Document LoJ6yXr1veam0GwMa2Nz7QpQQ
Report Number: Indexed Pile: 1865
ESR-69-9
Distribution on last page
, E. I. du Pont de Nemours & Company
F & P, Research Division
'<"iBXperiinental Station Laboratory
NOT FOR CIRCULATION
Research Report
\o
POLYURETHANE MODIFIED ACRYLIC ENAMELS
1. Acrylic Prepolymers/Polyisocyanates 2. Pot-Life Extenders/Catalysts 3. Desmodur N Modified Acrylic Clears
Date Issued: Period Covered: Project Number: Previous Reports: Notebook Numbers:
FEB 1 7 1969
June 16, 1968 - January 24, 1969 211229 ESR-67-3, ESR-67-33, ESR-68-7, ESR-68-52 320E, 399E
PREPARED
H. F. REINHARDT
APPROVED
A. W. ANDRESEN
When this report is no longer needed, please return it to the Pile Room, P & P Department, Experimental Station.
r et ur n t o
MARSHALL LAB. L!BPWY
TABLE OP CONTENTS
Page
INTRODUCTION-----------------------------------------------------------------------------------------------------OBJECTIVES---------------------------------------------------------------------------------------------------------SUMMARY AND CONCLUSIONS--------------ACTION TAKEN OR PROPOSED------------------------------------------------------------------------------PATENT STATUS----------------------------------------------------------------------------------------------------ACKNOWLEDGMENTS------------------------------------------------------------------------------------------------DISCUSSION------------------------------------------------------------------------------------------------------ --
1 1 1 3 5 5 6
I. Polyurethane Modified Acrylics------------------------------------------------------- 6 II. Acrylic Prepolymer------------------------------------------------------------------------------ 7
A. Solvents----------------------------------------------------------------------------------------------- 8 B. Polymerization Catalysts---------------------------------------------------------------- 8
III. IV. V.
Polyisocyanates------------------------------------------------------------------------------------ 9
Pot-Life Extenders-----------------------------------
10
Curing of Desmodur N Modified Acrylics--------------------------------------- 10
A. Metal Catalysis--------------------------------------------------------------------------------- 10 B. Amine Catalysis--------------------------------------------------------------------------------- 11 C. Curing Under Varied Humidity Conditions---------------------------------- 12 D. Effect of NCO/OH Ratio on Curing andProperties------------------------ 12
VI. Evaluation of White Desmodur N/AcrylicCoatings------------------------ 12
A. Physical/Mechanical Properties---------------------------------------------------- 12 B. Exposure Series - Durability-------------------------------------------------------- 13
VII. VIII.
IX. X.
XI.
Evaluation of Desmodur N/Acrylic Clears------------------------------------MEKO-Blocked Hylene W----------------------------------------------------------------------Scale-Up of Acrylic Prepolymers----------------------------------------------------Field Testing---------------------------------------------------------------------------------------Toxicity of Desmodur N Modified Acrylics-----------------------------------
14 14 15 15 16
EXPERIMENTAL DETAILS--------------------------------------------------------------------------------------- 16 BIBLIOGRAPHY------------------------------------------------------------------------------------------------------- 19
TABLES I - VII
ABSTRACT GLOSSARY DISTRIBUTION LIST
DUP030013108
INTRODUCTION
Aliphatic isocyanate based finishes have Increased their market penetration considerably since their introduction several years ago despite their high cost compared to conventional finishes. Their outstanding features comprise excellent durability, color retention, and chemical resistance which other systems including finishes based on aromatic Isocyanates cannot match. For this reason, the aliphatic isocyanate finishes. In particular systems based on Desmodur N/De3mophen 650, are now being used almost exclusively for painting jet aircraft. They have also made inroads In the railway industry, in construction, and other special appli cations.
Successful completion of this project should result in a new line of polyurethane modified acrylic finishes for aircraft, railway, and automotive applications enhancing our ability to meet future competition. We think that these finishes will be superior to Desmodur N/Desmophen 650 based coating systems in durability, flexibility, and color retention at lower cost.
OBJECTIVES
The overall objective is to develop profitable, nondis coloring, durable polyurethane modified acrylic enamels for indus trial and automotive end uses.
The immediate technical objectives are to determine If the selected JO MMA/50 HEA-Desmodur N system meets the requirements for aircraft, railway, and automotive refinish applications and to assist Marshall Development Laboratory in further development of this or modified candidates for commercialization.
SUMMARY AND CONCLUSIONS
The emphasis of our work during the reporting period was on the development and evaluation of two-package white and clear Desmodur N modified acrylics.
Particular attention was given to the development of the acrylic prepolymers including 70 MMA/50 HEMA, 70 MMA/50 HEA, and 70 EA/50 HEA. All three prepolymer combinations were scaled-up successfully using Marshall Lab's 20-gallon kettle. Special poly merization procedures were worked out to assure the production of
DUP03001 3109
2
clear, colorless polymer solutions of high conversion. The pre ferred solvents for the 70 MMA/50 HEMA and 70 MMA/50 HEA polymers are mixtures of n-butyl acetate and Cellosolve acetate. The most efficient catalyst Is t-butyl peroctoate for the polymerization conditions chosen. The 70 MMA/50 HEA prepolymer was chosen for further evaluation and development because of its better overall properties including flexibility and initial gloss compared to the 70 MMA/50 HEMA composition. The 70 MMA/50 HEMA as well as a pre viously scaled-up 70 EA/30 HEMA copolymer were formulated into paints by Marshall Lab personnel and used to refinish passenger cars. Field testing of the 70 MMA/50 HEA paints has also been initiated.
