Analysis on the application of waterborne polyurethane (WPU) in coatings

2019-01-17

Waterborne polyurethane

Analysis on the application of waterborne polyurethane (WPU) in coatings

Waterborne polyurethane is used in waterborne wood coatings, which is expected to obtain excellent film hardness, heat resistance and dielectric properties, and good film-forming properties. The higher the degree of microphase separation of aqueous polyurethane, the greater the difference of softening temperature, the better the film formation and heat resistance, but for wood coatings, film hardness and resistance to media is also an important measure of the performance of the index. In order to improve the dielectric resistance and the hardness of the coating, it is necessary to increase the crosslinking density and increase the proportion of the rigid segments in the molecular segments, it certainly will reduce the flexibility and relative molecular mass of the waterborne polyurethane molecules. These are not conducive to the micro phase separation, the mixing degree increased, unfavorable to the film.

The research route is of high hardness, low molecular weight (less than 1000) polyester polyurethane preparation to obtain a high degree of crosslinking, heat resistance, chemical resistance and film hardness.  At the same time, with good flexibility, high molecular weight (more than 2000) linear polyester preparation or low branching polyurethane, to improve the degree of microphase separation, the coating has excellent film-forming properties, reduce film-forming agent dosage, improve the film hardness rise velocity. And through these 2 kinds of polyurethane copolymerization to obtain comprehensive performance.

 

Test method for aqueous polyurethane dispersion

Huajinsi  The aqueous poly (ethylene glycol) dispersion 4188/4100 (FOD) does not contain any free OH group, but they are still able to react with poly (ethylene glycol) as a hardening agent. This is due to the reaction of the amide backbone of the polyurethane dispersion. Because we can not calculate correctly, we can only recommend the following methods: 2, 4, 6, 8, 10, 12, 16%, a combination of isocyanate curing agent to quickly test. Aqueous ammonia fat dispersion with different curing agent, stirring for 10 minutes and then construction in plastic or wood substrate. After drying at room temperature on the 7 film angels bridge complete placement. 7 days after the test of chemical resistance (water, alcohol, coffee, fruit pulp, etc.) and mechanical properties (pendulum hardness, pencil hardness, scratch resistance, etc.), the results can be seen how much hardener. In this case, the hardener with 10~12% can achieve good film performance.

The relationship between hardening agent weight and paint performance of hydroxylamine

PUD binder Hardening agent

Film state

Film properties

PUD binder No hardener: bad alcohol resistance

Flexible elastic membrane

Not very scratch resistant

PUD binder Add 2% hardener: bad alcohol resistance

Flexible elastic membrane

Not very scratch resistant

PUD binder Add  4% hardener: bad alcohol resistance

Flexible elastic membrane

Good scratch resistance

PUD binder Add 6% hardener: bad alcohol

Flexible elastic membrane

Good scratch resistance

PUD binder Add 8% hardener: bad alcohol

Flexible elastic membrane

Good scratch resistance

PUD binder Add 10% hardener: bad alcohol

Flexible elastic membrane

Good scratch resistance

PUD binder Add 12% hardener: bad alcohol

Flexible elastic membrane

Good scratch resistance

PUD binder Add 14% hardener: bad alcohol

Hard elastic membrane

Good scratch resistance

PUD binder Add 16% hardener: bad alcohol

Hard elastic membrane

Good scratch resistance



PUD wood decorative painting stickers (paper glazing) can be used with sinograce "4188/4100 Aqueous polyurethane dispersion emulsion.

sinograce 4188/4100 water polyurethane emulsion has good light flood and super scratch resistance, the following chart:

Sinograce  Waterborne polyurethane emulsion paint light flood test 

60 gloss50μ Wet film

100

100

100

100

100

100

100

60 gloss24μ Wet film

95

96

96

96

96

96

96



Sinograce Waterborne polyurethane emulsion paint Nan hydroxylamine scratch resistance test

Scratch resistance50μ Wet film

十十

十十

十十

十十

十十

Scratch resistance24μ Wet film

十十

 



Note:

Good: + +

Poor

 

