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Epoxide Polymers in Coatings
The University of Southern Mississippi
Hattiesburg, MS 39406
PSC 470/570, Fall Semester 2006
Outline for Epoxy PolymersI. Basic SynthesisII. Reactions of EpoxidesIII. Types of epoxy resins
A. BPA & BPF epoxidesB. Multifunctional epoxidesC. Miscellaneous epoxidesD. Cycloaliphatic epoxides
IV. Epoxide curing agentsA. AminesB. Aliphatic aminesC. Aliphatic amine adductsD. Aromatic aminesE. Acid anhydridesF. Carboxylated polymers
V. Modified epoxidesA. Acrylated epoxidesB. Coal Tar modified epoxidesC. Epoxide estersD. TGIC-PolyesterE. Amino epoxides
VI. DiluentsA. Epoxide based diluentsB. Acrylic monomersC. Non-reactive diluents
VII. Waterborne epoxides
Typical Epoxide Polymer
O CH2 CHOH
CH2 OH2C CH CH2 OO
CCH3
CH3
CCH3
CH3
O CH2 CH CH2
O
( )n
DGEBA Based
Typical Characteristics of Epoxide Polymers
Chemical and heat resistanceAdhesionLow shrinkageEase of fabricationToughnessFlexibilityAbrasion resistanceSuperior elevated temperature performance
Reactions of Epoxides
OCC + R CH
OR`
OR`R CH
OR`
O C C OR`
OCC + H3C C CH2 C
O O
OR C
C
C C
C
CH3
OH
OO
OCC + RCH2CN C C C CN
R
HOH
OCC + HC CR C C C CR
OH
OCC + RC
O
O CR
ORC
O
O C C O CR
O
OCC + RC Cl
O
Cl C C O CR
O
Acetals
Acetoacetates
Acetonitriles
Acetylenes
Acid Anhydrides
Acyl Halides
Handbook of Epoxy Resins, Lee and Neville, McGraw-Hill Book Company, New York, NY, 1967.
Reactions of EpoxidesO
CC + R OH RO C C OH
OCC + R C
O
HBF3 C
C
O
O
CR
H
OCC + RC NH2
ORC
O
NH
C C OH
RC
O
NH
C C OH
OCC + RC
O
N
C C OH
C C OH
OCC + RNH2 HO C C NHR
HO C C N
R
C C OH
Alcohols
Aldehydes
Amides
Amines - primary
Handbook of Epoxy Resins, Lee and Neville, McGraw-Hill Book Company, New York, NY, 1967.
Reactions of Epoxides (continued)O
CC + R2NH HO C C NR
R OCC + R3N
H2O HO C C N RR R
OH
OCC + NH3 HO C C NH2
HO C C N
H
C C OH
HO C C N C C OH
C
C
OH
Amines - secondary
Amines - tertiary
AmmoniaCarboxylic acids
OCC + C CORC
O
OHRC
O
OH
Handbook of Epoxy Resins, Lee and Neville, McGraw-Hill Book Company, New York, NY, 1967.
Reactions of Epoxides (cont.)
OCC + RC
O
RC
C
O
OC
R
R OCC + H3PO4 O P
O
O
O
C
C C
C OH
OH
C OHC
OCC CH2 CH2 O CH2 CH2 O CH2 CH2 O
n - 2
OCC + H2O HO C C OH C OHCOCCHO
Ketones Phosphoric acid
Self - polymerization
Water
Handbook of Epoxy Resins, Lee and Neville, McGraw-Hill Book Company, New York, NY, 1967.
