance

The anti-shrinkage performance of silicone auxiliaries is a response to their ability to reduce surface tension and is usually closely related to silicon content. In addition, it is also related to the absolute molecular weight of the additive and the connection between the groups. At the same time, due to the nature of the system is very different, some additives in the water and oil system shrinkage hole capacity also has a great difference, especially some water-based silicone shrinkage hole additives, often used in the oil system without obvious shrinkage hole effect.

5、 flow speed and flow leveling effect

From the theoretical point of view, the leveling speed reflects the migration speed of the leveling agent to the surface of the paint film. This is related to several factors:

----- The poorer the compatibility between the incompatible chain segment and the system in the leveling agent molecule, the faster the leveling speed; Usually, the incompatibility between organosilicon chain segment and system is far more than that of non-silicon chain segment, so usually organosilicon leveling agent has faster leveling speed than non-silicon leveling agent. From the molecular structure analysis, the larger the m/n, the faster the leveling speed.

----- The smaller the molecular weight of the leveling agent, the faster the motion speed, the faster the leveling agent; In terms of molecular structure, the smaller m+n is, the faster the leveling speed is.

----- The higher the temperature of the system, the faster the molecular motion and the faster the leveling speed.

Except the temperature, which is an external factor, the rest are related to the molecular structure of the leveling agent, which is controllable in the design stage of the leveling agent. From the structural analysis, the influence of the numerical values of m, n, x and y on the leveling effect is complicated. Generally speaking, when the value of m/n is between 1 and 2, the leveling effect is better. For the fixed value of m/n, the larger the value of x+y is, the better the leveling effect is.

6、 painting

The influence of leveling agent on recoating performance is mainly related to the mobility of leveling agent between paint films. If the leveling agent migrates freely between paint films, then theoretically the leveling agent will have less effect on recoating at normal addition amounts. On the contrary, if for some reason the leveling agent is fixed on the surface of the paint film, its free migration is limited, it will have an impact on the recoating. From the aspect of molecular structure: (1) the high molecular weight of low surface tension leveling agent is affected by the slow migration rate; (2) The leveling agent with reactive functional group can not migrate after the reaction and affect the recoating. Among them, the latter is the main factor. In the amino baking paint and polyurethane paint system, the hydroxyl group is the group that may affect the recoating. In the photocuring system, the acrylate group is the group that affects the recoating. In epoxy systems, epoxide or amino groups are the groups that affect recoating.

Generally speaking, the larger the value of m+n and the higher the value of m/n, the more likely to appear the problem of recoating, in addition, the type of polyether end group R group will also have an impact on recoating.

The amount of silicone additive and the curing temperature of the first coat also affect the recoating property. When excessive silicone leveling agent is added, some organosilicon molecules remain at the interface of the two layer coating, which affects the interlayer adhesion. For polyether modified silicone leveling agent, when the temperature difference exceeds 140-150℃, decomposition will occur due to oxidation, through the oxidation reaction process, reflected fragments with reactive groups such as hydroxyl, and then through the crosslinking with the coating and loss of migration ability, thus affecting the recoating.

7、antiblocking properties

Anti-viscosity is a property closely related to surface tension and friction coefficient. Generally speaking, when the surface tension of an interface is less than 24 dyne/cm and the friction coefficient is less than 0.26, it is considered to have obvious anti-adhesion and release effect. The less interfacial tension, the better.

From the analysis of molecular structure, the higher the silicon content, the larger the molecular weight, the better the orientation ability of organosilicon chain segment on the coating surface, the better the anti-adhesion effect. Its performance and feel sequence is similar. If a certain agent can be used as an anti-adhesion agent, then its feel has reached a very high level. Some good effect of anti-adhesion agent even does not have the function of leveling, and can only be used as a simple anti-adhesion agent.

8、 resistance to high temperature

Usually in the paint system, due to the use of relatively high temperature, and the usual polyether modified silicone oil leveling agent, due to the polyether chain segment in more than 150℃ will begin to gradually decompose, produce some small molecular fragments, this kind of dispersion products often lead to a variety of paint film disadvantages. Polyester modified silicone, acrylate modified silicone or aryl alkyl silicone, fluorocarbon modified silicone and so on have better temperature resistance, can be used in high temperature baking paint system. Polyester modified silicone oil and acrylate modified silicone oil have good compatibility with paint resin and can be used in varnish and color paint system. The aryl-alkane silicone oil has limited compatibility and can only be used in high temperature color paint system.

9、 wetting ability

The relationship between the wetting ability and the structure of the auxiliaries is relatively complicated. Usually, if the coating requires wetting the substrate, the surface tension of the coating must be lower than the surface tension of the substrate, otherwise it is easy to appear poor wetting condition.

The wetting degree of liquid to the substrate can be measured by the contact Angle, usually the greater the surface tension difference between the liquid and the substrate, the smaller the corresponding contact Angle, the better the wetting effect.

In general, the greater the ability of the leveling agent to reduce surface tension, the better its ability to moisten the substrate. But different from the shrinkage hole capacity, the shrinkage hole capacity is usually related to the static surface tension of the leveling agent, and wetting is often a dynamic process, is a phenomenon produced in the process of coating or ink construction, so the wetting effect is closely related to the level of the dynamic surface tension of the leveling agent. In addition, the same as the capacity of shrinkage hole prevention, the wetting capacity of additives is often related to the system used. Due to the large difference in physical and chemical properties between the oily system and the water-based system, the wetting effect of additives in it is also relatively large. Some additives have a good wetting effect in water-based systems, but for oil-based systems, the effect may not be obvious.

10、mute powdered orientation

Matte orientation is a typical phenomenon closely related to surface tension. Usually the orientation of matte powder depends on the ability of the entire surface of the paint film to maintain uniform surface tension during the film formation process. If the end of the solvent volatilization process or the curing reaction process of the paint film can not maintain uniform surface tension, there are surface defects similar to Bennard vortex, then eventually in the formation of the paint film surface will appear the commonly called matte powder flower phenomenon.

In general, the type of matte powder, the type of resin and the type of additive used can all affect the final matte orientation. The organosilicon additive has advantages in eliminating the flaring of matte powder and improving the orientation ability of matte powder. Usually, the stronger the ability of silicone leveling agent to reduce the surface tension and the more limited the compatibility with the system, the easier it is to migrate to the surface of the paint film at the early stage of the formation, to maintain the uniformity of the surface tension, so as to obtain excellent matte powder orientation effect. In this way, it can be easily seen from the structure that for polyether modified organosilicon, the greater the m/n is, the greater the absolute value of m is, and the better the orientation ability of matte powder is. Because of its limited compatibility, arylane modified silicone has excellent matte orientation.