What is the difference between PU and PA?
What is the difference between PU and PA?
PA painted white and PU coated white or coated with PA and PU transparent glue are difficult to distinguish from the outside, but there are still differences between PA and PU. One is the feel: PA’s feel is astringent, PU is smoother, and PU’s elasticity is better than PA’s. Good; one is gloss: PA has no gloss, PU is glossy and brighter; the other PU has a good film feel and feels like a film to the touch. In short, PU is brighter, has good elasticity and has a filmy feel, while PA does not have these conditions. Of course, it’s still difficult for novices to tell the difference just by relying on these. By the way, let me teach you a little trick: 1. Use the rubber to press hard on the cloth and then lift it up. PA will stick to the rubber but PU will not stick to it. . 2. Put a few drops of toluene on each coating surface of the two pieces of cloth (if possible), and then rub it gently with your hands (pay attention to protection and do not touch the toluene directly with your hands). The PA coating will fall off, but the PU will not.
Polyacrylate coating glue (Polyacrylate referred to as PA)
Polyacrylate fabric coating glue is one of the commonly used coating glues at present. It has the following advantages:
2. Good fastness to sunlight and weather, not easy to yellow;
2. Good transparency and co-compatibility, which is beneficial to the production of colored coating products;
2Good washing resistance;
2. Strong adhesion;
2 The cost is lower.
Its disadvantages are:
2. Poor elasticity and easy to wrinkle;
2Poor surface finish;
2. The feel is difficult to adjust.
The original polyacrylate coating glue was a purely waterproof product. After decades of development, the current varieties not only have multiple functions such as waterproof, moisture permeable, and flame retardant, but also have low-temperature and energy-saving features. Polyacrylate coating glue is generally copolymerized by hard components (such as polymethyl acrylate, etc.) and soft components (such as polybutyl acrylate, etc.). The main monomers of polyacrylate coating include acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, etc. In order to improve its waterproof performance, acrylamide and acrylonitrile can be added when necessary. The polymerization initiator generally uses peroxide ( Such as potassium persulfate, etc.).
Polyurethane coating glue (Polyurethane referred to as PU)
The full name of polyurethane is polyurethane. It is a polymer compound containing -NHCOO- unit in its molecular structure. This unit is formed by the reaction of isocyanate group and hydroxyl group. The reaction formula is as follows:
-N=C=O+HOˉ→-NH-COOˉ
In the 1970s, Germany’s Otto Bayer first synthesized PU. Around 1950, PU appeared in Europe as a textile finishing agent, but most of them were solvent-based products for dry coating finishing. In the 1960s, due to the increase in people’s environmental awareness and the introduction of government environmental regulations, water-based PU coatings came into being. After the 1970s, water-based PU coatings developed rapidly, and PU-coated fabrics have been widely used. Since the 1980s, breakthroughs have occurred in PU research and application technology. Compared with foreign countries, domestic research on PU textile finishing agents is relatively late.
Polyurethane coating agent is the main type of development today. Its advantages are:
The coating is soft and elastic;
The coating strength is good and can be used for very thin coatings;
The coating is porous and has moisture permeability and ventilation properties;
Resistant to wear, moisture and dry cleaning.
Its shortcomings are:
Higher cost;
Poor weather resistance;
It will be hydrolyzed when exposed to water, heat and alkali.
PU coating agents are classified according to composition: polyester polyurethane; polyether polyurethane; aromatic isocyanate polyurethane; aliphatic isocyanate polyurethane. According to the medium used, it is divided into solvent type and water type.
Textile coating finishing agent, also known as coating glue, is a polymer compound that is evenly coated on the surface of fabrics. It forms one or more films on the surface of the fabric through adhesion, which not only improves the appearance and style of the fabric, but also increases the functionality of the fabric, making the fabric waterproof, water pressure resistant, breathable, flame-retardant, anti-fouling and light-shielding. Reflection and other special functions. As early as more than 2,000 years ago, the ancient Chinese people had applied coating glue to the surface of fabrics. At that time, they were mostly natural compounds such as raw lacquer and tung oil, and were mainly used in the production of waterproof cloths. In modern times, a variety of synthetic polymer coating glues with superior performance have appeared. The original product had the disadvantage of being only waterproof but not moisture-permeable. The coated fabric felt stuffy and had poor comfort when used. In order to improve the breathability and moisture permeability of coating adhesives, since the 1970s, scientific researchers have developed a series of coating adhesives for waterproof and breathable fabrics by modifying the chemical structure of coating adhesives and changing coating processing methods. In recent years, functional coating glue and composite coating glue have also developed greatly.
There are many ways to classify coating glues. The main classifications according to chemical structure are:
1. Polyacrylate (PA);
2. Polyurethane (PU);
3. Polyvinyl chloride (PVC);
4. Silicone;
5. Synthetic rubber (such as neoprene).
In addition, there are polytetrafluoroethylene, polyamide, polyester, polyethylene, polypropylene and protein types. At present, the main applications are polyacrylates and polyurethanes. According to the medium used, it is divided into two types: solvent type and water type. The solvent type has the advantages of high water pressure resistance, good film-forming properties, fast drying, and low solid content, but at the same time it has permeability on fabrics. It has the disadvantages of being strong, rough to the touch, highly toxic, easy to catch fire, requiring solvent recovery equipment and high recycling costs. Compared with solvent type�Water-resistant, but highly toxic and flammable. In terms of components, it is also divided into two-group classification and single-group classification. The two-component product consists of a prepolymer and a cross-linking agent. The prepolymer is a prepolymer with hydroxyl groups at the end produced by the reaction of isocyanate and oligomeric polyol. Cross-linking agents are compounds containing multiple (three or more) isocyanate groups. During coating finishing, the prepolymer reacts with the cross-linking agent to form a thermosetting network film, giving the textile excellent properties. Such products include Crisvon7367SL from Dainippon Ink Company. The one-component product has a linear structure, with both amorphous and crystalline areas, and is thermoplastic. The one-component product is made of isocyanate-terminated (-NCO) prepolymer through chain extension. Products such as domestic AR-1401 and foreign products include Dainippon Ink Company’s Crisvon2016EL and 2116EL. Bayer’s Impranil series. Most solvent-based PU coating glues use DMF or a mixture of toluene and isopropyl alcohol as the solvent. In order to achieve waterproof and moisture-permeable effects, solvent-based coating finishing agents generally use wet coating processes to process fabrics.
3.2 Water-based PU coating glue
The water-based type is divided into two types: water-soluble and water-dispersible. Water-based PU is used for fabric coating and finishing, with large quantities and wide coverage, such as Japan’s Superflex series and Germany’s Imperanil water-dispersed series. Water-based PU has good film-forming properties and good waterproof properties. ElastronCT-7 and C-52 are both water-based PU, used for waterproof and moisture-permeable coatings. Water-dispersed PU can be made into nonionic, anionic and cationic dispersions. Water-dispersed PU is sensitive to acid and alkali. In the presence of acid, anionic PU will condense, while cationic PU is not resistant to alkali. weffdgdb
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