The 70 EA/50 HEA-Desmodur N system will also be evaluated as topcoat for Corfam poromeric material at Old Hickory.
The search for a better and less expensive pot-life extender than acetyl acetone has been unsuccessful so far. How ever, the use of triethylenedlamine (DABCO) as catalyst may elimi nate the necessity for a pot-life extender. Preliminary results indicate that DABCO catalyzed coating solutions have satisfactory pot life (> 8 hours) and curing rates. Hardness build-up and gloss retention (AWC-II) of DABCO cured coatings are equal or better com pared to the conventionally cured DTDL-acetyl acetone systems. Yel lowing does not seem to pose a problem. This lead will be explored further.
A 70 MMA/50 HEA-Desmodur N clear coating was found to be an attractive candidate for aluminum trailer and truck finishes.
Several Weather-Ometer exposure series of Desmodur N modified acrylic coatings were concluded. Overall results indicate that the gloss retention increases in the following order:
80 EA/20 HEMA< 70 EA/30 HEMA< 70 MMA/50 HEA/50 MMA/50 HEMA. The differences in gloss retention between 70 MMA/50 HEA and 70 MMA/ 50 HEMA are insignificant. Increasing levels of humidity during curing results in somewhat poorer gloss retention while excess Desmodur N75 (up to 10#) and deficiency of Desmodur N (minus 10#) has no significant effect on gloss retention.
Florida exposure (6 months) shows a greater tendency of mildew formation on the polyurethane modified acrylics compared to Desmodur N/Desmophen 650 (Model I). We will determine the practi cal significance of this observation.
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Evaluation including AWC-II and Florida exposure of poly urethane modified acrylic clear coatings for aluminum is in progress.
Nafton's (supplier of Desmodur N) toxicity reports indi cate that Desmodur N has low toxicity. Haskell Laboratory has started testing of urethane enamels to determine their toxicity relative to other well established coating compositions.
ACTION TAKEN OR PROPOSED
The Marshall Development Laboratory will continue formu lation and field testing of preferred candidates in various market areas. A special effort will also be made by the Development Labora tory to develop a new primer for the polyurethane enamels and to further evaluate the amine cure of these systems.
In the coming period, our work will concentrate on opti mization of the MMA/HEA-Desmodur N system including polymer char acterization, prepolymer scale-up, definition of the mildew problem, and ways to reduce cost. The search for alternatives to acetyl acetone pot-life extenders including the study of potentially useful catalyst systems will continue.
PATENT STATUS
Competitive Patents
In addition to the references given in previous reports (Refs. 1, 2), the following patents may have a bearing on our work:
U.S, 3,351,573 to Allied Chemical Corp., patented Nov. 7, 1967, claims isocyanate pending can-stable tin catalyzed coating compositions.
U.S. 3,367,956 to Bayer, A.G., patented Feb. 6, 1968, claims a process for the preparation of biuret polyisocyanates.
U.S. 3,392,183 to Bayer, A.G., patented July 9, 1968, claims a process for the preparation of biuret polyisocyanates.
DUP0300131 11
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Neth. 6,611,071 to Std. Products Co., patented Peb. 6, 1968, claims polyurethanes terminated with NCO and acrylate groups.
Pr. 1,532,739 to Allied Chemical Corp., patented July 30, 1968, claims polyurethane coating compositions containing prepoly mers derived from 4,4*-raethylene-bis-(cyclohexylisocyanate).
Neth. 6,802,858 to Ferro Corp., patented Sept. 2, 1968, claims polyurethane coating compositions catalyzed with tin com pounds containing aromatic groups.
Brit. P. 1.090,449 to Allied Chemical Corp., patented Oct. 12, 1966, claims 4,4,-methylene-bis-(cyclohexylisocyanate) based coating compositions.
Du Pont Patents
FFD-3093, covering durable, nondiscoloring, chemical resis tant coatings from hydroxy bearing acrylic prepolymers and aliphatic isocyanates was filed Nov. 11, 1968. This case will be refiled to Include a claim for amine catalyzed compositions in which the amine is part of the acrylic prepolymer backbone.
FFD-1301, claiming urethanes and poly(methyl methacrylate) containing urethane coatings, transferred to Legal Department on Dec. 23, 1968.
Elchem's PC-3586, claiming polyurethane coating compositions using organotin catalyst/pot-life extender combinations, was filed on Nov. 12, 1968.
It is the Legal Department's opinion that United Aircraft's patent U.S. 3,314,834, patented April 18, 1967, claiming the use of acetyl acetone as a curing rate modifier in two-package polyurethane propellants does not interfere with Du Pont's patent applications PC-3586 and FFD-3093.
Elastomer Chemicals Department Patent Cases Irwin 5X and 5Y (formerly LC-1084) claiming Hylene W were filed 5/12/67 and have Issued in England as Brit. P. 1,117,629 (6/19/68) and Brit. P. 1,127,338 (9/18/68).
DUP03001 31 12
5* ACKNOWLEDGMENTS
The assistance and advice of H. P. Panning, H. B. Hitchins, W. H. Steinmetz, and G. C. Sun of the Marshall Laboratory; J. P. Herring, Engineering Department; and E. B, FitzGerald, Exp. Station, are greatly appreciated.
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DISCUSSION
I. Polyurethane Modified Acrylics
Several recent publications (Refs. 3-8) describe the progress made with isocyanate finishes in general and Isocyanate modified acrylics in particular (Ref. 9).
