CA1190713A - Glass flake reinforced reaction injection molded polymers - Google Patents

Abstract

GLASS FLAKE REINFORCED REACTION
INJECTION MOLDED POLYMERS
Abstract:
The physical properties of reaction in-jection molded (RIM) polymeric articles are substanti-ally improved by internally reinforcing them with flake glass filler particles. The flake glass is incorporated in the liquid chemical polymer precursors, and is co-injected with them into the mold. The flow of the liquids in the mold orients the glass flake to provide maximum improvement in physical properties in the hardened polymerized article. Molding with glass flake filler also substantially alleviates problems of surface waviness in RIM panels.

Description

7~3 D-5,778 GL~SS ~LAKE REINFORCED REACTION
I~J~C~l~ION MOLDED POLYME~S

Background:
This invention relates to improved reinEorced reaction injection molded (P~IM) polymeric articles and to a method o~ makin~ them. More particularly, the inventlon relates to the incorporation of flaked glass particles in liquid RIM precursor constituents. The constituents are molded such that the glass flakes are pre~erentially oriented to improve physical character-istics of the polymerized article.
Reaction injection molding (RIM) i9 a process by which highly chemically reactive liquids are in-jected into a mold where they rapidly polymerize to form a coherent molded article. The most common RI~
processes today involve a rapid reaction between highly catalyzed polyether or polyester polyol and isocyanate constituents~
The constituents are stored in separate tanks prior -to molding and are first mixed in -the mixhead upstream of a mold. Once mixed, they react rapidly to form solidified polyurethane polymers. While the invention will be specifical]y described in terms of urethane R~M systems, the invention has general application to RIM processes based on other chemical systems.
~lth~ugh RIM urethane materials have many desirable physical characteristics, they also have generally high coe~ficients of thermal expansion (CTE), poor dimens~onal stability, and considerable flexibility at room temperature. A RI~ panel attached to rigid support will permanently buckle and wave when exposed to elevated temperatures~ Thus, as molded, unreinforced RIM urethanes are not generally directly suitable for use as structural panels. The relatively large surface area and thin aspect of large panel structures only serve to ayyldv~Le the inherent shortcomings of RIM urethane materials.
As a consequence, the use of reinfoxcing fillers in RIM urethanes has been extensively e~m;ned~
Currently, automotive body panels are made from RI~
urethanes filled with short ~less than 1/8") milled glass fiber, generally in amounts less than about 25% of the polymer weight. For applications such as automotive ascia where a higher coefficient of thermal expansion and higher heat sag can be tolerated, unfilled RIM
urethanes may be used.
While filling RIM urethanes with milled glass iber substantially improves certain physical properties, other problems still exist. For example, while stability and strength are increased, these improvements occur only in the direction of flow of liquid in the mold. Physical properties measured perpendicular to the direction of flow may be unimproved or only slightly improved over un-filled coun~erparts~ Moreover, the inclusion of milled glass fibers in reinforcing amounts of more than a few weight percentcause inherent waviness in panel-like structu~es. This waviness is ve~y apparent in panels which are coated with high gloss paints.
~n an e~ort to get around the adverse affects of glass fiber fillers, and the high CTE of unfilled panelsl I have ~xperimented with a number of other filler systems for RIM. ~ ha~e ~ound that any significant amount of talc, clay or other amorphous filler increases the ~iscosity of liquid precursors to the extent that they cannot be impingement m'xed. The use of hollow or solid glass spheres does not improve the physical properties of RIM urethanes either ~;men~ionally or in terms of o~erall strength. Mica flake was found to be unaccept-`
abie because it interferes with the polymerization reaction of urethane in the mold.

Objects:
It is therefore an object of the inventlon to pro~ide a method of reaction injection molding articles' with substantially improve~ coefficients of thermal expansion, strength, and less surface wavines~
th~n ~rticles made'heretofore by RIM processes.
Tt is a more particular object to improve the physical properties of RIM articles by the in-clusion of glass flake fillers. A more particular object is to incorporate glass flakes in liquid RIM
precursors and to inject these constituents into a mold in a manner to ori~nt the flakes so as to opti-miæe the physical characteristics of the finished ~icle.
Another object is to provide a method of ~aking a paneI or paneI-like RIM article'where the physical properties are'particularly improved in all directions in the'plane of the paneI. More specific-ally, it is an object to reinforce RIM panels with glass 1akes to effect such improvement. In a panel in accordance with the'invention, the glass flake is incorporated in a reinforcing amount such that the flakes are aligned with their planar surfaces sub--stantially parallel to the planar sur~aces o~ the p~nel. Such' reinforced panels are stronger, have reduced coefficients of thermal expansion, and have less wavy suraces than prior art RIM panels.
' Brief ~um~ary~
In accoxdance with a preferred embodiment of the invantion, these'and other ob~ects may be accomplished as ~ollo~s.

