Coatings Technology Handbook Episode 2 Part 8 potx

72-4 Coatings Technology Handbook, Third Edition72.4.1.2 Acetal The most effective mold release agents in acetal are fatty amides in general and fatty bisamides amides in particular.. Ot

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72-4 Coatings Technology Handbook, Third Edition

72.4.1.2 Acetal

The most effective mold release agents in acetal are fatty amides in general and fatty bisamides amides

in particular Ethylene bisoleamide shows 25.1% reduction of mold release force at 5000 ppm but causes

a visible darkening of the resin during processing Ethylene bisstearamide, a saturated amide, is nearly

as good, showing 23.3% reduction at a level of 5000 ppm; it does not cause any color problems Other secondary amides, such as stearyl stearamide and stearyl erucamide, give mold release improvement nearly as good as the bisamides (see Table 72.3) Primary amides such as erucamide, oleamide, and stearamide also show good mold release enhancement in acetal

None of the nonamide materials examined has the mold release effectiveness of the amides The best ester mold release agent is cetyl palmitate, which exhibited a 16.5% reduction in mold release force at a

5000 ppm treatment level

The optimum amount of ethylene bisstearamide is 5000 ppm When used above that level, there is little increase in effectiveness; below that amount, the maximum effectiveness is not reached

The use of fatty amides as mold release agents has negligible effect on mechanical properties (see Table 72.4)

72.4.1.3 Polybutylene Terephthalate

Fatty bisamides are the best mold release agents in polybutylene terephthalate (PBT) Both saturated and unsaturated bisamides show about 10% reduction of ejection force when used at a level of 5000 ppm The bisoleamide, however, causes some darkening of the resin during processing (see Table 72.5)

TABLE 72.3 Effectiveness of Mold Release Agents in Acetal Release Agent Level (ppm) Reduction of Ejection Force (%)

N,N′ -Ethylene bisstearamide 7500 26.0

N,N′ -Ethylene bisoleamide a 5000 25.1

a Causes resin to darken during processing.

TABLE 72.4 Mechanical Properties of Acetal with N,N′ -Ethylene Bisstearamide Present

Property

N,N′ -Ethylene Bisstearamide (ppm)

Tensile strength at yield, psi 9965 9883 9818 Elongation at break, % 36 39 41 Izod impact, ft-lb/in 1.30 1.32 1.35

TABLE 72.5 Effectiveness of Mold Release Agents in PBT Release Agent Level (ppm) Reduction of Ejection Force (%)

N,N′ -Ethylene bisoleamide 5000 9.8

N,N′ -Ethylene bisstearamide 5000 9.4

a May cause resin to darken during processing.

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

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Nonmetallic Fatty Chemicals as Internal Mold Release Agents in Polymers 72-5

Other mold release agents, such as fatty esters, amines, and acids, are not as effective as the amides

do not show any more effectiveness than 5000 ppm

The use of fatty amides as mold release agents in PBT has negligible effect on mechanical properties when tested at room temperature (see Table 72.6)

72.4.2 Polyolefins

72.4.2.1 Polypropylene

Glyceryl monostearate (GMS) has been found to be the best mold release agent in polypropylene At a level of 2500 ppm, GMS shows about 24% reduction of mold release force The reduction in mold release

Other glyceryl monoesters have also been tested, and only glyceryl monolaurate is as good a mold release agent as GMS In addition to glycerol esters, ethylene glycol distearate and monostearate, cetyl palmitate, and methyl stearate have been examined None is as good as GMS

The results of these experiments indicate that the greater the amount of free hydroxyl in the ester, the more effective the mold release agent, up to a certain amount Perhaps the hydroxyl groups make the additive less soluble in the resin, thus making it exude more to the surface After a certain amount of hydroxyl has been reached, the migration to the surface reaches a maximum and further increases do not further enhance migration

reduction of mold release force when used at a level of 5000 ppm This amount of reduction is comparable

to GMS, although the GMS is used at a lower level

The use of glyceryl monostearate or erucamide as mold release agent in polypropylene has a negligible

72.4.2.2 High-Density Polyethylene

The best mold release agent in high-density polyethylene (HDPE) is erucamide At a level of 2500 ppm

it shows a mold release force reduction of about 22% Other primary amides are also fairly effective as

TABLE 72.6 Mechanical Properties of PBT with N,N′ -Ethylene Bisstearamide

Property

N,N′ -Ethylene Bisstearamide (ppm)

Tensile strength at yield, psi 9640 8664 8840 Elongation at break, % 299 249 227 Izod impact, ft-lb/in 1.00 1.05 1.030

TABLE 72.7 Effectiveness of Mold Release Agents in Polypropylene Release Agent Level (ppm) Reduction of Ejection Force (%) Glyceryl monostearate

