GB2319254A - Oligoester coatings - Google Patents

Abstract

A coating composition especially for use in automotive clear coatings for plastic articles to provide scratch-resistance contains an oligoester and an aminoplast resin or isocyanate cross-linker. Suitable oligoesters include those having the chemical formula: HO- -(CH 2 ) n -X y -(CH 2 ) n OH where X is selected from n is between 4-20 (preferably 5-12) y is between 1-15 (preferable 1.5-6); and Z is a alkane having between 0-7 carbons.

Description

OLIGOESTERS COATINGS The present invention relates to scratch-resistant coatmg compositions containing oligoesters and suitable cross-linkers.

It is desirable to provide durable, long lasting and glossy coatings for automobiles. Durability and gloss have been achieved by increasing the hardness of the automotive coating. While this method is useful for metal parts, it has disadvantages when the coated article is made from a flexible material such as plastic. Plastic parts require flexible coatings that adhere well even if the part bends or moves.

The article titled: Scratch resistant clear coats: development ofnew testing methods for improved coatings, Progress in Organic Coatings, 22 (1993), p. 27, Peter Betz and Angelika Bartelt, describes a method of measuring the elasticity of an automotive coating. Elastic coatings defonn when scratched but re-flow to fili the damaged area. The paper suggests that isocyanate groups having long and flexible chains may lead to better scratch resistance. This was especially true for acrylic coatings that are crosslinked with aliphatic isocyanate trimers. While the coatings produced with this composition had good elastic properties and re-flowed when scratched, the coatings were too soft and were not acceptable for automotive applications, id. at 34.

Others have suggested the addition of silane oligomers to increase the durability of acrylic coatings as exemplified by US patents 4,975,488 and 5,066,698. However, the saline oligomers did not provide the flexibility and scratch resistance necessary for coated plastic parts.

It is desirable to provide a low cost coating that combines both resistance to surface marring and durability. It is a further desire of the present invention to provide a flexible clear coating suitable for application atop plastic automotive parts such as bumpers. facias and cladding.

The present invention reIates to scratch-resistant coating compositions containing oligoesters and suitable cross-linkers. Suitable oligoesters include those having the chemical formula: HO-[{CH2)ff-X]y{CH2)nOH where X is selected from

n is between 4-20 (preferably 5-12) y is between 1-15 (preferable 1.5-6); and Z is an alkane having between 0 -7 carbons.

In addition to the oligoesters presented above, other oligoesters included in the table below are also suitable for the coating compositions descnbed. The examples labeled nGI and 1OES are also included from the formulas described above but are included in the table below for purposes of identification.

Table 1 Formulation of Oligoesters

Raw IU~ Slrudure OliWerdlols Name H3C02C C02CH3 O O 11 HO(CH2)n { ' O--(CH2)n- OH n Gl HO(CH2)"0H n n=3.4,5.6and10 H3C02CoC02CH3 SeeStruclurelbelow i6Gi CH3 H0H-(CH2)4-0H H3C02C Co2cHa O 0 CH - CH2 CH3 CH3 HO-CH2-CJ 1 (CH0H HO-CHT:HIMI CH3 CH3 CH3 CH3 H3CO2C CO2CH3 O O BEP-I C2H5 ii " Cf5 C2H5 I C C I H0-CH2-C1-CH OCH2CCH;G; HO-CH2-C-CH2OH CHg C4Hg HZ-OH CIHg CqHg 1 CqHS HOCH2 s CH20H HOCH2 + CH - oCt CH2+CHz -OH 3cOzcw3 r o o-(CH2)l0 i O-(CH2)10 OH ICES HO-(CH2)o "" H3C02C-C02CH3/ HO-(CH2)10-OH M-1OGT See jNcture 2 below oho H-9Ji-CH2%1-cR3 0 0 where X is a repeat unit between 1-15 (preferably 1.5-6); and

o 0 0 0 II II CX3 I II CH3 HOW I C C I O-(CH2)4-CH O O-cH-(cH2)oH Structure 1 1 0 0 P o ,o,r 0 O1-C-(cH2 CI (CH2)10-O CO(2)IoLo -C-(CH2 C- 0 cIH2 CH2 CH-CH2-O- C-CR3 R -c -o -CH2CH I ii II I OH O Stnore2 O OH Structure 1, where X and Y are repeat units between 0 and 6.

Structure 2, where R is an alkane having from one to seven carbons, and X is repeat unit between 3-12 Suitable cross-linkers include aminoplast resins, preferably melamine-formaldehyde resins, and polyisocyanates, preferable aliphatic tri- and other polyisocyanates, and other cross-linkers capable of reacting with the hydroxyl group of the oligoesters.

