CA1137724A - Fiber reinforced multi-ply stampable thermoplastic sheet - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Reinforced thermoplastic polymer composite sheets, formable into smooth, shaped objects in a stamping process.
The composite sheet is produced by laminating together (1) a first layer of thermoplastic resin containing short glass fibers and a mineral filler such as kaolin, (2) a backing reinforcing layer comprising a long glass mat impregnated by thermoplastic resin and (3) optionally a third layer similar to said first layer. The long glass mat is positioned within the reinforcing layer during impregnation, whereby the mat becomes encased in a resin matrix.

Description

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BACKGROUMD OE? THE INVEI`~TION
FI~LD OF TllF: INVEI`1'rION
__ This invention relates to reinforced thermoplastic mate~
rial and more specifically to apparatus and method for extruding a stampable, reinforced thermoplastic composite sheet containing, as reinforcement, a glass fiber mat.

DESCRIPTION OF T~IÆ PRIOR ART
In the apparatus and method used to form stampable rein~
forced thermoplastic composite sheets, a long glass fiber mat is sand~iched between a glass ~iber filled layer of thermoplastic resin and a fiber~free layer of the resin, and laminated into a multi-ply product while the fiber-free resin layer is in a molten condition.
One of the major problems with such systems is the difficulty of coating substantially all of the fibers of the mat during lamination. The problem is particularly troublesome when 1 ' , mats having a high concentration of glass fiber or utilizing chopped glass fiber strands are employed. In order to alleviate the problem of incomplete coating, it has often been necessary to reduce mat weight and filler concentration, increase resin ~uantity, utilize resin modifiers and decrease processing speeds.
These constraints increase the cost and reduce performance characteristics of the laminated product.
SUMMARY OF T~]E INVENTION
The prescnt invention provides a strong, light stamp-able thermoplastic sheet and a method and means for producing such sheet in an economical, reliable manner. The sheet is essentially - free of surface waviness and long glass show-through, comprising in terms o~ percent by weight of each layer (a) at least one layer 30 comprising from about 40 percent to 100 percent o~ a synthetic ' thermoplastic polymer, about 0 percent to 50 percent o~ a par-,~
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ticulate filler, and 0 percent to 45 percent short glass fibers having a length ranging from 0.01 to 3/4 of an inch and ~ arranged generally parallel to the plane of the sheet surface, - (b) a reinforcing layer adjoining said one layer comprising 50 percent to 100 percent of synthetic thermoplastic polymer on an extruded basis, a long glass fiber mat comprised of fibers having a length of at least 1 inch and having a weight ranging from .1 to 16 ounces per square foot of mat surface area and particulate fillers ranging from 0 percent to 50 percent, and (c) mat positioning means disposed between said at least one layer and said mat, for holding said mat within said reinforcing layer during formation of said composite, said mat being substantially encased in,a matrix of the thermoplastic polymer and said ~ reinforcing layer being essentially free of short glass fibers.
- In addition, the present invention provides composite : laminated sheet comprising the steps of (a) blending and eY~truding a first sheet layer comprising from about 40 percent to 100 percent of thermoplastic polymer, about 0 percent to 50 percent of a parti-culate filler and 0 percent to 45 percent short glass fibers 20 having a length ranging from 0.01 to 3/4 of an inch and arranged in a plane generally parallel to the sheet surface, (b) embossing said first sheet layer in a roll stack to form an embossed surface thereon containing a plurality of projections, (c) blending and extruding a second sheet layer comprising from about 50 percent to 100 percent of synthetic thermoplastic polymer and from 0 percent to 50 percent particulate filler, but beiny essentially free of glass fibers, (d) feeding said first sheet, said second sheet and a long fiber glass mat, the fibers of which have a length of at least 1 inch, into the nip of a set of laminating rolls while the ; 30 resin of the second sheet is still in a molten condition, the ; clearance between the rolls being less than the thickness of the ~ -2-' sheets and glass mat beinc~ fed to the nip of said rolls, whereby ; the long fiber glass mat is positioned within said second sheet during impregnation of said mat thereby and said first and second sheets are laminated into a smooth multi-ply product.
BRIEY D~SCRIPTION OF Tl]E DRAWINGS
The invention will be more fully understood and further advantages will become apparent when reference is made to the following detailed description and the accompanying drawings in ; which: .
~igure 1 illustrates schematically a system for pro-; ducing composite sheets of this invention;
E'igure 2 illustrates a stamping press for the sheets of of this invention;
Figure 3 illustrates a schematic cross section of a composite sheet of this invention;
Figure 4 illustrates an alternate construction of the sheet shown in Figure 3;
Fi~ure 5 illustrates an alternate embodiment oE the invention.
DE~SCRIPTI N OF THE PREF'ERRED EMBODI~qENT :~
Referring to the drawings, a first extruder 11 receives a mixture of thermoplastic resin such as nylon, short glass and particulate filler and extrudes same through a die to produce a filled sheet 13 which is embossed by roller 70 of stack 14 so as .~ to form an embossed surface 72 thereon containing a plurality of projections 74. A similar thermoplastic sheet 15 is produced from extruder 16 and embossed in similar fashion by roller 76 of stac~
17. A third extruder 19 feeds a thermoplastic sheet 20 into laminating rolls 21 simultaneously with sheets 13 and 15, and long ~' 30 ,, : 3 - `
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glass mat or mats 23 which are fed from roll or rolls 24. It is important that the sheet 20 be in a molten condition at the point where the sheets converye on the rolls 21 and that the sheets 13 and 15 be b~low the melting point of the polymer so that projec-tions 74 position the glass mat or mats 23 within the molten sheet 20 during impregnation of the mat(s) 23 by the sheet 20. In this manner, the long ylass reinforcing mat becomes substantially encased in the sheet 20 and does not a~ect surface qualities of sheets 13 and 15 when they are laminated together. The sheet is subsequently cut with cutter mechanisrn 26 on conveyor 27 and fed to stacking table 28.
An important feature of this embodiment of the method is the processing conditions at the roll stack 21.
The clearance between rolls 21(a) and 21(b) is less than the combined thickness of the four cornponer.ts 13, 15, 20 and 23.
(Thickness of mat 23 is measured under little or no compression.) This is necessary to effect an impregnation of mat 23 by sheet 20, and lamination of the resulting product to sheets 13 and 15.
The temperature of the sheet 20 should be above (at least 10 C. above) the thermoplastic melting point to provide adequate residual heat to allow for cooling o sheet 20 between the e~truder die 30 and the roll stack 21 and allow the glass mat to be uniformly impregnated thereby. Preferably, the sheet is 50C. to 100C. above the polymer melting point at the point of convergence between rolls 21(a) and 21(b). Heating the sheet to a ;

