Molded plastic product having a plastic substrate containing a filler and an in-mold plastic coating firmly bonded thereon and a process for its manufacture

A molded part containing plastic substrate and a firmly adherent coating thereon, the plastic substrate containing a filler therein present at least in part in proximity to the surface of the substrate. The coating is transferred from the mold surface to the substrate during the molding operation and during solidification of the molded part. The molded part has a smooth surface as molded and without any subsequent finishing thereof.

This invention relates to a plastic molded part and to a process for its 
production. 
In the preparation of plastic molded parts, fillers such as fibrous 
reinforcement material, are frequently added to the plastic to obtain 
higher impact strength, greater dimensional stability or for other 
purposes. The fillers, added, for example, in the form of loose fibers or 
as a woven or unwoven mat, normally extend to the proximity of the surface 
of the part and create a rough surface on the as-molded part. The surface 
can be sanded or subjected to equivalent post-molding treatment to create 
a smooth finish but this adds considerable expense to the cost of 
production of the part. Subsequent coatings on the molded part will not 
produce a smooth surface--the roughness is usually of greater depth than 
can be covered by any practical coating thickness. The use of loosely 
woven glass fiber reinforcement in molded polyurethane parts is shown, for 
example, in U.S. Pat. No. 3,970,732 which issued on July 20, 1976. 
Copending U.S. application Ser. No. 149,996, filed May 15, 1980 and now 
U.S. Pat. No. 4,282,285 and copending U.S. application Ser. No. 162,682, 
filed June 25, 1980, both assigned to the present assignee, disclose 
processes for producing injection and compression molded parts having a 
coating thereon transferred from the mold surface to the substrate while 
within the mold. The processes there disclosed show the filling of the 
mold with a reactive plastic molding material and then, prior to molding, 
spraying the surface of the mold with a coating composition containing a 
reaction promoter for the reactive molding material. The reaction 
promoter, which may be a catalyst for the reactive molding material, acts 
to transfer the coating composition to the substrate during the molding 
operation so that the shaped part removed from the mold contains a firmly 
adherent coating of the coating composition. 
The present invention involves the discovery that the aforementioned 
in-mold coating technique may be used to produce a smooth surface on a 
plastic molded part containing a filler which is present at least in part 
in proximity to the surface of the substrate and which would by previously 
known molding techniques produce a rough or uneven surface on the molded 
part. The in-mold coating process permits transfer of the coating to the 
substrate during the time the plastic substrate solidifies and while the 
filler is being locked in place at or near the surface of the substrate. 
Using prior molding techniques, the filler at or near the surface is 
locked in place in the substrate before a coating is applied. This results 
in a rough surface on the molded part which cannot be made smooth by a 
coating of any practical thickness. By transfer of the coating from the 
mold surface to the plastic substrate during the molding operation and 
prior to solidification of the substrate, we have found we can obtain a 
completely smooth surface on the molded part. 
In general, the product of the present invention is a molded part 
containing a plastic substrate and a firmly adherent coating thereon, the 
plastic substrate containing a filler therein present at least in part in 
proximity to the surface of the substrate. The coating has been 
transferred from the mold surface to the substrate during the molding 
operation and during solidification of the molded part. The molded part 
has a smooth surface as molded and without any subsequent finishing 
thereof. The molded part is produced by coating the surface of the mold, 
prior to molding the part, with a coating composition containing a 
reaction promoter for the reactive plastic molding material, introducing 
the reactive plastic molding material and the filler into the mold, the 
molding material and filler together comprising the plastic substrate, the 
reaction promoter in the coating being present in an amount sufficient to 
transfer the coating composition from the mold surface to the substrate 
and bond it thereto, molding the part and removing the molded part from 
the mold. The molded part upon removal from the mold has a smooth surface 
thereon as molded and without any subsequent surface treatment thereof. 