The oligoesters are combined with melamine or polyisocyanate resin to form a crosslakable binders for coatings. The oligoesters were synthesized by melt transesterification between diesters and diols using zinc acetate as the catalyst. Because polyisocyanate cross linkers are to be used, very low levels ( < 02% by weight) of zinc acetate were used. The amount of diols exceeded the diesters and formed oligoesters having two terminal-OH groups which can further react with crosslinker.

The structures of oligoesters were designed by changing the diols or diesters and controlling the average degree of polymerization (DP) to improve the properties of the coatings. The structure of the synthesized oligoesters and the starting material are shown in Table 1 above. Isophthalate oligoesters were denoted as nGI, i-6GI, NPG-I, 1 OES, CHDM-I and BEP-I.. The nGI oligoesters were fiuther divided into 3GI, 4GI, 5GI, 6GI and 1061 according to the number n in the diols HO(CH2)nOH, where 3GI is n= 3, etc. A modified terephthalate oligoester was denoted M-IOGT.

The synthesis procedures of the various oligoesters were the same. The raw materials used to prepare the oligoester included: dimethyl isophthalate, dimethyl terephthalate, dimethyl 1 ,4-cyclohexane dicarboxylate, 1 ,10-decanediol, 1 ,6-hexanediol, 1 ,5-hexanediol, 1,5 -pentanediol, 1 ,4-butanediol, 1,3 -propanediol, 1 ,4-cyclohexanedimethanol, 2,2 dimeiylpropanediol (NPG), 2,2-butyl ethyl propanediol (BEP), succinic anhydride, zinc acetate dihydrate and benzyl triphenylphosphonium chloride were reagent grade (from Aldrich) and were used without purification. Glydexx N- 10, Glycidyl neodecanoate, was from EXXON Chemical Co.

Example 1.

Syntheses of Oligoesters nGI, i6GI, BEP-I, CHDM-I and 1OES Oligoesters were prepared by charging the constituents listed in Table 2 respectively into a reactor equipped with a thermometer, a heating mantle, a stirrer, a Dean-Stark trap, a reflux condenser and nitrogen inlet. The reactor was heated gently to 1400C and held at the range from 140 to 700"C for 3-4 hours (most ofthe time, the temperature was 1900C). Nitrogen was passed slowly through the reactor to help methanol out. Methanol was collected in a Dean-Stark trap. Heating was continued for 30 minutes after all of the liquid dropped from the condenser. The hot product was poured into a glass container. H-NMR spectra showed that the dimethyl isophthalate (at 3.9 ppm) had been completely consumed. Product yields were nearly 100%.

Table 2. PreParation of olipoesters.

Oligoester Diester Diol Catalyst (g) (mole) (g) (mole) (g) Dimethyl isophthalate 1.1 0-Decanediol ZnAc2 lOGI -a 38.80 0.20 52.30 0.30 0.15 -b 19.40 0.10 29.60 0.17 0.08 Dimethylisophthalate 1,6-Hexanediol ZnAc2 6Gl -a 19.90 0.10 17.70 0.15 0.07 -b 58.20 0.30 48.90 0.41 0.20 -c 58.20 0.30 50.10 0.43 0.20 -d 20.20 0.10 17.70 0.15 0.07 -e 20.00 0.10 20.00 0.17 0.07 Dimethyl isophthalate 1,5-Hexanediol ZnAc2 i 6Gl 4.86 0.03 4.39 0.04 0.01 Dimethyl isophthalate 1,5-Pentanediol ZnAc2 5GI 5.44 0.03 4.78 0.05 0.01 Dimethyl isophthalate 1,4-Butanediol ZnAc2 4G1 -a 19.40 0.10 14.78 0.16 0.06 -b 4.86 0.03 4.00 0.05 0.02 -c 4.85 0.03 4.60 0.05 0.02 -d 3.88 0.02 4.40 0.05 0.02 Dimethyl isophthalate 1,3-Propanediol ZnAc2 3G1 5.44 0.03 4.78 0.06 0.01 Dimethyl isophthalate 2,2-Butyl ethyl propanediol ZnAc2 BEP-I 19.40 0.10 13.50 0.15 0.07 Dim ethyl isophthalate 1,4-Cyclohexanedimethanol ZnAc2 CHDM-I 19.40 0.10 21.70 0.15 0.08 1,4 Dimethyl cyclohexanecarboxylate 1,10-Decanediol ZnAc2 10ES 20.00 0.10 26.20 0.15 0.08 Example 2.