temperature higher than 350C. in the eY.truder may cause degrada-tion of the polymer and results in excessive energy consumption.
Lower temperatures result in inadequate impregnation of the mat 23 by sheet 20, including inadequate flow of the polymer into the interstices of the glass mat, inadequate bondiny of sheets 13 and , ~ .

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15 to sheet 20, and inadequate binding of the fibers to tlle poly-mer resulting in poor physical properties in the final product.
For the same reasons, the pressure applied by rolls 21(a) and 21(b) should range from 100 to 1500 pounds per linear inch, and prefc-rablY from 150 to 400 pounds per linear inch, to ensure adequate bonding of the layers and impregnation o~ the glass mat 23 by sheet 20. Rolls 21ta) and 21~b) must have ade-quate diamcter and wall thicl;ness and bearings of sufficient load bearing capacity to prevent excessive deflection of rolls 21(a) and 21~b) Excessive deflection of rolls 21(a) and 21(b), that is dc1ection of the order of about 3 thousandths inch or more, can result in non-uniform impregnation of glass mat 23 by sheet 20, non-uni~orm bonding of sheets 13 and 15 to sheet 20, non-uniform sur~ace appearance, and non-uniform thickness of sheet 25.
Sheet 13 after leaving embossing stack 14 contacts roll 21'd) and then roll 21(a). Sheet 15, after leaving embossing stack 17 cont~cts roll 21(c) and then roll 21(b). Rolls 21(c~ and 21(d) are maintained at a temperature close to but below the polymer melting point, preferably 5 to 40C. below the polymer melting point. Rolls 21(a) and 21(b) are maintained at a temperature 10 t~ 70C. belo~ the polymer melting point. The temperatures of rolls 21(a), 21(b), 21(c) and 21(d) and infrared heaters 30(a), ~O(b) are adjusted so that the temperature of sheets 13 and 15 is higtl enouyh to achieve strong bonding of sheets 13 and 15 to sheet 20, but not so high as to result in sticking of sheet ]3 to roll 21(d) or 21(c~ or of sheet 15 to roll 21(a) or 21(b), softéning of ;
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pro~cctions 74 or degradation of the surface quality of sheet 25. ~-~

Cooling rolls, such as rolls 29(a) and 29(b), can be used to quickly lower the temperature of laminate 25 sufficiently for cutting on cutter mechanism 26.

