STAMPABLE REINFORCED THERMOPLASTIC SHEETS

Abstract: A multilayer integral sheet of reinforced thermoplastic material. The sheet includes a plurality of alternating polymeric and fibrous materials. The sheet is characterized by having an outermost surface layer of thermoplastic polymer, a layer of fine stranded fibrous material having a weight of 30 to 120 g/m<2> adjacent to the outermost surface layer, at least one layer of coarse fibrous reinforcing material, a layer of thermoplastic polymer having an initial linear shrinkage of less than 2 percent adjacent to at least one surface of the layer of reinforcing material closest to the outermost layer and wherein each of the polymer layers has a minimum crystallization half-time of one minute or less. The sheet can be formed in a stamping apparatus. The surface of the sheet is free from "print through" and blistering.

Description: STAMPABLE REINFORCED THERMOPLASTIC SHEETS This invention relates to multilayer thermo¬ plastic sheets and particularly to glass-reinforced thermoplastic sheets of laminate or composite con- struction for forming automotive parts as well as for other applications. Forming of the sheets can be accomplished by the use of various sheet metal forming techniques, such as by stamping apparatus. Automotive companies have been changing from the use of die-cast metal to the use of reinforced plastics for many different parts of an automobile in order to take advantage of the resulting reduced weight. For large parts, these reinforced plastics have been in the form of sheet molding compounds (SMC) which are based on thermoset resins which require a chemical reaction to occur in order to cure the plastic. Generally the forming equipment requires apparatus more simple than that required to injection mold parts of comparable size. Many disadvantages exist, however, such as long cycle time in order to cure the thermoset resin, poor surface finish and complexity of resin compositions. U.S. Patent No. 3,765,998 discloses a thermoplastic resin sheet which is formable in shaping apparatus held at ambient temperature and concerns a glass mat having a glass fiber length of at least one inch, impregnated with poly(ethylene terephthalate) (hereinafter sometimes referred to as "PET") having a weight average molecular weight from about 5,000 to about 45,000. U.S. Patent No. 4,263,364 discloses rein¬ forced thermoplastic polyester sheets which are rapidly quenched from the melt to a stable amorphous state. The quenched, amorphous sheets may then be stamp-formed at temperatures that are below the melting point (T m ) of the polyester but above its glass transition (T ) temperature, or the quenched amorphous sheets may be stored and then stamp-formed at another time. In this manner, therefore, con¬ siderable energy is saved as compared to some of the other prior art processes involving the necessity of heating to or above the melt temperature of the polymer involved. The reinforced sheet has a center layer or layers which is or are comprised of a more slowly crystallizing polymer than the outer layers of the sheet. This construction reduces the need to rapidly quench the core of the sheet so as to form the amorphous sheet and thus enables higher produc¬ tion rates and the production of thicker amorphous sheets. As will be seen in the comparative examples below, several problems have been encountered with the sheets of U.S. Patent 4,263,364 (as well as with sheets which contain all poly(ethylene terephthalate) polymer). First, the sheets sometimes exhibit fiber "read through". That is, the fiber pattern of the relatively coarse reinforcing layer or layers is visible on the surface of the sheets. Further, it is desirable in some processes to rapidly preheat the sheets before they enter the stamping apparatus. When this is done, undesirable blistering often occurs again causing a surface defect. These pro¬ blems are solved by the present invention. According to the invention there is provided a multilayer integral sheet of reinforced thermo¬ plastic material characterized by having an outermost surface layer of thermoplastic polymer, a layer of fine stranded, fibrous material having a weight of 30 to 120 g/m 2 adjacent to the outermost surface layer, at least one layer of coarse fibrous reinforc¬ ing material, a layer of thermoplastic polymer having an initial linear shrinkage of less than 2 percent adjacent to at least one surface of the layer of reinforcing material closest to the outermost layer and wherein each of the polymer layers has a minimum crystallization half-time of one minute or less. Sheets of the present invention are suitable for forming high quality parts, since the surface defects associated with prior art materials are eliminated. More particularly, the sheets of the present invention are free from "read through" and blistering. Further, the fine stranded fibrous layer effectively isolates the outermost