Synthesis of Oligoester NPSI NPG-I was prepared by charging 19.4g of dimethyl isophthalate (0.10 mole), 20.8g 2,2 dimethyl propanediol (0.20mole), and 0.08g zinc acetate dihydrate into the same reactor as descried in Example 1, with the same reaction conditions for 4 hours. Some white powder was attached to the wall of the reactor at the end ofthe reaction. The white powder attached to one neck ofthe reactor was separated and the hot product was poured out carefillly from this neck NMR spectra indicated that the dimethyl isopirthalate had been consumed and the white powder was 2,2--dimethyl propanediol (NPG).

Example 3.

Synthesis of Oligoester 10GT The 1 0GT oligoester was prepared by charging the constituents in Table 3 into the same reactor as described in Example 2, with the same reaction conditions for 3 hours. The hot reaction product was poured into a beaker to cool and then transferred into a flask equipped with a reflux condenser and 500 mL toluene was added. The flask was then heated until all of product was dissolved. The solution was cooled to room temperature and kept overnight. The white precipitate was collected and washed with methanol. The final product yield was 75%.

Table 3. Prwarationof 10GT.

Oligoester Dimethyl terephthalate(g) 1,10-Decandediol (g) ZnAc(g) IOGT -a sus.2 78.5 0.27 -b 38.8 69.7 0.22 Example 4.

Synthesis of M-1OGT The modified 10GT, denoted M-lOGT, was prepared by charging the constituents in Table 4 into a reactor equipped with a thermometer, a heating mantle and a stirrer. The reactor was heated gently to 1400C and held at this temperature for 4 hours. The NMR spectra howed that the 10GT had been consumed. Then Glydexx N- 10 and benzyltriphenylphosphonium chloride (BTPPC) were added into the reactor and the reaction temperature was held at 150-1600C for 3 hours. The hot product was poured into a beaker. After cooling, the product was transferred into a flask equipped with a condenser and 200 mL of toluene was added. The flask was then heated until all of the product dissolved. The solution was cooled to room temperature and kept overnight. The turbid solution was separated by centrifuge and the transparent solution was concentrated by rotary evaporator. The sticky product was washed by petroleum ether and then dried.

Table 4. Preparation of M-IOGT.

Oligoester Succinic anhydride(g) GIydexx N-lO(g) BTPPC(g) M-IOGT(2.3) 26.2g iOGT(2.3) 6.0 16.5 0.03 M-IOGT(1.5) 24.OglOGT(l.S) 10.0 27.5 0.06 Properties of oligoesters Physical State: Oligoesters 10GI, 6GI, 4GI, 10ES, NPG-I and CHDM are white solids. M-1OGT and 361 are white semi-solids. i-6GI and 561 are sticky liquids. BEP-I is a very sticky liquid.

Solubility: Oligoesters 1061, 661, i-6GI, 5GI, NPG-I, BEP-I, lOES and M-1OGT are soluble in xylene, methyl amyl ketone and propyl acetate.

Oligoester 4GI, with a DP of 1.36, can only be dissolved in a large amount of warm propyl acetate. Oligoester 4GI with a DP of 1.79 or greater are not soluble in these solvents. Only a large amount of warm propyl acetate can dissolve 3GI with a DP of 2.24 and the solution remains a little turbid.

These solvents are unable to dissolve CHDM-I.

Degree of Polymerization (DP) le DP of all oligoesters, except i-6GI, was determined by H-NMR using the following equation: DP = A(H2-OH) where A(-CH2-O-CO-)and A(-CH2-OH) are NMR peak areas of the -CH2 group in -CH2-O-CO- and -CH2-OH, respectively. The DP of i-6GI was determined by size-exclusion chromatography. The DP values (DPNMR) are listed in Table 5 together with the feed mole ratios.

Table 5. Feed mole ratios and DP Oligoester Feed mole ratios ( Diester/ Diol ) DPNMR 10GI-a 0.667 2.30 -b 0.588 1.60 6GI -a 0.667 6.40 -b 0.725 3.15 -c 0.706 2.65 -d 0.687 2.31 -e 0.606 1.73 i-6GI 0.676 3.30 5GI 0.609 2.65 4GI -a 0.610 2.51 -b 0.556 2.45, 1.79 (p=98%) -c 0.490 2.02 -d 0.480 1.36 &commat;=96%) 3GI 0.444 2.24 lOES 0.667 2.30 NPG-I 0.500 3.70 BEP-I 0.667 2.50 CHDM-I 0.680 2.66 M-1OGT -a 0.667 2.20 -b 0.500 1.50 where p is the extent of reaction, and was determined by the ratio of peak area at 3.95 ppm to the sum of peak area at 3.95 and at 4.40 ppm in H-NMR.