Epoxide Polymers
Polymers in which the epoxide ring plays a part either in polymer synthesis or curing
Most of the epoxides are based on the condensation products of bisphenol-A and epichlorohydrin
This reaction, known as the “Taffy” process, is used to produce lower molecular weight epoxides
Protective Coatings, Clive H. Hare
Ambient-Cure Coatings Baking FinishesAir drying esters Baking systems
Industrial baking finishes
Maintenance & Marine Container coatings
Coatings
Electrodeposition coatings
High solids maintenance
and marine coatings Decorative powder coatings
UV cure coatings Powder coatings for pipe
UV cure coatings Electrical insulation
Decorative powder coatings
Epoxide Polymers in Coating Science
DriersAmino-plast resins
Aminoplast and phenoplast resins
Polyamides, amine adducts
Fattyacids
Ketoimineamidoamines
Cationic initiators
Free radicalinitiators
Acrylicacids
Isocyanates
Acid functionalpolyester and acrylic resins
Acid anhydride
Dicyandiamide
EpoxidePolymer
Epoxyesters
Acrylateesters
Synthesis of DGEBA
Chlorohydrin intermediate
Diglycidyl ether of bisphenol A (DGEBA)
2 + HO CCH3
CH3
OH
ClCH2CHOH
CH2 O CCH3
CH3
O CH2 CHCH2ClOH
+ NaOH2
H2C CH CH2
OO C
CH3
CH3
+ NaCl2 + H2O
ClCH2CH CH2
O
O CH2 CH CH2
O
NaOH
Epoxide Polymers
n value Molecular E.E.W. Meltingweight Point oC
0 -1 350-600 170-310 < 401-2 600-900 310-475 40-702-4 900-1600 475-900 70-1004-9 1400-2900 900-1750 100-1209-12 2900-3750 1750-3200 130-150
O CH2 CHOH
CH2 OH2C CH CH2 OO
CCH3
CH3
CCH3
CH3
O CH2 CH CH2
O( )
n
Epoxide Polymers (cont’d)
Pure DGEBA is not available commercially as it tends to crystallize easily
Low molecular weight epoxides are a polydisperse mix of epoxides with “n” values between 0 and 1 and have an average molecular weight of 350-600
The higher molecular weight epoxides are synthesized by the “fusion” or “advancement” process using benzyl trimethylammonium hydroxide as a catalyst
R.A. Pearson, A.F. Yee, “Toughening mechanisms in elastomer-modified epoxies,” Journal of Materials Science, 2571-2580, 1989.
R.A. Pearson, A.F. Yee, “Toughening mechanisms in elastomer-modified epoxies,” Journal of Materials Science, 2571-2580, 1989.
“Fusion” aka “Advancement” Process
H2C CH CH2
OO C
CH3
CH3
O CH2 CH CH2
OHO C
CH3
CH3
OH+
O CH2 CHOH
CH2 OH2C CH CH2 OO
CCH3
CH3
CCH3
CH3
O CH2 CH CH2
O( )
n
CH2 N(CH3)3 OH+ -
“Fusion” Process (cont.)
Commercial bisphenol-A contains mono- and trifunctional byproducts which interfere with the linear structure of epoxide polymers
Hence, the “Fusion” process is preferred for preparing very high molecular weight epoxides due to the reduced likelihood of chain branching and unwanted increase in melting point and viscosity
Classes of Epoxide Resins
Low molecular weight
Medium molecular weight
High molecular weight
Very high molecular weight
Low Molecular Weight Liquid Epoxides
Liquid epoxides (n<1) are important in formulating zero and low VOC coatings for high performance applications
Two-pack systems with VOCs below 250 g/L (2.1 lb/gal) are commercially available
Cross-linkers with high equivalent weights such as amidoamines, polyamides, and polyglycol diamines are preferred to provide for flexibility
Medium molecular weight epoxides (n=2) are widely used as binders for two-pack amine and amide cured coatings
These polymers are normally available as 75% solutions in aromatic or ketone solvents with viscosities between 20-100 Poise
Amide cured epoxide coatings provide the best balance of properties with very good chemical resistance, hardness, flexibility, and adhesion
Medium Molecular Weight Epoxides
Pot lives varies from 1 hour to 24 hours depending on curing agents employed but dry-to-touch times are typically 4-8 hours.
Full cure may take up to 10 days for polyamide cured epoxide coatings
Applications include maintenance coatings for offshore oil rigs, bridges, aircraft primers, interior coatings for water and sewage treatment, concrete floor coatings, and swimming pool coatings
Medium Molecular Weight Epoxides (cont.)
High molecular weight epoxides (n=4) are used in the manufacture of epoxide esters
Epoxide esters are widely used in metal primers for appliances and automobiles and clear finishes for concrete floors
Linseed oil, DCO, and tall oil fatty acids are used in air-drying epoxide ester synthesis while coconut oil fatty acids are used for heat-curing epoxide esters
High Molecular Weight Epoxides
Epoxide esters are also classified according to their oil content as long, medium, and short oil epoxide esters like oil-modified polyesters
0.3-0.9 equivalents of acid per oxirane are used
This corresponds to 55-65% fatty acid modification for long oil esters and 30-45% fatty acid modification for short oil esters
High Molecular Weight Epoxides (cont.)
Epoxides with n = 4 are also used in dicyandiamide-cured powder coatings, cathodic electrodepositioncoatings, and in metal primers
Epoxides of n = 7 to 9 with high hydroxyl contents are used as co-reactants with:
Amino polymers Phenolic polymers in high temperature curing wire enamels, coil coatings, can coatings, and drum coatings Powder coating polymers for high build applications (>15 mils)
High Molecular Weight Epoxides (cont.)