An alternate embodiment, illustrated in Figure 5, would ,~ :

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have the glass mat 123 impregnated by sheet 120 in a separate operation. Under these circumstances the roll 121(a) is provided with a plurality of projections 174 for positioning the mat 123 within sheet 120 during impregnation of the mat 123 by the sheet 120. The ends of the projections force the mat 123 into the sheet 120, causing molten portions of the sheet 120 from extruder 119 to flow within passageways formed by adjacent projections to encom-pass the mat 1~3. The projections thus position the mat centrally of the sheet 120 and hold it therewithin~ facilitating coating of the mat 123 by the sheet during impregnation. The impregnated mat - 125 thus produced can be used in a stamping operation or laminated to sheet(s) 13, 15 as described hereinafter in more detail. Fur-ther, a plurality of embossing rolls 121(a) and 121(b) can be employed, the roll 121(b) being provided with a plurality of ; projections 174' similar to projections 174 of roll 121(a), for positioning mat 123' in sheet 120.
Mat positioning may also be accomplished by means of a -~ screen 80, show in Figures 3 and 4, interposed between sheet 13 and mat 23 prior to lamination, the strands of the screen 80 form-~20 ing porjecl:ions and the openings thereof forming passageways that function in substantially the same way as the projections and passageways of sheets 13, 15 or roll 21(a). The screen 80 facilitates impregnation of mat 23 melt 20 and provides a further reinforcing means for the composite sheet. Typically, the screen 80 has a mesh size ranging from about 1 in. to No. 8 U.S.
~ Sieve Size, and is composed of metal, plastic, fibrous material ,~ such as glass, graphite, cotton, nylon, polyester, cellulose -acetate or the like. As used herein, the term i5 intended to include such mat positionin~ means as a perforated plate, expanded metal sheet, scrim and the like.

!' Whether the projections are located on the sheets 13, ::

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15 or on the roll 21~a), their number and configuration will vary depcnding on sucll processing parameters as mat density, filler concentration, laminating time and temperature and the like~
Typically, the projections are cone-shaped members having a hcight of about .01 to ~1 inch and a base perimeter of about .2 to .8 inch, and either randomly or regularly spaced about .06 to 1 inch apart over substantially the entire area of the mat contacting surface of the sheet or laminating ro:Ll employed. The projections can, alternatively, be shaped in the form of a pyramid, cylinder, cube, or the like of regular or irregular configuration arranged to form a regular pattern or an irregular pattern such as a doodle or the like.
Following impregnation of glass mat 123 by sheet 120 in a separate operation, the combined sheet 125 can be laminated to sheet ]3, or to sheets 13 and 15 in a laminating process wherein ; the layers are bonded under heat and pressure. Lamination of the combined sheet 125 to sheet 13 or to sheets 13 and 15 may also be effected during the heating and stamping operation wherein differ-ent laminates are assembled depending on the part to be produced.
An example of the latter method is shown in Fig. 2. A sandwich 25 built ~rom layers 13, 15 and combined sheet 125 is heated in oven 34. This heating step serves to condition the sheets for stamping in press 36 and a]so to effect a slight bond between the layer interfaces. The subsequent pressure in press 36 has the effect of ~-~
simultaneously laminating the mat containing sheet 125 to sheets 13, 15 and forming the resulting composite into a part.
A composite sheet typically produced is illustrated in ~ig. 3. It comprises: ta) one or more surface layers containing 40~ to 100% polymer, 0~ to 45~ of well-dispersed, randomly ori-ented, short glass fibers and 0% to 50~ particulate filler, (b) areinforcing layer consistiny essentially of long glass reinfol-cing ~l~ 3~7~

