GB2073658A

GB2073658A - Preparation of composite laminated sheet

Info

Publication number: GB2073658A
Application number: GB8107753A
Authority: GB
Original assignee: Allied Chemical and Dye Corp; Allied Chemical Corp
Current assignee: Allied Corp
Priority date: 1977-07-18
Filing date: 1978-07-18
Publication date: 1981-10-21
Also published as: DE2831363A1; IT1160423B; IT7868689A0; FR2397938B1; GB2001282B; FR2397938A1; JPS6054183B2; JPS5421476A; CA1132325A; GB2073658B; GB2001282A

Abstract

A composite laminated sheet formable into smooth, shaped objects in a stamping process is prepared by (a) extruding a sheet comprising from 50 percent to 100 percent by weight of the sheet of synthetic thermoplastic polymer and from 0 percent to 50 percent by weight of the sheet of 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 sheet and the glass mat being fed to the nip of said rolls; (c) positioning said long fiber glass mat within said sheet during impregnation of said mat, whereby said sheet and mat are laminated into a smooth multi-ply product, one of the said laminating rolls having a mat- contacting surface provided with a plurality of projections, said long fiber glass mat being positioned within the said sheet by the ends of the said projections. <IMAGE>

Description

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GB 2 073 658 A 1

SPECIFICATION 65

Preparation of composite laminated sheet

This invention relates to the preparation of a composite laminated sheet. This sheet can be 5 employed in the production of a stampable, - 70

reinforced thermoplastic composite sheet containing, as reinforcement, a glass fiber mat.

In conventional apparatus and methods used to form stampable reinforced thermoplastic 10 composite sheets, a long glass fiber mat is 75

sandwiched between a glass fiber filled layer of thermoplastic resin and a fiber-free layer of the resin, and laminated into a multi-ply product while the fiberrfree resin layer is in a molten condition. 15 One of the major problems with such systems 80 is the difficulty of coating substantially all of the fibers of the mat during lamination. The problem is particularly troublesome when mats having a high concentration of glass fiber or utilizing chopped 20 glass fiber strands are employed. In order to 85

alleviate the problem of incomplete coating, it has often been necessary to reduce mat weight and filler concentration, increase resin quantity, utilize resin modifiers and decrease processing speeds. 25 These constraints increase the cost and reduce 90 performance characteristics of the laminated product.

According to the present invention there is provided a process for producing a composite 30 laminated sheet, which process comprises: 95

(a) extruding a sheet comprising from 50 percent to 100 percent by weight of the sheet of synthetic thermoplastic polymer and from 0 percent to 50 percent by weight of the sheet of

35 particulate filler, but being essentially free of glass 100 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

40 the resin of the sheet is still in a molten condition 105 the clearance between the rolls being less than the thickness of the sheet and the glass mat being fed to the nip of said rolls;

(c) positioning said long fiber glass mat within

45 said sheet during impregnation of said mat, 110

whereby said sheet and mat are laminated into a smooth multi-ply product, one of the said laminating rolls having a mat-contacting surface provided with a plurality of projections, said long 50 fiber glass mat being positioned within the said 115 sheet by the ends of the said projections.

In the description which follows, reference will be made to the accompanying drawings in which:

Figure 1 is a cross-section showing an 55 embodiment of the process of the invention; and 120

Figure 2 illustrates a stamping press for the sheets of this invention.

Referring to the accompanying drawings,

Figure 1 shows a glass mat 123 impregnated in a 60 thermoplastic sheet 120 which may contain up to 125 50% particulate filler but essentially no glass fibers. A 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 thesheet 120, causing molten portions of the sheet 120 from extruder 119 to flow within passageways formed by adjacent projections to encompass the mat 123. 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. As shown in Figure 1 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.

It is important that the thermoplastic sheet be in a molten condition at the point where it converges on the laminating rolls so that the glass mat is positioned within the molten sheet. In this manner, the long glass reinforcing mat becomes substantially encased in the thermoplastic sheet.

The clearance between the laminating rolls is less than the combined thickness of the thermoplastic sheet and the fiber glass mat. The thickness of the fiber glass mat is measured under little or no compression. This is necessary to effect impregnation of the mat in the thermoplastic sheet.

