- Email: [email protected]
A new cure for coating plastics
A N e w Cure for Coating Plastics UV technology overcomes ago-old processing problems. By S. Smeets, Technical Service and Development Radcure; E. Boerrigter, Market Manager, Radcure Europe; and S. Peeters, Global Lead New Development and Applications, Radcure, Surface Specialties UCB
manufacturers, formulators, and raw material supplie increasing use of plastic as a construction ers face new challenges when attempting to introduce aterial in the automotive, electronic, a n d this technology further into the field of plastic coatings. lecommunication fields means their coatabiliUV-curing technology consists of drying a coating ty is becoming very important. through exposure to UV light, leading to polymerFinding a universal coating for all types of plastics ization between the components of the formulation. is still a utopia. Their low surface energies and senThe chemistry used in UV polymerization is almost sitivity to temperature and solvents make many entirely based on acrylate functionalized materials. plastics difficult to coat. The number of different A UV formulation always contains the following materials consisting of homopolymers or blends of ingredients: diluting acrylates and acrylated different polymers is enormous and most require oligomers, which are reactive materials forming the tailor-made solutions. backbone of the coating after drying; photoinitiaMoreover, due to different intrinsic properties tors, which under exposure to UV light form radicals within a polymer family, different properties are targeted. Optimization and fine-tuning of wellthat initiate a polymerization reaction between diluting acrylates and acrylatknown materials by blending ed oligomers; and fillers and or using additives to obtain additives, which mostly do not better properties require participate in the polymerizasimultaneous adjustment of tion reaction and thus remain the coating properties. in the cured network. The current drive towards cheaper polymers is deteriPMMA mined primarily by their coata~v~ DILUTING ACRYLATES bility to obtain the required UV coatings are, by their surface aesthetics. With UV nature, solvent free, so they technology, one is no longer have to be formulated in a way limited to coating plastics with that compensates for the lack of solvent-based products. Solvent solvent adhesion. The adhesion PE coatings are inhibited by their to a plastic substrate is difficult high VOC emissions; space- Figure 1: Effect of diluting acrylates on adhesion to sev- due to the inherent polymerizaeral substrates. Blue regions: highly preferred. Green consuming, long thermal dry- regions: tion process of the UV resins. optional in balance with other properties ing tunnels are required; and When exposed to UV light, the curing speed is limited. photoinitiator starts a chain Not only does UV technology overcome these reaction leading to polymerization of the liquid coatproblems, it offers other advantages such as the ing accompanied by a decrease in volume and thus shrinkage. ability to coat heat-sensitive substrates and performance improvement such as scratch and stain The liquid coating consists mainly of high-viscous resistance, which are becoming increasingly oligomers and low-viscous monomers. The purpose important. UV resins are well established for surof the diluting acrylates or monomers is the reducface protection and decoration in many applications tion of the viscosity of the total UV formulation. such as electronics, furniture, and construction. But These diluting acrylates play the role of "reactive" their use on plastic substrates is still limited. solvents within conventional formulations. But as they react in the final polymer, they influence the final properties as well. UV CURING TECHNOLOGY Low-viscous acrylates with high functionality and Despite the advantages of UV technology, equipment 80
www.metalfinishing.com
low molecular weight will give high reactivity and cross link DilutingAcrylate Shrinkage% 208 ~soL,~rnyl .... ' ,5~2 IBOA density, but also high shrinkage, Oxy~hy~ed phenot'a~late ......... 236 ..... Ebem~l 11'4 0.8 decreasing the adhesion of a UV Octadecy~ acrylate 200 ODA ,, ,8,3 coating. Low-viscous acrylates 304 Tricyclodecane diol diacrylate TCDA. . . . El~rcry~ i45 Propoxytated neopentyt 328 with low functionality will give ~llycol diacrytate , ,, , low reactivity, low cross link den13,0 "DPGDA Dipropylene91ycOIdiacwlate 242 sity, and a high flexibility. T~DA 300 18,1 I Trip°PY lone glyco! diacrytate The speed of the UV polymerHexane diol dlacrylate ....H ' b 0 A ........ 226 ..... 1~i0 Ebemry1160 428 14.1 Trimathylolpropane ethoxY ization process produces internal I triacryiate stress in the coating, which is not 480 15.1 Propoxylated glycerol OTA 480 found in conventional t h e r m a l ! triacrglate ,, Trimethylolpropane TMPTA 25.1 296 drying processes. The shrinkage triacwlate of some diluting acrylates is Ebercry140 571 8,7 Alkoxylated pentaewth r'Roi shown in Table I. The shrinkage tetraacry~ate is expressed as the change in den438 Ditd methyiol propane Eb~rcnfl i4o 10.0 , ...... :~ii!;, tetraacryiate sity during curing of a formulation containing 100% resin and 5% photoinitiator. Although these Surface Tension values give a good indication of Diluting Acrylate Deecription (mN/m~ the intrinsic properties of dilutIBOA I8obomyl acrylate ' 32 ::' C~xyethylated phe n01 acrylate 39 Ebe mryl 114 ing acrylates, the behavior in a Octadecyl acrylate , 30 , ODA final formulation depends on the Ebercryl 1039 33 Urethane monoacrylate other components as well. Tricyclodecane diol diacwiate TCDA The solubility p a r a m e t e r s of Propoxylated neopentyl 31 Ebecryi 145 both polymeric substrate and forglycol diacrylate mulation give an indication of Dipropylene glycol diacrylate DPGDA 5 : w h e t h e r adhesion is expected to Tripopylene glycol diacrytate 34 TPGDA be difficult or not. Generally, a 36 Hexane diol diacwlate HDDA diluting acrylate that can attack Trimethylolpropane ethyox¥ 39 Ebe rcryl 160 or swell a substrate will form an triacrylate i n t e r p e n e t r a t i n g polymer netPropoxylated glycerol 36 OTA~ triacrylate work between substrate and coat, ~lr, Trimethylol propane 38 TMPTA ing, leading to an excellent adhetriacrylate sion. Diluting acrylates, such as Alkoxylated pentaeryth dtol Ebecrg! 