Coating composition for pultrusion process and method of application

A continuous process for manufacturing a coated fiber reinforced pultruded article and the coating composition for use in this process. The coating composition includes an isocyanate resin, at least one active hydrogen-containing resin and at least one solvent having an evaporation rate equal to or less than about 0.5. The process and coating composition of the present invention produce fiber reinforced plastic articles having smooth, adherent surface coatings.

BACKGROUND OF THE INVENTION 
The present invention relates to a coating composition useful in coating a 
continuously advancing article, such as in a pultrusion process. This 
coating composition can be applied contemporaneously or in-line with the 
pultrusion process. 
The pultrusion process generally involves the steps of drawing a bundle of 
filaments from a source of such filaments; wetting these filaments or 
reinforced fibers and impregnating them with a preferably thermosetting 
resin by passing the filaments through a resin bath in an open tank or 
through a resin impregnating die; pulling the resin-wetted and impregnated 
bundle through a heated shaping die to align the fiber bundle and to 
manipulate it to the proper cross-sectional configuration; and then curing 
the resin while maintaining tension on the filaments. Since the fibers 
progress completely through the pultrusion process without being cut or 
chopped, the resulting products have exceptionally high longitudinal 
strength. 
It is often desirable to apply a coating, such as paint, to the pultruded 
article. Typical systems for applying paint to the cooled pultruded 
article include spray guns and rollers. However, these systems result in 
the loss of a significant amount of excess coating composition and are 
time consuming. In-line coating apparatus have been developed which permit 
the application of a coating of a predetermined thickness to the hot 
pultruded article as the pultruded article advances through the apparatus. 
An example of such an in-line coating apparatus is described in U.S. Pat. 
No. 4,883,690, incorporated herein by reference. 
The present invention is directed to a coating composition for use in 
coating the hot pultruded article shortly after it exits the heated 
shaping die. In a typical pultrusion process, the pultruded article exits 
the heated shaping die at a temperature of about 300.degree. F. The 
surface of the pultruded article is then water or air cooled to about 
150.degree.-180.degree. F. before the coating is applied. However, the 
surface temperature of the pultruded article quickly rises to 
200.degree.-280.degree. F. due to the residual heat of the pultruded 
article. The coating composition must be capable of withstanding these 
high temperatures to produce an adherent, blister-free coating of the 
desired thickness on the pultruded article. 
It is an object of the present invention, therefore, to provide a coating 
composition having sufficient viscosity to provide the desired coating 
thickness on the pultruded article as the pultruded article advances 
through the in-line coating apparatus. It is a further object of the 
present invention to provide a coating composition for use in an in-line 
coating apparatus that produces an adherent, blister-free coating upon 
cure. 
SUMMARY OF THE INVENTION 
The present invention is directed to a process for continuously forming a 
coated fiber reinforced plastic article including the steps of: 
(1) continuously drawing a fiber reinforcing material through an 
impregnating station; 
(2) passing a continuous supply of liquid resin material to the 
impregnating station; 
(3) impregnating the fiber reinforcing material with the liquid resin at 
the impregnating station to form a continuous impregnated uncured article; 
(4) continuously drawing the uncured article through a forming and curing 
die; 
(5) forming the uncured article to a finished cross-sectional shape and 
curing the resin to a hardened condition to form a fiber reinforced 
article; 
(6) continuously drawing the fiber reinforced article through a coating 
station; and 
(7) applying a coating composition to at least a predetermined portion of 
the surface of the fiber reinforced article. 
The coating composition of the present invention contains an isocyanate 
resin; at least one active hydrogen-containing resin; and at least one 
solvent having an evaporation rate less than about 0.5. The viscosity of 
the coating composition is at least about 15,000 cps (at 25.degree. C. 
using a Brookfield viscometer, spindle 7 and 20 rpm.) and the solids 
content is about 60-90% by weight. Preferably, the solvent contains a 
dibasic ester and the active hydrogen-containing resin contains a 
hydroxy-functional acrylic resin. The coating composition of the present 
invention may also contain silica, pigments, additional solvents, 
thixotropic additives and UV absorber. 