The invention is useful with both injection and compression molded filled 
or reinforced plastic parts, including parts produced by reinforced 
reaction injection molding. The compression and injection molding of 
thermosetting and thermoplastic resins, both with and without fibrous 
reinforcement, is well known and is described at many places in the 
literature, as for example, in Modern Plastics Encyclopedia, October 1978, 
Vol. 55, No. 10A, pages 256-261 and 304-313. The invention is particularly 
useful in reaction injection and compression molding operations because 
surface finish problems are apt to be greatest with filled parts produced 
by these techniques. However, it is also useful with other molding 
operations using reactive molding material including injection and 
transfer molding and casting. The reinforced reaction injection molding 
process is very similar to the reaction injection molding process except 
that the reinforcing material in the form of chopped or milled fibers is 
incorporated in one or both of two reactive liquid streams used in the 
process. Alternatively, the reinforcement, in the form of a screen or mat, 
is laid out in the cavity of the mold or adhered to the core surface of 
the mold, the mold is closed and the reactants are injected into the mold. 
In carrying out the invention, the surface of the mold is first uniformly 
coated with a coating composition containing a reaction promoter for the 
reactive polymer in an amount sufficient to transfer the coating 
composition from the mold surface to the molded part and bond it to the 
latter. The amount of the reaction promoter will normally range from as 
little as 0.5% to as much as 10% based on the total coating weight. 
However, amounts of reaction promoter greater than 10% may be used, 
although normally they are unnecessary, and amounts even less than 0.05% 
may be adequate if a strong catalyst or other reaction promoter is 
employed. The coating plus reaction promoter are conveniently applied to 
the mold surface by spraying the coating at 30 to 60 psig in a solvent at 
about 10-35% solids content. In compression and injection molding, the 
mold surface may range from below ambient temperatures to elevated 
temperatures, e.g. from 50.degree. to 450.degree. F. In reaction injection 
molding, the mold surface should be from 90.degree. to 180.degree. F. The 
process of the invention is useful with a wide variety of metal mold 
surfaces, as for example, steel, aluminum, chrome and nickel plated steel, 
electroform nickel and kirksite (a zinc alloy) and with other mold 
surfaces such as epoxy and silicone. Flash time, for evaporation of 
thinner after coating the mold surface and prior to molding, will normally 
vary for compression and injection molding from 15 to about 60 seconds, 
depending on temperature of the mold and solvent composition and normally 
will be less than 15 seconds for reaction injection molding. 
The substrate is a reactive plastic molding material. By reactive plastic 
molding material, we intend to identify the starting materials from which 
the molded part is made, which starting materials undergo polymerization 
and/or crosslinking during the molding cycle. Included within this 
definition are the reactant isocyanate and polyol components of 
polyurethane molding systems and the large number of thermosetting 
polymers which undergo during the molding cycle further reaction and/or 
crosslinking in the presence of a reaction promoter which can be a 
catalyst, a crosslinking promoter or crosslinking initiator. Examples of 
such reactive thermosetting polymers are polyurethanes, unsaturated 
polyesters, epoxy resins and phenolics. Typical examples of reaction 
promoters for polyurethanes are urethane catalysts which may be metal 
chlorides, amino compounds or organometallic salts such as dibutyltin 
dilaurate, stannous octoate or phenyl mercuric propionate. Other 
polyurethane catalysts are disclosed in the aforesaid copending 
application Ser. No. 149,996. The polyurethanes useful as reactive plastic 
molding materials for compression and injection molding are not 
necessarily the same urethane polymers which are used in reaction 
injection molding. The polyols used in preparing urethane polymers for 
compression and injection molding are not necessarily capped with ethylene 
oxide to give high reactivity, as in the case of polyols used in reaction 
injection molding. However, the catalysts disclosed in copending 
application Ser. No. 149,996 are useful as reaction promoters with both 
types of polyurethanes. Epoxy resins are crosslinked by amines, 
anhydrides, aldehyde condensation products and Lewis acids. Typical 
catalysts useful as reaction promoters for epoxy resins are diethylene 
triamine and hexahydrophthalic anhydride. Phenolic polymers are 
crosslinked by acid catalysts, of which a suitable example is 
hexamethylene tetramine and by a basic catalyst such as ammonium 
hydroxide. In the case of polyesters, examples of reaction promoters or as 
they are known, free radical or crosslinking initiators, are organic 
peroxides, alkyl peresters and azonitriles. Examples of peroxides are 
tertiary butyl peroxide, lauryl peroxide and diacyl peroxide; examples of 
alkyl peresters are tertiary butyl perbenzoate and tertiary butyl 
peracetate; an example of an azonitrile is 1-t-butyl azo-1-cyano 
cyclohexane. The foregoing reaction promoters may of course be used alone 
or in combination. 
