涂装基本知识之Organic coatings

Organic coatings Jotun Korea Coatings Co., Ltd. Coating advisor : Danny (Dan Guo-qiang)
2015-07
Contents
1.Air-oxidizing coatings(Dry oil, Alkyd )
2.Solvent dry lacquers(Acrylic , C/rubber)
3.Co-reactive coatings(Epoxy , Polyurethane)
4.Emulsion-type coatings(Acrylic , Epoxy)
5.Heat-condensing coatings( Phenolic )
Natutral Air-oxidizing coatings
Drying oil
If the iodine value (碘值)of oil is more than 130 , the oil in the air will gradually cure and form a film.
Remark:
Natutral Air-oxidizing coatings
When the glycerol and the fatty acid are combined into oil , the chemical formula shown below results:
Natutral Air-oxidizing coatings
The difference between fats and oils is that fats are triglycerides formed with saturated fatty acids(no
double bond ) and oils are formed with unsaturated fatty acids (one or more double bonds) .
Linseed oil acid :CH3CH2 CH=CH CH2CH=CH
CH2CH=CH(CH2)7 COOH 亚麻油的主要成分
Tung oil acid :CH3(CH2)3 CH=CH CH=CH CH=CH（CH2)7 COOH 桐油的主要成分
Castor oil acid:CH3(CH2)5CH(OH)CH2 CH=CH(CH2)7 COOH 蓖麻油的主要成分
Natutral Air-oxidizing coatings The drying of an oil :
Oxygen attacks the carbon double bonds
Natutral Air-oxidizing coatings The drying of an oil :
The carbon double bonds rebuild
Natutral Air-oxidizing coatings The drying of an oil :
The carbon-carbon cross link
Natutral Air-oxidizing coatings
The drying of an oil : ―C-O-O- ― group attack ―C=C‖ bonds
Natutral Air-oxidizing coatings
Driers for natural drying oils:
Oils dry slowly without the use of metallic driers , metallic driers are used as catalyst to achieve practical drying time .
Co2+ + ROOH —— RO· + OH- + Co3+
Co3+ + ROOH —— ROO· + H+ + Co2+
Most common used driers are lead , manganese , cobalt napthanates , aluminum , zirconuim .
Natutral Air-oxidizing coatings
Saponification : to convert (a fat) into soap by treating with an alkali
The lack of resistance to alkali is one of the major drying oil deficiencies .Even mild alkalies tend to react with the oil part of the molecule , causing the
disintegration of the coating .
Synthetic Air-oxidizing coatings
All of the oil-modified resins are based on unsaturated fatty acids , such as Alkyd , Epoxy ester , oil-
modified urethane , and varnish .
Synthetic Air-oxidizing coatings
Alkyd are undoubtedly the most common of all of the oil modified materials , as they have the broadest usage
Synthetic Air-oxidizing coatings
Alkyds can be classified in a number of different ways , the most common of which is according to the oil
length:
1, Short length (oil level < 40%)
2, Medium length
3, Long length (oil level > 60%)
The length influences all properties and is the primary factor in determining solubility, viscosity, flexibilty, and hardness
Synthetic Air-oxidizing coatings Modified alkyd:
Vinyl alkyd – Good weather resistance
Silicone alkyd – Good heat resistance
Uralkyd– High quality maintenance finishes
Polyamide modified alkyds– Greater film build is ok Epoxy ester – A step above alkyd resin for chemical resistance , and make it harder
Solvent dry lacquers
Lacquers are materials that form a coating by evaporation of solvents.
1,Vinyl coatings
2,Chlorinated rubber coatings
3,Acrylic polymers
4,Coal tar coatings
Vinyl coatings
All the materials which contain the vinyl double bond group could be called vinyl materials technically.
Vinyl coatings
•Good chemical resistance(e.g., acids,alkalies, and salt)
•Good water resistance(used as a seal coat)
•Good age resistance
Vinyl coatings
•Good chemical resistance(e.g., acids,alkalies, and salt)
•Good water resistance(used as a seal coat)
•Good age resistance
Chlorinated rubber coatings
Chlorinated rubber coatings consist of naturall rubber reacted with chlorine. This forms a very hard, horny-
textured resin lacking in the elastic of rubber product. It is odorless, tasteless, and nontoxic (usually used on the concrete surface of swimming pool).