The coatings systems developed under this project con sist of hydroxy pending acrylic copolymers which are reacted with polyisocyanates to form polyurethanes.
** acrylic--OH + OCN- -----
acrylic--OC--NH--
f!
0
The coating composition Is a two-package system which crosslinks at room or elevated temperature and has a limited pot-life.
The moisture introduced Into the coating solution by the solvents and pigments, as well as the moisture present In the air during the curing stage, can lead to the formation of polyurea as by-product.
--NCO + H-- 0--H
* ... -- NH--C-^-OH ------
it
carbamic acid (unstable)
--NH2 + COs
NCO + NH2------------------------------NH--C--NH-- . . n 0
polyurea
The urea can further react with Isocyanate to form a biuret structure. A similar reaction can also occur between the urethane and isocyanate to give an allophanate. The latter two reactions, however, are slow at room temperature, but can be a factor In baking compositions.
DUP03001 31 14
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II. Acrylic Prepolymer
The acrylic prepolymers investigated include combinations of EA/HEMA, EA/HEA, MMA/HEMA, and MMA/HEA. The emphasis In the reporting period was on 70 MMA/30 HEMA and 70 MMA/30 HEA. The latter composition was chosen for further evaluation because of Its better flexibility and initial gloss as well as lower viscosity compared to the corresponding 70 MMA/50 HEMA system. Cost and durability of MMA/ HEMA, however, is slightly preferable to MMA/HEA.
The durability (gloss retention of white coatings) of Desmodur N modified acrylics increases in the following order as observed from AWC-No. II exposures:
MMA/HEMA> MMA/HEA > EA/HEMA > EA/HEA Hardness increases and flexibility decreases in the same order. The % OH varies with the copolymer ratio as follows:
Copol. Comp. 70 EA 70 EA (molar ratio) 30 HEA 50 HEMA
OH
4.87 4.68
70 MMA 30 HEA
4.87
80 MMA 20 HEA
3.22
70 MMA 30 HEMA
4.68
Desmophen 650
8.0
The # OH of Desmophen 650 is considerably higher compared to the acrylic prepolymers. The OH content of the acrylics does not change much with the type of monomer used and only a change in the molar ratio of the monomers has a significant effect on the # OH. The lower OH content of the acrylics accounts for most of the lower cost of the acrylic system because less of the costly Isocyanate Is used as compared to the competitive Desmodur N/Desmophen 650 system (Model II). Whether additional cost advantages can be realized by changing from the presently used 70 MMA/30 HEA ratio to a 80 MMA/20 HEA ratio without sacrifice in flexibility, gloss, and chemical resis tance will have to be established.
The molecular weight (weight average) of a 70 MMA/30 HEMA copolymer (Gardner-Holdt viscosity of 40$ solids solution In n-butyl acetate/Cellosolve acetate was K = 2.70 Poise) waB found to be 33,000. The corresponding 70 MMA/30 HEA polymerization carried out under similar conditions results in lower viscosity solutions (GardnerHoldt viscosity of 40^ solution was D/E = 1.12). Molecular weight determination of this polymer Is in progress. In general, it is found that the replacement of methacrylate by acrylate results in lower viscosity polymer solutions. This may be due to branching of the acrylates during polymerization.
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An increase in the OH content of the acrylic prepolymers leads to compatibility and solubility problems in some cases and, in addition, would increase the cost of the coatings system,
A. Solvents
Solvents for the acrylic prepolymers Include n-butyl acetate, Cellosolve acetate, methylethyl ketone, ethyl acetate, methyl isobutyl and methyl isoamyl ketone, or mixtures thereof. Most of the MMA/HEMA and MMA/HEA polymers were prepared in a mix ture of 5.5 n~butyl acetafce/l Cellosolve acetate because of their favorable reflux temperature/catalyst half-life time relationship. Lately, a small amount of ethyl acetate is added to avoid popcornpolymer formation at the monomer feed-line inlet or in the reflnxcondenser. This solvent mixture also gives a good balance of gloss, leveling and rate of drying. The use of all Cellosolve acetate results in hazy coatings from the DTDL catalyzed compositions. This is probably due to crosslink formation before solvent evaporation leading to shrinkage and micro-wrinkling of the coating later. The amine cured coatings, however, do not show this phenomenon and can tolerate excess Cellosolve acetate.
With the exception of acetyl acetone, the various solvents used with a 70 MMA/50 HEMA-Desmodur N coating solution had no sig nificant effect on the pot-life as can be seen from Table I. Diglyrue extended the pot-life above seven hours, but the coating solution turned cloudy and evolved gas.
The acrylate polymers are more soluble than the methacrylate containing polymers. A 70 EA/50 HEA prepolymer is, for example, soluble in a 50/50 mixture of ethyl acetate/xylene, while the other polymer compositions can only tolerate much smaller portions of xylene or none at all.
B. Polymerization Catalysts
A variety of catalysts can be employed depending on the polymerization temperature. For practical and cost reasons, polymer ization at reflux temperature and a cycle of eight hours or less is preferable. High polymerization temperatures also lower the molecu lar weight of the polymer effectively. The best overall polymeriza tion procedure for 70 MMA/50 HEA and 70 MMA/30 HEMA employs 5.5-4.0# (of monomer) of t-butyl peroctoate using mixtures of n-butyl acetate/ Cellosolve acetate/ethyl acetate as solvents. The scale-up polymer ization procedure of a 70 MMA/50 HEA copolymerization is described in
DUP0300131 16
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detail in the Experimental Section, This catalyst gives clear color less polymer solutions of low viscosity. The monomer conversion is above 98.5#. The t-butyl peroctoate has a half-life of ~ 5.5 minutes at 115C. Tertiary butyl peracetate can also be used, but the poly merization time is longer (half life at 120 C is 2,0 hours) and the conversion was not as good tinder the conditions chosen.