40 40 oxyethylated phenol acrylate, tetraacrylate DPGDA or HDDA, are able to Ditrimethylol propane 38 Ebecry~ 140 attack and swell polycarbonate. tetraacrylate Another important parameter to consider is the surface tension of A formulation leading to a good adhesion on a parthe substrate. Good adhesion is obtained when the ticular plastic may not deliver good performance on surface tension of the substrate is higher than that of another type of the same plastic family. The ability of the coating, gi~ing an optimal wetting of the subseveral diluting acrylates to serve as an adhesion prostrate. The surface tension of typical diluting acrylates rooter in a coating is shown in Figure 1. In the blue is shown in Table II. region, one can find the preferred diluting acrylates, The surface tension of common plastic substrates whereas the products in the green region are used in may vary from 20 mN/m (Teflon) to 44 mN/m (PET). balance with other properties such as diluting power The wide range of surface tensions of certain suband reactivity. strates is explained by the different treatments of Due to its capacity to swell the plastic surface, their surfaces. For example, u n t r e a t e d polypropyHDDA is an interesting adhesion promoter. In the lene m a y have 28 mN/m whereas the surface tencase of PC or impact-resistant PS, only a small sion of corona-treated PP can go up to 40 mN/m. A amount of HDDA is needed in a formulation, wheresurface t r e a t m e n t with corona or flame results in as for harder PS, higher quantities are necessary. the formation of polar groups on the substrate. May 2005
81
f¢
Figure 3: A schematic drawing of a UV-PUD.
diluting acrylate for rigid SMC/BMC as it has a low shrinkage combined with excellent hardness. E
PE Figure 2: UV-adhesion promoters for plastics. Blue regions: main component; green regions: optional additive; white region: optional diluting acrylate.
Because of its low surface tension, ODA is a very useful diluting acrylate for PP and PE. ODA is mostly used in small amounts due to its incompatibility with m a n y acrylated oligomers at high concentration. Ebecryl 1039 is preferred above Ebecryl 40 when a higher flexibility is required. TCDA is a difunctional
UV ADHESION PROMOTERS Diluting acrylates in a UV formulation reduce the viscosity and increase the adhesion on several plastic substrates, however, t h e y can reduce the high performance of a UV coating. In order to limit the percentage of diluting acrylates in a UV formulation, one can switch from a one-layer to a multilayer approach with primer, basecoat, and topcoat. As the primer is necessary for the adhesion to the substrate, both basecoat and topcoat may contain less diluting oligomers. Almost all automotive paints use the primer/basecoat/clearcoat buildup in order to fulfill the high quality requirements. The basecoat has the color pigment while the topcoat will provide resistance to scratches, etc. This multilayer approach makes it easy to switch from one color to another without
Mason Corporation S t a n n i c C h l o r i d e (Tin T e t r a c h l o r i d e ) , (Tin IV C h l o r i d e ) , (Tin Chloride) Stannic Chloride S o l u t i o n ..................;~. Stannous Chloride Anhydrous
Mc izeq biJJ'lyJn packaging of fhe chemicals to meef fhe cusfomers' needs, I
Mason Corporation P.O.Box 38 • Schereville, IN 46375 1-219-865-8040 • Fax: 1-219-322-3611 800-326-3075 • Email: [email protected] www.tinchemical.com Circle 118 on reader information card or go to www.thru,to/webconnect 82
Circle 054 on reader information card or go to www.thru.to/webconnect www.metalfinishing.com
changing the primer and topcoat. The use of one UV primer for several plastic parts could simplify the coating process considerably. Several of our UV resins (Table Dispersions III) provide good adhesion to difo~ ferent plastic substrates. Since a co" plastic can vary from one supplier to another, be filled or nonfilled, Ucecoat DW 7770 >10 .... al, 5B ,i, :,!,9o and be a blend of two miscible or Ucecoat OW 7773 5B >100 352 <20 5B compatibilized polymers, the Ucecoat DW 7825 295 5O >100 0B, value of these resins has to be Ucecoat DW 772 >100 312 5B <20 5B e v a l u a t e d with experimental Ucecoat DW 7849 >100 0B : 2s3 30 work on each plastic. The ability of these to serve as an adhesion promoter in a primer and/or in a coating is shown in Figure 2. As the adhesion of UV resins towards PC, PVC, and PMMA is mostly obtained with a small amount of diluting acrylate, no adhesion promoter is required. Surface treatments, such as corona, flame~ plasma, or IPA cleaning are advised to activate the surface but also to remove processing additives and contamination. Figure 2 is comprised of three areas (blue, green, and white) and diluted with one of the diluting acrylates from the should serve as a guideline to coat several plastic white region. substrates. The resins in the blue region represent Ebecryl 740-40TP, 767, and 745 are acrylic acrythe major component in a formulation, which can be , ,i,
iiii
i
A
HECTRIO
THE CLEAR AND ODOR FREE SOLUTION IN MSA
MANUFACTURERS OF • Tin (II) Methane Sulfonate • Lead (II) Methane Sulfonate • Purified Methane Sulfonic Acid (MSA) • Stannous Sulfate solutions, 315 g/1 - highest concentration available worldwide 400 First Avenue, Royersford, PA 19468 Tel: 1-610-948-0734 Fax: 1-610-948-0744
• FIVE WIRE pH PROBES
Replacement for GLI Probes • TWO WIRE (4-20mA) pH PROBES
Replacement for GLI Probes • COMBINATION ELECTRODES • pH ANALYZERS • pH RECORDERS • CONDUCTIVITY CONTROLLERS • CONDUCTIVITY CELL
MARDON CONTROL SYSTEMS,INC. 1043 13THAVENUE GRAFTON,W153024
1-800- 784-9533 Circle 083 on reader information card or go to www,thrn.to/webconnect May 2005
Circle 045 on reader information card or go to www.thru.to/wnbconnect
Circle 053 on reader information card or go to www, thru,to/webconnect 83
{
..... ~
.