45% α -monoester 2500 23.9 60% α -monoester 2500 23.8 90% α -monoester 2500 22.4 Glyceryl distearate

12% α -monoester 2500 15.9

Fluorocarbon spray-on — 23.1

Fatty amides also show some utility as mold release agents in polypropylene Erucamide shows 25.8%

effect on the mechanical properties (see Table 72.8)

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Nonmetallic Fatty Chemicals as Internal Mold Release Agents in Polymers 72-7

72.5 Conclusions

It has been shown that it is possible to measure qualitatively the effectiveness of internal mold release agents in injection molding Numerous fatty chemicals were tested in polyolefins and engineering resins The chemical type that is the most effective mold release agent in a particular resin varies widely with resin type The required mold release pressure can be reduced for each of these resins without a significant change in the mechanical properties of the resin One or more preferred mold release agent has been suggested for each resin

Acknowledgment

Some of the information in this chapter is covered under an existing patent and a pending patent

TABLE 72.11 Effectiveness of Mold Release Agents in LLDPE Release Agent Level (ppm) Reduction of Ejection Force (%)

Ethoxylated tallow amine 2000 30.9 Ethoxylated oleyl amine 2000 29.6 Glyceryl monostearate 2000 26.0

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73 Organic Peroxides

73.1 Introduction 73-1 73.2 Types and Properties 73-1 73.3 Application in Coatings 73-4 73.4 Safety Factors and Producers 73-5 73.5 Future Trends 73-5 References 73-5

73.1 Introduction

Organic peroxides are derivatives of hydrogen peroxide, HOOH, wherein one or both hydrogens are

homolytic cleavage of the labile oxygen–oxygen bond to produce two free radicals:

(73.1)

depending on the nature of the R groups In addition to thermal decomposition, certain organic peroxides can be decomposed by activators or promoters at temperatures well below the normal decomposition temperature

A major application of these compounds is as free radical initiators in the polymerization of vinyl and diene monomers in the plastics and coatings industries They are also used as cross-linking and modifying agents for polyolefins, as vulcanizing agents for elastomers, and as curing agents for polyester resins

73.2 Types and Properties

Peroxide manufacturers now offer over 50 different organic peroxides in more than 100 formulations including dilutions in solvents, pastes, and filler-extended grades In most cases, these formulations are designed for specific applications and to allow shipping and handing with a reasonable degree of safety peroxides are commonly reported in terms of half-life (t1/2) temperature, that is, the time at which 50%

of the peroxide has decomposed at a specified temperature Table 73.1 lists the 10-hour t1/2 temperature ranges for the major organic peroxide types Peroxides of certain types, such as hydroperoxides and ketone peroxides, are primarily used in combination with promoters and are employed at temperatures

ROOR′ →∆RO⋅+ ⋅OR′

Peter A Callais

Pennwalt Corporation

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15 t-Amyl Peroxides (product bulletin), Lucidol Division, Pennwalt Corporation, Buffalo, NY, 1985

16 M Takahashi, Polym Plast Technol Eng., 15, 1 (1980)

17 L W Hill and Z W Wicks, Jr., Prog Org Coat., 10, 55 (1982)

Elsevier Applied Science, 1987, p 69

20 C J Bouboulis, U.S Patent 4,739,006 (1988)

21 D Rhum and P F Aluotto, U.S Patent 4,075,242 (1978)

22 Y Eguchi and A Yamada, U.S Patent 4,687,882 (1987)

23 W R Berghoff, U.S Patent 4,716,200 (1987)

24 R A Gray, J Technol., 57(728), 83 (1985)

25 R Buter, J Technol., 59(749), 37 (1987)

26 D Rhum and P F Aluotto, J Technol., 55(703), 75 (1983)

27 V R Kamath and J D Sargent, Jr., J Coat Technol., 59(746), 51 (1987)

28 V R Kamath, U.S Patent pending

29 F M Merrett, Trans Faraday Soc., 50, 759 (1954)

31 J Sanchez, U.S Patent 4,525,308 (1985)

32 A J D’Angelo and O L Mageli, U.S Patents 4,304,882 (1981), 3,952,041 (1976), 3,991,109 (1976),

3,706,818 (1972), and 3,839,390 (1974)

33 A J D’Angelo, U.S Patent 3,671,651 (1972)

34 R A Bafford, U.S Patent 3,800,007 (1974)

35 R A Bafford, E R Kamens, and O L Mageli, U.S Patent 3,763,112 (1973)

36 O L Mageli, R E Light, Jr., and R B Gallagher, U.S Patent 3,536,676 (1970)

37 H Ohmura and M Nakayama, U.S Patent 4,659,769 (1987)

38 C S Sheppard and R E MacLeay, U.S Patents 4,042,773 (1977) and 4,045,427 (1977)

39 T N Myers, European Patent Appl., 223,476 (1987)

40 P A Callais, V R Kamath, and J D Sargent, Proc Water-Borne Higher Solids Coatings Symp., 15,

104 (1988)

