FOLDA THOMAS J (US)
YOUNG JOHN J (US)
KLIPSTEIN JEFFREY L (US)
BROWN DAVID W (US)
GAINES WILLIAM R (US)
KLEESE EDWARD J (US)
STEINHAUSLER THOMAS (US)
FOLDA THOMAS J (US)
YOUNG JOHN J (US)
KLIPSTEIN JEFFREY L (US)
BROWN DAVID W (US)
GAINES WILLIAM R (US)
KLEESE EDWARD J (US)
US20020151630A1 | ||||
US20030092823A1 | ||||
US5100935A | ||||
US5202366A |
CLAIMS
What is claimed is:
1. A thermosetting, powder-coatable molding composition which comprises the following components:
A. an unsaturated, uncured, curable polyester, vinyl ester or blend thereof;
B. a monomer which will copolymerize with the unsaturated polyester, vinyl ester or blend thereof;
C. at least two thermoplastic polymers;
D. a filler; and
E. a reinforcing agent,
wherein a product molded from the composition has an excellent surface with a Loria of about 30 to about 85 before powder coating and a Loria of less than about 150 after powder coating.
2. A molding composition as defined by Claim 1 wherein the thermoplastic polymer component is a blend of an acrylic polymer and a styrene- butadiene copolymer.
3. A molding composition as defined by Claim 1 wherein the composition contains from about 10 to about 25 percent of the thermoplastic polymer component based on the total weight of components A 5 B and C.
4. A molding composition as defined by Claim 1 wherein the composition contains less than about 10 percent of a saturated polyester alkyd based on the total weight of components A, B and C.
5. A molding composition as defined by Claim 1 wherein the composition contains less than about 5 percent of a vinyl acetate containing polymer based on the total weight of components A, B and C.
6. A molding composition as defined by Claim 1 wherein the composition contains less than about 10 percent of a saturated polyester alkyd and a vinyl acetate containing polymer based on of the total weight of components A, B and C.
7. A molding composition as defined in Claim 1 wherein the volumetric change during cure of the composition is from about 0.02 percent shrinkage to about 0.07 percent expansion.
8. A process for the manufacture of a powder-coatable, cured, thermosetting molding composition for use in the manufacture of molded products which have excellent surface, wherein the process comprises the steps of mixing the following components:
A. an unsaturated, uncured, curable polyester, vinyl ester or blend thereof; B. a monomer which will copolymerize with the unsaturated polyester, vinyl ester or blend thereof;
C. at least two thermoplastic polymers;
D. a filler; and
E. a reinforcing agent,
and curing the composition in a heated compression mold at a temperature above 80° C.
9. A process as defined by Claim 8 wherein the temperature of the mold is from about 130 to about 180 0 C.
10. A process as defined by Claim 8 wherein the mold is under a pressure of from about 50 to about 1500 psi.
11. A process as defined by Claim 8 wherein the thermoplastic polymer component is a blend of an acrylic polymer and a styrene-butadiene copolymer.
12. A process as defined by Claim 8 wherein the composition contains from about 10 to about 25 percent of the thermoplastic polymer component based on the total weight of components A, B and C.
13. A process as defined by Claim 8 wherein the composition contains less than about 10 percent of a saturated polyester alkyd based on the total weight of components A, B and C.
14. A process as defined by Claim 8 wherein the composition contains less than about 5 percent of a vinyl acetate containing polymer based on the total weight of components A, B and C.
15. A process as defined by Claim 8 wherein the composition contains less than about 10 percent of a saturated polyester alkyd and a vinyl acetate containing polymer based on the total weight of components A 5 B and C.
16. A process as defined in Claim 8 wherein the volumetric change during cure of the composition is from about 0.02 percent shrinkage to about 0.07 percent expansion. |
NON-PROVISIONAL PATENT APPLICATION
POWDER-COATABLE MOLDING COMPOSITIONS
This application claims the benefit of U.S. Provisional Application Serial No.
60/688,659, filed June 8, 2005.
TECHNICAL FIELD
The present invention relates to powder-coatable molding compositions. In a
more specific aspect, this invention relates to such molding compositions which provide
products with a Class A surface after powder coating. This invention also relates to a
process for the manufacture of these powder-coatable molding compositions.
BACKGROUND OF THE INVENTION
Molding compositions have been manufactured and used for many years in
forming various articles. Examples of these compositions include sheet molding
compositions (SMC) and bulk molding compositions (BMC).
Automotive painting operations are typically carried out on a body-in-white,
which is the unpainted unitary body structure comprising body panels and structural
components. The body structure is usually formed mostly of steel panels but may include
polymer composite panels. The paint shop practice is well known for the steel portion of
the body structure, as the steel portion is electrically conductive and, therefore, receives
several coating layers for corrosion resistance, paint adhesion and painted surface finish
quality.