It was important to careflilly control the reaction variables.

Dimethyl isophthalate and terephthalate easily sublimed and some liquid diols, such as 1 ,5-hexanediol (b.p. 242 C), 1.4-butanediol (b.p. 2300C), and 1 ,3-propanediol (b.p. 214 C) possessed high vapor pressure at reaction temperature. Both the phthalates and diols may be carried from the reactor by the flowing nitrogen, resulting in a change of the mole ratio of the two reagents or the DP of the oligoester. In order to get the desired results, the rates of heating and nitrogen flow should be as gentle and slow as possible during the different syntheses. Alternatively, or additionally, excess diol may be added to compensate for the loss.

Syntheses of Coatings The liquid coatings were prepared by dissolving oligoester, crosslinker, catalyst and additive in solvent. Melamine resin, R-747, and triisocyanate resin, Desmodur N-3300, were used as crosslinkers. In the case of R-747, the weight ratio of oligoester and R747 was 65/35 for all of oligoesters in the formulations. In the case of Desmodur N-3300, a 1/1.1 equivalent ratio of oligoester to Desmodur N-3300 was used. The equivalent weight of Desmodur N3300 was 168 as provided by Bayer Co.

Coatings were prepared by casting the paints on panels. Even coatings were applied using a draw-down bar. A #26 draw-down bar was used to apply an even coating of approximately 15clam. The samples were baked in an oven at the specified temperatures. Different panels were used for different purposes. Steel panels were used for measurement of pencil hardness, impact resistance and resistance to methyl ethyl ketone (MEK).

Aluminum panels painted with black enamel (black alluninum panels) were used for the "Crockmeter" test (described below), while primed plastic panels were used for flexibility, humidity and gasoline resistance tests.

The coating materials and substrates included: The series of oligoesters as descried in Examples 1-3.

p-Toluenesulfonic acid monohydrate (p-TSA), 4-ethyl morpholine and all solvents were reagent grade (from Aldrich) and were used without purification.

a monomeric methylolated melamine-formaldehyde resin, CASe 68002-20-0, from Monsanto Co.

Desmodur N-3300: Isocyanurate oligomer of HDT (CAS#S 1-2); 1,6-hexamethylene diisocyanate (CAS#822-0601) from Bayer Co.

FC-430: FLUORADX coating additive from 3M Industrial Chemical Product Division.

Steel, aluminum and tin coated steel panels are 3"x6" size purchased from Q-panel Co. Black aluminum panels were made by casting a commercial black paint named Rust Scat from Coronado Paint Co. on the aluminum panel, using a draw-down bar and baking at 290 F.

Primed thermo plastic olefin (TPO) plastic panels were primed with a pigmented chlorinated polyolefin primer from Red Spot Company.

BYK-300 and BYK-301: Solution of a polyether modified dimethyl polysiloxane copolymer from BYK Chemie.

BYK Catalyst-451: Solution of an amine salt of para-toluene sulfonic acid from BYK Chemie.

NACURE-155: Dinonyl naphthalene disulfonic acid in isobutanol from King Industries.

RKR54550/RK7018: Commercial two-package polyurethane coating from Dupont Co.

Gen-3: Commercial acrylic coating from Dupont Co.

Cargill 57-5776: Commercial polyester resin from Cargo Co.

K-FLEXQ)XMg3 10: Commercial polyurethane dispersion from King Indusnies.

Example S.

Preparation of coatings made from 10GI, 6GI, i-6GI, 5GI, 10ES, NPG-I, BEP-I and M-1OGT, using R-747 as crosslinker Coatings made from lOGI, 6GI, i-6GI, SGI, 10ES, NPG-I, BEP-I and M-IOGT were prepared in accordance with the formulations listed in Table 6.

Table 6. The Preparation of chains from 10GI. 6GI. ie6GI 5GL 10ES, NPG-I BEP-I and M-1OGT.

Oligoester(g) R-747(g) Xylene(g) FC-430 sol. (g)* p-TSA sol. (g)** 0.65 0.35 0.40 0.10 0.16 (0.5%) * 2.5% xylene solution, ** 3.2% p-TSA solution formed by dissolving 0.22g P-TSA in a mixture of 5.5g xylene and 0.5g lbutanol.

Solutions were prepared by first charging the above constituents, except the P-TSA solution, into vials respectively and heated to about 50 C on a hot plate with swirling to form a solution. Then the p-TSA solution was mixed with the warm solution. Coatings with thickness of 15 to 20pm were prepared by casting the above solution on steel panels and on black aluminum panels. Panels were then baked at 150 C for 30 minutes, using a OSTABL-THERM oven from Blue M Electric Company. The panels were kept at ambient temperature for at least one day before testing.