.
.
.
.
.
.
.
.
.
~ ~
Figure 5: Gloss monitoring in Xenon. Figure 4: Monitoring of b values in Xenon. Appearance of first crack.
lates, which give good adhesion to m a n y plastics mainly due to their low functionality and thus shrinkage. Ebecryl 303 is a polymeric resin diluted in HDDA that shows good adhesion in combination with acrylic acrylates. Ebecryl 436, 438, and 584 are chlorinated polyester resins respectively diluted in TMPTA, OTA 480, and HDDA. They have good reactivity combined with very low shrinkage (< 4%). The amount of diluting acrylate must be chosen
depending on the required viscosity, but also the rigidity of the substrate. To increase the reactivity, one can take a higher functional diluting acrylate or add Ebecryl 7100, which is a low-viscous amine functional acrylate. Ebecryl 168 and 170 are methacrylated or acrylated acidic components, which are able to etch the surface of a filled plastic. The efficacy of the UV resins to adhere to plastic depends on the application process and the contact and drying times. The best way to evaluate this is through industrial trials.
APPLICATIONS:
,o Close loop rinses/Drag out 'o Process chemistry Recovery ° Wastewater reduction up to 98%
O
High efficiency, vertical packed tower in polypro, CPVC, or PVDE Low temperature evaporation. Built-in scrubber type mist eliminator. Complete engineered systems including tank, heater, pump, and controls. Gas-fired, steam, electric and other heating systems available.
(973)
226-6010
F a x : (973) 2 2 7 - 4 1 5 5 = E - m a i l : j t i i t o n @ t i l t o n - r n b . c o m 66 Passaic Avenuc - Fairfield, NJ 07004-3509
Circle 094 on reader information card or go to www.thru.to/webconnect 84
Tower units or complete s y s t e m s available
www.burtprocess.com Burt Process Equipment 1050 SHERMAN AVENUE * HAMDEN CONNECTICUT 06514 PHONE: 203-287-1985 • Email: [email protected]
Circle 108 on reader information card or go to www.thru.to/webconnect www.rnetalfinishing.com
\
LOW-VISCOUS, H I G H - P I ~ q ) m V l A N ~ I N RESgVS The design of low-viscous, high-performance resins for a spray application to coat three-dimensional objects has led to a new generation ofbinders--radiation curable polyurethane dispersions (UV-PUD). A schematic presentation of a UV-PUD is shown in Figure 3. The reaction of diisocyanates (blue) with different polyols (polyester, polyether, polycarbonate) results in a polyurethane that forms the basic chemistry of a UV-PUD. The relative high molecular weight of UV-PUDs means they show almost no shrinkage after curing, resulting in excellent adhesion to many substrates. The combination of this property together with the very low viscosity and the advantages of UV technology m a k e these s t r u c t u r e s very suitable for either primer or topcoat. This urethane technology provides versatile solutions combining different chain structures. Such polymers combine hard segments, which could be urethane, urea, allophanates, and soft segments such as polyester, polyether, and polycarbonate. When compared to traditional 100% UV systems, the UV-PUD's
morphology could be adjusted depending on the cross linking degree needed and the desired stiffness. The adhesion of different radiation curable PUDs on different substrates has been tested. In addition to adhesion (12-~m dry coating), the persoz hardness (50-pm dry film on glass), flexibility (impact resistance of a 12-1am film on aluminium) and solvent resistance (Acetone Double Rubs of a 12-pm film on PC) are shown in Table IV.
U V R E S I N S FOR EXTERIOR A P P L I C A T I O N S Damage of common plastics by solar radiation depends on the susceptibility of the polymer type to solar UV wavelength as well as the complexity of the weathering environment to which it is exposed. The magnitude of the damage can be controlled using stabilizers in the plastic composition. Expansion of the use of radiation-cured coatings on exterior plastics depends on the development of binders, which combine excellent weathering performance with other increasingly more stringent requirements. Accelerated weathering tests are widely used to assess the w e a t h e r a b i l i t y of polymers. The most i m p o r t a n t difference b e t w e e n the various equip-
CONDS e OLD e NEW
"
11111 DISPOSABLE, SLIP-ON Ii DANGLER HEADS
,,
• Scale R e m o v a l Tool & D i e Cleaning
S.S. WHITE ....