For polymerization at higher temperatures, e.g., in Cellosolve acetate at 145-155C, di-tertiary butyl peroxide or 2,5-di methy1-2, 4- di(t-butylperoxy) hexane (Lupersol 101) can be used suc cessfully.
Vazo polymerization catalyst is unsuitable for the prepa ration of low viscosity MMA/HEMA and MMA/HEA copolymers. It also tends to discolor the polymer solutions. It, however, proved to be a useful catalyst for the preparation of a 70 EA/50 HEA copolymer In ethyl acetate/xylene at 86-89C (see Experimental Section).
Ill. Polyisocyanates
Only the aliphatic or alicyclic polyisocyanates give durable nondiscoloring coatings. While some progress has been made to improve the light stability of aromatic isocyanates, such as in "Desmodur" L (Ref. 10) and Nafton*s E-268 (Ref. 11), they cannot match yet the light stability of the aliphatic isocyanates. A previous report (Ref. 2) lists the various available aliphatic polyisocyanates. Of these, only "Desmodur" N was used in our work mainly because of its lower toxicity and proven acceptability in the field. Du Pont's alicyclic diisocyanate "Hylene" W has not been evaluated further because of potential toxicity hazards.
"Desmodur" N is a hexamethylene diisocyanate biuret obtained from the reaction of hexamethylene diisocyanate and water. The urea formed Is reacted with additional HMDI to the biuret.
3 OCN--{CH2 )--NC0 + HaO----- OCN(CH2)e-NHCONCONH(CHa)aNCO
+ CO2 NCO biuret Isophorone diisocyanate,which has two NCO groups of dif ferent reactivity, may be of particular interest for systems involving isocyanate pending prepolymers.
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IV. Pot-Life Extenders
Our search for pot-life extenders having similar or better effectiveness than acetyl acetone has continued.
Kojlc acid, a known metal complexing agent, was found to be a very effective pot-life extender In a ETDL catalyzed 70 MMA/30 HEA-Desmodur N composition as shown in Table II-A. This effect, however, is only obtained at an unacceptable sacrifice in tack- and tape-free time of the coatings.
The addition of 2-butanol and t-butyl alcohol to a DesmodurN modified 70 MMA/50 HEMA coating solution did not result in an exten sion of the pot life. We had hoped that secondary or tertiary alco hols would form a labile addition product with the isocyanate which could then be reversed by interaction with the primary OH groups of the acrylic prepolymer and lead to polyurethane formation.
The addition of citric acid, which is also a metal chelating agent, results in a cloudy, gas-evolving coating solution. The results are summarized in Table II-B.
Other efforts to extend pot-life without sacrifice in drying properties include catalyst studies which are discussed in paragraphs V-A and -B.
V. Curing of Desmodur N Modified Acrylics
The NC0-0H crosslink reaction in the absence of added catalysts is too slow for practical applications. Certain metals and aliphatic tertiary amines are the most effective catalysts for this reaction as discussed in the following paragraphs.
A. Metal Catalysis
DTDL Is the best overall catalyst for curing of polyurethane modified acrylics. However, because of its high activity, combina tion with a pot-life extender such as acetyl acetone is necessary to keep the coating solutions from premature gelation. This system gives an acceptable balance of rate of cure and pot-life, but it necessi tates separate packaging of the pot-life extender/catalyst portion because of the reaction of the acetyl acetone with the tin can. It also softens presently used primers and its enol form reacts slowly with the isocyanate. The high cost of acetyl acetone ($0.91/lb) is also an important consideration in the economics of the coating system.
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Our efforts to find a better metal catalyst system were unsuccessful so far. Various metal acetyl acetonates were screened Including the acetyl acetonates of vanadium, chromium, cobalt, zinc, zirconium, titanium, potassium, and nickel. The metal acetyl acetonates mentioned above are either Insoluble, deeply colored, ineffective, or do not give an acceptable balance of cure rate and pot life.
We found recently that phenyl mercury propionate and phenyl mercury oleate, which are commonly used mildewcides, catalyze the NCO-OH reaction. Preliminary experiments indicate that 0.1# (rel. to coating solution solids) of these compounds result in acceptable cure rates in the absence of DTDL or DABCO. These compounds are also expected to improve the mildew resistance of polyurethane coatings.
We plan to evaluate several tin acetyl acetonates which will be prepared and supplied by Prof. S. Yolles of the University of Delaware.
B. Amine Catalysis
Tertiary amines are known to catalyze polyurethane forma tion. We evaluated triethylenediamine (DABCO), heptamethylisobiguanide and dimethylaminoethyl ether (NIAX-AI) as catalysts for polyurethane modified acrylics and Desmodur N/Desmophen 650 (Model II). Only DABCO gave an acceptable balance of cure rate and pot life.
In Table III, we have summarized the coating properties of a white Desmodur N/Desmophen 650 finish catalyzed with various amounts of DABCO and NIAX-AI. The results show that in this case the addition of 0.2# DABCO to the coating solution gives a gel time of more than eight hours, but the tack- and tape-free time is increased to 2, respectively six hours. The best overall balance of properties is expected to be obtained with a level of O.25# of DABCO relative to binder. NIAX-AI, which is a good catalyst for moisture cure isocyanate systems, was found to be too slow in the above system at the levels evaluated.