The polymer composite panels do not respond to the coating procedure in the
same way as the steel panels. For example, automotive painting operations often involve
the separate application of a zinc phosphate base layer, an electrocoated liquid prime coat
using water or an organic solvent, a liquid or powder primer surfacer layer, a liquid base
color coat and a liquid or powder clear top coat.
Following each of the prime coat, primer surfacer and clear top coat applications,
a baking step at temperatures of 250° F or higher is generally used to cure or dry the new
layer and to promote flow of the top coat films to a commercially acceptable finish for a
vehicle. Such aggressive heating of the painted composites typically leads to "out-
gassing", which is the release of entrapped air, solvent, moisture, uncured chemicals and
uncured polymer precursor materials from the somewhat porous composite substrate. Too
often the result is an unsightly and unacceptable rough surface. Out-gassing was initially
experienced with liquid primer surfacer paints at their 250° F bake temperature. The
occurrence of surface roughness with such paint systems has been reduced in some
instances by the use of a specially formulated, electrically conductive polymer prime coat
as a barrier coat after molding. This polymer prime coat on the composite surface may
reduce out-gassing at that location.
However, the prior art molding compositions often experience problems with
achieving excellent surfaces with powder primers on parts molded from sheet molding or
bulk molding compositions. These problems can be attributed to the kind and amount of
components contained in the SMC or BMC compositions.
Examples of prior art efforts to improve the surface of molding compositions after
powder prime include U.S. Patents No. 6,872,294 and 6,875,471, which describe that the
quality of painted surfaces of polymeric articles is improved by depositing a coating of a
metal such as zinc or zinc alloy on the surface of the article to be painted. The metal
coated polymeric surface provides a good base for electrostatic deposition of either liquid
or powder paint, and the metal surface prevents the formation of defects in the painted
surface during heating of the article to dry or cure the paint film.
U.S. Patent No. 6,843,945 describes in-mold coating of polymer composite parts
for metallization and painting.
U.S. Patent No. 4,039,714 describes pre-treatment of plastic materials for metal
plating by conditioning their surface by a treatment with sulfur trioxide vapor or a
material which contains sulfur trioxide.
All the processes mentioned above require some kind of pre-treatment of the
composite surface before powder-painting to result in a Class A surface, which increases
cycle-time and adds cost. Therefore, there is a need in the industry for molding
compositions which will provide an excellent surface to the molded products and painted
parts without pre-treatment steps.
SUMMARY OF THE INVENTION
The present invention provides powder-coatable molding compositions for the
manufacture of sheet molded products and bulk molded products which surprisingly have
an excellent surface after powder prime and paint. The present invention also provides a
process for the manufacture of these powder-coatable molding compositions.
Accordingly, an object of this invention is to provide powder-coatable molding
compositions.
Another object of this invention is to provide powder-coatable molding
compositions for sheet molded products and bulk molded products.
Another object of this invention is to provide powder-coatable molding
compositions which, when molded and powder-primed, provide products with an
excellent surface.
Still another object of this invention is to provide a process for the manufacture of
powder-coatable molding compositions.
Still another object of this invention is to provide a process for the manufacture of
powder-coatable molding compositions for sheet molded products and bulk molded
products.
Still another object of this invention is to provide a process for the manufacture of
molding compositions which, when molded and powder-primed, provide products with
an excellent surface.
These and other objects, features and advantages of this invention will become
apparent from the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 shows a digital image of the reflection of a fluorescent ceiling light on a
powder primed panel made from a sheet molding composition of the prior art.
Fig. 2 shows a digital image of the reflection of a fluorescent ceiling light on a
powder primed panel made from a sheet molding composition of this invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a new and unique thermosetting, powder-coatable
molding composition which comprises the following components: an unsaturated,
uncured, curable polyester and/or vinyl ester; a monomer which will copolymerize with
the unsaturated polyester and/or vinyl ester; at least two thermoplastic polymers; a filler;
and a reinforcing agent.
The present invention also provides a process for the manufacture of these new
and unique powder-coatable molding compositions.
As used in this application, the term "new and unique" will be understood as
referring to the resulting excellent surface of sheet and bulk molded products made from
the compositions of this invention after powder coating, and the term "excellent surface"
will be understood as referring to either a Class A surface which has a Loria less than
about 85 or a near Class A surface which has a Loria less than about 150. (The Loria
values are measured on a Loria™ surface analyzer from Ashland Chemical Company).
Of course, depending upon the intended use, the molding compositions of this
invention may optionally contain other additives, such as dyes, pigments, thickening
agents, viscosity reducers, inhibitors, peroxides, mold release agents, catalysts, etc.