DETAILED DESCRIPTION OF THE INVENTION 
According to the method of the present invention, fiber reinforced articles 
may be coated with a paint or coating composition during the pultrusion 
process used to form the fiber reinforced articles. This method generally 
involves the following steps. Fiber reinforcing material, such as 
continuous strands or mat, are continuously drawn or pulled through a 
resin impregnating station. This impregnating station may be a die or a 
tank through which the strands or mat are drawn. A thermoplastic or 
thermosetting resin, preferably a thermosetting resin, is continuously 
supplied to die or tank so that the fiber reinforcing material is 
impregnated with the resin to form an uncured resin-impregnated fiber 
reinforced article. The uncured article is then continuously drawn through 
a forming and curing die. This forming and curing die shapes the uncured 
article into the desired cross-sectional configuration or profile and the 
resin is cured to a hardened condition. The resin is usually cured by the 
application of heat from the die, but may also be cured by chemical 
reaction. 
After the resin is cured to a hardened state, the fiber reinforced article 
is then continuously drawn through a coating station. This coating station 
may be a die to which the coating composition is continuously supplied, or 
a tank containing coating composition. The coating composition is applied 
to the fiber reinforced article as it is being drawn though the die or 
tank. Typically, as the article enters the die or tank, the surface 
temperature of the article is in the range of about 
150.degree.-280.degree. F. If the coating station consists of a die and a 
coating apparatus such as that described in U.S. Pat. No. 4,883,690, 
incorporated herein by reference, it is possible to apply the coating 
composition to the entire surface of the article or to a predetermined 
section or sections of the surface of the article as the article passes 
through the coating station. 
The coating composition of the present invention generally contains an 
isocyanate resin, at least one active hydrogen-containing resin and at 
least one slow evaporating solvent, and has a viscosity of at least about 
15,000 cps at about 60-90% solids by weight. Preferably, the viscosity of 
the coating composition is in the range of about 15,000 cps to about 
25,000 cps at about 70-80% solids by weight. The coating composition may 
also contain thixotropic additives, UV absorbers and pigments. 
The slow evaporating solvents useful in the present invention include those 
solvents having an evaporation rate less than or equal to about 0.5, and 
which do not contain hydroxyl groups. Evaporation rate is a measure of the 
length of time required for a given amount of a substance to evaporate, 
compared with the time required for an equal amount of n-butyl acetate to 
evaporate (i.e., the evaporation rate of n-butyl acetate is 1.0). Examples 
of such slow evaporating solvents include methyl isoamyl ketone, methyl 
amyl acetate, methoxy propyl acetate, amyl acetate (primary), methyl 
n-amyl ketone, isobutyl isobutyrate, cyclohexanone, diisobuyl ketone, 
ethyl 3-ethoxypropionate, n-methyl-2-pyrolidone, n-butoxyethyl acetate, 
2-ethylhexyl acetate, isophorone, diethylene glycol monoethyl ether 
acetate and dibasic esters, and mixtures thereof. Preferably, the 
evaporation rate of the solvent is less than 0.01. More preferably, the 
slow evaporating solvent of the coating composition of the present 
invention is a dibasic ester. DBE-9 from Dupont, a mixture of dimethyl 
adipate, dimethyl glutarate and dimethyl succinate, is an example of a 
commercially available dibasic ester. Aromatic solvents such as AROMATIC 
100 and AROMATIC 150, which are mixtures of C8-C10 alkyl substituted 
benzenes commercially available from Exxon Corp., are also useful slow 
evaporating solvents. In addition to the slow evaporating solvent, the 
coating composition of the present invention may contain additional 
solvents. If additional solvents are used, the amount of solvent having a 
slow evaporating rate contained in the coating composition should be at 
least about 60% by weight based on the total weight of solvent. For 
example, butyl acetate may be used in combination with a dibasic ester. 