“Phenoxy”™ polymers have very high melting points, produce very high viscosity solutions, and do not require curing agents to form useful films
They are sold either as solids or as dilute solutions (35% solids) in MEK or cellosolve acetate
Thermoplastic coatings based on these polymers have good flexibility, impact and abrasion resistance, chemical resistance and excellent adhesion, but poor resistance to solvents from which they are cast
Very High Molecular Weight Epoxides
PhenoxyTM polymers can be crosslinked with amino polymers, phenolics or isocyanates to improve their hardness and resistance to heat and chemicals, but flexibility and impact resistance are adversely affected
Isocyanate cured systems have been used for jet fuel tank linings
Very High Molecular Weight Epoxides (cont.)
Other Epoxide Polymers
Bisphenol F based
Multifunctional
Cycloaliphatic
Miscellaneous
Bisphenol F Epoxide Polymers
H2C CH CH2
OO O CH2 CH CH2
OCH2
The isopropylidene linkage and presence of only para-para isomer confer rigidity to bisphenol-A polymers.
Bisphenol-F has ortho-ortho, ortho-para, and para-para isomers along with a methylene linkage which produces more flexible polymers.
The presence of isomers in bisphenol-F also reduces the crystallization tendency and produces polymers with a lower viscosity than bisphenol-A.
Bisphenol F Epoxide Polymers
Resole SynthesisAlkaline conditions:
The reactions possible are - a) Methylolation:OH
CH2O+OH-
OH
CH2OH
OH
CH2OH+
Di- and tri-methylol phenols are also producedOH
CH2HO CH2 OH
2,6 di-methylol phenol
OH
CH2 OH
CH2 OH
CH2HO
2,4,6 tri-methylol phenol
OH
CH2 OH
CH2 OH2,4 di-methylol phenol
The greater mobility of bisphenol-F facilitates a higher degree of crosslinking than bisphenol-A polymers of similar molecular weight leading to a higher Tg, and better solvent and chemical resistance
The lower viscosity facilitates formulating of low VOC coatings with a high degree of chemical resistance
Bisphenol-F epoxide coatings are replacing bisphenol-A epoxide coatings in many applications
Bisphenol F Epoxide Resins (cont’d)
Multi-functional Epoxides
Multi-functional epoxides are used in extreme service condition systems to produce a crosslinked polymers with outstanding chemical resistance.
Examples of such epoxides are:Epoxide novolacsTetraglycidyl-1,1,2,2-(para-hydroxyphenol) ethaneTriglycidyl para-amino phenolTriglycidyl isocyanurate
Tetraglycidyl-1,1,2,2-(para-hydroxyphenol) ethane
O CH2 CH CH2O
OCH2CHH2CO
O CH2 CH CH2
OOCH2CHH2C
O
CH CH
O CH2 CH CH2
O
NCH2 CH CH2
OCH2CHH2C
O
NN
N
O
OOCH2 CH CH2
OCH2CHH2C
O
CH2
HC
H2CO
Trigylcidyl para-aminophenol Triglycidyl isocyanurate
Multi-functional Epoxides
Cycloaliphatic Epoxides
Cycloaliphatic epoxides differ from conventional bisphenol-A based epoxides in several ways:
All aliphatic React readily with acids but not with amine/amide type conventional epoxide curing agentsViscosity of 350 cPsExcellent weatherability
Cycloaliphatic Epoxides
O
O
OO
OO
O
O
O O
3,4-Epoxycyclohexylmethyl 3,4-epoxycyclohexane carboxylate
Bis-(3,4-epoxycyclohexyl) adipate
UVR-6105
UVR-6128
Miscellaneous Epoxides
Polyglycol epoxidesReplacing the bisphenol-A of conventional epoxides by polyoxyalkylene produces epoxides with all aliphatic structures, high flexibility and elongation, but also lower chemical, solvent and heat resistance properties
These epoxides are used as modifiers for conventional epoxides at levels up to 30 wt%
H2C CH CH2
OO CH2 CH
RO CH2CHCH2
OCH2 CH
RO
n
Cardanol based epoxidesCardanol (3-n-pentadecenyl phenol) is a major constituent of cashew nut shell liquid (CNSL)
Epoxidation is introduced via the phenolic hydroxyl or the unsaturation on the aliphatic chain
Miscellaneous Epoxides (cont.)
O CH2 CH CH2
O
(CH2)7 CH
CH3
(CH2)6
O CH2 CH CH2
O
Miscellaneous Epoxides (cont.)
Brominated epoxidesBrominated epoxides are used specifically in fire-retardant applicationsVarious levels of halogen substitution are feasible
O CH2 CHOH
CH2 O
Br
Br
H2C CH CH2 OO
CCH3
CH3
Br
Br
CCH3
CH3
Br
Br
O CH2 CH CH2
O
Br
Br
n
Epoxide Curing Agents
AminesKetimines
Amine adductsAromatic aminesAcid anhydridesAcrylics or PolyestersTGICAmino polymers
Amine Curing Agents
Primary and secondary amines are the most widely used curing agents for epoxides
Amine cured systems are employed as two-pack, ambient-cured coatings
The molecular weight of the amine, its nature, i.e., aliphatic/aromatic, primary/secondary/tertiary, controls the reaction rate and physical/chemical properties of the finished film
Protective Coatings, Clive H. Hare
Amine Curing Agents (cont.)