Sinograce Chemical Key points of aqueous polyurethane dispersion

Sinograce Chemical is the sole agent of aliphatic polyurethane dispersions with unique nanotechnology, excellent performance of full Bai polyurethane body. Use them with placement of paint, see the other system There is nothing comparable to this gloss and toughness, to help you improve the quality of products. In the course of many years of practice and test, we summarized the use of well water polyurethane products and water paint formulations are as follows: 

1, about drying conditions

In general the water-borne wood coatings, does not require mandatory bake drying, but if the customer has the need to improve the production speed of coating, hot air drying furnace using traditional. Recommended maximum baking temperature: 40 degrees of cork; wood at 40 degrees C; plastic; time is 10~80 minutes. 

2, the relevant factors of wood coating primer grinding hard:

The hardness of the primer will vary due to the hardness of the resin, the chemical system, the residual moisture of the film, the co solvent, and even the surface temperature of the coating. According to our experience, 4188/4100 aqueous polyurethane dispersions have excellent sanding characteristics. 

3, method  improving the grinding: many operators by adding zinc stearate.

4, determination of water resistance:

The wet cotton ball on the water-borne wood coating on the surface, and the glass cover, after 16 hours, check whether the film appeared whitening or blistering.

5, wood furniture coating:

Usually in European wood to be coated with 2-4 layer, the simple way is to use the same water-based resin as primer and topcoat. The standard thickness of each wet hydroxylamine is 80^120μm. Some wood has many pores, then can be coated with a colored bottom and a road filling material is a primer, then again primer, then finish.Generally speaking, hot air oven does not need, but to speed up the painting speed can be used.

6, Sinograce 4188/4100 waterborne polyurethane dispersions suitable for use in furniture:

A.  Sinograce 4188/4100 aqueous polyurethane dispersions have good scratch resistance and chemical resistance. It can be used as a primer, primer and finish. 

B. Sinograce 4188/4100 aqueous polyurethane dispersion and acrylic ester mixture has a good scratch resistance. Suitable for primer, topcoat.

 

Aqueous polyurethane dispersion

Aqueous polyurethane dispersion is a kind of polyurethane particles dispersed in water, smaller particle size than acrylic emulsion. At present, there are three types of waterborne polyurethane dispersions: anionic, cationic and nonionic. Most of the anionic polyurethane dispersions are used in the coatings industry. Its characteristics are: single component, and no free isocyanate, non-toxic. Room temperature film formation, no need to add film additives, it can make the system of VOC content reduced to 0, with the use of safe, no environmental pollution, etc. Waterborne polyurethane also has good leveling, strong hiding power, strong adhesion, coating cold, heat. Aqueous polyurethane dispersions have high molecular weight. However, the viscosity is low, easy to process, convenient construction, and its mechanical properties comparable to solvent based polyurethane, with outstanding hardness, wear resistance and chemical resistance. Different kinds of monomers and synthetic process can be used to produce products with different properties. Mainly used in wood (including wood furniture and floors, etc.) painting and protection. Because of the relatively high cost, it is generally used in the coating system with high performance requirements. However, waterborne polyurethane wood paint used in addition to the high cost but also by some other properties such as its restrictions on wood wettability and poor dispersion of pigment, poor weatherability of aromatic polyurethane.  The development of polyurethane acrylate copolymer emulsion has become the focus of attention because of its excellent weatherability and good wettability to the base material and pigment. 

At present, a new type of waterborne coatings, which is produced by the waterborne polyurethane dispersion, is gradually replacing solvent based polyurethane coatings; And the film abrasion resistance, fast drying, good appearance, good solvent resistance of waterborne polyurethane coatings in the field of domestic wood coatings market share is gradually increasing. Waterborne polyurethane leather coating (light oil) has good low temperature resistance, and is gradually replacing the traditional acrylic leather finishing coating, which has become the main varieties of leather coatings. In addition, aqueous polyurethane dispersion can be used as waterborne plastic coatings, waterborne industrial coatings, waterborne anticorrosive coatings, waterborne polyurethane external wall paint, waterborne polyurethane adhesive, meet the performance requirements of different industries.

 

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