:
"The World Leader in Mirco Abrasive Blasting Equipment"
732-474-1708
ADVANTAGES: u.s.~at,,~,111,781 Fo,eig~ Rights Reserved. NO LOST PLATING TIME. Slip off built-up heads, and slip on fresh, new heads without removing Dangler Assembly from barrel. LONGER CABLE LIFE. Removing heads before the plating build-up is excessive, prolongs the life of the Dangler Assembly. ECONOMICAL. Field studies have shown that using our disposable heads costs just pennies per barrel load to use. FAST. The state-of-the-art design and construction
ezllllB .~ l ts yo~wChp;~e wohr;:~2inm/dS::g~ en:s~htm I "~ E-maih [email protected] ~11
L.)ANGLERS'c
35OAKDALE AVE., JOHNSTON,RI02919(401)274-7742
Circle 122 on reader information card or go to www.thru.to/webconnect M a y 2005
Circle 109 on reader information card or go to www.thru.to/webcoaaect RK
ment is the nature of the light source employed. The short wavelength emission of UV-B lamps can cause unnatural acceleration or degradation whereas UVA lamps have no output below the normal solar cutoff of 295 nm and may allow enhanced correlation with actual outdoor weathering. With appropriate filters, the Xenon arc spectral light distribution mirrors well the sunlight in both UV and visible range. This makes the Xenon test together with the humidity control feature the most widely accepted standard. At Surface Specialties UCB, extensive test experience has been gained with different types of accelerated tests and cycling conditions. In this article we only concentrate on the Xenon test, using a Xenon WeatherOMeter, according to the ASTM G26 method. Due to the huge variety of plastics, we decided to test the UV clearcoats on weather-stable white thermoset polymer coated panels at a 20-pm coating thickness. A visual evaluation was carried out along with color and gloss monitoring during the tests. Aliphatic urethane acrylates, in general, outperform other oligomer types in both accelerated and natural weathering tests. Aromatic polymers, in general, are inherently not stable to light and tend to yellow and degrade rapidly. Also, conventional polyether and polyester acrylates are more sensitive to degradation. Table V shows UV resins suitable for formulation of coatings for exterior application. These include aliphatic urethane acrylates based on chemical backbones that are stable towards degradation under influence of light and moisture. These resins have excellent color and gloss retention properties. Di- and tri-functional products result in relatively lower cross link densities and are, in general, less sensitive to crack formation than higher functional products, which result in more densely cross-linked systems. Nevertheless, hexafunctional urethane acrylates are indispensable in providing superior scratch resistance. In a comparative study, the products, except Ebecryl 1290 and Ebecryl 5129, have been diluted with 30% HDDA. HDDA is one of the best performing diluting acrylates for exterior use. Ebecryl 1290 and Ebecryl 5129, both hexa-functional urethane acrylates, have been tested by a 20% addition to Ebecryl 284. Figure 4 illustrates the monitoring of the "b" value in the Xenon test for the six urethane acrylates. The color retention is excellent, after a relaxation phase (b decreasing), b values increase very slightly. The visual appearance of the first crack formation is also indicated for each product. Pictorial standards are used to note degradation with cracking (ASTM D660). Ebecryl 284, 294/25
HD, 1290 and 8402, which are also tested by natural exposure in Belgium and Florida, are still free of cracks after three years. Figure 5 illustrates the monitoring of the gloss in the Xenon test. In general, the gloss retention is excellent up to 2000h of Xenon exposure. Upon prolonged exposure, the gloss decreases. CONCLUSION
UV-curing technology for industrial coatings has been established for decades. The advantages in terms of processing (high speed, smaller equipment), performance (scratch resistance, stain resistance, etc.) and environmental friendliness are well known. The use of UV technology for coating plastics has been limited. However, the translation of the advantages of UV technology into the field of plastic coatings has led to an optimization of existing UV resins as well as the development of new UV binders.