CH CH2O
RNH2 CH CH2
OHNHR
CH CH2O
CH CH2
OHNR
CH2 CHOH
+
Protective Coatings, Clive H. Hare
Amine Curing Agents (cont.)
Unmodified alkylene amines such as diethylenetriamine (DETA), triethylene tetramine (TETA), and tetraethylene pentamine (TEPA) were among the first amines used as curing agents
These amines cure exothermically and generate highly crosslinked films with excellent resistance properties but low flexibility
These amines have high vapor pressures and are skin sensitizers and respiratory irritants
Protective Coatings, Clive H. Hare
Handbook of Epoxy Resins by Lee H. and Neville K.
80
90
100
110
120
9 10 11 12 13
2
3
4
5
6
Def
lect
ion
tem
pera
ture
, oC
DETA
TETA
H2N CH2CH2 NH CH2CH2 NH2
H2N CH2CH2 NH CH2CH2 NH CH2CH2 NH2
phr of curing agent with DGEBA
Effect of Curing Agent Concentration on Epoxide Properties
Amine Curing Agents (Cont.)
Phenolic tertiary amines e.g. tris(dimethylaminomethyl) phenol, p-toluenesulfonicacid, salicylic acid and hydrogen bond donors such as phenol, alkyl phenols serve as catalysts for the epoxide-amine reaction
Hydrogen bond acceptors such as ethers, esters, and nitro groups act as retarders for this system
Ketones, especially acetone and MEK, form ketimineswith amines and hence act as retarders
Protective Coatings, Clive H. Hare
Epoxide Reactivity DataReactivity of DGEBA vs. Basicity of Tertiary Amine
Amine Ionization constant Gel time (hours)
Benzyldimethylamine 8.5 x 10-6 5.3Benzyldiethylamine 3.6 x 10-5 >300Triethylamine 6.4 x 10-4 11.2Tripropylamine 5.5 x 10-4 29Pyridine 2.3 x 10-9 54
Substituent Effects on Tertiary Amine Reactivity with DGEBAAmine Gel time, hours
Benzyldimethylamine 5.3Benzyldiethylamine >300Dimethylethanolamine 4.3Diethylethanolamine 17.2Triethylamine 11.2Tripropylamine 29Tributylamine 33Pyridine 54
Handbook of Epoxy Resins, Lee and Neville, McGraw-Hill Book Company, New York, NY, 1967.
Epoxide Reactivity Data (cont.)
N CH3N
CH3
N CH3CH3
2-Picoline4-Picoline 2,6-Lutidine>50011258
Handbook of Epoxy Resins, Lee and Neville, McGraw-Hill Book Company, New York, NY, 1967.
Aliphatic Amine Adducts (cont.)
KetiminesKetimine blocking has become important in the formulation of two-pack, high solids systems where the maintenance of low application viscosities are critical
H2N R NH2C OR1
R2
CR1
R2
N R N CR2
R1+
H2O
H2O
-
Protective Coatings, Clive H. Hare
Amine Curing Agents (cont.)
Unmodified amines react rapidly with atmospheric carbon dioxide and moisture to form carbamates that produce “blushing” on the film surface, especially at low temperatures and high humidities
H2O CO2 H2CO3
H2CO3 RNH2 RNHCOOH
RNHCOOH RNH2
+
+
+ O CC
NH
R-
RNH3+
O
Protective Coatings, Clive H. Hare
Amine induced blushing may be reduced by allowing an induction period after mixing the two components just before application
Amine Curing Agents (cont.)
Protective Coatings, Clive H. Hare
Amine Adducts
Epoxide-amineCyanoethylated aminePolyamidesAmido-aminesImidazolinesMannich basesPolyoxyalkyl amines
Aliphatic Amine Adducts
Epoxide amine adducts
H2C CH CH2
OO C
CH3
CH3
O CH2 CH CH2
OH2N R NH2+
CCH3
CH3
O CH2 CH CH2
OHNHRCH CH2 O
OHCH2RNH NH2H2N
2
Protective Coatings, Clive H. Hare
Aliphatic Amine Adducts (cont.)
Cycloaliphatic amines
Isophorone diamine, diamino cyclohexane, and 4,4-bis(p-amino cyclohexyl) methane are the commonly used cycloaliphatic amines with epoxides
H3C
H3C
NH2
H3C CH2NH2
CH2H2N NH2
NH2
NH2
Isophorone diamine Diaminocyclohexane
4,4-bis(p-amino cyclohexyl) methane
Protective Coatings, Clive H. Hare
Aliphatic Amine Adducts (cont.)