layer, as will be described more fully below, so that its properties are unaffected by mixing with the other polymers in the structure. As noted, a layer of fine stranded fibrous material, preferably of continuous filaments randomly patterned, having a weight of about 30 to 120 g/m 2 is positioned contiguously with respect to one of the outer layers of the sheet. These are referred to in this art as "surfacing mats" or "surfacing veils" and are lightweight mats varying in thickness from about 0.25 to 0.75 mm, with the filament diameters generally averaging 15-25 microns. As pointed out in the Handbook of Fillers and Reinforcements for Plastics (1978), Van Nostrand Reinhold Company, on page 476, surfacing mats or veil mats have been applied to the inside of wet-layup composites, such as tanks and the like, to provide a resin-rich, chemical resistant layer and to protect the under¬ lying reinforcement layers. They are also employed as a surface covering in press-molded items, prevent- ing the reinforcing fiber pattern from appearing in the prime molded exterior. As used in this inven¬ tion, the surfacing mat or veil does not perform any substantial reinforcing function, although some modicum of reinforcement may result, but rather the surfacing mat or veil inhibits the flow-through or interchange of polymers. That is, this layer keeps the polymers on one side thereof substantially O isolated from the polymers on the opposite side despite the pressure that would otherwise cause flow and interchanges as a result of the compression applied to form the sheet. In this manner the physical characteristics of one polymeric layer on one side of the surfacing mat will be substantially unchanged by any flow-through or exchange with the polymeric material of the layer on the opposite side of the surfacing mat or veil. According to the present invention, it has been found that a layer of fine stranded fibrous material, that is a layer having a weight 30 to 120 g/m 2 , will perform this function. A fibrous layer having this weight will be referred to herein as a surfacing mat for convenience. In contrast, a typical coarse reinforcing mat allows polymer inter¬ change. Although surface smoothness is improved with the aid of a surfacing mat alone, there still would be some fiber read-through due to the effects of the pressure applied when the sheet is being formed under compression but for the combination of the surfacing mat and the particular polymer chosen for a layer contiguous to the outermost coarse reinforcing layer. It will be noted from an example given herein that when the low shrinkage polymer was omitted or replaced with PET, even though the surfacing mat was present, there was observed visual read-through of the outermost reinforcing mat. Thus, the surfacing mat and the low shrinkage polymer adjacent to a coarse reinforcing layer cooperate to provide, the desired exterior surface. Owens-Corning Fiberglas makes a surfacing mat identified as M-514 Surfacing Mat. Nicofibers, Inc. makes a fiber glass surfacing mat called "SURMAT", which is a highly uniform, randomly pat¬ terned continuous-filament mat. "SURMAT 100" is still another example of a surfacing mat. For a mat that has a 0.5 mm thickness, the average weight per square meter is 80 grams; and for a mat having a 0.75 mm thickness, the average weight per square meter is 104 grams. The filament diameters are about 21 microns. A layer of polymeric material having par¬ ticular properties is contiguous with at least one side of the layer of relatively coarse reinforcing fibrous material which is closest to the outermost surface. This polymer has low shrinkage and, in contrast to the interior layer of the sheets des¬ cribed in U.S. Patent 4,263,364, a short crystalliza¬ tion half-time. More particularly, this polymer has a shrinkage of less than 2 percent and a minimum crystallization half-time of one minute or less. This polymeric layer is preferably selected from: a. copolymers of ρoly(l,4-cyclohexylenedimethylene 1,4-cyclohexanedicarboxylate) with about 10 to about 30 mole percent dimer acid; b. a polyetherester comprised of 1. a dicarboxylic acid component comprised of A. 100 to 60 mole percent terephthalic acid, and B. 0 to 40 mole percent of an aliphatic or aromatic dicarboxylic acid having a molecular weight of less than 300, and 2. a diol component comprised of A. a glycol comprised of 100 to 60 mole percent tetramethylene glycol and 0 to 40 mole percent of an aliphatic or aromatic glycol having a molecular weight of less than 300, and B. 10 to 60 weight percent, based on the weight of the polyetherester, of a poly(alkylene oxide) glycol having 2, 3 or 4 carbon atoms in the repeating unit and having a molecular weight in the range of 400 to 5000, wherein the sum of the total mole percent amount of aliphatic or aromatic dicarboxylic acid having a molecular weight of less than 300 in item b.l.B., the mole percent amount of