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74 Surfactants for Waterborne Coatings

Applications

74.1 Introduction 74-1 74.2 Chemistry 74-1 74.3 Theory 74-2 74.4 Foam Control 74-3 74.5 Wetting 74-4 74.6 Conclusion 74-5

As governmental regulations become increasingly restrictive, waterborne coatings appear to be the logical choice for many paint manufacturers However, the technological switch from solvent to waterborne systems requires an understanding of the challenges that lay ahead with respect to wetting, foam control, and coverage over difficult-to-wet substrates

This chapter will help explain the important contribution of wetting agents and defoamers to the emerging technology of waterborne coatings Topics will include the chemistry of several surfactants along with a thorough analysis and understanding of surface tension Surface tension reduction and mechanisms relating to foam stabilization will be reviewed

74.2 Chemistry

All surfactants fall into two classifications, nonionic and ionic Within the ionic category, surfactants can

be further subdivided into anionic, cationic, or amphoteric types For coatings, most surfactants utilized are either nonionic or anionic For wetting agents, the products we will compare include alkylphenol ethoxylates, sodium dioctyl sulfosuccinates, sodium laurel sulfates, block copolymers of ethylene and propylene oxides, alkyl benzene sulfonates, and, finally, a specialty class called acetylenic glycols We start with this

Acetylenic glycols are a chemically unique group of nonionic surface active agents that have been especially designed to provide multifunctional benefits to a wide array of waterborne coating products Two key benefits include an unusual combination of wetting and foam control properties

adjacent hydroxyl groups, and four symmetrical methyl groups Based on acetylene chemistry, this product is unlike any other surfactant molecule The combination of the triple bond and the two hydroxyl groups creates a domain of high electron density, making this portion of the molecule polar and thus

Samuel P Morell

S P Morell and Company

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75 Surfactants, Dispersants, and Defoamers for the Coatings, Inks, and Adhesives Industries

75.1 Introduction 75-1 75.2 Wetting and Dispersing Process 75-2

75.3 Silicones and Surface Flow Control Agents 75-6

75.4 Defoaming Additives 75-9

75.5 Conclusion 75-12 References 75-12

Over the history of coatings, inks, and adhesives, many evolutionary changes have occurred; not only have the ingredients used to make the formulations been changed, but also the physical characteristics

of the formulations along with their application, cure, and performance parameters have changed

Of course, each trend poses challenges to both raw material suppliers and formulators alike Because additives are used to enable and enhance system performance, the evolution of resins, pigments, solvents, and application technologies pose special challenges for additive suppliers

Resin and solvent combinations used in the good old days were typically quite low in surface tensions

in comparison to modern formulations Today’s more environmentally friendly formulations with little

or no solvents, or in the case of aqueous formulations, with little or no cosolvents, require increased use

of interfacially active materials in order to provide adequate substrate wetting, surface flow, and the prevention of foaming and air entrapment

John W Du

BYK-Chemie USA

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Surfactants, Dispersants, and Defoamers 75-5

Controlled flocculation means that pigments and extenders are stabilized as defined and selectively interactive units or groups of multiple particles Rheology will be modified to exhibit thixotropic behavior, resulting in improved resistance to settling and sagging A coating system stabilized in this manner will also be more resistant to flooding or floating

75.2.4.1 Deflocculating Additives

Depending on the actual ingredients of a given formulation, wetting and dispersing behavior can be tailored on a case-by-case basis One of the more important parameters is the pigment’s surface polarity Highly polar pigment surfaces generally require the use of lower molecular weight polymeric additives, whereas nonpolar pigment surfaces require higher molecular weight species

Deflocculating additives possess at least one pigment affinic group Higher molecular weight defloc-culating additives generally have multiple pigment affinic groups, arranged in such a manner that all of the groups are available for adsorption onto a pigment particle’s surface

Following additive adsorption, the binder-compatible molecular chains of the additive can then extend into the liquid binder Enveloping the pigment particles with additive and preventing direct pigment–pig-ment contact, these binder-compatible chains of the deflocculating additive, in conjunction with the binder, are responsible for steric hindrance In the case of incompatibility between the molecular chins

of the deflocculating additive and the binder, the molecular chains cannot extend into the liquid phase but rather coil, thus failing to provide sufficient spacing and adequate steric hindrance

Deflocculation generally leads to more efficient pigment utilization, which (especially in the case of some rather expensive organic pigments) is not, economically, unimportant The degree of deflocculation

or flocculation greatly impacts the developed shade or tint of a pigment If, for example, a system tends

to settle during storage, then color shifts may occur In situations where this is especially critical (such

as in the base components of a mixing system), the only acceptable method for producing coatings with

a constant and defined color and shade is the complete deflocculation method as described below