- mat weighin~ .1 to 16 ounces per square foot, together with the mat positioning means herein shown in the form of a screen 80, encased in a thermoplastic polymer matrix containing, on an extruded basis, from 50 to 100 percent thermoplastic resin and from 0 to 50 percent particulate filler, such that there is essentially no migration of the long glass fibers to the surface layer 13 and no migration of the short glass fibers, if present, to the reinforcing layer.
The stampable composite sheet may have one or two defect-free surfaces. The short, well-dispersed fibers 38, if present, are randomly but predominantly two-dimensionally oriented in the plane of the sheets 13 and 15. That is, more than 50% of the fibers are aligned substantially parallel to the plane of the sheet. Such orientation of the short fiber is easily achieved in extrus,on, rollingl drawing or similar orientation-inducing proce~es, and is preferable for purposes of this invention in achieving smooth surfaced sheets.
The thickness of the surface sheet should be at least 10 mils greater than the height of the projections 74, if present 1 20 thereon, to prevent tearing during lamination. Typically, the surface sheet 13 has a thickness of at least 20 mils. A thinner surface sheet may also permit the pattern of the reinforcing mat 23 to be visible on the surface of the composite sheet 25. The minimum thickness of sheet 20 is determined by the need to impreg-nate glass fiber ma~ 23 and is typically about 30-80 mils. If ;

thickness of sheet 20 is less than about 30 mils, then ~lass fiber mat 23 is likely to be non-uniformly impregnated into sheet 20 and composite sheet 25 is likely to have non-uniform properties.
The thermoplastic polymers which can be used in forming the sheet compositions which may be stamped into shaped objects in accordance with the methods of the present invention include the ~377~

various thermoplastic materials normally used in injection molding, extrusion, vacuum forming, blow molding, fiber spinning, or simi-lar thermoplastic processing techniques.
Suitable thermoplastic resinous materials which may be utilized in making the composite laminate of the invention include, for example, the alkenyl aromatic resins typified by polystyrene, styrene copolymers, b]ends and graft copolymers of styrene and rubber and the like. The invention may be practiced utilizing polyvinyl chloride or copol~mers o vinyl chloride or vinylidene chloride.
Particularly desirable thermoplastics in such composi-tions are the polyamides, that is, polymers having regularly recurring amide groups as an integral part of the main chain.
i Polyamides such as nylon 6,6 (a condensation product of hexa-methylene diamine and adipic acid) and nylon 6 (the polymerization product of -aminocaproic acid or E-caprolactam) are examples of two polyamides or nylons.
Polyolefins may also be employed, including polymers and copolymers of ethylene, propylene, methylpentene and blends thereof.
Additional polymers which can be utilized include poly-urethane, polysulfone, polycarbonate and linear polyesters such as polyethylene terephthalate and polybutylene terephthalate; cellu-lose esters such as cellulose acetate, and cellulose propionate;
halogenated polylefins and polyacetals.
Also included in the term "polymer" are blends or copoly-mers of two or more polymeric materials. Illustrative of such polymers are polyethylene/polypropylene, ethylene-acrylic acid-vinylaceta~e terpolymers and the like.
The glass fiber used in making the fiber mat is prefer-ably used in the form of strands or bundles ~hich are at least about 1 inch to continuous in length. The reinforcing mat may bc _g_ ~37'7;~

woven or nonwovcn. l'he strand~ or iber comprislng the reinforc-ing ~at, if nonwoven, are held together either by resinous adhe-sive binders (thermosetting or thermoplastic resins) or by "need-ling" or, if woven, by the mechanical interaction of the randomly patterned weblike structure.
The individual glass strands in the mat are comprised of about 2 to 400, preferably 5 to 120, filaments per strand. Each ; filament is about 0.00030 to about 001 inch, preferably 0.00035 to 0.00085 inch in diameter. The glass mat comprising the rein-forcing phase may have a weight of from 0.3 to 16 ounces per ;~ square foot.
The short glass fiber reinforcement is at least about 0.01 inch in average length in the final product. These short lengths of fibrous reinforcement are obtained because of the characteristics of the processing apparatus used to compound or blend this reinforcement with the thermoplastic resin. For example, if fibers 1/8 inch or longer are placed in the feed hopper of a single screw extruder along with the resin, the fibers will ordinarily be broken down into lengths shorter than the original 1/8 inch starting length because of abrasion, shear, turbulence, and mechanical work perforrl)ed upon the fibers. Longer lengths (e.g., mean lengths longer than 0.010 inch in a major portion of the short fiber reinforcement) may be retained by minimizing the amount of shear or mechanical breakdown of fiber length, with some sacrifice in homogeneity or prolonged processing times although lengths greater than 3/4 inch are not desirable for the object of this invention since they must flow into ribs, etc.
during stamping. Another processing machine which may be used to J, blend and/or manufacture the short fiber-filled resinous sheet is a twin screw extruder~ In this case, the filamentary reinforcing material may be added to agitated heat plastified polyrner between ~10-"~