aliphatic or aromatic glycol having a molecular weight of less than 300 in item b.2.A., and the weight percent, based on the weight of the polyetherester, of the poly- (alkylene oxide) glycol in item b.2.B equals at least 25 but does not exceed 80; c. a polyetherester comprised of 1. a dicarboxylic acid component comprised of A. 100 to 98 mole percent terephthalic acid, and B. 0 to 2 mole percent of a trifunctional carboxylic acid of molecular weight less than 300; 2. a diol component comprised of A. a glycol comprised of 90-60 mole percent 1,4-cyclohexanedimethanol and 10 to 40 mole percent ethylene glycol or a tetramethylene glycol such as 1,4- or 1,3-butylene glycol, and B. 10 to 50 weight percent, based on the weight of the polyetherester, of a poly(alkylene oxide) glycol having 2 to 4 carbon atoms in the repeating unit and having a molecular weight in the range of 400 to 2000; d. a polyetherester comprised of 1. a dicarboxylic acid component comprised of A. 100 to 98 mole percent 1,4-cyclohexane- dicarboxylic acid and B. 0 to 2 mole percent of a trifunctional carboxylic acid of molecular weight less than 300; 2. a diol component comprised of A. 1,4-cyclohexanedimethanol and B. 10 to 60 weight percent, based on the weight of the polyetherester, of a poly(alkylene oxide) glycol having 2 to 4 carbon atoms and a molecular weight in the range of 400 to 2000. The polyesterethers described above are similar to some of those described in Nishimura et al, J. Macromol. Sci. , Part A (1)4, 617-25 (1967) and U.S. Patents 3,766,146, 3,651,014, 3,891,604 and 3,890,279. Item (c) above in the sheet may comprise poly(about 70 to about 75 mole percent/about 30 to about 25 mole percent 1,4-cyclohexylenedimethylene/- butylene terephthalate) modified with about 28 to about 33 weight percent poly(oxytetramethylene) of molecular weight 1000 or poly(about 70 to about 75 mole percent--about 30 to about 25 mole percent 1,4-cyclohexylenedimethylene/butylene terephthalate) modified with about 0.5 to about 0.8 mole percent (based on the acid component present) trimellitic anhydride and about 28 to about 33 weight percent poly(oxytetramethylene) of molecular weight 1000. Item (d) above preferably comprises poly- (1,4-cyclohexylenedimethylene 1,4-cyclohexanedicar- boxylate) modified with about 0.25 to about 0.75 mole percent (based on the acid component present) tri¬ mellitic anhydride and about 22 to about 28 weight percent poly(oxytetramethylene) of molecular weight 1000. The outermost layer of the sheet is any crystallizable thermoplastic material that is capable of being formed into an integral sheet. For example, the layer can be a nylon. However, polyesters and polyester blends such as those described more com- pletely below are preferred. Polyester and polyester blends are less hygroscopic than are nylons. The outer layers of the sheet are of a crystallizable material preferably selected from (1) poly(ethylene terephthalate) such as having an inherent viscosity (I.V.) of about 0.4 to about 0.9; (2) copolymers of poly(ethylene terephthalate) having about 5 mole percent or less of 1,4-cyclohexanedi- methanol, neopentyl glycol, butylene glycol, 2,2,4,4-tetramethyl-l,3-cyclobutane diol, bisphenol A, propylene glycol, diethylene glycol, hexamethylene glycol, isophthalic acid, adipic acid, or 1,4-cyclo- hexanedicarboxylic acid; (3) poly(l,4-cyclohexylene- dimethylene terephthalate) ; (4) copolymers of poly- (1,4-cyclohexylenedimethylene terephthalate) having about 20 mole percent or less of ethylene glycol, neopentyl glycol, butylene glycol, 2,2,4,4-tetra- methyl-l,3-cyclobutanediol, bisphenol A, propylene glycol, diethylene glycol, hexamethylene glycol, isophthalic acid, adipic acid, or 1,4-cyclohexanedi- carboxylic acid; (5) blends of poly(ethylene tere¬ phthalate) with 35 weight percent or less of the polymers and copolymers of items (2) , (3) or (4) above; and (6) blends of poly(l,4-cyclohexylenedi- methylene terephthalate) with 35 weight percent or less of the polymers and copolymers of items (1) , (2) or (4) above; having a minimum crystalization half- time of one minute or less. In copolymers and blends of poly(ethylene terephthalate) and poly(l,4-cyclohexylenedimethylene terephthalate) [items (2), (4), (5) and (6)], the minimum crystallization half-time will depend upon the composition, the inherent viscosity, the catalyst system used, the presence of inert fillers and, possibly, the presence of impurities. For example, poly(1,4-cyclohexylenedimethylene terephthalate) copolymerized with 5 mole percent ethylene glycol has a minimum crystallization half-time of about 40 seconds, whereas that copolymerized with 26 mole percent ethylene glycol has a minimum crystallization half-time of three minutes. Also, the inherent viscosity, being a measure of molecular weight, affects the crystallization half-time, the minimum crystallization half-time becoming greater as the inherent viscosity