Stefan Smeets can be reached at (e-mail) [email protected]; Egbert Boerrigter at (e-mail) [email protected]; and Stephan Peeters at (email) [email protected], fl~
B-9 N I C K E L S T R I P P E R S The only one-component, non-toxic powdered immersion nickel strippers on the market, removes nickel from steel, copper, brass and zinc diecast. NO ELECTRICITY • NO CYANIDES NO P H O S P H A T E S • NO CAUSTIC A M I N E S NO A M M O N I A • NO FUMES 5 FORMULATIONS
• B-9 Formula removes electrlytic and electroless nickel from steel • B-9 Plus for use by shop operators on all substrates • B-929 Formula strips nickel from zinc diecast, copper, brass, silver and gold with no etching of the softer substrates • B-913 Removes nickel from aluminum with no hydrogen embrittlement aftereffects • B-9 Nickel-iron strips nickel-alloy from ferrous substrates with no attack Military and Aerospace Specs METALX B-9 NICKEL STRIPPERS GET THE JOB DONE! METALX,
INC
2600 Roby Martin Road Lenoir, NC 28645 Telephone: 828-758-4997 • Fax 828-758-5033 E-maih [email protected] Circle 094 on reader information card or go to www.thru.to/webconnect
86
www.metalfinishing.com
manufacturers, formulators, and raw material supplie increasing use of plastic as a construction ers face new challenges when attempting to introduce aterial in the automotive, electronic, a n d this technology further into the field of plastic coatings. lecommunication fields means their coatabiliUV-curing technology consists of drying a coating ty is becoming very important. through exposure to UV light, leading to polymerFinding a universal coating for all types of plastics ization between the components of the formulation. is still a utopia. Their low surface energies and senThe chemistry used in UV polymerization is almost sitivity to temperature and solvents make many entirely based on acrylate functionalized materials. plastics difficult to coat. The number of different A UV formulation always contains the following materials consisting of homopolymers or blends of ingredients: diluting acrylates and acrylated different polymers is enormous and most require oligomers, which are reactive materials forming the tailor-made solutions. backbone of the coating after drying; photoinitiaMoreover, due to different intrinsic properties tors, which under exposure to UV light form radicals within a polymer family, different properties are targeted. Optimization and fine-tuning of wellthat initiate a polymerization reaction between diluting acrylates and acrylatknown materials by blending ed oligomers; and fillers and or using additives to obtain additives, which mostly do not better properties require participate in the polymerizasimultaneous adjustment of tion reaction and thus remain the coating properties. in the cured network. The current drive towards cheaper polymers is deteriPMMA mined primarily by their coata~v~ DILUTING ACRYLATES bility to obtain the required UV coatings are, by their surface aesthetics. With UV nature, solvent free, so they technology, one is no longer have to be formulated in a way limited to coating plastics with that compensates for the lack of solvent-based products. Solvent solvent adhesion. The adhesion PE coatings are inhibited by their to a plastic substrate is difficult high VOC emissions; space- Figure 1: Effect of diluting acrylates on adhesion to sev- due to the inherent polymerizaeral substrates. Blue regions: highly preferred. Green consuming, long thermal dry- regions: tion process of the UV resins. optional in balance with other properties ing tunnels are required; and When exposed to UV light, the curing speed is limited. photoinitiator starts a chain Not only does UV technology overcome these reaction leading to polymerization of the liquid coatproblems, it offers other advantages such as the ing accompanied by a decrease in volume and thus shrinkage. ability to coat heat-sensitive substrates and performance improvement such as scratch and stain The liquid coating consists mainly of high-viscous resistance, which are becoming increasingly oligomers and low-viscous monomers. The purpose important. UV resins are well established for surof the diluting acrylates or monomers is the reducface protection and decoration in many applications tion of the viscosity of the total UV formulation. such as electronics, furniture, and construction. But These diluting acrylates play the role of "reactive" their use on plastic substrates is still limited. solvents within conventional formulations. But as they react in the final polymer, they influence the final properties as well. UV CURING TECHNOLOGY Low-viscous acrylates with high functionality and Despite the advantages of UV technology, equipment 80
www.metalfinishing.com
low molecular weight will give high reactivity and cross link DilutingAcrylate Shrinkage% 208 ~soL,~rnyl .... ' ,5~2 IBOA density, but also high shrinkage, Oxy~hy~ed phenot'a~late ......... 236 ..... Ebem~l 11'4 0.8 decreasing the adhesion of a UV Octadecy~ acrylate 200 ODA ,, ,8,3 coating. Low-viscous acrylates 304 Tricyclodecane diol diacrylate TCDA. . . . El~rcry~ i45 Propoxytated neopentyt 328 with low functionality will give ~llycol diacrytate , ,, , low reactivity, low cross link den13,0 "DPGDA Dipropylene91ycOIdiacwlate 242 sity, and a high flexibility. T~DA 300 18,1 I Trip°PY lone glyco! diacrytate The speed of the UV polymerHexane diol dlacrylate ....H ' b 0 A ........ 226 ..... 1~i0 Ebemry1160 428 14.1 Trimathylolpropane ethoxY ization process produces internal I triacryiate stress in the coating, which is not 480 15.1 Propoxylated glycerol OTA 480 found in conventional t h e r m a l ! triacrglate ,, Trimethylolpropane TMPTA 25.1 296 drying processes. The shrinkage triacwlate of some diluting acrylates is Ebercry140 571 8,7 Alkoxylated pentaewth r'Roi shown in Table I. The shrinkage tetraacry~ate is expressed as the change in den438 Ditd methyiol propane Eb~rcnfl i4o 10.0 , ...... :~ii!;, tetraacryiate sity during curing of a formulation containing 100% resin and 5% photoinitiator. Although these Surface Tension values give a good indication of Diluting Acrylate Deecription (mN/m~ the intrinsic properties of dilutIBOA I8obomyl acrylate ' 32 ::' C~xyethylated phe n01 acrylate 39 Ebe mryl 114 ing acrylates, the behavior in a Octadecyl acrylate , 30 , ODA final formulation depends on the Ebercryl 1039 33 Urethane monoacrylate other components as well. Tricyclodecane diol diacwiate TCDA The solubility p a r a m e t e r s of Propoxylated neopentyl 31 Ebecryi 145 both polymeric substrate and forglycol diacrylate mulation give an indication of Dipropylene glycol diacrylate DPGDA 5 : w h e t h e r adhesion is expected to Tripopylene glycol diacrytate 34 TPGDA be difficult or not. Generally, a 36 Hexane diol diacwlate HDDA diluting acrylate that can attack Trimethylolpropane ethyox¥ 39 Ebe rcryl 160 or swell a substrate will form an triacrylate i n t e r p e n e t r a t i n g polymer netPropoxylated glycerol 36 OTA~ triacrylate work between substrate and coat, ~lr, Trimethylol propane 38 TMPTA ing, leading to an excellent adhetriacrylate sion. Diluting acrylates, such as Alkoxylated pentaeryth dtol Ebecrg! 