A desired amount of glass 1ake'is mixed ~ith and dispersed in one or more'of the chemically re~ct'~e'liquid precursor constituents ~or reaction in~ect'ion ~olding. Generally, at least about 5 weight percent based on the total polymer weight is desirable~
The re~n~orcing effect of the glass flake increases proportionately to the amount incorporated.
Herein, glass flake'is defined as small particle~ of friable amorphous material having a generally planar surface, the area of that ~urface being substantially greater than the particle thickness.
The flakes are'preferably no more than a few microns thick and have aspect ratios (flake surface area to thickness xatios) of at least about 40:1. The dia-meters of the particles must be small enouyh to flowthrough ~IM metering, mixing and injecting equipment ~i~hbut clogging. A preferred type of flake glass is made by melting a suitable glass composition based on silica; extruding the molten material through a bushing to ~orm glass film, cooling the film, and breaking it ~etween ~ooperatin~ rollers. The particles so produced ma~ be'~urthe~ reduced in siæe in a ~uitable mill.
The'indi~idu~l particles closely resem~le minute panes of broken window gl~ss~ Th~ymay be'coated with surface ~ct'ive'agent~ such''~s silane to improve'their dis-pers~on and bonding ~racteristic~.
All the chemically reactive liquid constitu-ents and the glas~ flakes dispersed therein are thor-oughly mixed prior to delivery to the mold. However, it is the shape of the mold and the flow of the liquid constituents therein that ultimately determine the orientation of t,he'flake glass in the polymerized pro-duct. The flake orientation, in turn, determines the direction and degree o~ improvement in physical characteristics provided by -the flake glass filler Generally, the glass flakes align in the mold with their longest dimensions parallel to the direction o~ flow of the liquid constituents in which they are carried. In molds for making articles with relatively thin cxoss sections, the flakes also become oriented with their planar surfaces parallel to the mold surfaces. Substantial rein~orcement is provided by glass flake in all directions in the plane of the flake~ Thus, in glass flake filled reaction injection molded panels, substantial improvement in physical characteristics is provided in all directions in the panel planeO
What may be even more significant for certain applications is the fact that glass flake filled RIM
panels have much less wavy surfaces than their glass fiber-filled counterparts and do not develop waviness when ~herm~lly cycled. This means that articles such as automotive body panels can be molded, painted and installed without special finishing procedures needed to eliminate surface waviness in glass fiber filled panels. Moreover, glass flake filled panels can fill applications where unfilled panels cannot be used.

2~ Clearly significant advantages are to be gained by incorporating glass flake as a filler in reaction injection molded plastics~
Detailed Description My invention will be better understood in 3U view of this more detailed description.
A molding trial was conducted using glass flake filler in an otherwise conventional urethane ~eaction injection malding system. In the trial, flat plaques were molded ~rom un~illed urethane, urethane filled with short lengths of milled glass fiber and flake glass.
The crosslinked urethane was the reaction product of a polyether polyol with a hydroxyl function-ality greater than two and diisocyanate terminatedprepolymer based on methylene diisocyanateO The polyol was NIAX D337~ Resin made by Union Carbide and the lsocyanate was ISONATE 143L~ made by Upjohn. The polyol and isocyanate were initially retained in separate pres-surized agitated tanks with nitrogen or dry air blankets.These urethane forming chemicals have ~een used heretofore to make fiber glass filled structural panels.
The polyol and isocyanate were metered into the mixer by means of a Krauss Maffei PU80~ metering machine.
The unit was capable of processing the reinforcements only on the polyol side. Positive displacement piston pumps were used to eject the polyol and isocyanate into an impingement mixing chamber. The chamber itself had a cylindrical shape, the polyol and isocyanate ports being located at 90 intervals of a circumference of the cylinder in alternating order. The port for the filled polyol had a diameter of 4.2 mm and that for the unfilled isocyanate 2.0 mm. The injection pressures of the polyol and isocyanate were 2350 psi and 2200 psi, respectively.
The polyol was maintained at a tank temperature of approximately 46.1C (115F) and the isocyanate at 33.9C
(93F). The output capacity of the metering equipment to the mold cavity was approximately 3.5 pounds per secondO
The molding machine used was a Kannegeisser Model MFT. A two-piece mold was mounted on the stationary and movable press platens. The mold had a ,, ."