increases. For example, poly¬ ethylene terephthalate) copolymerized with about 5 mole percent 1,4-cyclohexanedimethanol has a minimum crystallization half-time of one minute when the I.V. is about 0.6, but this increases to two minutes if the I.V. is about 0.75. Further, depending upon their ability to initiate crystallization, such materials as inert fillers, catalyst metals and impurities may also serve to decrease the minimum crystallization half-time at a given composition and inherent viscosity. The reinforcing layer or layers are prefer- ably made from fiber glass of continuous strand, such as of high end count roving, laid down in an overlap¬ ping swirl pattern to provide high mat uniformity, such as M-8610 Series from Owens-Corning Fiberglas, which may range from about 305 g to about 915 g/rn''. Other types of reinforcing layers include woven roving, fabrics and chopped strand mats all made of fiber glass to mention but a few. All are well known in this art. See, for example, the Handbook of Fillers and Reinforcements for Plastics cited above. The function of the reinforcing layer is to provide strength, such as in tensile, flexural and impact strength properties; dimensional stability to hold form and shape under severe mechanical and environmental stresses; and heat resistance to the composite; to mention only a few results from the use of such reinforcing mats. The reinforcing layer can be made up of multiple layers of fibrous reinforcing material or a single heavy layer. The total weight should preferably be between 305 and 1220 g/m 2 for the reinforcing layer. Where multiple reinforcing layers are used, the reinforcing glass mat plies may be oriented in different directions to orient the fiber lengths and obtain the desired property. In addition, combina¬ tions of different types of reinforcing material, such as continuous and chopped strand, may be used. Chopped random fibers and/or fillers may also be added between plies. Different types of mat and/or fibers may also be employed, such as synthetic polymeric fibers, such as poly(aramide) fibers or graphite. As noted, at least one and optionally both of the layers contiguous to the outermost coarse reinforcing layer is a layer of polymer which is a rapidly crystallizing, low shrinkage polymer. The other contiguous layer, if any, can be any crystal- lizable polymer, for example, those identified for the outermost layer. Preferably, the other contigu¬ ous layer is poly(about 70 to about 75 mole percent/- about 30 to 25 mole percent 1,4-cyclohexylenedi- methylene/butylene terphthalate) modified with about 0.5 to about 0.8 mole percent (based on the acid component present) trimellitic anhydride and about 28 to about 33 weight percent poly(oxytetramethylene) of molecular weight 1000. The polymeric material for all polymeric layers including the low shrinkage rapidly crystal¬ lizing layer optionally contains 5 to 50% by weight fillers selected from chopped strands of fiber glass of length less than about 6.35 mm, milled glass, glass spheres, novaculite, talc, mica, calcium carbonate, barium sulfate and kaolin. Preferably the filler selected will be the chopped strands of fiber glass of length less than about 6.35 mm. The crystallization half-time is defined as the length of time required at a given temperature for an originally amorphous polymer sample to crys¬ tallize 50% of the amount to which it eventually crystallizes at that temperature. For example, poly(ethylene terephthalate) crystallizes at about 60% at 180°C. and never 100%. Thus only 50% of 60%, or 30%, crystallinity is obtained after one crystal¬ lization half-time. The minimum crystallization half-time is that half-time which corresponds to the minimum point of the curve when half-time is plotted against temperature. Values reported as "crystallization half- times" can be measured in the following manner. A sample of the polyester is placed in the sample pan of a differential ' scanning calorimeter. An amount of fine mesh Al 2 0 s sufficient to minimize transient responses is placed in the reference pan. The sample is then heated to a temperature above the melting point of the polyester (for example about 285°C. for PET). When the sample is thoroughly melted, it is quickly cooled to the desired crystal¬ lization temperature and allowed to crystallize isothermally while the crystallization exotherm is recorded as a function of time. Zero time is taken as the moment at which the instrument reaches the chosen crystallization temperature. The exothermic response as recorded by the instrument will pass through a maximum and the time at which that maximum occurs is a good approximation of the crystallization half-time. For the purposes, of these measurements, the time at the maximum will be taken as equivalent to the crystallization half-time. The minimum crystallization half-time is found by performing the above experiment at a number of crystallization temperatures