Coatings Technology Handbook Episode 2 Part 10 pot

Organic Pigments 78-378.3.1 Organic Blues 78.3.1.1 Copper Phthalocyanine Blue The major blue used within the coatings industry is copper phthalocyanine blue PB 15, with its usage far out

Trang 2

Organic Pigments 78-3

78.3.1 Organic Blues

78.3.1.1 Copper Phthalocyanine Blue

The major blue used within the coatings industry is copper phthalocyanine blue (PB 15), with its usage far outweighing other blues such as Indathrone blue (PB 60)

Phthalocyanines are planar molecules with a tetrabenzotetraazoporphin structure as shown in Figure 78.1 Manufacture is comparatively easy despite the superficial complexity of the phthalocyanine mole-cule Reaction of a phthalic acid derivative at temperatures approximating 190°C with a source of nitrogen such as urea and a metal or metal salt is usually all that is required to produce the appropriate metal phthalocyanine Molybdate, vanadates, and certain compounds of titanium have been found to be useful catalysts for this condensation reaction

Figure 78.2 illustrates the chemistry behind the production of copper phthalocyanine blue This condensation reaction results in the formation of copper phthalocyanine in a crude, nonpigmentary form The product has thus to be finished or conditioned to give the pigment grade of choice Typically crude phthalocyanine blue is characterized by a crystal size of the order of 50 µm, a purity in excess of 92%, and a poor pigmentary strength

Metal-free phthalocyanine blue (PB 16) is normally manufactured via the sodium salt of phthalonitrile Acid pasting is used to condition the crude and give the pigment

Copper phthalocyanine is commercially available in two crystal forms known as the α and β The α form is described by the designations Pigment Blue 15, 15:1, and 15:2 and is a bright red-shade blue pigment The β form is described as Pigment Blue 15:3 and 15:4 and is a bright green or peacock shade The α form is meta-stable and requires special treatment to stabilize the crystal against its tendency to

FIGURE 78.1 Structure of copper phthalocyanine blue (pigment blue 15).

FIGURE 78.2 Chemistry of copper phthalocyanine a Molybdate or vanadate.

N

N N

C

C C

C

Cu

O O

NH

NH NH

O

4

NH

O NH

NH

NH NH Urea

Heat

Copper Salt Catalysta Heat

Copper

N

N N

C

C C

C

Cu DK4036_book.fm Page 3 Monday, April 25, 2005 12:18 PM

Trang 3

78-4 Coatings Technology Handbook, Third Edition

revert to the more stable, green-shade β crystal If either of the unstable α crystal forms (PB 15 or 15:1)

is used with strong solvents, conversion to the β form will occur upon storage of the system Conversion from the α to the β form is usually accompanied by an increase in crystal size with subsequent loss of strength and shift to a greener hue

As stated earlier, copper phthalocyanine gives excellent service in most coatings applications, but there

is considerable variation between both the chemical and crystal types available

Pigment Blue 15 is an α crystal with the reddest shade of the types commonly available It is the least stable of the family and as such is often referred to as crystallizing red-shade (CRS) blue This crystal form cannot be used in any solvent containing systems

Pigment Blue 15:1 is also an α crystal, but chemical modifications have been made to stabilize the structure against crystallization Most commonly the molecule is chlorinated to the extent of introducing one chlorine molecule to give “monochlor” blue Another technique involves the use of a substituted phthalocyanine, added to the pigment at levels approaching 10 to 15%, that confers crystal stability to the system The monochlorinated grade is, as a consequence of the introduced chlorine atom, greener than the additive-stabilized crystal

Pigment Blue 15:2, described as “noncrystallizing nonflocculating” red-shade blue, is widely used within the coatings industry The product is an α crystal that is stabilized against both crystallization and flocculation using additive technology

Pigment Blue 15:3 represents the green-shade, β crystal phthalocyanine blue and, as it exists in the stable crystal form, it is less susceptible to crystallization Most commercial grades of Pigment Blue 15:3, however, contain from 4 to 8% of the α crystal, which will be adversely affected by strong solvent systems

A 100% β blue is too dull, opaque, and weak to be commercially attractive; hence, a proportion of the