A new group of additives has been recently developed — high molecular weight polymeric wetting and dispersing additives Such additives provide complete deflocculation and, consequently, differentiate themselves from their conventional low molecular weight analogs through molecular weights sufficiently high to allow these additives to have resin-like characteristics Additionally, these new additives contain

a considerably higher number of pigment-affinic groups per molecule Because of these structural features, such additives can form durable adsorbed layers onto many organic pigments Stabilization arises, in part, from steric hindrance (exactly as with the conventional products) in which well-solvated polymer chains are utilized; however, optimal stabilization is possible only when such polymer chains are properly uncoiled (fully extended) and highly compatible with the surrounding resin solution If this compatibility is compromised (by resin or solvent composition changes), the polymer chains collapse Consequently, particulate spacing, steric hindrance, and dispersion stabilization are lost

75.2.4.2 Controlled Flocculation Additives

If the pigment affinic groups are not confined to a small region of the additive molecule but rather are distributed in a specific fashion over the entire molecule, then such an additive will be capable of simul-taneously contacting two or more pigment particles in a bridge-like fashion, and controlled flocculation results At this point, it is important to clarify the difference between the above condition of controlled flocculation and the normal flocculated state Without additives, the pigment particles make direct contact with one another in uncontrolled flocculation In contrast, no direct pigment-to-pigment contact occurs

in controlled flocculation; additive molecules are always present between the pigment particles

Ordinary flocculation without additive (resulting in direct pigment-to-pigment contact) is not control-lable Such a flocculated coating will exhibit batch-to-batch variation in properties such as color and shade

or perhaps even shelf life; unpredictable nonrecoverable settling and sedimentation occurs during storage Controlled flocculation provides a means for particulates to associate with each other without actually coming in contact This association allows large domains of controlled flocculates to move as a single unit while maintaining the individual particle-to-particle spacing that is required for stability This type

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required to draw a defined mass across the coating’s surface Silicone additives generally reduce friction, i.e., they improve slip depending on their chemical structures and concentrations Generally, the more dimethyl groups in the structure, the more slip is enhanced Better slip may be the desired property, but oftentimes, slip is desirable for other reasons, because coatings with improved slip will simultaneously display better mar and scratch resistance, along with improved blocking resistance An added benefit is nearly always improved resistance to soiling

75.3.3.4 Mobility of Siloxanes/Intercoat Adhesion

Next, comparing reactive versus nonreactive modifications to the polydimethylsiloxane, cross-linking the siloxane via functional modifications, with resin binders, will inhibit recoat This is shown at the bottom

of Figure 75.4 At temperatures greater than 150ºC/300ºF, nonreactive polyether-modified siloxanes will decompose, forming reactive groups that function to preventing migration Nonreactive silicones do not remain permanently at the surface of the first layer of cured paint; upon recoat, they migrate into the second coat and orient at its air interface This migration of silicone from the first coat is what permits the second layer of paint to wet and adhere to the first coat (This is shown in the upper two-thirds of Figure 75.4.) Through manipulation of the modifications to the basic polydimethylsiloxane molecule, intercoat adhesion can be controlled Specially designed, thermally stable polysiloxanes have also been developed for recoatability in high-temperature (up to 220ºC/430ºF) baking systems

75.3.3.5 Surface Tension Reduction for Substrate Wetting

Due to their surface activity, conventional silicones typically concentrate at the liquid/air interface Characteristic of silicones is their ability to reduce surface tension

In order for a formulation to wet a substrate, the liquid components of the formulation must have a lower composite surface tension than that of the substrate In solvent-based systems, and some waterborne systems, this requirement can be met by the use of silicone additives of the structures previously discussed

In waterborne systems, substrate wetting can be difficult, due to the high surface tension of water Conventional silicone additives (as described above) often cannot correct wetting defects, as they do not sufficiently reduce the surface tension of the coating The correct product to use for these situations are often “silicone surfactants.” Such products are able to provide very low surface tension values in waterborne coatings, thereby avoiding wetting problems They can often be used to replace fluoro surfactants However, fluoro surfactants, in addition to reducing surface tension (and being more expensive), also exhibit a pronounced tendency to stabilize foam It is important to note that silicone surfactants do not stabilize foam

75.3.3.6 Controlled Incompatibility

The compatibility of any particular silicone with a binder solution depends on its chemical structures

— the presence of modifying side chains and molecular weight Highly incompatible silicones tend to cause surface defects (such as craters) and may actually be used to generate hammer-tone finish coatings

FIGURE 75.4 Mobility of silicones.

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