40 40 oxyethylated phenol acrylate, tetraacrylate DPGDA or HDDA, are able to Ditrimethylol propane 38 Ebecry~ 140 attack and swell polycarbonate. tetraacrylate Another important parameter to consider is the surface tension of A formulation leading to a good adhesion on a parthe substrate. Good adhesion is obtained when the ticular plastic may not deliver good performance on surface tension of the substrate is higher than that of another type of the same plastic family. The ability of the coating, gi~ing an optimal wetting of the subseveral diluting acrylates to serve as an adhesion prostrate. The surface tension of typical diluting acrylates rooter in a coating is shown in Figure 1. In the blue is shown in Table II. region, one can find the preferred diluting acrylates, The surface tension of common plastic substrates whereas the products in the green region are used in may vary from 20 mN/m (Teflon) to 44 mN/m (PET). balance with other properties such as diluting power The wide range of surface tensions of certain suband reactivity. strates is explained by the different treatments of Due to its capacity to swell the plastic surface, their surfaces. For example, u n t r e a t e d polypropyHDDA is an interesting adhesion promoter. In the lene m a y have 28 mN/m whereas the surface tencase of PC or impact-resistant PS, only a small sion of corona-treated PP can go up to 40 mN/m. A amount of HDDA is needed in a formulation, wheresurface t r e a t m e n t with corona or flame results in as for harder PS, higher quantities are necessary. the formation of polar groups on the substrate. May 2005
81
f¢
Figure 3: A schematic drawing of a UV-PUD.
diluting acrylate for rigid SMC/BMC as it has a low shrinkage combined with excellent hardness. E
PE Figure 2: UV-adhesion promoters for plastics. Blue regions: main component; green regions: optional additive; white region: optional diluting acrylate.
Because of its low surface tension, ODA is a very useful diluting acrylate for PP and PE. ODA is mostly used in small amounts due to its incompatibility with m a n y acrylated oligomers at high concentration. Ebecryl 1039 is preferred above Ebecryl 40 when a higher flexibility is required. TCDA is a difunctional
UV ADHESION PROMOTERS Diluting acrylates in a UV formulation reduce the viscosity and increase the adhesion on several plastic substrates, however, t h e y can reduce the high performance of a UV coating. In order to limit the percentage of diluting acrylates in a UV formulation, one can switch from a one-layer to a multilayer approach with primer, basecoat, and topcoat. As the primer is necessary for the adhesion to the substrate, both basecoat and topcoat may contain less diluting oligomers. Almost all automotive paints use the primer/basecoat/clearcoat buildup in order to fulfill the high quality requirements. The basecoat has the color pigment while the topcoat will provide resistance to scratches, etc. This multilayer approach makes it easy to switch from one color to another without
Mason Corporation S t a n n i c C h l o r i d e (Tin T e t r a c h l o r i d e ) , (Tin IV C h l o r i d e ) , (Tin Chloride) Stannic Chloride S o l u t i o n ..................;~. Stannous Chloride Anhydrous
Mc izeq biJJ'lyJn packaging of fhe chemicals to meef fhe cusfomers' needs, I
Mason Corporation P.O.Box 38 • Schereville, IN 46375 1-219-865-8040 • Fax: 1-219-322-3611 800-326-3075 • Email: [email protected] www.tinchemical.com Circle 118 on reader information card or go to www.thru,to/webconnect 82
Circle 054 on reader information card or go to www.thru.to/webconnect www.metalfinishing.com
changing the primer and topcoat. The use of one UV primer for several plastic parts could simplify the coating process considerably. Several of our UV resins (Table Dispersions III) provide good adhesion to difo~ ferent plastic substrates. Since a co" plastic can vary from one supplier to another, be filled or nonfilled, Ucecoat DW 7770 >10 .... al, 5B ,i, :,!,9o and be a blend of two miscible or Ucecoat OW 7773 5B >100 352 <20 5B compatibilized polymers, the Ucecoat DW 7825 295 5O >100 0B, value of these resins has to be Ucecoat DW 772 >100 312 5B <20 5B e v a l u a t e d with experimental Ucecoat DW 7849 >100 0B : 2s3 30 work on each plastic. The ability of these to serve as an adhesion promoter in a primer and/or in a coating is shown in Figure 2. As the adhesion of UV resins towards PC, PVC, and PMMA is mostly obtained with a small amount of diluting acrylate, no adhesion promoter is required. Surface treatments, such as corona, flame~ plasma, or IPA cleaning are advised to activate the surface but also to remove processing additives and contamination. Figure 2 is comprised of three areas (blue, green, and white) and diluted with one of the diluting acrylates from the should serve as a guideline to coat several plastic white region. substrates. The resins in the blue region represent Ebecryl 740-40TP, 767, and 745 are acrylic acrythe major component in a formulation, which can be , ,i,
iiii
i
A
HECTRIO
THE CLEAR AND ODOR FREE SOLUTION IN MSA
MANUFACTURERS OF • Tin (II) Methane Sulfonate • Lead (II) Methane Sulfonate • Purified Methane Sulfonic Acid (MSA) • Stannous Sulfate solutions, 315 g/1 - highest concentration available worldwide 400 First Avenue, Royersford, PA 19468 Tel: 1-610-948-0734 Fax: 1-610-948-0744
• FIVE WIRE pH PROBES
Replacement for GLI Probes • TWO WIRE (4-20mA) pH PROBES
Replacement for GLI Probes • COMBINATION ELECTRODES • pH ANALYZERS • pH RECORDERS • CONDUCTIVITY CONTROLLERS • CONDUCTIVITY CELL
MARDON CONTROL SYSTEMS,INC. 1043 13THAVENUE GRAFTON,W153024
1-800- 784-9533 Circle 083 on reader information card or go to www,thrn.to/webconnect May 2005
Circle 045 on reader information card or go to www.thru.to/wnbconnect
Circle 053 on reader information card or go to www, thru,to/webconnect 83
{
..... ~
.