~9~

plaque-shaped cavity with a flat surface area of 2411 x 42" and a ~hickness of 0.1 inch. The upper platen tilted away from the lower platen in the mold open position to facilitate demolding.
The mold cavity walls were coated with Green Chem MR 6023~ pa~te and sprayed with Chem Trend XMR 136~
mold release before each shot. The mold temperature was maintained at about 170-185F. For filled plaques a minimum mold temperature of about 180F was desirable to prevent skinning. The gate to th~ mold had an elongated slit shape which ran the length of the shorter side of the ~old (approximately 16 inches).
Preparatory to molding unfilled urethane plaques, the polyol and isocyanate outputs of the RIM
machine were calibrated to achieve a weight ratio of 100 parts polyol to 102.5 parts isocyanate. While this produced a relatively brittle urethane, it was suitable for comparing the properties of unfilled, glas~ fiber filled and glass flake filled plaques molded in like manner in the mold described above. All plaques were post cured in a flat position for 30 minutes at 250F to complete polymerization.
The calculation of a predet~rmined weight fraction filler in a molded urethane plaque was made as follows (iso refers to isocyanate):
wt polyol ~ wt iso 1.00 - weight - (wt~ polyol + wt lSO) G Wt. filler fraction filler Because the machine used to mold plaques could only accommodate ill~r on the polyol side, the weight percent filler to be dispersed was calculated as follows:

7~ 3 ~t polyol ~ wt filler = wt ~raction filler in polyol The ratio of filled polyol to isocyanate was then re calculated on the basis of 100 parts polyol and filler ts allow for the filler in the polyol:
wt polyol * wt ~f iller - 100 parts filled polyol wt iso X parts llnf; 11~ iso For example, if 15 weight percent glass fiber was to be introduced into the urethane system described above at a polyol to iso ratio o~ 100:102.5 then 100 poIyol 1 102~5 iso _ ~100 polyol + 102.5 iso) = 35 7 paribtsr Then to determine the amount of glass to be mixed with the polyol constituent 100 polyol ~ 35.7 glass fiber ~ 26-3 wt percant glass f~x~ in Then to readjust the mix ratio to maintain the pre-determined chemical ratio of 100 parts polyol to 102.
parts isocyanate 100 polyol ~ 37~5 glass fiber _ 100 parts polyol-& glass fi~er 102.5 isoc~ana-te ~ 75.53 iso Thus the machine was set ~o deliver 100 parts polyol and glass per 75.53 part~ isocyanate to achieve a 15 weight percent fiber glass filler in the molded urethane article. O~viously, the calculations would be the same ~or ~lass flake, glass fiber or other solid ~iller.

7~L3 Table I indicates the Sample Designation and number of plaques that were molded during an experimental run in accordance with ~he invention:

TABLE I
SAMPLE NUMBER
DESIGNATION MOLDED REINFORCEMENT/LEVEL
N- 10 Unfilled G-15 ~ OCF P117B~ 1/16" milled glass fibers, G-25 8 lS% ~ 25~ by weightr respectively.
S5-15 10 OCF P117B~ Low aspect ratio milled SG-25 10 glass fib~rs (<1/32n), 15% and ~5%
by weight, respectively.
F-10 10 OCF Hammermilled "C"Flakeglas~-1/64"
F-15 11 10% and 15% by weight, respectively.
GF #1 10 5% Flakeglas~/5% P117B - 1/16"
GF #2 10 5% F~lakeglas~/10% P117B - 1/16"
GF #3 10 10% Flakeglas~/5% P117B - 1/16"
GF ~4 11 10% Flakeglas~/10~ P117B - 1/16"