and plotting the half-times as a func¬ tion of crystallization temperature. This curve will pass through a minimum and the half-time at that minimum is the minimum crystallization half-time. The shrinkage referred to herein in relation to the polymers adjacent a reinforcing layer is the initial linear shrinkage when going from the molten to molded state and not the shrinkage which occurs as the molded sheet ages. Shrinkage is preferably measured using ASTM Method D-955. The overall thickness of the sheet may range from about 1 to about 6.35 mm, and the layers of glass fiber may comprise about 20 to about 50% by weight of the stampable sheet. The stamped sheet of reinforced material from the stampable sheet described above preferably has a heat deflection temperature under 1820 kPa load greater than T -5 ' 0°C. where T is the melting point of the outer layers of the sheet. The thickness of the overall sheet may range from about 1 mm to about 6.35 mm, preferably from about 1.27 mm to about 3.87 mm and still more prefer¬ ably from about 1.52 mm to about 2.54 mm. Of this thickness, at least 0.25 mm but not more than 40% of the total thickness is composed of the layer having a shrinkage of less than 2%, and a minimum crystalliza- tion half-time of one minute or less. The fibrous layers comprise 20 to 50% by weight of the sheet, preferably 30 to 40%. The polyester material of the outermost layer may comprise polyesters having inherent vis- cosities of about 0.3 to about 1.5; inherent vis¬ cosity being determined by a concentration of 0.5 grams polymer in 100 milliliters of solvent (60 percent by weight phenol and 40 percent by weight tetrachloroethane) , the polymer being dissolved at 125°C. and being measured at 25°C. It may be desirable that additives be incorporated in the polymeric layers to impart OMPI characteristics such as mold release, stability, flame retardancy, UV resistance and color. Reinforced sheets are made by laminating alternating layers of polymer film and reinforcing fiber glass mat by heating in a compression press or continuous laminating press to temperatures above the melting point of the polymers, e.g., 260°C for PET or higher. The sheet is then cooled under pressure. This produces an integral sheet, i.e., one in which all layers are firmly adhered one to another. In the present invention, the reinforced sheet preferably has at least one layer of a fibrous reinforcing material of such density as to impart reinforcement to the sheet, one layer of a fine stranded glass mat referred to in the trade as a surfacing mat or veil, one layer of a low shrinkage polymer contiguous to at least one side of the reinforcing layer and finally two outer layers of polyester-based material. The outermost layers preferably comprise polyesters which will, crystallize to a greater extent than the low shrinkage polymer under the conditions used to stamp the final part. For purposes of stamping, the sheets are formed and held in a mold until the outer layers of the resulting part become crystalline, causing the sheet to retain the shape of the mold. To avoid or ' control warpage, it may be desirable to produce a sheet of balanced construc¬ tion. To accomplish this, the sheet can contain a single low shrinkage polymer layer in the center or an even number of such layers symetrically situated about the center layer. The sheets of the present invention have been described with reference to the outermost layers of one side. It will be understood that the sheet can contain additional layers, usually alternating layers of reinforcement and polymer. Further, both LEAZ sides can comprise the arrangement of outermost layers so as to provide desirable surface character¬ istics to both sides. The following examples are intended only to illustrate the invention since numerous variations and modifications will be apparent to those skilled in the art. The sheets of the present invention have been described with reference to the outermost layers of one side. It will be understood that the sheet can contain additional layers usually alternating layers of reinforcement and polymer. Further, both sides can comprise the arrangement of outermost layers so as to provide desirable surface character- istics to both sides. Example 1 This example includes a comparison. Poly(ethylene terephthalate) film (PET), inherent viscosity (I.V.) 0.67, minimum crystalliza- tion half-time - 40 seconds, 0.25 and 0.75 mm thick¬ ness; pol (73/27 l,4-cyclohexylenedimethylene/l,4- butylene terephthalate) modified with 32 weight percent poly(oxytetramethylene) of molecular weight 1000 film [abbreviated "(CHDMT)-based polyether- ester"], I.V. 1.2, having a shrinkage of less than about 2%, as determined in accordance with ASTM Method D-955, a minimum crystallization half-time 20 seconds, 0.75 mm thickness; Owens-Corning Fiberglas M-8610 continuous strand 610 g/m 2 ; and Owens- Corning Fiberglas M-514 surfacing mat, 