How to select resin efficiently in UV coating formulation?
The role of oligomer in UV coatings
Oligomer: Oligomer used in light-curing coatings, also known as prepolymer. In earlier years, it was translated as zwitterion, with the following significant features: small molecular weight, characteristic polymerization groups, and large viscosity. Is the main body of light-curing coatings and skeleton role (many physical and chemical properties of the paint film)
UV curing reaction characteristics
UV curing is a polymerization reaction between unsaturated molecules. by initiator initiation mechanism there are free radical polymerization and cationic polymerization. However, the polymerization that we have studied a lot is free radical polymerization (this talk is based on free radical polymerization). This final C-C cross-linked structure is a rigid cross-link.
聚合机制
Free radical polymerization has: rapid reaction; large shrinkage; small change in polymerization degree; large effect of blocking polymerization (0.01-0.1% blocking agent to prevent the reaction).
— The most unfavorable to the coating is shrinkage, according to foreign W.J. Bailey and other studies found that the double bond is not polymerized time distance is long, once polymerized, generate covalent bonds, spacing shortened, causing volume reduction, all unsaturated polymerization double bond shrinkage up to 11%.
The complexity of UV coating formulation
1、Many types of monomers
2、Basic oligomers (resins) of many kinds are currently divided into unsaturated polyester PE, epoxy EA, polyurethane PUA, polyester PEA, amino, polyether, silicone, phosphate, mixed, etc. by functional group at the time of synthesis.
Resins commonly used in UV coatings by function
Hard resin – Tg high
High hardness, good chemical resistance, most curing speed
1、Standard bisphenol A type EA.
2、High functional group PUA and small molecular weight 2fPUA;
3, high functional group amino acrylate.
4、Methacrylate oligomers.
Soft resin – Tg small
Good flexibility, low curing speed, low crosslink density.
1, modified epoxy – epoxy soybean oil acrylate, etc.
2、Long-chain polyester acrylates.
3、PUA with straight chain structure fractional mass over 1200.
4、Part of pure acrylate oligomers
极性树脂
Oligomers containing reactive hydrogen or easy to form hydrogen bonds, changing polarity or surface tension
1、Phosphate acrylate
2、Organic silicon oligomer-special
3、Carboxyl acrylate oligomers
Aqueous UV oligomer
Emulsion type, water dispersion type, water soluble type
1、Polyurethane type —- mainly.
2、Epoxy acrylate class.
3、Polyester acrylate class.
Application of non-crosslinking class resins in UV
Filling role, improve cross-link density, increase adhesion, change flexibility, enhance wettability and other auxiliary role
1、Long oil alkyd resins.
2、Thermoplastic acrylate resins.
3、Aldehydes and ketones resins.
4、Petroleum resin, etc.
How to choose resin for designing UV coating formula
Before designing the coating formula, it should be clear that.
1, the coating type of the process of coating construction —- clarify the primer, topcoat, color paint.
2. understanding the basic properties of the material to be coated —- polarity size (surface tension), presence or absence of crystallization, thermoplastic heat-set.
底漆树脂的选择
1, adhesion requirements: this is the generality of the primer resin, relatively difficult adhesion at present are mainly.
A, glass —— choose methacrylate oligomers and non-film forming resins and some special polar resin – thiol siloxane system with (but water resistance is a barrier to the current formulation) ;
B, metal, distinguish the metal type, for metal adhesion in the coating industry is basically applied to destroy the cross-linking method, the international common is phosphate treatment. UV is currently the most common is phosphate ester combined with some pure C method.
C, plastic class (including plasticized paper and it class of paint finishing), which is currently a relatively large class of particularly complex class, mainly because of the complex structure of plastic, crystalline forms vary, surface tension varies, relatively difficult BMC, PET, PP, etc.. There is no unified formula can be eaten, generally speaking, with soft PUA, and pure C and some non-film-forming resin and polar resin have certain effects, but we must pay attention to chemical resistance, water resistance, pay strict attention to the relevant resin with.
D, oil-containing wood: At present, mainly some hard sandalwood such as clone wood, rosewood, green shank mulberry, big hippopotamus wood and other wood oil adhesion is relatively difficult, to seal the oil on the market is still very few pure UV good cases, you can first seal with PU and then do UV adhesion primer. Mainly with some polar resin or monomer and filler resin can do a good job of adhesion.
2, wettability: for the wetting of color fillers and substrate wetting, which are two different functions, because it can not guarantee that the surface tension of the substrate and color fillers just the same.
A, for the wetting of the color filler can ensure the storage stability of the paint and paint film compatibility performance of transparency, such as some PUA, PEA and epoxy soybean oil acrylate has this effect.
B, for the substrate wetting such as amino resin and PEA, the effect is better.
3、Flexibility: about sandability and interlayer adhesion.
Generally choose standard EA and some PEA and some monomers to coordinate the treatment of flexibility, so as to regulate the sanding and interlayer adhesion.
The current market also emphasizes the hardness of the hardened primer —- attention to the hard resin curing and do the amount of coating, otherwise it is easy to lead to paint film burst.
The market also has requirements for the so-called elastic primer —- more flexible resin, preferably with polyester class PUA, polyether class is not very good toughness, mechanical modulus is not enough.
The choice of top coat resin
1, richness, leveling
To meet this requirement, we must choose the resin and monomer with good compatibility, improve the wetting and leveling of the primer, crosslinking appropriate to improve the use of higher refractive index of the resin.
Generally choose high functional group PUA, amino resin, standard EA as the main resin.
2, toughness (hardness and abrasion resistance).
These two paint film properties have many inevitable correlations, but not necessarily identical, there are differences in treatment.
Hardness: In addition to the traditional wood coating has 80-120Unm thick film and some thick spray, a large part of the hardness of this case from the film itself, there is a part of the illusion of hardness to pay sufficient attention to, such as substrate, primer, surface sense, etc., rolling surface and thin spray is a typical example, you can choose the aforementioned high official resin outside can also use some silicone resin or silicon additives to improve.
Wear resistance: the general choice of PUA is better than others, mainly hydrogen bonding to provide some toughness to increase wear resistance. But the wear resistance of the thin coating is also can not rely on resin to solve.
3、Layer adhesion
Solve the good wetting leveling and resin polarity with, had between the adhesion can be solved, special when you can choose some methacrylate resin.
4、Chemical resistance
EA, PUA (polyester class) have good chemical resistance, PE, polyether class is poor
5、Yellowing resistance
Generally, aliphatic PUA, pure polyether acrylate, pure propylene, amino class have good resistance to yellowing. The first category is the most loved, but the yellow resistance is not the best. The latter two categories are less used because there is a lack of items, but the best comprehensive performance of yellow resistance amino class.
6、Matte class
At present, with some slightly smaller molecular weight resin or huge are effective, in addition to some polyurethane is also very effective (currently on the market, there is a two-functional hardness of good polyurethane competitive).
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