A particularly useful class of reactive molding materials useful in the 
invention are the so-called bulk molding or sheet molding compounds. These 
materials are a composite of specialty polyester resins, and as 
commercially sold usually contain thickeners, thermoplastic copolymers, 
styrene, inorganic filler, fiber reinforcement, catalyst, mold release and 
pigment. The sheet molding compounds are particularly useful in 
compression molding operations. 
The polyester resin is formed from the condensation polymerization of 
anhydrides, dicarboxylic acids, or polycarboxylic acids with bifunctional 
or polyfunctional alcohols or polyols. A wide variety of polyesters are 
used with varying properties to meet specific performance requirements. 
The thermoplastic copolymers are a minor part of the compounds and are 
formed from the addition polymerization of one or more types of monomers. 
Some important addition polymers are acrylic, polyethylene, polypropylene, 
polyvinylchloride, polyvinylacetate, polymethylmethacrylate and 
polystyrene. The purpose of using thermoplastics in the compound is for 
their performance as low shrink additives in the polyester molding 
compound. The monomer styrene used in the formulation is a crosslinking 
reactant. It crosslinks or bonds with the polyester forming a rigid 
tightly bonded structure. Other crosslinking monomers such as vinyl 
toluene or diallyl pthalate can also be used. Fillers are normally 
inorganic powders, usually processed from minerals commonly found in the 
ground, such as calcium carbonate and aluminum silicate. The thickeners 
are used to increase the viscosity of the compound and the most commonly 
used are oxides and hydroxides of calcium and magnesium. Internal mold 
release agents such as zinc stearate and calcium stearate are unnecessary 
for the purpose of the invention but may be present in the commercial 
formulation. Pigments are added for imparting colors. They are essentially 
metallic oxides such as TiO.sub.2. The reaction promoters that can be used 
with these polyester resins are free radical initiators. These are usually 
selected based on the temperature of curing, half life and activity. The 
glass reinforcement in these formulations is used to improve certain 
properties, most important of which are impact and tensile strength and 
coefficient of thermal expansion. 
In the case of reaction injection molding, the polyurethane reactants are 
fed into the mold and reacted during the molding cycle. In the case of 
compression and injection molding, the plastic molding material introduced 
into the mold is a reactive polyester, epoxy resin or other polymer which 
is cured or crosslinked during the molding cycle. The reaction promoter 
used in the coating is a polyurethane catalyst in the case of reaction 
injection molding or a catalyst, crosslinking promoter or initiator for 
curing the resin in the case of compression or injection molding. 
A more detailed description of the processes as applied to reinforced 
reaction injection molded parts is as follows. The two liquid components 
used in reaction injection molding are polyol and isocyanate. If a loose 
fibrous reinforcement is used in the process, a slurry of the 
reinforcement fibers is prepared with one or both of the liquid 
components. Preferably, however, the reinforcement is added to the polyol 
because it is more viscous and thus less prone to settle. The slurry is 
brought to the desired component temperature, and maintained by constantly 
agitating, heating and recirculating. The recirculating and agitation help 
keep the fibers from settling. The two liquid streams, one isocyanate and 
the other polyol, with the reinforcement if used, is metered exactly in 
the desired weight ratio and fed into a self-cleaning type impingement 
mix-head under 2,000-3,000 psig pressure. This mix-head is specially 
designed to handle highly abrasive materials. The two reactive high 
pressure liquid streams impinge upon each other in the mixing chamber of 
the mix-head and the resulting mixture is pushed into the mold with the 
help of a hydraulically operated piston, which simultaneously cleans the 
mixing chamber because of the close tolerances. 
Prior to the injection in the mold, the mold is cleaned thoroughly, brought 
to the desired molding temperature, which is in most cases between 
140.degree.-160.degree. F. The mold cavity and/or core surface is coated 
with the coating composition by spraying with a spray gun to give a 
desired coating thickness, which may vary from 0.1 to 2.5 mils or more but 
normally is less than 0.5 mil with a particulate filler and less than 2.0 
mils with a fibrous reinforcement as filler. (These coating thicknesses 
also apply to molded products produced by other molding processes.) A 
flash off time to evaporate the solvent of 10 to 15 seconds is allowed to 
dry off the coating. 