Example 6 Preparation of coatings made from 4GI( 1.36) and 3GI(2.24) using R-747 as crosslinker Coatings made from 4GI, 3GI were prepared in accordance with the formulations listed in Table 7.

Table 7. The t,rearation of coatings from 4GI and 3G1.

Oligoester(g) R-747(8) Propyl acetate(g) FC430 sol. (g)* p-TSA sol. (g)** 0.65 0.35 1.00 0.20 0.20(1.5%) * 5.0 /O propyl acetate solution; ** 9.3% p-TSA solution formed by dissolving 0.76 g p-TSA in a mixture of 5.5 g propyl acetate and 1.0 g of l-butanol.

The procedures were the same as Example 4. except the panels were baked at 1200C for 30 minutes with 1.5% catalyst (see Table 11.).

Example 7 Preparation of Coatings made from lOGI and 6GI, using Desmodur N-3300 as crosslinker.

Since a 1/1.1 equivalent ratio was used when Desmodur N-3300 was the crosslinker, the formulations were different for oligoesters with different molecular weights and are shown in Table 8. The formulation procedures were the same for the various oligoesters.

Solutions were prepared by first charging the oligoester, xylene, and FC--430 solution into vials respectively and heating to about 50"C on a hot plate with swirling to form a solution. Then, the solution was cooled to room temperature. Desmodur N-3300 was mixed with the solution while making sure that there were no air bubbles in the solution before use.

Coatings with a thickness of 15 to 20pun were prepared by casting the formed solutions on steel panels and black aluminum panels.

They were baked at 120 OC for 30 minutes. It is thought that residual tin salts in the oligoester catalyze the crosslinicing reaction.

Table 8. The Dreparation of coating from 1OGI and 6G1 using Desmodur N-3300 as crosslinker.

(g) of Oligoester Desmodur N-3300 (g) Xylene (g) FC-430 (g) SPNMR) 1.0 of 10GI(2.3) 0.46 0.7 0.2 1.2 of 6GI(2.65) 0.93 1.0 0.4 1.2 of 6GI(2.3) 0.75 0.4 0.4 2.5 of 6GI(1.7) 2.10 1.3 0.4 Example 8 Preparation of Coatings made from RKR54550/RK7018 A coating of 100 parts of acrylic RKR54550 and 42 parts of isocyanate resin RK7018 was mixed in a vial and then the mixture was cast on steel and black aluminum panels. The coatings were baked at 260 "F for 30 minutes.

Control Example 9 Preparation of Coatings made from Gen-3 A coating of Gen-3 was cast on steei and black aluminum panels. The coatings were baked at 2600F for 40 minutes.

Control Example 10 Preparation of Coatings made from Cargill 57-5776 A solution was made charging the constituents listed in Table 9 into a vial and heating to about 50"C on hot plate with swirling to form a solution. Then the solution was cooled to room temperature and cast on steel and black aluminum panels. The resultant coatings were baked at 275 "F for 30 minutes.

Table 9. The preparation of Olizoesters using Cargrill 57-5776.

57-5776 (g) R-747(g) Methyl amyl ketone(g) BYK-300 sol. (g)* BYK 1 sol.(g)** 1.74 0.50 0.76 0.17 0.85 * Solution made by dissolving 0.22 g BYK- 300 in 8.8 g methyl amyl ketone; ** Solution made by dissolving 0.24 g of BYKAS 1 in 4.05 g methyl amyl ketone Control Example ff Preparation of Coatings made from K-@@@@@XM-4310 A solution was prepared by charging the constituents listed in Table 10 into a vial and heating the mixture to about 50 C on a hot plate with swirling to form a solution.

Table 10. The of Oligoesters using: K-FLEXSXM 4310.

K-FLEXQ9XM4310 R-747 4-Ethylmorpholine BYK-301 NACURE-155 Propylacetate 2.0g 0.50g 0.53g 0. 15g 0.05g 0.50g The solution was cooled to room temperature and cast on the steel panel and black aluminum panel, baking at 150 C for 30 minutes.

Test methods Pencil hardness was measured according to ASTM D3364-74 standard test method for film hardness by pencil test.

Impact resistance was measured according to ASTM D 2794-84, standard test method for resistance of organic coatings to the effect of rapid deformation (Impact).

Resistance to methyl ethyl ketone (MEK) was measured by double rubbing with MEK saturated non-woven paper (Kim-Wipe) until failure. Failure is the fewest number of rubs required to break through the film. If no breakthrough occurred after 200 rubs, the test was discontinued and the result was recorded as > 200. The non-woven paper was kept saturated by MEK during the measurement.