Chlorinated rubber coatings •Good heat resistance (up to 125 C) •Good electrical properties(dielectric constant at 25 C is 2200 volts per mil) •Good adhesion
•Good chemical resistance
•Fast through dry
Chlorinated rubber coatings
Acrylic polymers
Acrylic resins are primarily polymeric derivatives of acrylic and methacrylic acid.
Acrylic polymers
•The polymers can vary from very hard, brittle materials to very soft, flexible plastics due to the variation in
esterification and the copolymerization of various
esterified acrylic monomers.
•Acrylic resins are characterized primarily by their water-white color, resistance to change in color over time. •Excellent durability properties due to the chemical nature of the polymer itself.
•Used mainly as a finish coat(e.g., on automobiles , freezers etc.)
Coal tar coatings
Coal tar coatings
There are a number of coal tar coatings made by dissolving processed coal tar pich, or a blend of these pitched, in suitable solvent. They dry entirely by
evaporation of the solvents and their properties depend to a great extent on the type of coal tar raw materials and the blending of these mateials.
Coal tar coatings
•Low permeability to moisture
•High dielectric resistance
•Not affected by mineral oil , but can be dissolved by a vegetable or animal oil, grease, and detergents •Have good resistance to weak acids, alkalies, salts, sea-water and other aggressive atmosphere
•Tendency to alligator when exposed to direct sun-light (the upper layer of the film contracts and slips over the softer under layer causing alligator marks)
Co-reactive coatings
They are usually relatively low in molecular weight during the application and then, due to cross-linking
with added material or from moisture in the air, cross-link in place to form a high molecular weight thermoset coating on the surface.
Cross-linkage increase the size of the molecule, which generally can increase the corrosion resistance and
definitely does increase the resistance to various solvent
Epoxy coatings
C CH 3CH 3
O
CH 2
CH OH
CH 2
O
O
CH 2
CH
O C CH 3CH 3
O
CH 2
CH
CH 2
O n
CH 2 Widely used epoxy polymer molecule(Comp. A):
Reaction with active hydrogen groups:
CH
CH 2O
+
H 2N
R
CH CH 2
OH
NH
R
CH
CH 2O
+
HN
R ′
CH CH 2
OH
R
N
R ′
R
Epoxy coatings
●Aliphatic amine-cured epoxy :
Reaction takes place readily at room temperature , greatly affected by the temperature , easy to absorb moisture and react with carbon doxide
●Cycloaliphatic amine-cured epoxy :
Slow reaction, need heat to rapid up. Low VOC coatings. Modification with other curing agent is needed to achieve a complete room temperature cure with epoxy
H 3C H 2N CH 2NH 2
CH 3NH 2H 3C CH 3H 3C
CH 2NH 2
Epoxy coatings
Mannich bases(Polyamine cured epoxy)
Amines may be modified with methylol phenol to produce a mannich base(as shown above), which has a better compatibility with epoxy resins than unmodified amines. these systems may be applied under cold or damp condition with good adhesion.
Easy to chalking !!!(massive amount of C=C in it )
OH HCHO OH CH 2OH H 2NCH 2CH 2NHCH 2CH 2NH 2OH
CH 2NHCH 2CH 2NHCH 2CH 2NH 2
Amine blush
Amine blush
Not practical !!
Epoxy coatings
Polyamide cured epoxy
As the formula shown above, the product has 3 active hydrogen atoms. It is not as sensitive to moisture as polyamine , has a good permeability.
Polyamide epoxy coatings are generally considerably softer and more resilient and flexible than the amine cured epoxy. Larger molecules, good pot life, good alkali resistance , less good acid resistance compare with amine cured epoxy.