Cyanoethylated amines
These are less reactive than amines but have lower vapor pressure and higher equivalent weight which facilitates mixing in convenient volumesThese systems possess excellent chemical resistance and color, and cure satisfactorily under damp conditions to give blush-free films
H2C CH C NH2N R NH2
H2N R NH CH2 CH2 C N
+
Protective Coatings, Clive H. Hare
Aliphatic Amine Adducts (cont.)
PolyamidesLong chain fatty acid dimers derived from vegetable oils are reacted with slight excess of primary amines to synthesize polyamides
(CH2)7
C OOH
CHCHCH
CHCHCH
HCHC
(CH2)7 CO
OH
(CH2)5CH3 (CH2)5
CH3
H2N R NH2
(CH2)7
C O
CHCHCH
CHCHCH
HCHC
(CH2)7 CO
(CH2)5CH3 (CH2)5
CH3
R NH2NH
R NH2NH
+ 2
Protective Coatings, Clive H. Hare
Polyamide-epoxide systems are the workhorse of high performance protective coatings Increased distance between crosslinking sites produces films that are more flexible and impact resistant than films cured with aminesResistance to chemicals and solvents are lowered though water resistance and corrosion protection are enhancedThe higher molecular weight of polyamides also facilitates mixing in convenient ratiosAn induction period is necessary after mixing and before application
Aliphatic Amine Adducts (cont.)
Protective Coatings, Clive H. Hare
Amido-aminesAmido-amines are condensation products of an amine and a monofunctional fatty acid
Viscosity of amido-amines ranges from 2-6 Ps while polyamides have viscosities above 16 PsLow viscosity and low VOC coatings can thus be formulated using amido-aminesResistance properties of epoxide-amido-amine systems are lower than epoxide-polyamide systemsApplications include concrete coatings, floor coatings, and coatings designed for damp substrates
Aliphatic Amine Adducts (cont.)
CH3 (CH2)n COOH H2N R NH2 CH3 (CH2)n CO
NH R NH2+
Protective Coatings, Clive H. Hare
Aliphatic Amine Adducts (cont.)
ImidazolinesImidazolines are the condensation products of amines and monofunctional acids reacted at high temperatures
H2OH2O-
CH3 (CH2)n COOH
H2N (CH2)2 NH (CH2)2 NH2
+ CH3 (CH2)n CO
NH (CH2)2 NH (CH2)2 NH2
CH3 (CH2)n CN
N
CH2
CH2
(CH2)2 NH2
H2O H2O-
Protective Coatings, Clive H. Hare
Imidazoline formation is accompanied by loss of the reactive amine functionality
Imidazolines are utilized in low VOC formulations due to their low viscosity, good compatibility with epoxides, and high equivalent weights
Like amido-amines, imidazolines have reduced reactivity, reduced cross link density and lower resistance properties
Imidazolines are also used to extend the pot life of aliphatic and cycloaliphatic amine catalyzed epoxide systems
Aliphatic Amine Adducts (cont.)
Protective Coatings, Clive H. Hare
Aliphatic Amine Adducts (cont.)
Mannich basesAliphatic and cycloaliphatic amines are reacted with methylol phenols to yield Mannich bases
The functionality of the amine is reduced, but the phenolic hydroxyl acts as a catalystThese systems possess excellent adhesion and chemical resistance and can be applied and cured under damp and cold conditions (~0oC)
OH
CH2OH H2N R NH2+
OH
CH2NHRNH2
Protective Coatings, Clive H. Hare
Unmodified cycloaliphatic amines require high temperatures for reaction with epoxides
Modification involves use of acid accelerators such as salicylic acid (dissolved in benzyl alcohol)
Use of cycloaliphatic amines improves color retention on exterior exposure
These systems cure well in cold and damp conditions and exhibit good adhesion to damp surfaces
Aliphatic Amine Adducts (cont.)
Protective Coatings, Clive H. Hare
Polyoxylalkylene amines
Polyoxyethylene and polyoxypropylene amines are primary amine derivatives of polyethylene and polypropylene glycol
These amines react slowly and contribute considerable flexibility to the crosslinked film
The oxyalkylene structures provide considerable water sensitivity leading to inferior water and corrosion resistance
These amines are mostly employed as flexibilizing agents in conjunction with other curing agents
Aliphatic Amine Adducts (cont.)
Protective Coatings, Clive H. Hare
Aliphatic Amine Adducts (cont.)