The temperature of the thermoplastic sheet should be above (at least 10°C. above) the thermoplastic melting point to provide adequate residual heat to allow for cooling of the sheet between the extruder die and the laminating rolls and allow the glass mat to be uniformly impregnated thereby. Preferably, the sheet is 50°C. to 100°C. above the polymer melting point at the point of convergence between the laminating rolls. Heating the sheet to a temperature higher than 350°C. in the extruder may cause degradation of the polymer and results in excessive energy consumption. Lower temperatures result in inadequate impregnation of the fiber glass mat in the thermoplastic sheet, including inadequate flow of the polymer into the interstices of the glass mat, and inadequate binding of the fibers to the polymer resulting in poor physical properties in the final product.

For the same reasons, the pressure applied by the laminating rolls should range from 100 to 1500 pounds per linear inch, and preferably from 150 to 400 pounds per linear inch, to ensure adequate impregnation of the glass mat in the thermoplastic sheet. The laminating rolls must have adequate diameter and wall thickness and bearings of sufficient load bearing capacity to prevent excessive deflection of the rolls. Excessive deflection of the rolls. Excessive deflection of the rolls, that is a deflection of the order of about 3 thousandths inch or more, can result in nonuniform impregnation of the glass mat in the thermoplastic sheet, non-uniform surface appearance, and non-uniform thickness of the resulting sheet. The laminating rolls are preferably maintained at a temperature 10° to 70°C. below-the polymer melting point. The temperatures of the laminating rolls should be adjusted so as not

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GB 2 073 658 A 2

to be so high as to result in sticking of the thermoplastic sheet to the laminating rolls or degradation of the surface quality of the resulting sheet.

5 Following impregnation of glass mat 123 into sheet 120 in a separate operation, the combined sheet 125 can be laminated to a sheet or sandwiched between sheets containing 40% to 100% of a synthetic thermoplastic polymer, 0% to 10 45% of well-dispersed, randomly oriented, short glass fibers having an average length of from 0.01 to 0.75 inch and arranged in a plane generally parallel to the sheet surface and 0% to 50% of a particulate filler (the percentages being by weight 15 of the layer) in a laminating process wherein the layers are bonded under heat and pressure. These sheets to which sheet 125 is to be laminated may have an embossed surface containing a plurality of projections. This method surface faces sheet 125 20 during famination. A process for preparing a composite laminated sheet from a first sheet having an embossed surface, a second, thermoplastic, sheet and a long fiber glass mat whereby the mat is positioned and impregnated 25 in the second sheet is described and claimed in Application No. 30168/78 (published as Specification No. 2001282A) out from which the present specification has been divided.

Lamination of the combined sheet 125 to a 30 sheet or between sheets containing 40% to 100% of a synthetic thermoplastic polymer, 0% to 45% of well-dispersed, randomly oriented, short glass fibers having an average length of from 0.01 to 0.75 inch and arranged in a plate generally parallel 35 to the sheet surface and 0% to 50% of a particulate filler (the percentages being by weight of the layer) and which may have an embossed surface may also be effected during a heating and stamping operation wherein different laminates 40 are assembled depending on the part to be produced. An example of this method is shown in Figure 2 of the accompanying drawings. A sandwich 25 built from layers containing 40% to 100%. of a synthetic thermoplastic polymer, 0% to 45 45% of well-dispersed, randomly oriented, short glass fibers having an average length of from 0.01 to 0.75 inch and arranged in a plane generally parallel to the sheet surface and 0% to 50% of a particulate filler (the percentages being by weight 50 of the layer) and combined sheet 125 is heated in oven 34. This heating step serves to condition the sheets for stamping in press 36 and also to effect a slight bond between the layer interfaces. The subsequent pressure in press 36 has the effect of 55 simultaneously laminating the mat containing sheet 125 to the layers between which it is sandwiched and forming the resulting composite into a part.

The projections on the laminating rolls, and 60 those optionally forming the embossed surface of a sheet to which a composite laminated sheet produced by the process of the invention may be bonded are present in a number and configuration varying depending on such processing parameters 65 as mat density, filler concentration, laminating time and temperature and the like. Typically, the projections are cone-shaped members having a height of about .01 to .1 inch and a base perimeter of about .2 to .8 inch, and are 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 roll 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.