Desmodur N modified acrylic coating systems require a higher DABCO level for acceptable cure rates compared to Desmodur N/Desmophen650. A 70 MMA/50 HEMA-Desmodur N coating catalyzed with 0.5# DABCO gave a tack-free time of 1.5 hours and a tape-free time of 5 hours. The gel time was above 8 hours. Comparisons of DTDL and DABCO cata lyzed coatings systems are presented In Table VT. Evaluation of amine cured MMA/HEA-Desmodur N systems Is in progress.
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C. Curing Under Varied Humidity Conditions
A 70 EA/30 HEMA-Desmodur N white coating composition was cured at 23, 50, and 90# relative humidity. The hardness of the coatings cured at 50 and 90# relative humidity was lower and the flexibility better compared to the coating cured at 23# rel. humid ity. Tack- and tape-free time, as well as gloss of all three coat ings, were essentially the same. The results are summarized in Table IV.
The gloss retention of the panels exposed on the AWC-II Weather-Ometer decreases somewhat with increasing humidity levels during cure as will be discussed in paragraph VT-B.
D. Effect of NCO/OH Ratio on Curing and Properties
A 70 MMA/30 HEA white coating solution was modified with 1.5* 5-0, and 10# excess and a 10# (by weight) lack of Desmodur N75. The properties are summarized In Table V. While tack- and tapefree time and hardness of the coatings are similar, the impact resis tance of the coating with the 10# lack of Desmodur N-75 Is poorer com pared to the other coatings. The gel time of all coating solutions was above 8 hours. No significant differences in gloss and gloss retention of the coatings were observed before and after AWC-II Weather-Ometer exposure.
VI. Evaluation of White Desmodur N/Acrylic Coatings
Drying characteristics and properties of white Desmodur N modified acrylic coatings have been described in a recent report (Ref. 2). In the following, up-dated results and observations are discussed.
A. Physical/Mechanical Properties
We concentrated In the reporting period on the evaluation of white Desmodur N modified 70 MMA/30 HEMA coating compositions. The results are summarized in Table VI. All paints were pigmented with W-185 because of earlier results (Ref. 2) indicating better gloss retention compared to W-131. The pigment/binder ratio was In most cases 64/100 except when stated otherwise. The coatings were sprayed on Alodine A1 1200S substrate and Alelad A1 primed with 818-012 Pretreatment Coating Wash Primer and 825-8140 "Corlar" Intermediate Coat White. In order to follow the application con ditions in the field, the primer was cured for a minimum of 4 hours
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13
and a maximum of 36 hours at room temperature. Gloss, leveling. Impact resistance and flexibility of the 70 MMA/30 HEMA-Desmodur N system does not quite match the competitive Desmodur N/Desmophen 650 finish yet. We have, therefore, recently shifted the emphasis to 70 MMA/30 HEA-Desmodur N systems which appear to overcome these shortcomings. Detailed evaluation is still in progress.
The addition of 1,4-butanediol to a white 70 MMA/30 HEMADesmodur N paint in order to Increase the OH content from 4.7 to about 856, which matches Desmophen 650, did not result in a signifi cant improvement in gloss or impact resistance.
B. Exposure Series - Durability
The AWC-II Weather-Ometer exposure results of white Desmodur N modified 70 EA/30 HEMA, 80 EA/20 HEMA, 70 MMA/30 HEA and 70 MMA/30 HEMA coatings (Exposure Series 21608) show superior gloss retention compared to Desmodur N/Desmophen 650 except the 80 EA/20 HEMA-Desmodur N systems which were similar to Desmodur N/Desmophen 650 after 300, 600, and 900 hours. The 70 MMA/30 HEMA-Desmodur N coatings showed the best gloss retention.
AWC-II (Exposure Series 21669) exposure of white 70 EA/30 HEMA-Desmodur N coatings cured at 23, 50, and 90$ relative humidity shows that gloss retention decreases with increasing humidity after 600 and 900 hours. White 70 MMA/30 HEA-Desmodur N coatings formu lated with up to 10$ excess as well as a 10$ deficiency of Desmodur N75 showed no significant differences in gloss retention. A 70 MMA/ 30 HEA-Desmodur N coating baked for 30 min. at 130C had better gloss retention than its air-dried counterpart.
AWC-II (Exposure Series 21718) exposure of DABCO cured 70 MMA/30 HEMA-Desmodur N coatings show that they are equal and in some cases slightly superior to the corresponding DTDL catalyzed coatings. The same Is true for the Model II controls. The gloss retention of a DTDL catalyzed 70 MMA/30 HEMA coating having a P/B ratio of 45/100 was similar to a coating having a P/B ratio of 64/100 (W-185 pigment).
The gloss retention of an 80 MMA/20 HEMA-Desmodur N coating catalyzed with DTDL was inferior to the corresponding 70 MMA/30 HEMA coating.
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A DTDL catalyzed 70 EA/50 HEA-Desmodur N coating showed good gloss retention after 900 hours AWC-II exposure, but a fair degree of yellow/brownish spots were observed on the panel.
Overall, the appearance and adhesion of the exposed coat ings were superior on Alodlne A1 1200S substrate compared to the coatings on the primed substrates. This suggests that an effort to develop an improved primer (faster cure, better solvent resistance and adhesion) would be a worthwhile objective.