H2N CH CH2
CH3
(OCH2CH)CH3
NH2n Polyoxypropylene diamine
H2N CH CH2
CH3
(OCH2CH)CH3
(OCH2CH2)CH3
NH2(OCH2CH)n m l
Diamine of mixed polyalkylene glycols
CH3 C CH2 (OCH2CH)CH3
NH23
Polyoxyalkylene triamine based on trimethylol propane
Protective Coatings, Clive H. Hare
Aliphatic Amines
CH2NH2
CH2NH2
CH2NH2
CH2NH2
m-xylene diamine 1,3 - bis (aminomethyl) cyclohexane
Aromatic amines generate crosslinked films with higher rigidity and brittleness due to the increased aromatic content
Resistance properties are also enhanced relative to the aliphatic amine cured epoxides
All aromatic amines are dark colored, irritating, and toxic by nature
Applications include concrete sewer pipe linings, flooring applications and chemical resistant tank linings
Aromatic Amines
NH2
NH2
m-phenylene diamine
CH2H2N NH2
4,4’ - methylene dianiline
H2N SO
ONH2
Diamino diphenyl sulfone
H2N CH2 NH2
H2N
2,4 -bis (para-aminobenzoaniline)
Aromatic Amines (cont.)
Aromatic Amines (cont.)
Some aryl diamines have amine groups removed from the ring by a methylene bridge
The methylene group enhances the reactivity of this class of amines providing rapid cure at ambient and sub-ambient temperatures
Hard, high gloss finishes are obtained with excellent chemical, water, and solvent resistance
These amines are also lighter in color and are less toxic than aromatic amines
Acid AnhydridesThe reaction of epoxides with anhydrides needs to be either acid or base catalyzed to facilitate the opening of the anhydride
In presence of acid catalysts, etherification reaction between epoxide molecules predominates and anhydride levels required drop to 55% of the stoichoiometric level
In presence of base catalysts, esterification reaction between the epoxide and anhydride ensues completely and stoichiometric levels of anhydrides are required for full cure
Curing temperatures are high, 1-2 hours at 200oC, as most anhydrides are solids and need to be melted
Anhydride cured systems have lower chemical resistance than the amine cured systems, but are less toxic, cure with lower exotherm, and have longer pot lives
These systems are used in casting and laminating applications, and in powder coatings
Acid Anhydrides (cont.)
Acid Anhydrides (cont.)
CC
O
O
O
Phthalicanhydride
CC
O
O
O
HOOC CC
O
O
O
CC
O
O
O
Trimelliticanhydride
Pyromelliticanhydride
CC
O
O
O
Hexahydrophthalic anhydride
Carboxylated Polymers
Epoxides will react with polymers containing carboxyl groups, such as acrylics and polyesters under base catalyzed conditions
Epoxides will also react with the hydroxyl groups in these polymers under acid catalyzed conditions
Curing temperatures are high, i.e. 175-200oC
TGIC-Polyester SystemsEpoxide (TGIC)-polyester systems are used extensively in powder coatings
NN
N
O
OOCH2
CH2
CH2
CH
CHCH CH2
CH2
O
O
H2CO
COOH
NN
N
O
OOCH2
CH2
CH2
CH
CHCH CH2
CH2
OH OH
OH
O
O
CH2O
C
CCO O
O+
Polyester
Amino Polymers
Epoxide polymers crosslink with amino polymers mainly through their secondary hydroxyl groups
Epoxide-amino polymer systems are widely used in coil coating primers and in beverage can coatings
Urea formaldehyde based systems cure faster or at a lower temperature than melamine formaldehyde based systems
Modified Epoxides
Acrylated epoxides
Coal tar modified epoxides
Epoxide esters
Diluents used with epoxides
Waterborne epoxides
Acrylated Epoxides
Acrylated epoxides are synthesized by reacting acrylic acid with low molecular weight bisphenol-A epoxides
These polymers are used to improve the chemical resistance, hardness and gloss of conventional acrylics
Applications include radiation cured coatings, inks, adhesives, and laminates
H2C CH CH2
OO C
CH3
CH3
O CH2 CH CH2
O
H2C CH COOH
O CH2 CH CH2
OHCCH3
CH3
O CO
CH CH2CH CH2 OOH
CH2OCO
CHH2C
Acrylated Epoxides (cont.)
Difunctional acrylated epoxide
2
Acrylated Epoxides (cont.)
H2C CH CH2
OO C
CH3
CH3
O CH2 CH CH2
OCH CH C
OOHC
ORO
O CH2 CH CH2
OHCCH3
CH3
O CO
CH CH CO
ORCH CH2 OOH
CH2OCO
CHCHCO
RO
CH CO
H2C Cl
O CH2 CH CH2
OCO CH CH2
CCH3
CH3
O CO
CH CH CO
ORCH CH2 OCH2OCO
CHCHCO
ROOCO CH CH2
+
Tetrafunctional acrylated epoxide
Coal Tar Modified Epoxides
Refined coal tar pitch is blended with epoxide-amine systems at levels of 1.5-3 times coal tar to epoxide-amine solids
While the exact mechanism occurring in the reaction is not clear, it has been proposed that the phenolic components of coal tar pitch react with the epoxides and also catalyze the epoxide-amine reaction
Medium hard grade coal tar pitches are preferred for use with epoxide systems for best chemical resistance
At higher levels of coal tar, resistance to water, corrosion and dilute acids improves
At lower levels of coal tar, hardness and resistance to solvent and alkalis improves
Coal Tar Modified Epoxides (cont.)