Representative polyisocyanate useful in the present invention include the 
aliphatic compounds such as ethylene, trimethylene, tetramethylene, 
pentamethylene, hexamethylene, 1,2-propylene, 1,2-butylene, 2,3-butylene, 
1,3-butylene, ethylidene and butylidene diisocyanates; the cycloalkylene 
compounds such as 3-isocyantomethyl-3,5,5-trimethylcyclohexylisocyanate, 
and the 1,3-cyclopentane, 1,3-cyclohexane, and 1,2-cyclohexane 
diisocyanates; the aromatic compounds such as m-phenylene, p-phenylene, 
4,4-diphenyl, 1,5-naphthalene and 1,4-naphthanene diisocyanates; the 
aliphatic-aromatic compounds such as 4,4-diphenylene methane, 2,4- or 
2,6-toluene, or mixtures thereof, 4,4'-toluidine, and 1,4-xylylene 
diisocyanates; the nuclear substituted aromatic compounds such as 
dianisdine diisocyanate, 4,4'-diphenylether diisocyanate and 
chlorodiphenylene diisocyanate; the triisocyanates such as triphenyl 
methane-4,4',4"-triisocyanate, 1,3,5-triisocyanate benzene and 
2,4,6-triisocyanate toluene; and the tetraisocyanates such as 
4,4'diphenyl-dimethyl methane-2,2',5,5'-tetraisocyanate; the polymerized 
polyisocyanates such as tolylene diisocyanate dimers and trimers, and 
other various polyisocyanates containing biuret, urethane, and/or 
allophanate linkages. For urethane coatings having good weatherability, 
aliphatic polyisocyanates are preferred. 
The active hydrogen-containing materials useful in this invention have at 
least one one active hydrogen group per molecule. Active hydrogen 
functionality means those reactive groups described by Kohler in J. Amer. 
Chem. Soc., 49, 3181 (1927) and include --OH, --COOH, --SH, and --NH. 
Preferred are the hydroxy-functional materials. Representative 
hydroxy-functional polymers include the hydroxy-functional polyethers, 
polyesters, acrylics, polyurethanes, and polycaprolactones. More 
preferably, the hydroxy-functional polymer is an acrylic polymer. 
Especially preferred are the hydroxy-functional acrylic polymers in a 
slow-evaporating solvent. 
The composition may also contain pigments. These pigments can be introduced 
by first forming a mill base with the active hydrogen-containing resin 
utilized in the composition or with other compatible polymers by 
conventional techniques, such as sandgrinding, ball-milling, attritor 
grinding, high speed dispersion or two roll milling to disperse the 
pigments. 
Other additives that may be contained in the coating composition of the 
present invention include flow control agents, UV absorbers, thixotropic 
additives and silica. 
In general, two-component compositions prepared in accordance with the 
present invention contain: 
COMPONENT 1: (a) about 10-25 parts by weight of active hydrogen-containing 
resin (at 100% solids); (b) about 20-35 parts by weight of solvent having 
an evaporation rate of less than 0.5; (c) about 5-45 parts by weight of 
silica; (d) about 0-40 parts by weight pigment, and wherein the parts by 
weight of ingredients (a)-(d) is based on the total weight of Component 1; 
and 
COMPONENT 2: isocyanate resin, wherein the ratio of equivalents of 
isocyanate resin reactive functionality (NCO) to equivalents of active 
hydrogen-containing resin reactive functionality (preferably, --OH) is 
from about 3:1 to about 1:1, and preferably about 2:1.