α crystal is left in the system, contributing considerably to the attractiveness of the system

Pigment Blue 15:4 represents a β blue that has been modified with phthalocyanine-based additives to give a green-shade blue that is resistant to flocculation and can be used in strong solvent systems Copper phthalocyanine approximates the ideal pigment It offers strength, brightness, economy, and all-around excellent fastness properties Perhaps the pigment’s only disadvantages are its tendencies to change to a coarse, crystalline, nonpigmentary form in strong solvents and to flocculate or separate from white pigments when used in paints and lacquers

78.3.1.2 Miscellaneous Blues

Although the organic blues used in the coatings industry are primarily copper phthalocyanines, brief mention must be made of other blue pigments that find use in the coatings marketplace

Indanthrone blue, Pigment Blue 60, belongs to the class of pigments described as “vat pigments.” This pigment is expensive relative to copper phthalocyanine, and thus economic considerations are a limitation

to its widespread use Idanthrone blue is a very red-shade pigment with outstanding fastness properties Carabazole violet, Pigment Violet 23, is a complex polynuclear pigment that is a very valuable red-shade blue of high tinctorial strength The pigment possesses excellent fastness properties, and only its relatively high cost and its hard nature limit its more widespread use From an economic standpoint it costs approximately three times as much as phthalocyanine blue

The pigment is used as a shading component in high performance coatings that call for particularly red-shade blue

78.3.2 Organic Greens

78.3.2.1 Copper Phthalocyanine Green

The major green pigment used as a self shade in the coatings industry is based on halogenated copper phthalocyanine and, as such, is termed phthalocyanine green The Colour Index names are Pigment Green 7 and Pigment Green 36

DK4036_book.fm Page 4 Monday, April 25, 2005 12:18 PM

Trang 4

Pigment Green 7, the blue-shade green, is based on chlorinated copper phthalocyanine with a chlorine content that varies from between 13 to 15 atoms per molecule

Pigment Green 36, the yellower shade, is based on a structure that involves the progressive replacement

of chlorine on the phthalocyanine structure with bromine The composition of Pigment Green 36 varies with respect to the total halogen content, chlorine plus bromine, and in the ratio of bromine to chlorine Figure 78.3 illustrates the proposed structures of the phthalocyanine greens In practice, no single pigment consists of a specific-molecular species; rather, each pigment is a complex mixture of closely related isomeric compounds

These pigments are ideal, since their tinctorial and fastness properties allow their use in the most severe application situations They possess outstanding fastness to solvents, heat, light, and outdoor exposure They can be used in masstone shades and tints down to the very palest of depths

Phthalocyanine greens are manufactured by a three-step process: crude phthalocyanine blue is first manufactured, then halogenated to give a crude copper phthalocyanine green, and finally conditioned

to give the pigmentary product

78.3.2.2 Miscellaneous Greens

may find some minor application in the coatings industry

FIGURE 78.3 Structure of copper phthalocyanine greens.

C

C C

C

C C

Cu Br

Br Br

Br Cl

Cl

Cl Cl

C C

N N

C

C C

C

C C

Cu Br

Br Br

Cl

Cl Cl

Br Br

C C

N N

Pigment Green 36 (Bluest shade also known

as 3y)

C

C C

C

C C

Cu Cl

Cl Cl

Cl

Cl Cl

Cl

Cl Cl

C C

N

N Pigment Green 7

Pigment Green 36 (yellowest shade also known as 6y) DK4036_book.fm Page 5 Monday, April 25, 2005 12:18 PM

Table 78.2 gives a summary of the properties of some other commercially available organic greens that

Trang 5

FIGURE 78.4 Structure of azo-based oranges.