Dry film thickness was measured with a magnetic coating thickness gauge from De Felsko Corporation.

Glass transition temperature (Tg) was measured by DSC (or MDSC) on a TA 2100 Thermal Analysis Instrument with the heating rate of 5 C/min. The samples were prepared by using the same formulations in Example 5, except using 1.5% catalyst. The solutions were then cast on un-primed plastic panels, and baked at 1200C for 30 min. After cooling, the films were separated from the plastic panels and used for Tg measurements. The samples were contained in a sealed aluminum pan and an identical empty pan was used as reference.

Scratch resistance (S.R.) was done on an "A.AT.C.C.

Croclaneter" apparatus Model CM-1 from ATLAS Co. The coated black panel was immersed in dry "Bon Ami" cleaning powder so that the panel was covered with the powder and the excess powder was gently poured off. The apparatus was modified by gluing a magnetic strip in front of the panel on the test bed to hold the panel in place dusting the test. A fresh green 50x50 mm2 felt pad was placed over the probe (diameter 15 mm) of the tester and secured with a spring clip. The test probe was moved back and forth over a portion of the panel in ten double strokes; the frequency was about one double stroke per second. The result was a marred area on the panel about 13mm x 220 mm. The panel was then cleaned in a stream of cold tap water, gently wiped with a wet wiper, and gently dried with a soft towel. The 20 gloss was measured using a micro-TRI-gloss" pocket gloss meter by slowly moving the meter across the panel, measuring gloss of the unmarried part, then of the marred part, then of the urinlarred part on the other side of the mar, and the readings were recorded respectively.

This measurement process was repeated three times on different parts of each marred area. The results were averaged, and the percent of gloss retained was recorded as a measurement of scratch resistance.

The DMA test for 6GI(2.3) and 10GI(2.3) were run on an AutovibronO Instrument (amass Inc.). The solutions of 6GI(2.3) and 10GI(2.3) were prepared using the same formulations and procedures as described in Example 5. Coatings of thickness more than 45pom were prepared by casting the prepared solutions on tin coated steel panels respectively, using a #30 draw-down bar (applying a 2Sym coating) and baking at 1500C for 30 minutes.

Micro-hardness and elastic recovery were measured on a Fischerscope H100 MicroHardness Tester using a Vicker Indenter.

Properties of Coatings The baking temperature and the amount of catalyst are two important factors which affect the properties of coating. The experimental results of varying these parameters are listed in Table 11.

Table II. The effect of baking temperature and catalvst amount.

Coating Baking temp. Catalyst Pencil S.R.* Resistance Tg (OC) Oligoester ("C) amount ( /O) hardness ( /O) to MEK (DPNMR) - Melamine 150 0.5 F 98.8 > 200 9.4 6GI(2.6)-R747 120 1.0 F < 200 120 1.5 H 97.8 > 200 17.5 150 0.5 F 98.6 >

The gloss of a coating not only depends on the properties of the coating, but is also related to the properties of the underlying panel.

For example, aluminum panels demonstrate a higher gloss than steel panels as shown in Table 12.

Table 12. The gloss of the same coasting made on different panels.

Coating Panel 20 Gloss ofunmarred area Oligoester (DPNMR)- (%) Melamine 10GI(2.3) and R-747 Black aluminum panel 92 Black steel panel 82 M-10GT(2.3) and R-747 Black aluminium panel 90 Black steel panel 81 The properties of the various coatings are listed in Tables 13 to 16. The experimental results demonstrate that the S.R. of coatings made from most of synthesized oligoesters is exceeds 97%, a result far greater than commercial resins in Examples 8-12. However, not all oligoesters perform well. In the cases of 10GI(2.3), 6GI with different DP (from 1.7 to 6.4) and 5G1 (2.65), all their coatings have excellent S.R.

whether the crosslinker is R-747 or Desmodur N-3300, but the S.R. of 4G1 to 3GI., NPG-I and BEP-I is worse. It is believed that the number of -CH2- groups in this series of oligoesters plays an important role for the S.R. of the coatings. Coatings made from 4GI are not quite as good (94%) as 5GI, 6GI and lOGI, but are still better than the best commercial products. Coatings with 4GI have the advantage of being harder, higher in Tg and better in gasoline resistance. Additionally, coatings made from 1 OES and M- 1 OGT suggest that either the phenyl ring or saturated cyclic rings in the structures may produce high S.R. coatings if there are sufficient -CH2- groups. The minimum number of-CH2- is four and the maximum is 20 or more. Coatings based on IOGI give especially good flexibility at -200F.

