Knowledge of water-based PU resin (resin synthesis, viscosity, solid content, film hardness, etc.)

Water-based PU resin is a polyurethane system that uses water instead of organic solvent as a dispersion medium, and is a new type of environmentally friendly polymer material
.
Because of its excellent environmental protection, excellent mechanical properties, and good compatibility with other water-based resins, water-based PU resins are widely used as adhesives, coatings, and coatings
.

Synthesis of water-based PU resin:

The synthesis of water-based PU resin is generally by prepolymerizing diisocyanate, oligomer polyol and chain extender.

Polyisocyanates: The commonly used varieties are aromatic diisocyanates, including TDI, MDI; aliphatic diisocyanates HDI and alicyclic diisocyanates IPDI, HMDI and so on

Macromolecular polyols: The macromolecular polyols used in the synthesis of water-based PU resins are mainly polyether polyols, polyester polyols, polyethylene glycols, polytetrahydrofuran ethers, polyester amides, acrylic polyols, and the like
.
Among them, the ether group in the polyether polyurethane is easy to rotate, has good flexibility, good low temperature performance, and the ether group is not easy to hydrolyze, and the water resistance is better than that of the polyester polyurethane
.
However, due to the poor hydrolysis resistance of polyester itself, polyester waterborne polyurethane prepared from general raw materials has a relatively short storage period
.

Chain extender: Small molecule chain extenders include 1,4-butanediol, ethylene glycol, adipic alcohol, ethylenediamine, etc.
Hydrophilic chain extenders are used to extend the chain of terminal isocyanates and polyurethane prepolymers.
At the same time, the substances that introduce hydrophilic groups are divided into three types: anionic, cationic and non-ionic.
Commonly used are dimethylolpropionic acid (DMPA), sodium ethylenediaminoethanesulfonate, and diethylenetriamine.
, Methyldiethanolamine,
etc.
These structures usually have carboxyl groups, sulfonic acid groups or secondary amino groups.
When their side chains are attached to the polyurethane molecular chain, the PU segments will have functional groups that can be ionized
.

Neutralizer: also known as salt-forming agent, which can react groups such as carboxyl groups and sulfonic acid groups to form polymer salts or generate ionic groups
.
The neutralizers used in anionic water-based PU mainly include triethylamine, ammonia, sodium hydroxide, etc.
, and the neutralizers used in cationic water-based PU mainly include acetic acid, CH3I, epichlorohydrin,
etc.

Solvent: The commonly used solvent is acetone, because the viscosity of water-based PU will increase during the reaction process, resulting in difficult stirring and insufficient reaction.
Adding acetone to reduce the viscosity is conducive to stirring and making the reaction sufficient
.
Acetone has a low boiling point, and the acetone in the water-based PU can be removed after synthesis
.

The performance advantages of water-based PU resin:

1.

2.
The moisture permeability and air permeability of water-based PU resin is much better than that of similar solvent-based PU products, because the water-based PU resin has strong hydrophilicity, so it has strong binding ability with water, and the product has good moisture permeability and air permeability.

.

3.
Water is used as the continuous phase, so that the viscosity of the water-based polyurethane system has nothing to do with the molecular weight of the polyurethane resin, and is lower than the solvent-based PU with the same solid content, which is convenient for processing and easy to operate
.
  

4.
The water-based PU resin system can be blended or copolymerized with other water-based emulsions, which can reduce costs or obtain PU emulsions with more diverse and excellent properties
.
 

5.
Water-based PU resin has good film-forming performance, firm bonding, cold resistance, water resistance, solvent resistance and wear resistance
.
Because of its adjustable hardness, the application field of water-based PU resin has been greatly broadened
.

Application fields of water-based PU resin:

Material compounding: bonding compounding of PVC, PP, ABS, XPE, PU, ​​PET, wood, cloth, paper and other materials;  

Car interior glue: car interior covering glue (covering door inner panel, instrument panel, armrest, etc.

  Flocking glue: It can be used for electrostatic flocking on various plastic parts (PVC, ABS, PU.
.
.
), sponge, metal parts and other materials
.
  