0.5 mm thick¬ ness, were cut into pieces 20 cm X 20 cm. For the comparison sheet "A", beginning with an outer layer of 0.75 mm PET film, alternating layers of film and reinforcing mat were placed in a compression molding die measuring 348 mm x 20 cm x 20 cm. to produce a composite as illustrated below: A. 0.75 mm PET xxxxxxxxxxxxxxx reinforcing glass mat ___ .27 mm PET xxxxxxxxxxxxxxx reinforcing glass mat 0.75 mm PET For sheet "B" of the invention, a surfacing mat was placed immediately below the outer PET film and one layer of (CHDMT)-based polyetherester was placed between the surfacing glass mat and the outer layer of reinforcing glass mat as illustrated below: B. • 0.75 mm PET v-v^-vv-vu-vu-vvv surfacing glass mat 0.75 mm (CHDMT)-based polyetherester xxxxxxxxxxxxxx reinforcing glass mat 0.5 mm PET xxxxxxxxxxxxxx reinforcing glass mat 0.75 mm PET Each sheet in turn was placed between two metal plates and inserted in a Wabash compression molding press preheated to 270°C. Slight pressure was applied to the composite until the polymer began to flow. Maximum pressure of 527 Kg/cm 2 was then applied to the composite for two minutes. To prepare samples for inspection and testing purposes, the composites were cooled grad¬ ually under pressure in the press to below 69 C. (the T of PET) to afford crystallization. Specimens were cut from the crystalline sheets and tested according to standard ASTM procedures. The crystallized all-PET sheet "A" contained 30 weight percent glass reinforcement. It possessed high strength properties, specifically flexural.and impact strength, and a high heat distortion tempera¬ ture (Table 1). However, fiber "read-through" was visually evident, giving a rough surface unsuitable for exterior appearance parts. The crystallized PET sheet containing the (CHDMT)-based polyetherester layer situated between a surfacing and a reinforcing mat, sheet "B", also contained 30 weight percent glass reinforcement. It possessed a significantly lower density than sheet "A" but maintained a high level of strength proper¬ ties. The flexural modulus remained high, as did the heat distortion temperature (Table 1). Unexpectedly the surface was smooth and the coarse reinforcing mat was not visible. - L / - Table 1 30% Glass Mat Reinforced Sheets Sheet "B" (CHDMT)-Based Poly¬ etherester Between Property, Sheet "A" Surfacing and Units All PET Reinforcing Mats Specific gravity x. 23°C. ASTM D-792 1.60 1.49 Deflection temp., °C @ 1820 kPa ASTM D-648 250 240 Flexural Modulus of elasticity, GPa ASTM D-790 6.62 5.34 Flexural strength MPa ASTM D-790 148 119 Tensile strength at fracture, MPa ASTM D-638 114 68.9 Notched Izod impact strength, J/M of notch @ 23°C. ASTM D-256 587 534 Unnotched Izod impact strength, J/M of of width @ 23°C. ASTM D-256 854 694 Hardness R scale 120 115 L scale 110 105 M scale 100 75 ASTM D-785 Fiber "read-through" yes no Surface smoothness no yes Example 2 This a comparative example. A sheet "C" (not of the invention) was made such that the (CHDMT)-based polyetherester was omitted but a surfacing mat was placed immediately between the outer PET film and the outer layer of reinforcing glass mat as illustrated below: C. 0.75 mm PET θ * V\# * VV\V * VV * V\ .VVV» * Λ# surfacing glass mat xxxxxxxxxxxxxxx reinforcing glass mat -_ .27 mm PET xxxxxxxxxxxxxxx reinforcing glass mat 0.75 mm PET The surface smoothness was improved over that of sheet "A" but was not acceptable for exterior automotive applications because of the visual "read- through" of the reinforcing mat. This illustrates that the surfacing mat alone will not afford the unusually smooth surface of sheet "B" and that the polymeric material having a shrinkage of less than 2% as determined in accordance with ASTM D-955 and a minimum crystallization half-time of one minute or less is required to obtain this effect. Example 3 Crystalline sheets of sheets "A" through "C" were primed with one layer of 25.4 micron taupe primer and baked in a forced-air oven for 30 minutes at 150 C C. They were then painted with one layer of a 50.8 micron white automotive enamel and baked in a forcedair oven for 17 minutes at 130°C. Fiber "read-through" in all sheets except "B" w s evident. The surface of "B" immediately over the surfacing mat and (CHDMT)-based polyetherester layer was smooth, glossy and absent of fiber read-through. Example 4 This is a comparative example. To demonstrate the advantages of these sheets in formability, a sheet "D" (not of the invention) was prepared. Sheet "D" was the same as "B" except the layer of (CHDMT)-based polyetherester in sheet "B" was replaced with a 0.75 mm layer of copol (69/31 ethylene terephthalate/- 1,4-cyclohexylenedimethylene tere¬ phthalate), abbreviated "copoly 69/31-1,4-CHDMT", I.V. 0.75. Copoly 69/31-1,4-CHDMT has a shrinkage of less than 2%, as determined in accordance with ASTM Method D-955, but a minimum crystallization half-time of 2650 • min. Sheets of "B" and "D" were, in turn, heated rapidly to a temperature above the melting point of the polymers (>260°C.) in an infrared oven. Heating was done for 36 seconds between banks of infrared tubes. The limber, molten sheet was transferred rapidly to a match-mated mold in a compression molding press which had been preheated to 160°C. The mold was closed rapidly and the sheet formed and crystallized for one-half minute under pressure. The formed, crystallized part was removed from the mold. While formed parts from neither sheets "B" nor "D" showed fiber "read-through" on the top sur¬ face, sheet "D" showed blistering, where it appeared that the upper layer(s) had separated in some loca¬ tions from the lower ones. Sheet "B" did not show this undesirable result. Example 5 This example is the same as Example 1 except that the layer of (CHDMT)-based polyetherester in sheet "B" was replaced with a 0.75 mm layer of poly- (1,4-cyclohexylenedimethylene 1,4-cyclohexanedicar- boxylate) modified with 0.5 mole percent trimellitic anhydride and 25 weight percent poly(oxytetramethyl- ene) glycol. of molecular weight 1000, abbreviated "poly-CCD", I.V. 1.28. "Poly-CCD" has a shrinkage of less than 2%, as determined in accordance with ASTM Method D-955 and a minimum crystallization half-time of 40 seconds. The surface of the crystallized PET sheet prepared in the manner of sheet "B" but contain¬ ing the "poly-CCD" layer situated between a surfacing and a reinforcing mat was smooth and the coarse reinforcing mat was not visible. Example 6 This example is the same as Example 1 except, that the layer of (CHDMT)-based polyetherester in sheet "B" was replaced with a 0.75 mm layer of poly- (76/241,4-cyclohexylenedimethylene/ethylene tere¬ phthalate) modified with 31 weight percent poly(30/70 oxyethylene/oxypropylene) golcol having an average molecular weight of 1850, abbreviated "poly-76/24". "Poly-76/24" has a shrinkage of less than 2%, as determined in accordance with ASTM Method D-955 and a minimum crystallization half-time of 25 seconds. As found for shes..: "B", the surface of the crystallized PET sheet containing "poly-76/24" situated between a surfacing and a reinforcing mat is smooth and the coarse reinforcing mat is not visible. Example 7 This is a comparative example. Three sheets, E, F, G, were prepared in a manner similar to the previous examples. Composition E is a comparative example since poly(ethylene tere¬ phthalate) was used for all polymeric layers. Sheet G is a comparative example since an interior polymeric layer is a slowly crystallizing polymer. The composition of E, F and G are shown in the following table as well as an indication of the surface appearance. This example again illustrates the importance of the combination of the surfacing mat and the low shrinkage rapid crystallizing polymer. This example also illustrates the use of fillers in various layers and the use of the low shrinkage, rapid crystallizing polymer below (with respect to the outer surface) the reinforcing layer rather than between the reinforcing layer and the layer of the surfacing mat. Table 2 Layer Compo¬ sition E F G .1 PET 3 PET + 15% PET + 15% 0.75 mm chopped fiber chopped fiber glass, 0.75 mm glass, 0.75 mm 2 SURMAT 1 SURMAT SURMAT 3 PET 3 , PET + 15% PET + 15% 0.75 mm chopped fiber chopped fiber glass, 0.75 mm glass, 0.75 mm 4 OCF 2 M8621 OCF M8621 • OCF M8621 5 PET, poly-76/24 * * poly-69/31 5 0.5 mm 0.38 mm 0.38 mm 6 OCF M8621 OCF M8621 OCF M8621 7 PET, PET, PET, 0.75 mm 0.75 mm 0.75 mm Surface rough; "read- very smooth blistered Appear¬ through" of surface ance reinforcing (layer 1) mat evident 1 SURMAT - surfacing mat from Nicofibers, Inc., Shawnee, Ohio. Approximate density 61 g/m 2 2 OCF M8621 - reinforcing mat Owens-Corning—density 610 g/m 2 3 PET - I.V. 0.67 - pol (ethylene terephthalate) * poly-76/24 - poly(76/241,4-cyclohexylenedi- methylene/ethylene terephthalate) modified with 31 weight percent poly(30/70 oxyethylene/oxypropyl- ene) having an average molecular weight of 1850. Minimum crystallization half-time 25 seconds; shrinkage less than 2% according to ASTM Method D-955. b ρoly-69/31 - copoly(69/31 ethylene/l,4-cyclohexyl- enedimethylene terephthalate) ; minimum crystal¬ lization half-time 2650 minutes; shrinkage less than 2% according to ASTM Method D-955. Example 8 Sheets H and I were prepared in a manner similar to previous examples and demonstrate that the unexpected improvements in surface finish are obtained from other polymers in addition to "poly-76/24" located beow the outermost reinforcing layer. In both cases, the outermost layer 1 was very smooth. Layer Co - position H I PET + 15% chopped . PET + 15% chopped fiber glass, 0.75 mm fiber glass, 0.75 mm 2 SURMAT SURMAT 3 PET + 15% chopped PET + 15% chopped fiber glass, 0.75 mm fiber glass, 0.75 mm 4 OCF M8621 OCF M8621 5 CHDMT-based poly¬ poly-CCD, 0.38 mm etherester, 0.38 mm 6 OCF M8631 OCF M8621 7 PET, 0.75 mm PET, 0.75 mm OMPl.