The S.R. of coatings made from 5G1(2.7) and i-6GI(2.3) are 98.6% and 79.5% respectively. It can be seen that the S.R. of coatings made from 5GI(2.7) is much better than that from i-6GI(2.3), although their main chains are very similar (-CH2-CH2-CH2-CH2-CH2- and -CH(CH3)-CH2-CH2-CH2-CH2-). The only difference is that there is a -CH3 group on the side chain in i-6GI(2.3), instead of the hydrogen in 5GI. Moreover, the S.R. of coatings made from NPG-I and BEP-I are even worse, only 69.1% and 27.4%, respectively. In these cases, not only is the number of-CH2- groups insufficient for good SR., but also there are two side groups, i.e., for NPG-I, they are two -cH3 groups, and for BEP-I are two relatively large groups, -C2Hs and {24H9. These results show that the existence of side chains reduces SR. Coatings with more side groups and coatings with longer side groups demonstrate poorer S.R.

The results complied in Table 13 demonstrate that all coatings made from 6GI with different DPs (from. 1.7 to 6.4) have high S.R. While coatings made from other oligoesters having the same or similar DP have quite different SR. For example, the S.R. of coatings made from 10GI(2.3), 6GI(2.3) and 10ES(2.3) are high. but those from 3GI(2.3), i-6GI(2.3) and BEP-I(2.5) have poorer S.R. Therefore, it is believed that DP is not the sole determining factor for a coating's S.R.

The results of S.R., pencil hardness, micro-hardness, and impact resistance of coatings indicate that there is no direct relationship between S.R. and these mechanical properties. For example, the microhardness of coatings made from 6GI (1.7 to 3.15) and 10GI(2.3) changes in a wide range, from 13.6 to 580 N/mm2, meanwhile their S.R. are still high. S R. depends on the number of-CH2- groups and side groups in the oligoesters as described above. Mechanical properties depend on the crosslinking density, which is controlled by the -OH group density of oligoesters under the condition of the same weight ratios of oligoesters and crosslinker R-747.

The lower the DP, the lower its molecular weight, and the higher the -OH group density, the higher the crossliiik:ing density and consequently, the higher the hardness. This is shown by the results of DMA testing listed in Table 16. The crosslising density (end) for 6GI(2.3) is (2.3-2.4)x10-3 moles/cm3, higher than (1.8-1 .9)x10 moles/cm3 for 10GI(2.3). So, the Tg and E' for 6GI(2.3), 45.5 C and 2.32x108 dynes/cm2 respectively, are higher than 10GI(2.3), 17.0 C and I.68x108 dynes/cm2, respectively. E' is the storage modulus as measured by DMA. Refer to L.W. Hill, Mechanical Properties of Coatings, Federation of Societies for Coatings Technology, Blue Bell, PA, 1987 for more information on storage modulus.

Table 13.a. The Properties of coatinas made from synthesized oliqoesters with R-747 as a crosslinker.

Oligomer Tg Pencil Micro We Direct S.R. Resistance (DPNDR) ( C) hardness hardness (%) impact (%) to MEK (N/mm) resistance 10G1(2.3) -5.7 B 13.6 72.9 160 100 > 200 6G1(6.4) 8.4 F 150 37.6 160 98.7 > 200 6GI(3.1) 19.4 F 290 29.5 160 97.7 > 200 6G1(2.6) 17.5 F 144 28.6 160 98.8 > 200 6G1(2.3) 16 P 150 35.2 160 98.6 > 200 6G1(1.7) 30.1 H(3H) 580 40.2 100 98 > 200 5G1(2.7) 29.9 F 740 41.6 160 98.6 > 200 4Gl(1 .4) 44.3 H 640 43.6 80 94.2 > 200 3G1(2.2) 64 F 780 40.8 < 30 85.8 > 200 i6G1(3.3) 28 57 43.7 120 79.5 120 M-l0GT(2.3) HB 11.2 58.1 160 98.8 > 200 M-10GT(1.5) F 11.2 56.4 160 96.7 105 NPG-I(3.7) 47.9 F 140 69.1 15 BEP-1(2.5) -1.3 25 160 27.4 180 10ES(2.3) 2B 24.5 69.8 160 97.3 80 Table 13.b. The properties of coatings made from synthesized oligoesters with R-747 as a crosslinker.