NO2 N

N

C C CH

N HO

NO2

HO

Cl

SO3−

N N HO

Orthonitroaniline Orange

PO 2

PO 5

PO 13

PO 16

PO 34

PO 38

PO 46

Dinitroaniline Orange

N C

COCH3

CH3

CH3 Pyrazolone Orange

2

N

N N

C CH

CH3

H3C

H2N

2

NH C O

C O

C NH O

N N CH

Dianisidine Orange

Tolyl Orange

Naphthol Orange

H5C2

Clarion Red

Ba 2+

2

Trang 6

latex-based paints and, with the exception of high bake enamels, in both architectural and industrial coatings

Pigment Orange 13, Pyrazolone Orange, is synthesized by coupling tetrazotized 3,3-dichlorobenzidine onto 3-methyl-1-phenyl-pyrazol-5-one The pigment is a bright, clean yellow-shade product that

is tinctorially stronger than Pigment Orange 5 It may be recommended for interior coatings, particularly as a replacement for lead-based oranges

Pigment Orange 16, Dianisidine Orange, is a diarylide orange that is prepared by coupling tetrazotized 3,3-dimethoxybenzidine onto acetoacetanilide The pigment finds use in baking enamels, since its heatfastness is superior to that of other orange pigments with similar economics Usage in interior coatings at full tone levels is also recommended

Pigment Orange 34, Tolyl Orange, is produced by coupling tetrazotized 3,dichlorobenzidine onto 3-methyl-1-(4-methyl-phenyl)-pyrazo-5-one The pigment is a bright, reddish orange that offers moderate lightfastness and good alkali resistance, but poor solvent fastness As such, the material

is used in interior coatings applications, particularly where a lead-free formula is specified

3-amino-4-chloroben-zamide onto 4-acetamido-3-hydroxy-2-napthanilide The pigment is a bright reddish orange that exhibits excellent alkali and acid fastness, moderate solvent fastness, and acceptable light-fastness when used at full tint As such, the pigment finds use in baking enamels, latex, and masonry paints

Pigment Orange 46, Clarion Red, is a metallized azo pigment manufactured by coupling diazotized 2-amino-5-chloro-4-ethylbenzene-sulfonic acid onto β-napthol and metallizing the product with barium to yield the pigment The pigment has poor lightfastness, inferior alkali resistance, and inadequate solvent fastness, hence is not recommended for use in coatings

78.3.3.2 Benzamidazolone-Derived Oranges

The three benzimidazolone-derived oranges contain the azo chromophore and are all based on the 5-acetoacetylaminobenzimidazolone as the coupling component

Pigment Orange 36 is the product of coupling diazotized 4-chloro-2-nitroaniline to the benzimida-zolone Pigment Orange 60 is the product of the coupling of 4-nitroaniline to the benzimidabenzimida-zolone Because of the proprietary nature of this product, the structure of Pigment Orange 62 has not been fully declared (Figure 78.5 illustrates two typical structures):

Pigment Orange 36 is a bright red-shade orange of very high tint strength The opacified form of this pigment offers excellent fastness properties to both heat and solvents and a hue similar to the lead containing pigment, Molybdate Orange (PO 104) As such, Pigment Orange 36 finds major use

in lead-free automotive and industrial high performance coatings

FIGURE 78.5 Structure of the benzimidazolone oranges.

C

Cl

H

N H

H N N

NO2 H3 C

PO 36

PO 60

O

C

NO2

H

N H

H N N

H3C O

O

O Benzimidazolone Orange

Trang 7

Pigment 60 is a transparent, yellow-shade orange that also exhibits excellent heat and solvent fastness with an exterior durability that allows the pigment to be used in high quality industrial and automotive finishes

Pigment Orange 62 is also a yellow-shade orange that shares the lightfastness properties of the other two oranges Currently it is used in oil-based inks and artists’ colors Its use in the coatings industry has yet to be fully explored

78.3.3.3 Miscellaneous Oranges

The structures of Pigment Orange 53, a pyranthrone, Pigment Orange 64, a heterocyclic hydroxy, and Pigment Orange 67, a pyrazoloquinazolone, have not been fully declared Table 78.4 summarizes the properties of this class of pigments, which represents a series of oranges that are finding increased application in the coating industry

78.3.4 Reds

78.3.4.1 Metallized Azo Reds

Many of the reds used in the coatings industry fall into the chemical category of azo pigments because the azo chromophore —N=N— is a feature of the molecule