EXAMPLES 1-5 
The coating composition of the present invention can be illustrated by way 
of example. Examples 1-5 are two-component coating compositions prepared 
in accordance with the present invention. Component I is the basis of the 
coating and consists of a hydroxy-functional resin, solvents, pigments, 
fillers, flow agents and other products used in formulating the coating 
composition. The hydroxy-functional resin of Component I is an acrylic 
resin prepared by conventional addition polymerization from the monomers 
methyl methacrylate, butyl acrylate, hydroxy ethyl methacrylate, styrene, 
methacrylic acid glacial and an initiator. Hydroxy-functional Resin A 
contains 50% by weight of dibasic ester solvent, DBE9. Component II is an 
isocyanate resin which is reacted with Component I at a mole ratio of 
substantially two moles of isocyanate to one mole of hydroxyl group 
present in Component I to form the coating on the pultruded article. Table 
I lists the compositions of Examples 1-5 in weight percent. 
The coating composition was applied to a fiber reinforced article after the 
article exited a forming and curing die. The surface temperature of the 
article was in the range of 150.degree.-180.degree. F. A coating die was 
used to apply the coating composition to the article. The compositions of 
Examples 1-5 produced smooth, blister-free and uniform coatings on the 
pultruded article. 
EXAMPLES 6-9 
The coatings of Examples 6-9 were prepared substantially in accordance with 
the procedure of Examples 1-5. The Hydroxyfunctional Resin B of Component 
I is an acrylic resin prepared by conventional addition polymerization 
from the monomers methyl methacrylate, butyl acrylate, hydroxy ethyl 
methacrylate, styrene, methacrylic acid glacial and an initiator. 
Hydroxy-functional Resin B contains 40% by weight of butyl acetate 
solvent. The coatings of Examples 6 and 9 were unacceptable because of 
blistering on the surface of the coating which was most likely caused by 
rapid solvent evaporation. The coatings of Examples 7 and 8 were also 
unacceptable because of cracking and non-uniform coating application 
respectively. Examples 6-9 illustrate that both the rate of solvent 
evaporation and the viscosity of the coating composition are important to 
producing acceptable coatings on pultruded articles by the process of the 
present invention. 
TABLE 1 
__________________________________________________________________________ 
Exam- 
Example 
Example 
ple 1 
2 3 Example 4 
Example 5 
Example 6 
Example 7 
Example 
Example 
__________________________________________________________________________ 
9 
COMPONENT I 
Hydroxy-functional 
40.1 
37.0 42.9 38.5 30.3 -- -- -- -- 
Resin A 
Hydroxy-functional 
-- -- -- -- -- 25.0 23.6 24.3 25.5 
Resin B 
Cyclohexanone 
4.1 3.5 3.2 3.6 3.6 2.9 3.9 4.1 6.3 
Silica 4.7 41.7 39.2 44.3 30.4 5.5 8.5 5.4 5.6 
DBE9 10.5 
9.2 10.8 9.3 9.7 8.0 11.1 11.5 5.2 
Tinuvin 292 
0.7 0.6 0.7 0.6 0.6 0.5 0.5 0.5 0.5 
Bentone 1.9 2.3 3.3 2.1 1.6 0.4 -- 0.4 0.2 
Pigments 38.1 
5.8 -- 1.6 23.8 58.8 51.8 53.3 56.0 
COMPONENT II 
Desmodur N-100 
1.9:1 
1.9:1 
1.7:1 
1.9:1 2.1:1 2.5:1 2.5:1 2.1:1 2.9:1 
NCO:OH 
Mixed Viscosity 
21,000 
16-25,000 
16-25,000 
16-25,000 
16-25,000 
18,000 8,000 10,000 11,000 
NVM (After Mix) 
74.22 
72.05 
68.37 
70.00 74.18 80.3 78.6 77.6 79.6 
Results Good 
Good Good Good Good Small blisters 
Cracking 
No blistering, 
Blistering 
under 10.times. 
not complete 
magnification 
flow 
__________________________________________________________________________ 
While the invention has been shown and described with respect to a 
particular embodiment thereof, this is for the purpose of illustration 
rather than limitation, and other variations and modifications of the 
specific embodiment herein shown and described will be apparent to those 
skilled in the art and are within the intended spirit and scope of the 
invention.