Two types oE fiberglass were employed. The first was OCF P117B~-1/16" milled glass fibers sold by Owens-Corning. These samples are designated with a G, The glass was coated with a dispersion enhancing resin.
In an effort to improve the properties of fiberglass filled RIM plaques in directions other than the flow direction in the mold, very short glass fibers were used in some of the trials. These fibers were OCF P'91 17B~
~creened to include particles 1/3~19 in length and less.
These samples are designated SG f or short ~l ass .
The key constituent of the subject invention is flaked glass7 (Sample designa~ion F)~ Although flaked glass has been kn~wn since the mid '50's, it has heretofore not been used as a filler constituent -for RIM~ Flaked glass is made by melting a glass of desired chemical compositionO The molten glass is then ex~ruded through a heated annular bushing. The ex-trusion forms a cone-shaped glass film, generally about 2 to 10 microns thickr which is continuously pulled away ~rom the bushiny by a pair of pinch rollers. The ~il~ cool~ rapidly a~d i9 broken by the rollers. The broken films are h~mm~r-milled to create small particles of "~lake1' glass. TIle individual particles resemble broken panes of windo~ glass. Flake'glass suitable for use in the subject i~ ention is described in greater deta.il in 'l~lakeglas V - Filled Coatings: Past, Present and Future" by Dr. N~ Sprecher, published by Owens-Corning Fi~erglas European Operations. ~or the subject invention, I preer E or C type glass par-ticles which a~e less t~an about 8 microns thick, ~ith an average diameter less than about 1~32l'. The'preferred aspect r~tioof flake surface area to thickness is greater' than a~out 25:1 and preferably grea~er than 40:1~ Larger ~0 ~lass particles may be used, howe~er, they tend to be more abrasive and harder to handle in conventional re-inforced RIM systems. The flake glass may be coated wi~h silane or other dispersion enhancing coatings.
Howe~er, the'glass flake used in the molding trials reported herein were not so coated.
Some prel;m; n~ry work has been done with silane coated glass flake. Qualitatively, it appears that the silane coating promotes rapid dispersion of the flake in polyol resin. It also seems to promote bonding between the RIM polymer matrix and the flake particles. This in turn, enhances the effect of the flake filler on the physical properties of the polymer matrix.

Physical property data and rheometic impact data were taken using standard ASTM test methods fQr ea.ch type of plaque from Table I. The re~ults are sho~n in T~les 2 and 3~ Samples designated A were cut ~rom the 1/2 of the test plaque closest to the mold inlet runner ~hile those designated R were taken ~rom the half o the test plaque furthest ~rom the inlet runner. The tests were conducted on the samples both in the direction of flow in the mold Idesignated parallel~ and in the direction in the plane of the plaque perpendicular to the flo~ (designated perpendicular).