A further subdivision may be made into acid, monazo metallized pigments such as Manganese Red 2B (PR 48:4) and Calcium Lithol (PR 49:2) and nonmetallized azo reds such as the Naphthols (e.g PR 17 and PR 23) and Toluidine Red (PR 3) Typically, each of the acid, monoazometallized pigments contains

an anionic grouping such as a carboxylic (—COOH) or sulfonic acid (—SO3H) group, which will ionize and react with a metal cation such as calcium or manganese to form an insoluble, metallized pigment Nonmetallized pigments do not contain an anionic group in their structure and, as such, will not complex with a metal cation

All azo reds contain one or more azo groups and are produced by similar reaction sequences The initial reaction sequence, described as diazotization, involves reacting an aromatic primary amine with nitrous acid, formed in situ by reacting sodium nitrite with hydrochloric acid at low temperatures to yield a diazonium salt Invariably the diazonium salt that is formed by this process is unstable and should

be kept cold to avoid any decomposition

The diazonium salt is reacted quickly with the second half of the pigment, which is called the coupler The coupling reaction takes place rapidly in the cold to yield the sodium salt of the pigment This sodium salt is all but useless as a pigment for the coatings industry because of its marked tendency to bleed even

TABLE 78.4 Summary of the Properties of the Miscellaneous Oranges

Colour Index Name Common Name/Description Properties

PO 43 Perinone Red shade, strong, clean, vat pigment with excellent fastness

properties; used in metallized finishes and high grade paints; shows slight solvent bleed

PO 48 Quinacridone Gold Yellow shade; excellent lightfastness; lacks brightness in masstone;

used in metallic finishes

PO 49 Quinacridone Deep Gold Red shade; dull masstone; excellent durability; used in metallics

PO 51 Pyranthrone Orange Medium shade; excellent fastness to solvent, light, and heat; dull in

tin; exhibits slight solvent bleed; used in air dry and bake enamels

PO 52 Pyranthrone Orange, red

shade

Vat pigment with excellent fastness to solvent, light, and heat; dull

in tints; slight solvent bleed; used in air dry and bake enamels

PO 61 Tetrachloroisoindolinone

orange

Medium shade; exhibits some solvent bleed; used in metallic automotive finishes

PO 64 Bright shade red Excellent solvent and lightfastness; used in industrial coatings

PO 67 Yellow shade Excellent brilliance in full shade; good gloss retention; very good

weather- and lightfastness in full shade; used in industrial and automotive coatings

Trang 8

in the weakest of solvent systems The pigment is, therefore, metallized to confer improved properties

on the product The pigment suspension is then filtered and washed to remove any residual inorganics derived from the reaction

Figure 78.6 illustrates the structures of the different metallized azo reds that are readily available The Lithol Reds are primarily Barium Lithol (PR 49:1) and Calcium Lithol (PR 49:2) Although limited

in their application in the coating industry, these pigments do find some use at masstone levels — that

is, the pigment is not tinted with a white tint base — where their fastness properties are acceptable The pigments are bright reds with high tint strength and good dispersion characteristics The barium salt is lighter and yellower in hue compared to the calcium salt

(PR 48:2), and Manganese Red 2B (PR 48:4) The major use of the calcium and barium salts is in baked industrial enamels, which are not required to be fast to outdoor exposure Use in alkaline systems is severely restricted because of the poor alkaline fastness of these salts

FIGURE 78.6 Metallized azo reds.

Lithol Rubine Add Cl

CH3

N

HO COO −

N

SO3−

CH3

N

HO COO −

N

SO3−

PR 57

PR 48

PR 52

Cl

HO COO −

N

SO3−

Cl

PR 200

PR 53

PO 46

C2H5

N

HO COO −

–COO− Subtract–COOH N

SO3−

Cl

C2H5

C2H5 N

HO N

SO3−

Cl

CH3

N

HO N

SO3−

Cl

C2H5 Bon Red

Exchange Positions

CH3

Methylene (—CH2—) Addition

Clarion Red

Subtrat CH2

Red Lake C

Cl Red 2B

Trang 9

The barium salt is characterized by a clean, yellow hue and, although slightly poorer than the bluer calcium salt in lightfastness and tinting strength, it does possess a slight advantage in bake stability Manganese Red 2B has a sufficiently improved lightfastness to be used in implement finishes The manganese salt is slightly bluer, dirtier, and less intense when compared to the calcium salt