Florida exposed (6 months) Hylene W and Desmodur N modi fied acrylic coatings (Exposure Series 21554 and 21608) are superior In gloss retention to the controls including 868-95774 and 926-9577 Lucite, 95-21667 New Dulux, 962-21667 acrylic enamel and 959-8559 modified acrylic lacquer, but equal to Desmodur N/Desmophen 650 coat ings (Model I). The polyurethane modified acrylic coatings show stronger mildew formation than the Desmodur N/Desmophen 650 coatings (Model I). The use of several fungicides to eliminate this problem is being investigated.
VII. Evaluation of Desmodur N/Acrylic Clears
Various Desmodur N modified acrylic clears were formulated and evaluated as finishes for aluminum trailers and trucks. The 70 MMA/50 HEA-Desmodur N combination offers an attractive balance of properties including flexibility, impact resistance, hardness, rate of drying, and gel time of the solution. The results of the prelimi nary evaluation and the comparison with commercial controls are sum marized In Table VII. None of the coatings show any water whitening after two-day Immersion in tap water. The spotting of some of the experimental coatings is not considered a major problem because some of the commercial control coatings show the same phenomenon.
AWC-II and Florida exposure Is in progress.
VIII- MEKO-Blocked Hylene W
The preparation and evaluation of MEKO-blocked Hylene W/ hydroxy acrylic prepolymer baking finishes was discussed in an earlier report.
The production of MEKO-blocked "Hylene" W (75# in Cellosolve acetate) was scaled-up to a 75 lbs. batch without difficulty and samples for evaluation are available.
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The MEKO-Hylene W adduct is a solid which occasionally crystallizes from the solution in the form of white crystals which melt at 120-135C. The wide melting range is apparently due to the presence of several isomers.
IX. Scale-Up of Acrylic Prepolymers
Several acrylic prepolymerizations were scaled-up in a 20-gallon kettle at the Marshall Laboratory. The polymers scaledup include 70 EA/30 HEMA, 70 MMA/30 HEMA, 70 MMA/30 HEA and 70 EA/ 30 HEA. No unusual problems were encountered and the batches were made available to interested parties for evaluation in polyurethane modified finishes and paints.
X. Field Testing
The following field tests were conducted with Desmodur N modified acrylics:
1) 70 EA/30 HEMA-Desmodur N (Ref. 12) passenger car, off-white over sanded Dulux (2 yrs. old), control Desmodur N/Desmophen 650 (Model II), conducted by G. C. Sun.
Observations: Satisfactory flow and sag resistance, no over spray melt-in problems, no solvent popping, some film distortion, tack-free in 15 min., tape-free in -v 2 hrs. Model II control showed some solvent popping.
2) 70 MMA/30 HEMA-Desmodur N (Ref. 14) A) passenger car, off-white over white "Corlar" primer, control Desmodur N/Desmophen 650 (Model II), conducted by G. C. Sun.
Observations: Application properties were good, no overspray melt-in problems, initial gloss somewhat lower than Model II control. B) Diesel switcher, off-white over 825-006 zinc chromate epoxy primer, control Desmodur N/Desmophen 650 (Model II), conducted by E. R. Harkins (Ref. 15).
Observations: Good gloss but somewhat lower than Model II. Some sagging because of low viscosity, tendency to dry spray. The Model II control showed some surface bubbling and longer tack-free time.
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Field tests planned for the near future;
1) 70 mma/30 h e a
passenger car, off-white, control Dulux passenger car, metallic, control Desmodur N/Desmophen 650 (Model II), to be conducted by G. C. Sun.
2) 70 EA/30 HEA
topcoat for white shining Corfam, will be conducted by G. C. Johnson, Old Hickory.
XI. Toxicity of Desmodur N Modified Acrylics
Marshall Laboratory (J. A. Antonelli) has taken responsi bility in cooperation with Haskell Laboratory for testing of the urethane enamels to determine their toxicity relative to other well established products.
German toxicity reports Indicate that Desmodur N has a low level of toxicity. The author of the German toxicity study (Ref. 12) is known to Haskell Lab and is considered a reliable source of infor mation.
EXPERIMENTAL DETAILS
Scale-up of 70 MMA/30 HEA copolymerization
18 gallons)
(see Notebook 399E-125 and Marshall Lab Notebook 9335-24).
Equipment: 20-gallon stainless steel kettle Lbs.
Charge:
MMA (Du Pont HA-9345)
46.00
HEA (Dow Chem. Co., 97$)
24.29 (adjust, for 100$)
t-butyl peroctoate_____________ ________ 2.46 (3.5$ of monomer)
n-butyl acetate Cellosolve acetate
47.44 15.67 methane
ethyl acetate7.19
gra 6_________ ________
t-butyl peroctoate-booster
0.144 (65.4 g.)
In order to remove a slight haze in the monomer mixture, 0.1$ of "Celite Filter-Aid" Is added with stirring and then the mixture is filtered through a cartridge filter.
The solvent is charged to the reaction vessel and heated to reflux (ll8C) with stirring under a blanket of nitrogen. To the refluxing solvent Is added the monomer/catalyst mixture over a period of 4 hours. The reaction mixture Is maintained at reflux for 1 hour and then the temperature Is lowered to 100C. Then half of the booster catalyst is added and the mixture Is held at 100C for an additional 30 minutes. Then the second half of the booster catalyst Is added and the mixture is heated at 100C for another 30 minutes. The polymer
solution is then heated to reflux and maintained at reflux for 45 minutes. The polymer solution is cooled to ~ 50C and let-down through six layers of cheesecloth.