T~3LE 2 ~hYSI~ k~ 'Y ~;~TA ~
iEL--~. æWUl.US. H:At 'i~ tENSlLlE StREti~l ~P 1) '~P~ O ' NC0~ SI ) ~ 10~ ~ERCE~I~
- ~fV~ ~1 ( Il) lH RM~L EXP~S3`~1 51~ ',11) PART
`80~1~PLI: YEll;Hr SPEtlFie HEA / KAN~ ~ /IN x lo-6/~r3 50~,HEIW/ KAN~ / SHRINKA~
~ESC~lPTlCJII ~E~EH~ ERAY11~7 TD. OE~ ~TD. DE'J. t_~ tl~ I' I) STD. DE~I. STD. DEV. SID. OE~'. St3. ~
.011.0~ 89,000/216 92,100/53~~3.8 73.9 .7~/.6G 40901?0.9 4140/1~13.8 95.~1'11.11 112/lS.,q 1.~5/1.51 .oP19~ 91,~10/2i4 gl~,300~15. 7~.6 ~3.1 .79/.6~ 3930~156~ 3900196.2 92.6~Z0.7 8~.~112.~
~:15 ~) 19O3~.11 135,000/517 18?,00U/Z9 ~53.3 34.~l .b51.Z8 4220/91.5 ~Z90/126~2 35.q/10.2 23.216.2 .rJ2/.60 Gi5 ~ . Y6.Q~.0~ IS~OU/3~8 119,0Q~/43~51.1 33.Z .651.25 ~9030/143.6 420018,5.~ t718.4 21.~/2.4 G~5 ~A~ 1 22.91.~ 150,~0013Z7 299,000/40' 52~3 l~.G .88/.20 4580/129.9 49401275.4 38.811.9 19/5.7 .~01.2 ~;Z5 ~ 24.51.16 15a~000/862 Z85,0W/lOr2 53.q 1'6.0 .91/.Z3 4240/6~c4 5100J5~.2 '1917.B lq.4/3~3 ~G15 6A~ I lSo7 1.30 175,0001349 179,000/25. ~16.6 5~.9 2.291Z.03 5050/102.1 4890t4q.4 39.616.2 40.2J~.2 .9~t.~1 i~
$~5 ~Ei) IS~O 1.~ a63~0001339 172,00016~a 47.~ ~.1 2.1~11.82 488q/23.9 ~7601140.3 30.816.~ 3~.2/3.
St;25 ~ Z~,71.33 187,00Q/192 20e5QOQt49 S3.~ 50.1 2.08/.76 522ûl342.6 5250tqO6.0 2B.8/7.3 2B.~18.4 .921.11 !J3~5 e,B) -24.3 1.~ g~Q001358 213,9G~/28 59.6 ~6.~ .361.52 Ç81C/133.9 497QI19.5 29.çls.0 30f6.0 r ~-lQ 6Aa 1~ lt ~~ 155jQ9Ot329 169,000/52'. 50~7 ~ ~g~6 ~5Z1~311 i 3370tl8~?` 3570t63~1 19O~1!53~1 21;/5~a .ff;.
F'-10 ~8~ ~31~12 172~1D001422 183,~t0012~ 5~3 ~17.0 .611.3~1 ~13501~.1~ ~14~0187.6 25.6~5.~1 27.~111.5 ~-15 ~Al 1~ t'~l6000/~09 19G,OoO/30~ ~6~0 9~5 1~101~87 3870139~0 39tlO156~3 14~/2~ ~ 16~611~5 c90/~7k iF-15 ~B~ 15.91.14 .~ IY4,0001q51 Z08,00G/Sq ~ 3~.1 .721.6t 3790/57.9 3880J25.~ 2~,6/6cO 15.6/3.6 ~ Dg (~ 3 178,QOO/~95 216,00~5~h 58.~ 38.~ 1.6~ 1500l70.0 4670152.4 ~0~.6 20.~15.~ .ffl.78 GF ~1 ~B~ ll.Ç2.Z0 1~3,000/~04 232,0iDO/52~51.3 3S.8 l.~ql.91 4260/57.7 4500/l70.9 20f2/3~ ' 16.21i.l 5:F ~2 tA) 13.~ l.Z~ 189,000f~115 251,000/~1~ 52.~ 31.3 1.65/.75 ~40!237.0 4~'t0160.2 26.~l605 19.6f3.1 .9Q/.52 ~p ~Z ~B) l~.Z1.23 1~8,0~015~3 278,000/62h 5q.a 28.t 1.37/.72 4540/lGt.3 4990J94.~ Z1.415.7 15.6/~.3 GF ~3 (A? ~3.62.13 lS~,OOG/279 l91,000~57~ SO.? 34.5 .b31.3Z 40~10~38.3 4560/46.6 23.~qf5.4 W4.q .9QI.
G~ ~3 ~ 24.31.07 16~000/195 212,00Qi'54~ 4t.2 30.7 .701.51 366Q/33.9 3900f~1.6 ~6.2~2.~ Z213.7 e;F ~ A) 10.71.1~ 166,W~/630 2270009f~8~ 27.5 I.O~t.$5 414~/63.1 4i40/17.~ l9.1S16.i }9.4/O.i .7~1.51 GF ~4 S~ ~ 20.1 l.10 l~S~WO/61~ 201,000/69 39.~ 26.3 .991.45 374013Z.7 3810/Z42.? 18.8/~7 16.6/3~3 * Test3 ~t roor~ te~?erature (~C) unle~ otIlcrwi:3e indicate~.