The molding compositions of this invention can be molded into various products,
including sheet and bulk parts, such as automotive hoods, fenders, truck beds, bumpers,
etc.
The unsaturated, uncured, curable polyesters and/or vinyl esters useful in this
invention are commercially available products. These polyesters (sometimes referred to
as polyester alkyds) are a class of soluble, linear, low molecular weight materials which
contain both carboxylic ester groups and carbon-carbon double bonds as recurring units
along the main polymer chain. These polyesters may be prepared by condensation of
long chain polyols, diols, ethylenically unsaturated dicarboxylic acids or anhydrides to
impart the unsaturation and saturated dicarboxylic acids to modify the polymer.
Suitable unsaturated polyesters are the usual condensation products of polybasic
acids, in particular dibasic carboxylic acids and their esterifiable derivatives such as their
anhydrides, with polyhydric alcohols. Preferred unsaturated polyesters are those formed
from maleic anhydride and propylene glycol; I 3 3 -propanediol; I 5 4-butanediol; neopentyl
glycol; ethylene glycol; diethylene glycol; dipropylene glycol and/or dicyclopentadiene.
Suitable vinyl ester resins, also known as epoxy (meth) acrylates, that may be used
in the composition of this invention are addition products of polyepoxides and
unsaturated carboxylic acids, preferably acrylic acid and methacrylic acid. Suitable
polyepoxides are epoxy novolac resins and, in particular, polyepoxides based on
bisphenol A. Another suitable class of vinyl ester resins is the esterifϊcation products of
alkoxylated bisphenol A and (meth) acrylic acid.
The monomer used in this invention can be mono-or poly-functional but must be
copolymerizable with the unsaturated polyester and/or vinyl ester. Preferred monomers
are styrene, alpha-methyl styrene, chlorostyrene, vinyl toluene, divinyl benzene, methyl
methacrylate and mixtures thereof.
A third essential part of the molding compositions of this invention is a blend (i.e.,
at least two) of thermoplastic polymers (also referred to as low profile additives). As
with the unsaturated polyester, these thermoplastic polymers are commercially available
products and are especially useful in producing molded articles having a Class A surface
which is essential for molded automotive parts. Many thermoplastic polymers can be
used in this invention, including saturated polyester alkyds, vinyl polymers,
polymethacrylates, acrylic polymers and mixtures thereof. For purposes of this
invention, rubber-containing homopolymers and copolymers shall be considered as
thermoplastic polymers. Preferred thermoplastic polymers are poly(methylmethacrylate),
styrene-butadiene-copolymers, saturated polyester alkyds and mixtures thereof.
In this invention, the thermoplastic polymer component is present in amount of
from about 10 to about 25 percent by weight, based on the total weight of the unsaturated
polyester and/or vinyl ester component, the monomer component and the thermoplastic
polymer component.
The low profile additive most commonly used in the industry, a vinyl acetate
containing polymer, is not a preferred thermoplastic polymer to make the compositions of
this invention. However, a low amount of a vinyl acetate containing polymer, such as no
more than about 5.0 percent by weight, may be used to increase surface smoothness of
the molded part.
The molding compositions of this invention also contain a reinforcing agent.
Specific suitable reinforcing agents are made from glass, carbon and synthetic organic
fibers such as polyethylene, polycarboxylic esters, polycarbonates and mixtures thereof.
Our molding compositions also contain a filler. Preferred fillers are alumina
trihydrate, alumina powder, aluminosilicate, baruim sulfate, calcium carbonate, calcium
silicate, calcium sulfate, clay, dolomite, glass spheres, limestone dust, mica, quartz
powder, crushed silica, talc and mixtures thereof.
Other additives may also be used in formulating the curable resin composition of
the present invention. The additives and their functions are well known in the industry,
examples of which are tougheners, release agents, inhibitors, leveling agents, wetting
agents and adhesion promoters.
Examples of suitable compatibilizers are leveling agents (such as acrylic resins,
fluorocarbons, fluoropolymers and silicones) and wetting agents (such as boric acid
esters, phosphate esters, fatty acid salts and polyethers).
The composition may also contain conventional toughening agents such as core
shell rubbers or liquid rubbers having reactive groups.
Suitable inhibitors are phenolic compounds such as (substituted) hydroquinone,
pyrocatechol, t-butylpyrocatechol and ring-substituted pyrocatechols; quinones such as
benzoquinone, naphthoquinone and chloranil; nitrobenzenes such as m-dinitrobenzene
and thiodiphenylamine; N-nitroso compounds such as N-nitrosodiphenylamine; salts of
N-nitroso-N-cyclohexylhydroxylamine; and mixtures thereof.