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the screw, oi tlle extruder throuyh a feed port such ~s a volatile (vent) port. In the latter case, the filamentary reinforcing material may be ~ed to the twin screw extruder in the forrn of yarn or roving, and the short fiber lengths would be obtained by the mechanical breakup performed by the mixing action of the screws.
Glass fibers as normally used for reinforcement of thermoplastics may be treated or coated ~ith a sizing composition.
Standard sizing agents usually consist of several components, each of which possesses a distinct function. For example, a binder or film former gives the glass fiber strand integrity for workability and prevents fu~zing and aids in distribution o the sizing agent;
a lubricant prevents destruction of the strand by abrasion of the ,,~
individual filaments a~ainst each other and against fiber handling equipment; a coupling agent assists in obtaining greater adhesion between the glass fibers and the polymeric resin yielding improved strength characteristics; an emulsifying or dispersing agent allows sufficient dissolution of the various ingredients in the required carrying agent (frequently water) and improves compati-bility between the various ingredients. In addition, pH adjusters, antistatic agents, wetting agents and surfactants are also often added to sizing ~ormulations. Ordinarily, organosilicon compounds may suitably be employed as coupling agents. For example, halo-genated or nonhalogenated vinyl a~d alkyl containing, alkylal~;oxy, alkenyl, aminoalkyl, aminoalkoxy, acyloxy, alkenyl acyloxy and i similar silanes, their hydrolysis products and polymers of the 1~ hydrolysis product6 are suitable for such use. Formulations of this kind and methods of use are known to those skilled in the art.
Another constituent of the improved thermoplastic sheet material herein described is particulate filler. Such fillers may be selec~ed from a wide variety of minerals, metals, metal oxides, siliceous materials, metal salts, and mixtures thereof. These "
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fillers mcly optionally be~ treated with various coupling agcnts or adhesion promoters, as is known to those skilled in the art. Ad vantageo~s physical properties are achieved if the filler material has a Young's mod~lus of 107 psi or greater and at least a Young's modulus twice as great as that of the polymer. Examples of fillers included in these categories are alumina, aluminum hydrates, feldspar, asbestos, talc, calcium carbonates, clay, carbon black, quartz, novaculite and other forms of silica, kaoli~
nite, bentonite, garnet, mica, saponite, beidellite, calcium oxide, calcium hydroxide, etc. The foregoing recited fillers are illustrative only and are not meant to limit the scope of fillers that can be utilized in this invention.
The particulate filler may be added to the thermo-plastic resin before, during, or after the addition of the short ;. glass fibers to the resin. Thus, for example, filler and resin ~s, pellets may be fed to the feed hopper of a single screw extruder;
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, the mixture is blended and conveyed towards the die. Short glass fibers can be added to the molten mixture at a vent hole or other :~j such opening dowllstream of the feed hopper, and the mixture then ,~ 20 extruded into pellets, or preferably, directly into sheet of the appropriate thickness for lamination with the glass mat reinforce-; ment. In the extrusion process, the short fibers will emerge '. ~oriented randomly in the plane of the extruded sheet.
Other minor additives which may be of value in slleet ;~ formulations include antistatic agents, plasticizers, lubricants, nucleating agents, impact modifiers, colorants, heat and light stabilizers, or other similar processing aids and adjuvants.
Each of the foregoing constituel-tS performs a specific function within the composite material. The tllermoplastic resin ! 30 is, of course, the matrix which binds the other constituents ~to~ether. As the matrix, the resin influellces the mechanical and :~j .