exhibiting the high tinting ability typical of the azo reds of this class Its major use in coatings is in interior systems that call for an inexpensive red with good solvent and heat resistance Again, to maintain maximum fastness properties, use of the pigment at near to masstone levels is recommended

by outstanding cleanliness, brightness, and purity of color The manganese salt offers a very blue-shade red with improved lightfastness compared to the calcium salt As such, this salt is suitable for exterior coatings applications

considerably more importance than either the calcium or barium salts Its lightfastness is such that the pigment can be used at masstone levels for implement finishes

78.3.4.2 Nonmetallized Azo Reds

As implied by their classification, the nonmetallized azo reds do not contain a precipitating metal cation and, as such, offer increased stability against hydrolysis in strongly acidic or alkaline environments Synthesis of this class of pigment follows the previously described classical method of diazotization of

a primary aromatic amine followed by coupling of the resultant diazonium salt No anionic groups capable of accepting a metal cation are present in the molecule; thus metallization is not a factor in their synthesis Typical nonmetallized reds are Toluidine Red (PR 3) and the wide range of Napthol Reds as represented by Pigment Reds 17, 22, and 23

Toluidine Red is used in full shade in such coatings applications as farm implements, lawn and garden equipment, and bulletin paints, where a bright, economical red of adequate lightfastness is required Because of the pigment’s poor durability in tint shades, it is rarely used at any level other than a full shade The individual properties of the Napthol Reds depend on the specific composition of the product as well as the conditioning steps used during pigment manufacture As a class, they are a group of pigments that exhibit good tinctorial properties combined with moderate fastness to heat, light, and solvents Unlike the metallized azo reds, the Napthol Reds are extremely resistant to acid, alkali, and soap These properties lead to their use in latex emulsion systems and masonry paint

In terms of performance and economic characteristics, the Napthols form a link between the toluidine reds at the lower end of the scale and the perylene and quinacridone reds at the higher end

78.3.4.3 High Performance Reds

Pigments for the exacting standards of today’s automotive coatings are required to show satisfactory durability to outdoor exposure in such states as Arizona and Florida for 2 and possibly 5 years before being approved for use in automotive finishes Similar requirements are placed on pigments chosen for use in automotive repair systems and marine coatings

FIGURE 78.7 BON maroon.

N

HO COO −

Ca 2+

N

SO3− DK4036_book.fm Page 11 Monday, April 25, 2005 12:18 PM

Trang 10

High performance reds fall into four basic classes: quinacridone reds and violets, reds based on vat dyestuffs known to include the perylene reds, reds derived from the benzimidazolone diazonium salts, and the disazo condensation reds

78.3.4.3.1 Quinacridone Reds

Quinacridones may be described as heterocyclic pigments in that their structure comprises a fused ring structure in which the ring atoms are dissimilar In the case of quinacridones, the ring atoms are carbon and nitrogen (Figure 78.8) Addition of differing auxochromic groups such as methyl (—CH3) and chlorine (—Cl) gives Pigment Red 122 and Pigment Red 202, respectively

The two most commercialized routes in the synthesis of quinacridone (PV 19) involve either the oxidation of dihydroquinacridone or the cyclization of 2,5-diarylaminoter-ephthalic acid as outlined in Figure 78.9 Subsequent conditioning leads to the desired crystal modification Use of

2,5-diarylamino-FIGURE 78.8 Structure of translinear quinacridone.

FIGURE 78.9 Routes to quinacridone.

C N H

N H O

C O

A Cyclization of 2, 5-diarylaminoterephthalic Acid

CH2COOC2H5

CH2 COOC2H5

(i) cyclization (ii) + aniline (iii) oxidation NH

NH COOC2H5

COOC2H5

C2H5OOC

Ring Closure

in Polyphosporic Acid

C N H

N H

O C

C

N H

N H H H

O

C O

O

O O

COOH

N

oxidation

trans linear quinacridone

B Oxidation of dihydroquinacridone

Định dạng
Số trang	18
Dung lượng	450,24 KB