Oligomer Hml=FN/AI e=(ArAs)!Ai P=AdAI A=(As-AP)/AI (DPNMFt) Micro-indentation Elastic Plastic Abraded ( N/ m2)* recovery (%) Deformation (%) fracture (%) 10G1(2.3) 7.77 99.3 0.004 0.66 6GI(2.6) 24 95.3 1.01 3.66 6G1(1.7) 24.7 93.4 2.06 4.49 4Gl(1 .4) 49.8 77.5 22.5 0 * The scratch resistance properties from SFM FN: Normal force, FN#200 N Ai: Cross section area of indent at FN A,: Cross section area of scratch Ap: Cross section area of replacement material in plastic deformation 6GI(1.7), 6GI(2.3) and 10GI(2.3) show healing in 5-I hour after scratch.

Measurements are made after stabilization.

Table 14. The properties of coatings made firm synthesized oligoesters with Desmodur N-3300 as crosslinker.

Oligomer Tg ( C) Pencil Direct impact S.R. (%) (DPNMR) hardness resistance 10GI(2.3) -13.9 B 160 100 6GI(2.6) 7.1 HB 160 98.1 6G1(2.3) -10 HB 160 96.3 6GI( 17) 0.7 F 160 98.7 Table 15. Properties of coating made from commercial resins Resin Pencil hardness S.R. (%) We (%) Microhardness RKR94550/RK7018 F 70.4 30.9 500 Gen-3 H 91.4 31.3 540 Cargill 57-5776 3H 68.8 K-FLEXXM-4310 3H 86.5 r Table 16. Dynamic properties of coatings made from 10G1(2.3) and 6GI(2.3).

Oligomer Thickness Ig Tan# E' x104 (min) Temp. of XLD Ue by (1) (DPNMF?) (DFT, m) ( C) (max) (dynes/cm2) E'(min) (x10-3 moles/cm3) 6GI(2.3) 54 46 0.55 2.36 120 2.4 56 45 0.55 2.26 120 2.3 10G1(2.3) 65 17 0.58 1.64 86 1.8 63 17 0.59 1.72 84 1.9 The forgoing Examples teach coating compositions having good S.R. may be made from oligoesters synthesized by melt transesterification between phthalates and diols using zinc acetate as a catalyst. The DP of the oligoester may be controlled by the feed ratio of the raw materials. Coatings made from the foregoing described oligoesters may be made durable with high S.R. either by increasing the amount of hardness (pencil hardness) or increasing the amount of elastic flow (we).

Compositions may be formed that include a mixture of these oligoesters in order to combine the desired properties of each material.

The present invention has been described as an automotive clear coat paint. It may be pigmented or used with other products to provide a protective coating for metals and plastics. It is especially useflil for providing a high gloss clear coating for plastic materials. The invention has been described by a number of examples and summarized in a series of tables. Modifications and adaptations of the present invention may occur to those skilled in the art without deviating from the sprit and scope of the following claims.

Claims (15)

We Claim:

1 A coating composition having an oligoester of the group comprising: (a) HO-[-(CH2)n-X]y-(CH2)nOH where X is selected from:

n is between 4-20 (preferably 5-12) y is between 1-15 (preferable 1.5-6); and Z is an aflame having between 0 -7 carbons;

where x = 1 to 15;

wheres 1 to 15; (d)

where x= 1 to 15;

wherex=i tolS;or

where x is a repeat unit between 3 and 12; and R is analkane having between 1 and 7 carbons; or (g) mixtures of (a) - (f).

2. A composition as claimed in claim 1, wherein said coating further comprises an aminoplast resin.as.crosslinker

3. A composition as claimed in claim 2, wherein said aminoplast resin is selected from the group comprising melamine-formaldehyde or polyisocyanate resins.

4. A composition as claimed in claim 1, wherein said coating further comprises an aliphatic polyisocyanate resin as crosslinker.

5. A clear coating composition for use on plastic substrates having an oligoester of the formula:

6. A coating composition as claimed in claim 5, wherein n is between 5 and 10.

7. A coating composition as claimed in claim 5, wherein n is 6.

8. A coating composition as claimed in claim 5, wherein n is 10.

9. A coating composition as claimed in claim 5, further comprising a melamine resin.

10. A coating composition as claimed in claim 9, wherein the ratio of oligoester to melamine resin is between 5-.50 to 80/20 percent by weight.

11. A coating composition as claimed in claim 9, wherein the ratio of oligoester to malamine resin is approximately to 1.1 molar equivalents.

12. A clear coating composition for use on plastic substrates having an oligoester of the formula:

where x is a repeat unit between 3 and 12; and R is an alkane having between 1 and 7 carbons.

13. A coating composition as claimed in claim 12, further comprising a malemine resin.

14. A coating composition as claimed in claim 12, wherein the ratio of oligoester to melamine resin is approximately 65 to 35% by weight.

15. A coating composition as claimed in claim 1, substantially as hereinbefore described.