Claims: CLAIMS: 1. A multilayer integral sheet of rein¬ forced thermoplastic material characterized by having an outermost surface layer of thermoplastic polymer, a layer of fine stranded fibrous material having a weight of 30 to 120 g/m 2 adjacent to the outermost surface layer, at least one layer of coarse fibrous reinforcing material, a layer of thermoplastic polymer having an initial linear shrinkage of less than 2 percent adjacent to at least one surface of the layer of reinforcing material closest to said outermost layer and wherein each of said polymer layers has a minimum crystallization half-time of one minute or less. 2. An integral sheet according to claim 1 wherein the layers of said sheet include, in order, 1) the outermost surface layer of thermoplastic polymer 2) the layer of fine stranded fibrous material 3) the layer of low shrinkage polymer 4) the layer of reinforcing material. 3. An integral sheet according to claim 1 wherein the layers of said sheet include, in order, 1) the outermost surface layer of thermoplastic polymer 2) the layer of fine stranded fibrous material 3) a layer of thermoplastic polymer 4) the layer of reinforcing material 5) the layer of low shrinkage material. 4. An integral sheet according to any previous claim wherein at least one of said polymer layers contains 5 to 50 weight percent fillers. 5. An integral sheet according to claim 4 wherein said filler is chopped strands of fiber glass of lengths less than 6.35 mm. 6. An integral sheet according to any previous claim wherein said low shrinkage polymer comprises poly(about 70 to about 75 mole percent/- about 30 to about 25 mole percent 1,4-cyclohexylene- dimethylene/butylene terephthalate) modified with about 28 to about 33 weight percent poly(oxytetra- methylene) of molecular weight 1000. 7. An integral sheet according to any previous claim wherein said low shrinkage polymer comprises poly(about 70 to about 75 mole percent/- about 30 to about ' 25 mole percent 1,4-cyclohexylene- dime hylene/butylene terephthalate) modified with about 0.5 to about 0.8 mole percent (based on the acid component present) trimellitic anhydride and about 28 to about 33 weight percent poly(oxytetra- methylene) of molecular weight 1000. 8. An integral sheet according to any previous claim wherein said low shrinkage polymer comprises poly(l,4-cyclohexylenedimethylene 1,4- cyclohexanedicarboxylate) modified with about 0.25 to about 0.75 mole percent (based on the acid component present) trimellitic anhydride and about 22 to about 28 weight percent poly(oxytetramethylene) of molecu- lar weight 1000. 9. An integral sheet according to claim 6, 7, or 8 wherein said outermost layer is ρoly(ethylene terephthalate) . 10. An integral sheet according to any previous claim wherein said layer of coarse fibrous reinforcing material are comprised of glass fiber wherein said layer has a weight between 305 and 1220 g/m 2 . 11. An integral sheet according to any previous claim wherein the overall thickness of said sheet ranges from about 1 to about 7.35 mm, and said layers of glass fiber comprise about 20 to about 50% by weight of said sheet. 12. An integral sheet according to any previous claim wherein the overall thickness of said sheet ranges from about 1.52 to about 2.54 mm, and said layers of glass fiber comprise about 30 to about 40% by weight of said sheet. ■ OWΪ

Inventors: SEYMOUR ROBERT WILLIAM, WEAVER JAMES CLYDE, SEYMOUR, ROBERT, WILLIAM, WEAVER, JAMES, CLYDE
Applicants: EASTMAN KODAK CO, EASTMAN KODAK COMPANY
Application year: 1983
Main classification: B29D3
IPC codes: B29C70, B32B5, B32B27, C08K7