-~V7~3 T~BLE 3 R~O~RIC IMPACr TEST DA~

Y I E L D T O T A L
Sampl~ l~dcne~ Spe~d Fo2-c~ ~ralr21 EnerBY Tra~ En~rgy It~p~ tMM~ tMlS) ~N~ (MM) tJ)tMM) tJ) N- 2.46 2.230 2542 12.07 13.95 13.19 15.37.
G-lS Z.63 2.Z30 888 3.97 1.52 18.16 8.11 G-Z5 2.61 2.230 825 4.4Z 1.74 19.73 11.12 Sa-15 2.4~ 2.230 1533 6.17 4.09 17.90 11.39 SC-25 2. 44 2. 230 1224 5. 72 Z. 92 19. 62 9. 99 F10 2.69 2.230 1328 6.59 3.61 17.75 10.33 PlS 2.59 2.230 7S2 3.44 1.11 18.90 7.44 GF ~1 2. 342. 230 952 4. 71 1. 83 16. 86 8. 80 CF #2 2.432.230 ?q7 3.33 1.Z0 19.22 8.93 - GF ~3 2.702.230 828 3072 1;36 18.29 8.70 C;F ~ 2.812.23b 868 4.30 1.85 1a.56 9.70 Eadl V~lue is the a~erage o~ five ~5) s~les :tested at ro~ l~ Lc~L;~e ~23~C~
M~S = ~ters/Second N = Newtons ~ ~ ~oules MM- MilliTneters The unfilled plaques as molded had relatively low flex moduli and high coefficients of thermal expansion (CTE). They also had poor heat sag characteristics, tensile strengths, high elongations and relatively large shrinkage due to cure.
In the parts molded with l/16" glass, the glass fibers tended to orient substantially parallel to the flow of material into the mold. Thus, the plaques showed improved ~lex moduli, tensile strength, and part shrinkage only in the parallel direction.
However, these properties were not -improved to any appreciable extent in the direction perpendicular to mold flow. They exhibited the characteristic waviness o~ glass fiber filled RIM paneIs.
Parts molded from the short glass showed no appreciable improvement in some physical properties, particularly CTE and strength.

) PEBPEN~lCU ~ R PARAT~T

U G-15W/o F-15W/o U -G-15 h F-15 /o Flex M~dulus PSLX1000 A* 89 135 171 92 187 196 CTE (in/in Xlo-6/ ~ A 73.8 53.3 B 73.6 51.1 44.7 73.6 33.2 37.1 Heat Sag (1 Hr @ 250F) A 0.74 G.65 1.10 0.60 0.28 0~87 ~D
B 0.79 0.65 0.72 0.64 0.25 0.62 Tensile Sb~ A 4090 4220 3870 4140 4290 3900 Percent Elonga~ion A 95.8 35.4 14.8 112 23.2 16.6 B 92.6 27 20.6 88~8 21.4 15.6 Percent Part Shrink A 1.45 .92 .90 1.51 .60 .78 * A indicabed sl~ple cut from half of plaque adjacent ~old inlet r ~er.
B indicates sa~ple cut fram half of plaque re~Dt~ frQm m~ld inlet run~er.

.3 Table 4 sets out data taken ~rom TaDle :2 for unfilled, 15% glass ~iber ~illed ~G~lS~, and 15%
~lake glass filled ~F-15%~ panels ~or purposes of comparin~ t~eir physic~l properties parallel and per-pendicular to polymer ~low in the mold. The data show~mpro~ements in modulus, reduced coefficients of thermal expansion and lowered elongation for hoth glass fiber and flake fllled panels, especially in the p~ralleI direction. Howe~er, only the glass flake ~illed sample exhibited substantial impro~ement of these properti:es in the perpendicular direction. Thus, ~l~ke glass has been shbwn to be superior over all to glass ~iber ~illers and to subsfantially improve the physical properties of molded RIM panel~ in all lS directions in the plane of the panel.
~ mi n~tion of plaques molded from flake glass filled urethane showed that the glass ~lakes orient ~ith their planar surfaces su~stantially parallel to the plane of: the plaques. This arrangement of filler plates provides for improved properties in all direc~
. ~ions in th~ plane of a panel-like par~.: Although other plate~ ~illers have ~een tried, gla~s ~lakes : have thus ~ar ~een ~ound to ~e the only suita~le ~illers ~or makin~ ~IM panels with urfaces good enough ~X enameled automoti~e body panels.
The most remarkable and unexpected impxovement brought about ~y the use o flake :glass filler is the complete elimination o~ visually unappealing surface waviness.~ This improvement is particularly noticeable in panels coated with glossy paint. Distinctness o~ image refers to the akility of 7~L,3 a smooth, glossy surface to reflec~ an image without added distortion from irregularities in the coating or substrate. The glass flake fllled panels (as molded) all had dis~inctness of image properties at least-as good as glass fiber filled panels presanded to remove ~urface waviness. Furthermorer the glass ~lake filler eliminated any tendency for the RIM
plaques to warp, even when thexmally cycled. Even without the improved physical properties pointed vut above, the unexpected but great improvement in surface waviness and warpage brought about-by flake glass filler could warrant its use in RIM systems.
While my invention has been dPscribed in . term~ of the speci~ic embodiment thereof, clearly other forms may be readily adapted by one skilled in the art.
Accordingly, my invention is to be limited only by the ~ollowing claims.