If a continuous reinforcement, in the form of a screen or mat is used, it 
is laid in the cavity or is attached to the core part of the mold after 
the coating is applied. If desired, means can be provided in the mold to 
hold the mat. A double parting line can also be provided to the mold, if 
required, to avoid any leakage of the urethane material and for proper 
sealing. Then the mold is closed and held under 50 to 150 tons of clamping 
force in a mechanical clamp. The reaction mixture is injected from the 
mix-head attached to the mold. The reactive mixture injected may or may 
not have fibrous reinforcement. The reaction mixture flows into the mold, 
and encapsulates the mat reinforcement and simultaneously is coated with 
the coating which was sprayed onto the mold surface. The reactive mixture 
solidifies and takes the shape of the mold. The part is demolded in 
seconds to a few minutes depending upon the cure time. The reinforcement 
and coating become an integral part of the molded part. The coating does 
not allow the reinforcement to show at the surface and provides an 
excellent surface finish. The product thus produced containing a 
continuous mat reinforcement has very low coefficient of thermal 
expansion, very high impact properties, high mechanical strength and 
desired rigidity for automotive and non-automotive structural 
applications. This product thus has superior thermal, mechanical and 
physical properties coupled with excellent surface finish compared to 
parts containing only loose fiber reinforcement. 
After demolding from the mold, the part is usually trimmed and then usually 
post cured by application of heat, as for example, at 250.degree. F. for 
one hour in a hot air forced circulation oven. The post curing helps 
complete the chemical reaction. Since there is no mold release used in the 
molding operation, the part does not have to go through the extensive 
cleaning and drying operation and thus saves considerable amount of time 
and energy. The part can then be further coated, if desired, to give the 
desired gloss level and color matching. In many non-automotive 
applications this step may not be necessary since the part already has a 
coating on the part surface. 
Further disclosure of the details of the in-mold coating process and its 
applicability to reaction injection molding processes may be obtained from 
the aforesaid copending U.S. application Ser. No. 149,996 filed May 15, 
1980 U.S. Pat. No. 4,282,285. Further disclosure of the details of the 
in-mold coating process and its applicability to compression and injection 
molding processes may be obtained from the aforesaid copending U.S. 
application Ser. No. 162,682 U.S. Pat. No. 4,350,739. The disclosures of 
these applications are hereby incorporated by reference in this 
application. 
The coating may be any decorative or protective coating of the type applied 
by conventional coating technology to molded parts. The coatings may be 
either a thermoplastic or thermosetting polymer, with or without a 
plasticizer. The coating should of course be capable of withstanding the 
molding temperatures without decomposing or deteriorating. Among the 
useful coatings included within the foregoing description are, for 
example, acrylic and acrylic ester polymers, pre-reacted or blocked 
urethane polymers, saturated and unsaturated polyesters, epoxy esters, 
cellulose esters, polyolefins, vinyl and vinyl-melamine polymers and 
mixtures of the foregoing polymers with each other or with other coating 
compositions. A preferred class of coatings for polyurethane substrates 
are those based on urethane or acrylic polymers. For polyesters, a 
preferred class of coatings are those based on urethanes or polyesters. 
The coating may be used either as protective coatings or with a pigment as 
a paint coating. A particularly significant class of coatings are paint 
primers. The paint primers may be applied within the mold and the molded 
part thereafter top coated after removal from the mold. 