.
.
.
.
.
.
.
.
.
~ ~
Figure 5: Gloss monitoring in Xenon. Figure 4: Monitoring of b values in Xenon. Appearance of first crack.
lates, which give good adhesion to m a n y plastics mainly due to their low functionality and thus shrinkage. Ebecryl 303 is a polymeric resin diluted in HDDA that shows good adhesion in combination with acrylic acrylates. Ebecryl 436, 438, and 584 are chlorinated polyester resins respectively diluted in TMPTA, OTA 480, and HDDA. They have good reactivity combined with very low shrinkage (< 4%). The amount of diluting acrylate must be chosen
depending on the required viscosity, but also the rigidity of the substrate. To increase the reactivity, one can take a higher functional diluting acrylate or add Ebecryl 7100, which is a low-viscous amine functional acrylate. Ebecryl 168 and 170 are methacrylated or acrylated acidic components, which are able to etch the surface of a filled plastic. The efficacy of the UV resins to adhere to plastic depends on the application process and the contact and drying times. The best way to evaluate this is through industrial trials.
APPLICATIONS:
,o Close loop rinses/Drag out 'o Process chemistry Recovery ° Wastewater reduction up to 98%
O
High efficiency, vertical packed tower in polypro, CPVC, or PVDE Low temperature evaporation. Built-in scrubber type mist eliminator. Complete engineered systems including tank, heater, pump, and controls. Gas-fired, steam, electric and other heating systems available.
(973)
226-6010
F a x : (973) 2 2 7 - 4 1 5 5 = E - m a i l : j t i i t o n @ t i l t o n - r n b . c o m 66 Passaic Avenuc - Fairfield, NJ 07004-3509
Circle 094 on reader information card or go to www.thru.to/webconnect 84
Tower units or complete s y s t e m s available
www.burtprocess.com Burt Process Equipment 1050 SHERMAN AVENUE * HAMDEN CONNECTICUT 06514 PHONE: 203-287-1985 • Email: [email protected]
Circle 108 on reader information card or go to www.thru.to/webconnect www.rnetalfinishing.com
\
LOW-VISCOUS, H I G H - P I ~ q ) m V l A N ~ I N RESgVS The design of low-viscous, high-performance resins for a spray application to coat three-dimensional objects has led to a new generation ofbinders--radiation curable polyurethane dispersions (UV-PUD). A schematic presentation of a UV-PUD is shown in Figure 3. The reaction of diisocyanates (blue) with different polyols (polyester, polyether, polycarbonate) results in a polyurethane that forms the basic chemistry of a UV-PUD. The relative high molecular weight of UV-PUDs means they show almost no shrinkage after curing, resulting in excellent adhesion to many substrates. The combination of this property together with the very low viscosity and the advantages of UV technology m a k e these s t r u c t u r e s very suitable for either primer or topcoat. This urethane technology provides versatile solutions combining different chain structures. Such polymers combine hard segments, which could be urethane, urea, allophanates, and soft segments such as polyester, polyether, and polycarbonate. When compared to traditional 100% UV systems, the UV-PUD's
morphology could be adjusted depending on the cross linking degree needed and the desired stiffness. The adhesion of different radiation curable PUDs on different substrates has been tested. In addition to adhesion (12-~m dry coating), the persoz hardness (50-pm dry film on glass), flexibility (impact resistance of a 12-1am film on aluminium) and solvent resistance (Acetone Double Rubs of a 12-pm film on PC) are shown in Table IV.
U V R E S I N S FOR EXTERIOR A P P L I C A T I O N S Damage of common plastics by solar radiation depends on the susceptibility of the polymer type to solar UV wavelength as well as the complexity of the weathering environment to which it is exposed. The magnitude of the damage can be controlled using stabilizers in the plastic composition. Expansion of the use of radiation-cured coatings on exterior plastics depends on the development of binders, which combine excellent weathering performance with other increasingly more stringent requirements. Accelerated weathering tests are widely used to assess the w e a t h e r a b i l i t y of polymers. The most i m p o r t a n t difference b e t w e e n the various equip-
CONDS e OLD e NEW
"
11111 DISPOSABLE, SLIP-ON Ii DANGLER HEADS
,,
• Scale R e m o v a l Tool & D i e Cleaning
S.S. WHITE ....