The stampable composite sheet may have one or two defect-free surfaces. The short, well-dispersed fibers, if present, are randomly but predominantly two-dimensionally oriented in the plane of the outer sheet(s). That is, more than 50% of the fibers are aligned substantially parallel to the plane of the or each sheet. Such orientation is easily achieved in extrusion, rolling, drawing or similar orientation-inducing processes, and is preferable for purposes of this invention in achieving smooth surfaced sheets.

Where a thermoplastic sheet in which a glass fiber mat is impregnated according to the present invention is laminated to a further sheet(s) having an embossed surface, the thickness of the other sheet should be at least 10 mils greater than the height of the projections forming the embossed surface to prevent tearing during lamination. Typically, the surface sheet has a thickness of at least 20 mils. A thinner surface sheet may permit the pattern of the reinforcing glass fiber mat to be visible. The minimum thickness of thermoplastic sheet in which the glass fiber mat is impregnated is determined by the need to impregnate the glass fiber mat and is typically about 30—80 mils. If thickness is less than about 30 mils, then the glass fiber is unlikely to be uniformly impregnated into the thermoplastic sheet and the resulting composite sheet is unlikely to have uniform properties.

The thermoplastic polymers which can be used in the present invention include various thermoplastic materials normally used in injection molding, extrusion, vacuum forming, blow molding, fiber spinning, or similar 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, blends and graft copolymers of styrene and rubber and the like. The invention may be practiced utilizing polyvinyl chloride or copolymers of vinyl chloride or vinylidene chloride.

Particularly desirable thermoplastics in such compositions are the polyamides, that is, polymers having regularly recurring amide groups as an integral part of the main chain. Polyamides such as nylon 6,6 (a condensation product of hexamethylene diamine and adipic acid) and nylon 6 (the polymerization product of £-aminocaproic acid or £-caprolactam) are examples of two polyamides or nylons.

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GB 2 073 658 A 3

Polyolefins may also be employed, including polymers and copolymers of ethylene, propylene, methylpentene and blends thereof.

Additional polymers which can be utilized 5 include polyurethane, polysulfone, polycarbonate and linear polyesters such as polyethylene terephthalate and polybutylene terephthalate; cellulose esters such as cellulose acetate, and cellulose propionate; halogenated polyolefins and s 10 polyacetals.

Also included in the term "polymer" are blends or copolymers of two or more polymeric materials. Illustrative of such polymers are polyethylene polypropylene, ethylene-acrylic acid vinylacetate 15 terpolymers and the like.

The glass fiber used in making the fiber mat is preferably used in the form of strands or bundles. The strands or bundles are at least 1 inch to continuous in length. The reinforcing mat may be 20 woven or nonwoven. The strands or fiber comprising the reinforcing mat, if nonwoven, are held together either by resinous adhesive binders (thermosetting or thermoplastic resins) or by "needling" or, if woven, by the mechanical 25 interaction of the randomly patterned weblike structure. The individual glass strands in the mat can comprise about 2 to 400, preferably 5 to 120, filaments per strand. Each filament may be about 0.00030 to about .001 inch, preferably 0.00035 30 to 0.00085 inch in diameter. The glass mat comprising the reinforcing phase may have a weight of from 0.1 to 16 ounces per square foot.

The short glass fiber reinforcement, which may be present in a sheet to which a thermoplastic 35 sheet in which a glass fiber mat is impregnated according to the present invention is laminated, is at least 0.01 inch in average length in the final product. These short lengths of fibrous reinforcement are obtained because of the 40 characteristics of the processing apparatus used to compound or blend this reinforcement with a 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 45 ordinarily be broken down into lengths shorter than the original 1/8 inch starting length because of abrasion, shear, turbulence, and mechanical work performed upon the fibers. Longer lengths (e.g. mean lengths longer than 0.010 inch in a 50 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 of prolonged processing times although lengths greater than 55 3/4 inch are not desirable since they must flow into ribs, etc. during stamping. Another processing machine which may be used to blend and/or manufacture the short fiber-filled resinous sheet is a twin screw extruder. In this case, the filamentary 60 reinforcing material may be added to agitated heat plastified polymer between the screws of the extruder through a feed port such as a volatile (vent) port. In the latter case, the filamentary reinforcing material may be fed to the twin screw 65 extruder in the form 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 70 of thermoplastics may be treated or coated with 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 75 integrity for workability and prevents fuzzing and aids in distribution of the sizing agent; a lubricant prevents destruction of the strand by abrasion of the individual filaments against each other and against fiber handling equipment; a coupling 80 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 85 required carrying agent (frequently water) and improves compatibility between the various ingredients. In addition, pH adjusters, antistatic agents, wetting agents and surfactants are also often added to sizing formulations. Ordinarily, 90 organosilicon compounds may suitably be employed as coupling agents. For example, halogenated or nonhalogenated vinyl and alkyl containing, alkylalkoxyl, alkenyl, amonoalkyl, aminoalkoxy, acyloxy, alkenyl acyloxy and similar 95 silanes, their hydrolysis products and polymers of the hydrolysis products are suitable for such use. Formulations of this kind and methods of use are known to those skilled in the art.