DUP03001 3124
17 -
We obtained 140.86 lbs. (98.4# of theor.) of a clear color less polymer solution of Gardner-Holdt viscosity U/V at 49.6# solids.
Analytical Results:
# Polymer Solids - 49.7/49.5 # OH (solution) - 2.49/2.50 (corresponds to a 68.9 MMA/31.1 HEA
copolymer molar ratio) Acid No. (solution) - 2.33/2.37 # Vinyl (solution) - 0.215/0.211
MEKO-Blocked Hylene W (Code No. 399E-68) (see also Marshall Lab Notebook 9109-140)
Equipment: 20 gallon stainless steel kettle
Charge:
Hylene W
MEKO (h -584) Cellosolve acetate (ureth. grade)
Lbs. 33.00
22.05 (0.47# 18.33 73.38
excess)
The MEKO-Cellosolve acetate solution Is charged to the reaction vessel fitted with reflux condenser, water cooling, and nitrogen Inlet. To this mixture the "Hylene" W is added with stir ring under a blanket of nitrogen over a period of ~ 3.5 hours. The temperature is held below 50C (reaction is exothermic) by intermittant water cooling. The reaction product is stirred for an addi tional hour after the "Hylene" W addition is complete and then let down.
The reaction product is clear and nearly colorless and has a Gardner-Holdt viscosity of U (6.27 Poise). The solution contains 44.97# "Hylene" W or 14.39# NC0 (if regenerated).
Scale-Up of 70 MMA/30 HEMA Polymerization
(Code No. 399E-89, see also Marshall Lab Notebook 9159-81)
Equipment: 20 gallon stainless steel kettle
Lbs.
Charge:
MMA (Du Pont HA-9345)
32.41
HEMA (Rohm & Haas, 96#)
18.79
t-butyl peroctoate (4# ofmonomer)___________ .02
n-butyl acetate
39.80
Cellosolve acetate
11.40
t-butyl peroctoate (0.2#of monomer)
0.10
DUP030013125
- 18 -
The monomer/catalyst mixture was added to the refluxing solvent (128C) with stirring under a slow stream of nitrogen over a period of 5 hours. Reflux was continued for 50 minutes after the addition was complete and then the booster catalyst dissolved in some distillate was added. The mixture was held at reflux for an additional 1.5 hours. The polymer solution was allowed to cool overnight and then let-down through felt filter.
We obtained a clear colorless polymer solution of GardnerHoldt viscosity Z4/Z5 at 525j6 solids. At 4oj6 solids, the GardnerHoldt viscosity was K.
Analysis: $6 solids: 52.5; % OH (solution): 2.25 $> vinyl: 0.75/0.80; M.W. (weight average): 55,000
Scale-up of 70 EA/50 HEA polymerization (Code No. 599E-116, see also Marshall Lab Notebook
Equipment: 20 gallon stainless steel kettle
Charge:
Lbs.
EA (H-72)
28.0
HEA (Dow Chemical, 97#)
15.9
Vazo polymer catalyst (4%> of monomer) 0.168
Ethyl acetate (urethane grade)
21.0
Xylene (H-585)_________________________________20.9
Vazo polymer catalyst-booster
0.084
The monomer/catalyst mixture was added to the refluxing solvent (89c) with stirring under a slow stream of nitrogen over a period of 4 hours. Reflux was maintained for 45 minutes of the addi tion was completed and then the booster catalyst dissolved in some distillate was added. The mixture was held at reflux for an addi tional 1.5 hours, cooled to room temperature and let-down through cheesecloth.
The clear and nearly colorless polymer solution was char acterized as follows:
$6 Polymer Solids - 49.4/49.4 Gardner-Holdt Viscosity - H (at 49.456 solids)
Al/A (at 40# solids) 56 OH (polymer)-4.89/4.90; Acid No. (polymer) 5.52/5.52 56 Vinyl (solution) - 0.57/0.57
DUP030013126
19 -
BIBLIOGRAPHY 1. H. P. Reinhardt, Research Report, ESR-68-7. 2. H. P. Reinhardt, Research Report, ESR-68-32. 3. K. A. Pigott, E. R. Wells, and G. A. Hudson, Paint and
Varnish Prod.. Jan. 1968, p. 39-45,"Light Stable Polyurethanes." 4. H. Gruber; Paint and Varnish Prod.. November 1968, p. 27-32,
"Polyurethanes In the Building Industry." 5. R. Hebermehl, Paint Technology. Vol. 32, No. 4 (1968), p. 22-25,
'Recent Developments in Polyurethane Coatings." 6. W. Berger and G. Hentze, Paint and Varnish Prod.. April 1968,
p. 43-47,'^Two Component Polyurethane." 7. A. Mann, Paint and Varnish Prod.. April 1968, p. 23-27 -
"Seamless Flooring." 8. C. R. Martens, Technology of Paint3, Varnishes and Lacquers,
p. 205-22, N.Y. Relnhold, C 1968. 9. A. G. North, Paint. Oil and Colour Form.. Dec. 22/29 (1967),
p. 1139-40 - "New Room Temperature Curing Acrylics." 10. Naftone, Inc., Product Bulletin - Desmodur L, Desmophen. 11. Naftone, Inc., Product Bulletin - E-268. 12. Letter by H. J. Mueller of Naftone, Inc., to J. A. Antonelli
(includes supplemental toxicity report). 13. G. C. Sun, Urethane Enamel Field Test Report of August 27, 1968. 14. G. C. Sun, Urethane Enamel Field Test Report of December6, 1968. 15. E. R. Harkins, Trip Report, Kansas City Railroad, Shreveport,
Lousiana, October 8 & 9, 1968.