:
"The World Leader in Mirco Abrasive Blasting Equipment"
732-474-1708
ADVANTAGES: u.s.~at,,~,111,781 Fo,eig~ Rights Reserved. NO LOST PLATING TIME. Slip off built-up heads, and slip on fresh, new heads without removing Dangler Assembly from barrel. LONGER CABLE LIFE. Removing heads before the plating build-up is excessive, prolongs the life of the Dangler Assembly. ECONOMICAL. Field studies have shown that using our disposable heads costs just pennies per barrel load to use. FAST. The state-of-the-art design and construction
ezllllB .~ l ts yo~wChp;~e wohr;:~2inm/dS::g~ en:s~htm I "~ E-maih [email protected] ~11
L.)ANGLERS'c
35OAKDALE AVE., JOHNSTON,RI02919(401)274-7742
Circle 122 on reader information card or go to www.thru.to/webconnect M a y 2005
Circle 109 on reader information card or go to www.thru.to/webcoaaect RK
ment is the nature of the light source employed. The short wavelength emission of UV-B lamps can cause unnatural acceleration or degradation whereas UVA lamps have no output below the normal solar cutoff of 295 nm and may allow enhanced correlation with actual outdoor weathering. With appropriate filters, the Xenon arc spectral light distribution mirrors well the sunlight in both UV and visible range. This makes the Xenon test together with the humidity control feature the most widely accepted standard. At Surface Specialties UCB, extensive test experience has been gained with different types of accelerated tests and cycling conditions. In this article we only concentrate on the Xenon test, using a Xenon WeatherOMeter, according to the ASTM G26 method. Due to the huge variety of plastics, we decided to test the UV clearcoats on weather-stable white thermoset polymer coated panels at a 20-pm coating thickness. A visual evaluation was carried out along with color and gloss monitoring during the tests. Aliphatic urethane acrylates, in general, outperform other oligomer types in both accelerated and natural weathering tests. Aromatic polymers, in general, are inherently not stable to light and tend to yellow and degrade rapidly. Also, conventional polyether and polyester acrylates are more sensitive to degradation. Table V shows UV resins suitable for formulation of coatings for exterior application. These include aliphatic urethane acrylates based on chemical backbones that are stable towards degradation under influence of light and moisture. These resins have excellent color and gloss retention properties. Di- and tri-functional products result in relatively lower cross link densities and are, in general, less sensitive to crack formation than higher functional products, which result in more densely cross-linked systems. Nevertheless, hexafunctional urethane acrylates are indispensable in providing superior scratch resistance. In a comparative study, the products, except Ebecryl 1290 and Ebecryl 5129, have been diluted with 30% HDDA. HDDA is one of the best performing diluting acrylates for exterior use. Ebecryl 1290 and Ebecryl 5129, both hexa-functional urethane acrylates, have been tested by a 20% addition to Ebecryl 284. Figure 4 illustrates the monitoring of the "b" value in the Xenon test for the six urethane acrylates. The color retention is excellent, after a relaxation phase (b decreasing), b values increase very slightly. The visual appearance of the first crack formation is also indicated for each product. Pictorial standards are used to note degradation with cracking (ASTM D660). Ebecryl 284, 294/25
HD, 1290 and 8402, which are also tested by natural exposure in Belgium and Florida, are still free of cracks after three years. Figure 5 illustrates the monitoring of the gloss in the Xenon test. In general, the gloss retention is excellent up to 2000h of Xenon exposure. Upon prolonged exposure, the gloss decreases. CONCLUSION
UV-curing technology for industrial coatings has been established for decades. The advantages in terms of processing (high speed, smaller equipment), performance (scratch resistance, stain resistance, etc.) and environmental friendliness are well known. The use of UV technology for coating plastics has been limited. However, the translation of the advantages of UV technology into the field of plastic coatings has led to an optimization of existing UV resins as well as the development of new UV binders.
Stefan Smeets can be reached at (e-mail) [email protected]; Egbert Boerrigter at (e-mail) [email protected]; and Stephan Peeters at (email) [email protected], fl~
B-9 N I C K E L S T R I P P E R S The only one-component, non-toxic powdered immersion nickel strippers on the market, removes nickel from steel, copper, brass and zinc diecast. NO ELECTRICITY • NO CYANIDES NO P H O S P H A T E S • NO CAUSTIC A M I N E S NO A M M O N I A • NO FUMES 5 FORMULATIONS
• B-9 Formula removes electrlytic and electroless nickel from steel • B-9 Plus for use by shop operators on all substrates • B-929 Formula strips nickel from zinc diecast, copper, brass, silver and gold with no etching of the softer substrates • B-913 Removes nickel from aluminum with no hydrogen embrittlement aftereffects • B-9 Nickel-iron strips nickel-alloy from ferrous substrates with no attack Military and Aerospace Specs METALX B-9 NICKEL STRIPPERS GET THE JOB DONE! METALX,
INC
2600 Roby Martin Road Lenoir, NC 28645 Telephone: 828-758-4997 • Fax 828-758-5033 E-maih [email protected] Circle 094 on reader information card or go to www.thru.to/webconnect
86
www.metalfinishing.com