A disadvantage of these systems are their poor color and poor resistance to UV light
Being highly cohesive in nature, these systems require blast cleaned surfaces with a high surface profile for good adhesion
Coal tar epoxide systems have been used very effectively in buried, immersed, hidden, and similar difficult-to-access areas providing long-term service without much maintenance
Coal Tar Modified Epoxides (cont.)
Epoxide EstersOil Types Epoxide Ester Properties
Linseed Oil FA Fast air drying systems with poor color retention
DCO FA Fast air drying or heat cured systems with good flexibility and chemical resistance
Soybean FA Air drying systems with good color and soft flexible films
Coconut FA Non air drying systems with very good color, chemical resistance, and flexibility
With increasing fatty acid content:
Chemical resistance FlowFilm hardness Solubility in aliphaticDrying time hydrocarbon solventsAdhesion Water resistanceGloss retention FlexibilityCost Pigment wettingViscosity Exterior durability
Color retention
Epoxide Esters (cont.)
H2C CHO
CO
OH CO
O CH2 CHOH
+
CO
OH CHOH
CHO C
O
H2O+ +
Esterification
During these first two steps, viscosity rise is small corresponding to a large decrease in acid number
Epoxide Esters (cont.)
Etherification
CHOH
H2C CHO
CHO CH2 CH
OH
+
In order to produce commercially desirable low viscosity, low acid number esters, it is necessary to suppress the etherification while encouraging the esterification steps
Epoxide Esters (cont.)
They are similar to polyester polymers, yet they offer some superior film properties:
AdhesionFlexibilityChemical resistance
Overall properties are inferior to two-pack epoxide polymer films, but their advantages are:
Lower costBetter pigmentation propertiesLong shelf life
Epoxide Esters (cont.)
Applications of Epoxide Esters
Automotive primersAppliance primersFlexible tube coatingsDrum liningsMarine finishesFloor sealers and top coatsMetal decorating lacquersEnamels for hardware and metal furnitureIndustrial maintenance primers and topcoats
Epoxide-based Diluents
Mono- and di-functional epoxide diluents are employed to reduce the VOC of epoxide based formulations
Incorporation of such diluents lowers the hardness, chemical resistance, and heat resistance of coatings while flexibility may be improved due to a lower crosslink density
Epoxide-based Diluents (cont’d)
H9C4 O CH2 CH CH2
O
Butyl glycidyl ether Diglycidyl ether of neopentyl glycol
O CH2 CH CH2
OOCH2CHH2C
OCH2 C
CH3
CH3
CH2
CH3
O CH2 CH CH2
O
Cresyl glycidyl ether
O CH2 CH CH2
O
O CH2 CH CH2
O
Diglycidyl ether of resorcinol
CH2 CH CH2
OOC
OCR1
R2
R3
Glycidylneodecanoate
Acrylic Monomers
Acrylic monomers react readily with amines (by Michael addition) and hence when they are incorporated into an epoxide-amine system, they lower the crosslink density of the coating by reducing the amount of amine available for reaction with the epoxides
Acrylic monomers are lower in viscosity than low molecular weight epoxides which helps reduce the viscosity of epoxide coatings
Hexanediol diacrylate
(CH2)6 OO CO
CH CH2CO
CHH2C
CH3 CH2 CCH2
CH2
CH2
CH2CHOCO
CH2CHOCO
O CO
CH CH2
Trimethylolpropanetriacrylate
Acrylic Monomers (cont’d)
Non-reactive Diluents
Being non-reactive with the epoxides or its cross-linkers, these diluents serve to improve the flexibility of coatings, but solvent resistance, hardness, and heat resistance is lowered
Some common examples are:Coumarone indene copolymersPlasticizers such as butyl benzyl phthalate
CC
O
O
OC4H9
OCH2C6H5
Butyl benzyl phthalate
Non-reactive Diluents (cont’d)
2K Epoxy
Hardener is typically a polyamine or polyamide
O CH2 CHOH
CH2 OH2C CH CH2 OO
CCH3
CH3
CCH3
CH3
O CH2 CH CH2
O
Resin CO
NH RResin NH2 or
Epoxy Resin
+
ResinH2NEpoxy Resin CH2 CH CH2
O
Epoxy Resin CH2 CH CH2
OHNH Resin
+
Part A
Part B
2K Epoxy Properties
Toughness
Excellent adhesion
Commonly used as primers in the general metal industry
Waterborne Epoxides
Performance properties are lower than solventborne epoxides
Amine is used as surfactant
Epoxide is dispersed with surfactant in waterHigh concentration of surfactant
With all waterborne epoxide systems, viscosity increases are not a very reliable indicator of potlife as the crosslinking reaction takes place within a micelle
The gloss of waterborne epoxide systems begins to decrease with time once the crosslinking has proceeded beyond an unacceptable level in the can
This can lead to visibly distinct patches of different glosses especially on large architectural areas
Waterborne Epoxides
Advantages DisadvantagesNo organic solvents Short pot lifeEasy equipment cleaning Gloss stabilityExcellent adhesion Water evaporates slowlyExcellent interlayer adhesion Lower chemical resistCoating of plastics possible Wastewater treatment
Flash rust
Waterborne Epoxides (cont.)