HFR/jam 1/29/69
DUP030013127
TABLE I
Coating Solution:
10.0 g
polymer solids 70 MMA/50 HEMA (5056 n-butyl acetate/propyl acetate 2/1)
0.009 g 50 silicone SP-1025 (0.055* act. lngr.
of binder)
4.15 g Desmodur N-75 (1.05 NC0/1 OH)
0.0045 g DTOL (0.055* of binder)
8.0 g
solvent
(glass substrate, film thickness - 2 mil, room temperature cure)
Solvent
Cellosolve Acetate Propyl Acetate Methyl Isobutyl Ketone Diglyme Anlsole Acetyl Acetone Glyme Dlbutyl Ether Dloxane 2-Ethoxy Dihydropyrane
Gel Time (hrs) 1
Tack-Free (hrs) 1/2
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1 1/2
2
1 1/4
1/2
2
>7 5 >7
1 5/4
2
56 1/2
4
1 1/2
2
Incompatible
1 not determined
Incompatible
HFR/jam 1/50/69
DUP030013128
TABLE II-A
EVALUATION OP KOJIC ACID POT-LIFE EXTENDER (70 MMA/50 HEA-DESMODUR N)
KoJlc Acid/ DTDL Mol. ratio
0.5/1
1/1
2/1
4/i
8/1
DTDL only
DTDL AcAc
Gel Time (hrs) 5 15 26 56 44 1 1/4
Tack-Free (hraV
1
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6 0.6
1
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1
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soft
1
> 22
soft
1 1/4
> 22
soft
3/4 3 3/2 0.7
56
3/4
4 0.7
HFR/jam 1/50/69
DUP030013129
TABLE II-B EVALUATION OP POT-LIFE EXTENDERS
Coating Solution:
10.00 g pol. sol. 399E-89 (70 MMA/50 HEMA)
3.56 g Desmodur N (1.05 NCO/l OH) 2.00 g n-butyl acet./Cellos, acet. - 50/50 2.50 g additive (13.8# of total) 0.00395 g OTDL (0.05* of binder)
(glass substrate, coating thickness ~ 2 mil)
Additive
Gel Time (hrs)
TackFree (hrs)
TapeFree ,,(hrs)
KHNoc 1 30* at day 330*0
Acetyl Acetone
12 3/4 3 6.5 17.2
Celiosolve Acet. Res.
Excellent
Kojic Acid** Citric Acid
35 1/2 >4 3.0 17.6 Excellent
< 19
cloudy, gas evaoluatlon - discarded
2-Butanol
1 discarded
t-Butyl Alcohol
1 discarded
Diacetone Alcohol
1 discarded
Control (n-butyl ac./ Cellos, acet.- 50/50)
1
discarded
Control (n-butyl ac.. >31
Cellos, acet.-50/50)
3A > 7
<23
Soft 16.9
Excellent
no OTDL added ** 5# solution in MEK
ii KR/Jam 1/30/69
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DUP0300131 34
o
EVALUATION OP DBSMODUR N MODIPIEl? ACRYLIC CLEARS
) Reduced 1 s i w ith m e th yl Isoam yl ketonei
a) Reduced 1:1 w ith T-5864
a) Measured a fte r 5 days
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DUP03001 3135
ABSTRACT The development and evaluation of two-package white and clear Desmodur N modified acrylic coatings are discussed. The laboratory and scale-up production of hydroxy bearing acrylic prepolymers, including catalyst and solvent studies, are described. The acrylic prepolymers were formulated into white paints and clear coating compositions and their prop erties were investigated. Weather-Ometer and Florida exposure results of these coatings are reported. The amine catalysis of Desmodur N modified acrylics and Desmophen 650 is described.
DUP030013136
GLOSSARY
Desmodur ] [-75 ~ hexamethylene dilsocyanate biuret (75$) (Bayer, A. G.)
I
Desmophen 650 - hydroxy polyester (Bayer, A. G.)
MMA HEA HEMA EA DABCO DTDL
methyl methacrylate hydroxyethyl acrylate hydroxyethyl methacrylate ethyl acrylate fcrlethylenediamine dibutyltin dilaurate
DUP0300131 37
REPORT PIST8.MTXQN
TO RECEIVE ALL REPORTS
_ESR REPORTS PULL REPORT
FIRST PART
W. D. Lawson C. W,, Theobald P. I. Poindexter J. C. Richards J. A. Klaesmann W. S. Woods* C. F. Kalb** N. Pappas W. H Edwards C. 1. De Boer G. E. Lewis D. M. Glenn S. Hpehberg Information Services C. H. Knop Marshall Lab Library PRL Library G. I * Mulholland N. G. Fisher (CRD)
TO RECEIVE REPORTS ON POROMERICS
All those listed above pins:
G. I. Jenkins J. S. Allen J. L, Palermo G. T. vaala C. A. Lynch T. U. Young H. E. Batson G. E., Cornell E. K. Holden P. M. Hodgson B. H. Kirk (Engg.)
-I 1 1 -1 ** 1 1 -1
-1 ~1 -1 -1 -1 1 1 - . 16 3 16 16 I-
1 1 1 -l 1 1 -1 1 -1 -1 -1
* Except Consumer Product reports ** Except Consumer Product and Poromerie reports
2/11/69
DUP030013138
DUP03001 3139