The filler materials useful in the invention include any fillers used in 
the fabrication of molded plastic parts and which by known molding 
techniques would create unevenness on the surface of the parts. Many such 
fillers are of course known including those added as reinforcement, those 
added to improve or otherwise modify the properties of plastics and those 
added as diluents or extenders to increase the bulk or weight or to reduce 
the use of expensive plastics. They may be organic or inorganic, 
particulate, powdered or continuous, examples of the latter being a mat or 
woven cloth. Illustrative but not limiting examples of fillers are fibrous 
materials such as carbon fibers, fibers of a metal such as steel or 
aluminum, glass fibers such as milled or chopped glass, glass mats or 
fiberglass, fibers of synthetic polymers such as polyester, acrylic or 
nylon fibers. The fibrous reinforcement may contain fibers of any size or 
length of the type used in reinforced plastics. The fillers may be treated 
with a coupling agent for better wettability. The invention also 
contemplates the combined use of both powders or loose fibrous 
reinforcement and a continuous mat or screen reinforcement in a single 
molded part. In addition to fibrous reinforcement, the filler may also be 
a particulate filler such as carbon, sand, wood flour, glass beads, fly 
ash or a mineral filler such as clay, talc, mica, silica or other 
siliceous material. The proportions of filler may vary widely, depending 
on the type and form of filler used. It is only necessary that the filler 
be present in an amount sufficient to be present at least in part in 
proximity to the surface of the plastic substrate such that, in the 
absence of the present invention, a rough or imperfect surface would 
result. Normally the amount of filler will range from 2 to 60%, usually 
from 5 to 40% by weight, based on the weight of the molded part. However, 
this range is a practical range of usage and is not intended to be 
limiting.

The following examples illustrate the practice of the invention. All parts 
and percentages, unless otherwise indicated, are by weight. 
EXAMPLE 1 
This example illustrates the reaction injection molding of a glass mat 
reinforced polyurethane part. The resin component was ethylene oxide 
capped poly (oxypropylene) glycol grafted with 20 weight percent 
acrylonitrile polymer and ethylene glycol as chain extender, and contained 
0.05-0.075% dibutyltin dilaurate as catalyst. The isocyanate was a 
prepolymer of 4,4'-diphenylmethane diisocyanate. The isocyanate contained 
4% by weight of Freon II (a trademark for a fluorocarbon) as a blowing 
agent. 
The polyol and isocyanate were brought to 50.degree. C. and 24.degree. C. 
respectively and then mixed at 2000 psig in each feed line to the mixer. 
The ratio of isocyanate to polyol resin was 0.97 by weight. Nucleation of 
resin by mixing with air brought the specific gravity of the reaction 
product to one and facilitated better mixing of the two components. The 
high pressure recycle time for the two component streams was 5 seconds 
before injecting into the mold. The two liquid components did not contain 
any fibrous reinforcement. The mold surface was thoroughly cleaned with a 
solvent soaked rag. The mold surface was then uniformly sprayed at 30 psig 
with a paint primer coating. The coating consisted of nitrocellulose, a 
polymethylmethacrylate resin, monoethyl ether acetate as the plasticizer 
and a pigment to impart the desired color. The coating was mixed with an 
equal part by weight of thinner. The coating contained 1% by weight of 
dibutyltin dilaurate as the catalyst. Then the glass mat (11/2 ounces per 
square foot) was laid into the mold cavity. The mold in this case was an 
automobile bumper fascia. The mold was closed and clamped in a press. The 
two reactive streams of polyol and isocyanate were injected through the 
mix-head into the mold which was pre-heated and maintained at 140.degree. 
F. The part was demolded one minute after injection. The part thus 
obtained had a continuous glass mat reinforcement and a coating on the 
surface which was firmly adherent to the part surface. A number of parts 
were made in the same way and then post cured at 250.degree. F. for one 
hour. The parts were then tested for physical and mechanical properties, 
impact strength, and sag and compared with the parts made without any 
reinforcement under the same processing conditions. All the properties 
showed significant improvement, ranging as high as five to ten times 
greater than the properties of the same parts without reinforcement. The 
parts had excellent surface smoothness. 
EXAMPLE 2 
This example illustrates the preparation by compression molding of a molded 
plaque having a polyester substrate and a polyurethane coating. A 12-ton 
hydraulic press with electrically heated platens and an aluminum mold with 
matched die surfaces was used for molding an unsaturated polyester 
compound by compression molding. The formulation used for this example 
contained 60 parts of unsaturated polyester dissolved in styrene monomer 
(64% polyester, 36% styrene), 40 parts of a thermoplastic copolymer as a 
low shrink additive, 1.5 parts of tertiary butyl perbenzoate as 
crosslinking agent, 4.5 parts of zinc stearate mold release (not needed 
but present in the commercial formulation), 140 parts of calcium 
carbonate, 25 parts of aluminum silicate, 0.5 parts of a grey pigment, 4.5 
parts of magnesium oxide thickener and 25% of the total weight of the 
formulation of 1/2" loose glass fibers. 