RCOOH +H 2N (CH 2)2NH (CH 2)2NH 2NH (CH 2)2NH (CH 2)2NH 2RC O
Epoxy coatings
Solvent-less epoxy
Reduce the molecule weight
Reactive diluents
Functional pigments(don’t absorb too much solvent)
Additives are good for solvent-less
High build
Polyurethane
Polyurethane coatings contain resin made by the reaction of isocyanates with hydroxyl-containing compound
R1N H OR2[R1N C
OR2OH]R1N
H
C
O
OR2
C O+
Polyurethane
Where there is an active hydroxyl group, the isocyanate will react with it. So attention should be paid to the reaction with water!!! (two components polyurethane is sensitive to the water , this is also the basis of moisture cured polyurethane)
R N R N H C O OH H 2O C O +R NH 2+CO 2
Polyurethane Aliphatic urethane: •Outstanding abrasion resistance •Good chemical resistance •Flexibility
•Excellent gloss and color retention •Limited resistance in immersion
Polyurethane
Aromatic urethane:
•In some immersion service
•Not good gloss and color retention
Others:
•The curing agent of epoxy can react with base of polyurethane? ???
Organic silicone paint
Silicones are formed by chemical modification of quarts, sand, or silicon, and they may be thought of as hybrds of glass and organic resins.
Organic silicone paint
The organic groups that have the most desirable properties combined with the silicon are the methyl(甲基） and phenyl(苯基 better heat and oxidation resistance) groups.
R2R4 R6 R8
R1-Si-O-(Si-O)n(Si-O)m-Si-R10
R3 R5 R7 R9
Where ―R‖ = organic groups. More organic groups, the resin becomes more softer .
Properties of silicone coatings •Generally, somewhat softer than many organic coatings,
hardness can be improved with organic groups •Silicone adhesion is generally good to most substrates, depending, as in the case with organic materials, on the cleanliness of the surface
•Poor abrasion resistance
•Good chemical resistance(dissolved in hydrocarbon solvents
•High heat resistance
•Good weather resistance(thermal change, UV) •Excellent electrical properties(good electrical insulators even being burnt)
•Low surface tension( fouls are difficult to attach, little affect by the variation of temperature)
Emulsion type coatings
Water based or water borne paint : the resin particles discrete in the emulsion, and then to flow together to make a coalescence to form a continuous film
Emulsion type coatings Necessary Emulsion coating ingredient: •Prime pigment (hiding, color) •Extender pigment (hardness) •Reactive pigment (rust inhibition) •Pigment dispersant
•Defoamer
•Thickener
•Can preservative
•Coalescent
Emulsion type coatings
Degrees of coalescence
(a)Disperses resin particles
(b)Water evaporation
(c)Foam-like coalescence (d)Complete coalesence
Emulsion type coatings
•Active properties:
•Environmental friendly ：Water based
•Easy application : by roller, brush, spray, water as thinner. can be applied on slight wet surface. •Drawbacks:
•Temperature during application :above 5°C or 10°C •Storage temperature : above 0°C
Phenolic coatings
⏹Addition reaction
Phenol with formaldehyde
⏹condensation polymerization
Thermoplastic phenolic coating is the reaction between phenol and formaldehyde (mole ratio >1)under the acid catylist
Thermosetting phenolic coating is the reaction between phenol and formaldehyde (mole ratio >1)under the acid catylist
Thermoplastic phenolic coating OH
＋ CH
2O
OH
CH2OH
OH
OH
CH2
OH
OH
CH2
OH
CH2
OH
n
Thermosetting phenolic coating
OH
+H C O
H
OH
-
OH
CH 2OH
OH
CH 2OH
OH
CH 2OH
CH 2OH
HCHO
OH
CH 2OH
HOCH 2
OH
-
+OH
CH 2OH HOCH 2CH 2OH + HCHO HO
-
（Reaction temperature is
at about 65℃）
Thermosetting phenolic coating
+OH
CH 2OH n (n=0,1or 2)
CH 2O H CH 2OH OH
n
CH 2
HO C (n=0,1or 2)CH 2O n
CH 2OH OH
C H 2
OH
CH 2OH +H 2O n
n
CH 2OH OH
OH
CH 2OH n
CH 2+
H C O
H ...
+OH
CH 2OH n (n=0,1or 2)
CH 2O H CH 2OH OH
H n (n=0,or 1)
+H 2O
n
CH 2OH OH
CH 2OH
CH 2OH n。