Suitable thickeners include oxides or hydroxides of lithium, magnesium, calcium,
aluminium or titantium. Preferred thickeners include magnesium oxide and magnesium
hydroxide.
The resin compositions of this invention may be cured by a number of free- radical
initiators, such as organic peroxide and azo-type initiators. Peroxide initiators include
diacylperoxides, hydroperoxides, ketone peroxides, peroxyesters, peroxyketals, dialkyl
peroxides, alkyl peresters and percarbonates. Azo-type initiators include
azobisisobutyronitrile and related compounds. These initiators are preferably used in the
range of from about 1 to about 3 percent by weight.
Other optional additives are mold release agents, such as zinc stearate, magnesium
stearate and calcium stearate; curing accelerants such as octoates or naphthenates of
copper, lead, calcium, magnesium, cerium, manganese and cobalt; and thickening
accelerants such as water and polyols.
The composition of this invention can be used to mold various parts which, after
cure, exhibit a change of from about 0.02 percent shrinkage to about 0.07 percent
expansion, as compared to cold mold dimensions.
The present invention is further illustrated by the following example which is
illustrative of certain embodiments designed to teach those of ordinary skill in the art how
to practice this invention and to represent the best mode contemplated for carrying out
this invention.
EXAMPLE
A process for making a SMC is described as follows. All ingredients, except for
the glass, fiber strands are mixed together to form a resin paste. The paste is transferred
to a doctor box and then deposited onto a moving carrier film passing directly beneath.
At the same time, glass fiber strands are fed into a cutting apparatus above the resin paste
coated carrier film. The fibers are chopped to 1 inch length and dropped onto the resin
paste. The amount of glass is controlled by the speeds of the cutter and the carrier film.
After the glass deposition, a second resin paste coated carrier film is laid on top, paste
side down. The paste-glass-paste sandwich is subsequently sent through a series of
compaction rollers where the fibers are wet out with the paste and excess trapped air is
squeezed out of the sheet. At the end of the compaction rollers, the SMC sheet is bi-
folded into a bin which is covered tightly to avoid the evaporation of styrene and other
ingredients.
Before used for molding, the SMC must mature. The maturation is required to
allow the relatively low-viscosity resin to thicken chemically and also increase
significantly in viscosity. The thickened SMC is easier to handle and prevents the resin
paste from being squeezed out of the glass fiber bed. SMC typically requires 3 to 5 days
to reach the desired molding viscosity (~ 40 to 100 million mPa.s). ■
When the SMC is ready for molding, the sheet is cut into pieces of a
predetermined size and shape, and the carrier film on both sides removed. The pieces are
then placed on the hot mold surface in a pattern that was established earlier for optimum
flow and mold coverage during compression. Under heat and pressure, the SMC flows to
fill the mold cavity. The cure time of the SMC varies from 30 to 150 seconds, depending
mostly on the material formulation and the thickness of the molded part.
After curing, the mold is opened, and the part is ejected from the bottom mold
surface with the use of ejector pins. Care must be used during removal of the part from
the press to avoid stressing of the part.
The molded parts are then sent to the painting operation where the parts are
powder primed to customer specifications.
The following Tables 1-3 are used for comparison purposes. Table 1 illustrates a
standard Tough Class A ("TCA") SMC formulation (as described in U.S. Patent No.
6,759,466) which is widely used in the industry for the manufacture of composite
automotive body panels because of the ability of this formulation to significantly reduce
paint pops. Table 2 illustrates a Class A SMC formulation with a low profile additive
package containing poly (vinyl acetate). Table 3 illustrates a Class A SMC formulation
according to this invention which uses a for powder-prime surface optimized low profile
additive package.
All 3 SMC formulations contain 27.5 % by weight 1 inch glass fibers as a
reinforcing agent, and all 3 SMC formulations show a Class A capable surface (30 - 85
Loiϊa), after demolding from the press before powder prime.
Figs. 1 and 2 show digital images of sections of panels of the formulations of
Tables 1 and 3 after powder prime. Both images cover the same area on the respective
panels and are of identical resolution. The composition described in Table 3 (Fig. 2)
clearly outperformed the standard TCA system (Fig. 1). The term PHR refers to parts per
hundred resin, and the term resin refers to the sum of all polymers, polyester alkyds and
reactive monomers in the composition.
In terms of grades, the powder primed parts from the composition in Table 3
would be considered an A (highest grade), the parts from the composition in Table 2
would be a D and the parts from the composition in Table 1 would be an F.
Table 1
Table 2
-15-
Table 3
This invention has been described in detail with particular reference to certain
embodiments, but variations and modifications can be made without departing from the
spirit and scope of the invention as defined in the following claims.