The cavity and core of the mold was uniformly sprayed with a conventional 
air pressure spray gun at 45 psig to place a coating 0.5-1 mil thickness 
on the mold surface. The coating was a urethane type paint primer which 
was thinned with one-half part by weight of thinner to produce a 21% by 
weight solids content paint composition. The paint primer contained a 
blocked polyurethane, a paint curing agent to cure the urethane (in the 
proportion of 6 parts polyurethane to one part of curing agent), a 
plasticizer and a color imparting pigment. 
The paint primer contained 5% by weight of tertiary butyl perbenzoate as a 
reaction promoter for the unsaturated polyester to transfer the coating 
composition from the mold surface to the molded part and bond it to the 
latter. The mold surfaces were sprayed with the paint primer and allowed 
to flash for 30 seconds (time for solvent evaporation). The unsaturated 
polyester compound was charged into the mold cavity and the mold closed. 
The mold temperature was 250.degree. F. A clamping pressure of 5 tons was 
applied to the mold. After three minutes of curing the mold was removed 
from the clamp and the part was removed from the mold. An examination of 
the resulting molded product showed that the coating, sprayed onto the 
mold surface, had transferred onto and bonded to the molded part. The 
coating was approximately 0.5-1 mil in thickness and displayed excellent 
filling and adhesion characteristics on the plastic part. The surface of 
the plastic part was completely smooth and free of roughness. 
EXAMPLE 3 
Example 2 was repeated using a urethane paint primer as the coating except 
that it was reduced to 27% solids by mixing with a 50%/50% xylene/toluene 
solvent. The paint primer contained 5% by weight of 1-t-butyl azo-1-cyano 
cyclohexane as a reaction promoter for the unsaturated polyester to 
transfer the coating composition from the mold surface to the molded part 
and bond it to the latter. The coating was sprayed onto the mold cavity 
and core. Flash off time was 30 seconds. Mold temperature was 300.degree. 
F. Demolding time was 31/2 minutes. Paint adhesion, coverage of the 
plastic substrate and surface smoothness were excellent. 
EXAMPLE 4 
Example 2 was again repeated using the same coating except that it 
contained 5% of t-butyl peroxy isopropyl carbonate as the reaction 
promoter. The coating was sprayed onto the mold core. Flash off time was 
30 seconds. Mold temperature was 300.degree. F. Demolding time was 4 
minutes. Once again, paint adhesion, coverage and surface smoothness were 
excellent. 
EXAMPLE 5 
This example illustrates the reaction injection molding of a 1/16" milled 
glass reinforced polyurethane fender. The resin component was a blend of 
ethylene oxide capped poly (oxypropylene) glycol with diamine chain 
extender and 0.05-0.75% dibutyltin dilaurate as catalyst and contained 
1/16" milled glass suspended in it. The isocyanate was a prepolymer of 
4,4'-diphenylmethane diisocyanate to give a free NCO of 22.6%. The polyol 
slurry and isocyanate were brought to 32.degree. C. and then metered and 
fed into a self cleaning impingement mix-head, where the two streams 
impinged upon each other at 2000 psig and pushed into the mold. The mold 
was a steel mold heated to 55.degree. C. Prior to injecting the materials, 
the mold surface was coated with a paint primer coating containing 1% 
dibutyltin dilaurate as reaction promoter. The coating composition was the 
same as that of Example 1. The part demolded in one minute, had 10% by 
weight of 1/16" milled glass in polyurethane with the primer paint coating 
firmly adhered to the part surface giving a highly smooth surface. 
EXAMPLE 6 
Example 1 was repeated using a conventional wax mold release on the mold 
surface prior to injecting with polyol and isocyanate in place of the 
paint primer coating. Surface roughness of the molded part made it 
impossible to obtain a high gloss finish with a paint coating of 
reasonable thickness.