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physical properties of the colnposite sheet. If a stampcd product having an extremely high thermal resistance is required, for example, a nylon or linear polyester would be utilized as the matrix rather than polyethylene or polypropylene. If an extremely high impact resistance was required, Eor example, an impact resis-tant styrene copolymer or polycarbonate may be used rather than polystyrene or a more brittle linear polyester.
With sheets formed of nylon 6 resin, it is preferred to utilize talc as a nucleatiny agent for the nylon. For this pur-pose about .5 to 1.5% or more talc by weight of the nylon is incorporated into the sheet. Preferably, the sheet contains about 1~ talc based on the weight of the nylon. Other nucleating agents may alternatively be employed in similar amounts with nylon or other crystalline polymers.
While composites without filler may be formed, the most desirable sheets include filler.
The functions of the particulate filler are: (1) to , increase the modulus and stiffncss of the composite sheet and (2) to provide a more economical composition.
The functions of the short fiber reinforcement are: (1) to increase the sheet stiffness and mechanical strength, (2) to ,.~
increase the resin-phase melt viscosity, (3~ to provide reinforce-ment in addition to that provided by the long glass fiber mat, (4) ~i to allow flow o~ a reinforced plastic mixture into small holes, bosses, ribs, apertures, etc., during stamping and ~5) to yield an improved surface in which most short dispersed fibers are oriented ; and lie in the plane of the sheet. In addition to the ability to form relatively narrow reinforced ribs, bosses, or similar sec-tions, because of flow of short ibers into such sections, the high melt viscosity of the resin-filler-short fiber mixture aids in promoting uniformity of pro~erties. FurthermoL-e, because of ~ .
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the generally enhanced moldability of the present compositions,longer, thinner and more complex configurations or parts can be molded than heretofore known.
The short fibers oriented parallel to the plane of the sheet (in distinction to perpendicular to the plane of the sheet) result in a smooth surface free of glass mat and projecting fiber ends.
The present invention is more particularly described in . the following examples which are intended as illustrative only since numerous modifications and variations therein will be apparent to ,, those skilled in the art.
Shaping of the sheet can be accomplished in a deep drawing press which has a polished steel die-set to produce 5-inch diameter cylindrical cups. The temperature OL the polished steel , die-set can be adjusted by means of electric heaters, and main-3 tained at approximately 140~ C. The steel molds used are highly polished and chrome-plated (mirror finished~.
' The preheated sheet can be transferred to the stamping c~ press, and stamped at a pressure of 800 psi maintained for lO
~J' 20 seconds. The stamped part can be cooled to room temperature, main tained at room temperature for 24 hours, and the fla~ bottom of the ~.
cup then cut out for surface roughness testing.
The following examples are presented to provide a more si complete understanding of the invention. The specific techniques, `i conditions, materials, proportions and reported data set forth to illustrate the principles and practice of the invention are exem-plary and should not be construed as limiting the scope of the , . , invention.

EXAMPLE

Nylon 6 resin is blended with 25% short glass fibcrs and 15~ ~aolin in extruder ll and extruded into sheet 13.

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sheet 15 o similar composition is extruded by extruder 16. Shects 13, 15 are embossecl by rolls 70, 76 to provide each of the sheets - with a mat contacting surface having a plurality of projections 7~.
Both sheets 13, 15 are brought toge~her with glass mats 23 and molten sheet 20 at the nip of laminating rolls 21(a), 21(b). The mats 23 are positioned within sheet 20 by projections 74 to form a middle reinforcing sheet comprising 75~ nylon and 25~ glass mat.
The resulting sandwich is laminated and finished in the nip of rolls 21(a), 21(b) and on rolls 29(a), 29(b). The resulting sheet is cut into discrete blanks and stored.
~ laving thus described the invention in rather full detail, it will be apparent that these details need not be fully adhered to but that variolls changes and modifications may suggest themselves to one skilled in the art, all falling within the scope of the invention as defined by the subjoined claims.

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Claims (2)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN
EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS
FOLLOWS:

1. A process for producing a composite laminated sheet comprising the steps of:
(a) extruding a sheet layer comprising from about 50 percent to 100 percent of synthetic thermoplastic polymer and from 0 percent to 50 percent particulate filler, but being essentially free of glass fibers;
(b) feeding said sheet and a long fiber glass mat, the fibers of which have a length of at least 1 inch, into the nip of a set of laminating rolls while the resin of the sheet is still in a molten condition, the clearance between the rolls being less than the thickness of the sheets and glass mat being fed to the nip of said rolls;
(c) positioning said long glass mat within said sheet during impregnation of said mat, whereby said sheet and mat are laminated into a smooth multi-ply product, wherein one of said laminating rolls has a mat contacting surface provided with a plurality of projections, said mat being positioned within said second sheet by the ends of said projections

2. A process as recited in claim 1, wherein the ends of said projections have reduced configurations.