Claims (12)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of molding a reinforced polymeric panel by coinjecting a hardenable liquid polymer pre-cursor carrying high aspect ratio glass flake particles into a mold cavity defining said panel, causing said liquid to flow away from the point of injection such that said glass flakes are layered with their planar surfaces substantially parallel to the planar surfaces of the panel as the mold is filled, and thereafter hardening said liquid precursor in the mold such that the glass flakes are captivated in the hardened poly-meric panel in said layered positions, the amount of said glass flake dispersed in said precursor being such that the hardened panel has a reduced coefficient of thermal expansion in all directions in the plane of the panel compared to a like unfilled panel and a substantially less wavy surface than a like glass fiber filled panel both having been molded from like liquid polymer precursor in like manner.

2. A structural panel comprising a reaction injection molded polymer encapsulating a reinforcing amount of high aspect ratio glass flakes, wherein said panel the glass flakes are captivated within the polymer and aligned with their planar surfaces substantially parallel to the plane of the panel, the surfaces of said panel conforming to the mold contour without any substantial waviness after demolding and said panel having reduced coefficients of thermal expansion in all directions in the plane of the panel as compared to a like unfilled panel molded of like polymer in like manner.

3. A method of molding an internally re-inforced polyurethane panel comprising dispersing a reinforcing amount of high aspect ratio glass flake into one or both of the liquid polyol and isocyanate precursor constituents for said urethane polymer, rapidly mixing said polyol and isocyanate precursors to form a chemically reactive urethane forming liquid mixture, injecting said liquid mixture into a mold for a said panel under pressure such that the mixture flows away flow the injection port and causes the glass flake particles dispersed therein to be layered within the mold with their planar surfaces substantially parallel to the planar surfaces of the panel, allowing said polyol-isocyanate mixture to chemically react in the mold such that a hardened polymeric urethane panel is formed wherein said glass flakes are incorporated in their layered and surface parallel orientations, whereby said method the hardened urethane panel has a substantially wave free surface as molded and a substantially reduced coefficient of thermal expansion in all directions in the plane of the panel as com-pared to a like unfilled panel molded of like urethane constituents in like manner.

4. The method of Claim 3 wherein the liquid polyol precursor is a polyether polyol having a functionality greater than two.

5. The method of Claim 3 wherein the liquid polyol precursor is a polyether polyol having a functionality greater than two and the isocyanate pre-cursor constituent has an isocyanate functionality of about two.

6. The method of Claim 3 wherein the re-inforcing amount of high aspect ratio glass flake is in the range of from about five to 50 weight percent of the sum of the weights of the liquid polyol and isocyanate precursor constituents.

7. The method of Claim 3 wherein the average aspect ratio of the planar surface area of the glass flakes to their thickness is greater than about 25:1.

8. The method of Claim 3 wherein the re-inforced polyurethane panel is an automotive body panel.

9. The method of Claim 3 wherein the glass flake is precoated with surface active dispersion aid.

10. A reaction injection molded polyurethane panel reinforced with from about 5-50 weight percent glass flakes having an average aspect ratio of at least about 25:1 and a thickness less than about 8 microns, said flakes being encapsulated in said poly-urethane in a layered manner such that their planar surfaces lie substantially parallel to the planar surfaces of the panel, wherein said panel closely assimilates the contour of the mold in which it is formed without surface waviness and wherein said panel is substantially stiffened and strengthened by the presence of said glass flake.

11. The panel of Claim 10 wherein said panel is an automotive body panel.

12, The panel of Claim 10 wherein the poly-urethane is the reaction product of a polyol constituent having a hydroxyl functionality greater than two and a diisocyanate constituent.