Vacuum forming: vacuum forming of soft materials such as polyvinyl chloride (PVC) and MDF, particle board, wood, etc.
, used in paint-free doors, cabinets, computer desks, speaker panels,
etc.
 

 Coatings (coatings) for metals, glass, stone, wood, rubber, plastics, fabrics, etc.
Excellent performance such as high and low temperature resistance to acid and alkali
.
When used as fabric finishing, it can play the roles of soft and comfortable hand feeling, waterproof, breathable and moisture-permeable, bright and beautiful color, anti-wrinkle, anti-shrinkage and anti-pilling
.

Color of water-based pu resin:

Water-based pu resin will have different effects due to the difference of raw materials and formula composition during synthesis, and the color will vary from white, white, transparent, and translucent

  Generally speaking, water-based PU resin has no irritating odor, only a faint resinous smell, and cationic water-based PU resin can smell slightly sour, like the smell of white vinegar

Waterborne pu resin viscosity:

The water-based PU resin has a wide range of concentration gradients, with a small viscosity that can have the general flow properties of water, and a large one that can be as viscous as toothpaste

Waterborne pu resin solid content:

The solid content of water-based pu resin generally does not exceed 50%, and it is mostly 30-40%, which is also conducive to production and transportation
.
Water-based pu resin can dissolve in water in any proportion.
For some fabric finishing, it is necessary to dilute the water-based pu resin dozens of times or even more, and then soak the fabric into the water-based pu resin emulsion, and then some special properties can be obtained after drying.
(Anti-fuzz, improve hand feel, highlight, etc.
)
.

Water-based pu resin pH:

There are anionic water-based pu resin, pH>7; non-ionic water-based pu resin, pH=7, mainly for the use of water-based pu resin when electrolyte resistance is required; cationic water-based pu resin, pH<7, for use in acidic environments, such as with other For acid emulsion blending, cationic water-based pu resin can be used
.

Water-based pu resin film hardness:

The water-based pu resin can adjust the film from soft and tough to hard and strong by adjusting the formula.
The soft elongation at break can reach more than 1500%, and the hard hardness can reach more than 2H.
Most of the water-based pu resins have low film forming temperature requirements.
High and low temperature can also form film
.

Waterborne pu resin curing agent:

Polyisocyanate curing agent or aziridine curing agent, etc.
, for the requirements of water resistance, solvent resistance, temperature resistance, etc.
, but the water-based pu resin itself can not meet this requirement, by adding curing agent can effectively improve water resistance, resistance Alcohol and other properties
.

Water-based pu resin related additives:

The main additives used in water-based pu resin are thickeners used for viscosity adjustment; defoamer used to generate bubbles during mixing and stirring or transportation; poor leveling, shrinkage, etc.
need to add leveling and wetting pH adjuster to prevent system incompatibility when mixed with other different acid-base emulsions; film drying speed requirements are different in different application scenarios, it is necessary to add film-forming auxiliary or low-boiling point Solvents increase drying speed
.

Drying speed of water-based pu resin:

Because it is water-based, the volatilization of water is not as fast as that of organic solvents, so the drying speed of water-based PU resin is slow, and the drying speed is also related to the thickness of the coating film, ambient temperature and humidity
.
If the coating film is too thick, the surface layer will dry first and then form a dense film, which will greatly affect the volatilization of internal water molecules, so it will take longer to dry completely
.
When the temperature is high, the movement of water molecules is accelerated, which will flow to the environment faster, and the drying speed will be accelerated; if the humidity is too high, the water molecules in the environment will inhibit the diffusion of water molecules in the PU resin, thereby reducing the drying speed
.

The price of water-based pu resin:

This may be a problem that we are more concerned about.
Some consumers just heard that water-based PU resin is good, and then they all go to buy water-based PU resin
.
For example, the popular water-based PU waterproof coating on the market costs about a few dollars per kilogram.
This type of waterproof coating uses the brand of water-based PU to rub against the heat of water-based PU
.
Some of these waterproof coatings are mixed with water-based PU resin and other polymer emulsions, and some do not contain water-based PU resin at all
.
The price of really pure water-based PU resin is generally more than 20 per kilogram, and the price of high performance requirements will be higher
.