Waterborne Epoxides: Type I
Epoxy resinLow molecular weightEquivalent weight ~190
Amine curing agentPolyaminesSalt is formed by reacting with acid
• Increased ability to form micelles
Amine curing agent
R NH3+
O CO
R"
Liquid epoxy resin
Amine hardener emulsifies epoxy resin
Part A Part B
Mixing justprior to use -
Waterborne Epoxides (cont.)
With liquid epoxides (EEW ~ 190):The curing agents - polyamines or polyamides are neutralized to form quarternary ammonium salts which can emulsify epoxide polymers when the two components are mixed together
Cosolvents, non-ionic surfactants, defoamers/anti-foaming agents constitute the rest of the formulation
Waterborne epoxides based on liquid epoxides are generally used as concrete and floor coatings because of their ability to cure on damp concrete
Ref: Van de Mark M., et al, APCJ, Jan 15, 1997
Waterborne Epoxides: Type II
Epoxy resinPre-emulsified using surfactants, shear and/or hydrophilic modification of the epoxyEquivalent weight is >1000
Amine hardenerMixed with the epoxy to form an emulsionMay be salted or used as straight amine
Michael Van De Mark and Kurt A. Kirby, Amer. Paint & Coat. Jour., 81 (15), 20-21, 1997.
Emulsified epoxy resin Aqueous phase amine
Waterborne Epoxides (cont.)
Epoxides of medium molecular weight (n ~ 2) have been rendered water soluble by reacting with hydrated maleinized fatty acids
H3C COOH
OO OCC
CHHC
H3C COOHHC CH
C CO
OO+
JOCCA, Novakov P. et al, 1993 (3) pp 111-115
H3C COOHHC CH
C CO
OO
H3C COOHHC CH
COOHHOOC
H2O
H2C CHO
CH2CHO
H2C CHOH
O CO
CH2CHOH
O CO H3C COOH
HC CH COOHH3C
HC CH COOH
COOH
+
Waterborne Epoxides (cont.)
JOCCA, Novakov P. et al, 1993 (3) pp 111-115
The modified epoxide is then dissolved in water along with a neutralizing agent such as triethylamine
Cosolvents are also added to provide better film coalescence
These modified epoxides have been found to be suitable for electro deposition and dipping applications
Waterborne Epoxides (cont.)
JOCCA, Novakov P. et al, 1993 (3) pp 111-115
Waterborne Epoxides
2K - do not require solvents for stabilityEpoxy is low MW; low equivalent weightUsed as concrete and floor coatingsDefoamers are important
Type I1K- need solvents for freeze-thaw stabilityEpoxy is higher MW; higher equivalent weightUsed for masonry coatings, metal primers, and architectural coatingsLonger pot life
Type II
Michael Van De Mark and Kurt A. Kirby, Amer. Paint & Coat. Jour., 81 (15), 20-21, 1997.
Development and Use of Waterborne Coatings for Rail Vehicles in Germany
J. Kruger, Journal of Protective Coatings and Liners, p. 30-38, September, 2000.
Maintenance coatings for passenger cars, rail cars, and locomotives is being done exclusively with waterborne coatings:
Primer: two-pack waterborne epoxy
Topcoat: two-pack waterborne polyurethane(Hydroxy polyester/acrylic hardened with polyisocyanate)
Development and Use of Waterborne Coatings for Rail Vehicles in Germany
J. Kruger, Journal of Protective Coatings and Liners,p. 30-38, September, 2000.
New locomotives, rail cars, and passenger cars are currently coated with solventborne coatings.
Next year waterborne coatings will be used for all new rail vehicles.
Primer: two-pack WB epoxy or PUIntermediate: two-pack WB epoxy or PUTopcoat: two-pack WB aliphatic PUAnti-graffiti: solventborne clearcoat
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