A particulate filler for use in the present 100 invention may be selected from a wide variety of minerals, metals, metal oxides, siliceous materials, metal salts, and mixtures thereof. These fillers may optionally be treated with various coupling agents or adhesion promoters, as is known to those 105 skilled in the art. Advantageous physical properties are achieved if the filler material has a Young's modulus 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 110 categories are alumina, aluminum hydrates,

felspar, asbestos, talc, calcium carbonates, clay, carbon black, quartz, novaculite and other forms of silica, kaolinite, bentonite, garnet, mica, saponite, beidellite, calcium oxide, and calcium hydroxide. 115 The foregoing fillers are illustrative only and are not meant to limit the scope of fillers that can be utilized in this invention.

Where a particulate filler is present in a sheet containing also short glass fibers, the filler may be 120 added to the thermoplastic resin before, during, or after the addition of the short glass fibers to the resin. Thus, for example, filler and resin pellets may be fed to the feed hopper of a single screw extruder; the mixture is blended and conveyed 125 towards the die. Short glass fibers can be added to the molten mixture at a vent hole or other such opening downstream of the feed hopper, and the mixture then extruded into pellets, or preferably, directly into sheet of the appropriate thickness for 130 lamination with the glass mat reinforcement. In

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GB 2 073 658 A 4

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 5 sheet formulations include antistatic agents, plasticizers, lubricants, nucleating agents, impact modifiers, colorants, heat and light stabilizers, or other similar processing aids and adjuvants.

Each constituent performs a specific function. 10 The thermoplastic resin is, of course, the matrix which binds the other constituents together. As the matrix, the resin influences the mechanical and physical properties of the composite sheet. If a stamped product having an extremely high 15 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, for example, an impact resistant styrene 20 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 nucleating agent for nylon. For this purpose about 0.5 to1.5% or more talc by 2 5 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. 30 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 stiffness of the composite sheet and (2) to provide a more 35 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 reinforcement 40 in addition to that provided by the long glass fiber mat, (4) to allow flow of a reinforced plastic mixture into small holes, bossess, ribs, apertures, etc., during stamping and (5) to yield an improved surface in which most short dispersed fibers are 45 oriented and lie in the plane of the sheet. In addition to the ability to form relatively narrow reinforced ribs, bosses, or similar sections,

because of flow of short fibers into such sections, the high melt viscosity of the resin-filler-short fiber 50 mixture aids in promoting uniformity of properties. Furthermore, because of the generally enhanced moldability of the present compositions, longer, thinner and more complex configurations or parts can be molded than heretofore known. The short 55 fibers oriented parallel to the plane of the sheet (as distinct from perpendicular to the plane of the sheet) result in a smooth surface free of glass mat and projecting fiber ends.

Shaping of the composite laminated sheets can 60 be accomplished in a deep drawing press which has a polished steel die-set to produce 5-inch diameter cylindrical cups, the temperature of the polished steel die-set can be adjusted by means of electric heaters, and maintained at approximately 65 140°C. The Steel molds used are highly polished and chrome-plated (mirror finished).

The preheated sheet can be transferred to the stamping press, and stamped at a pressure of 800 psi maintained for 10 seconds. The stamped

70 part can be cooled to room temperature,

maintained at room temperature for 24 hours, and the flat bottom of the cup then cut out for surface roughness testing.

Claims

75 1. A process for producing a composite laminated sheet which process comprises:

(a) extruding a sheet comprising from 50 percent to 100 percent by weight of the sheet of synthetic thermoplastic polymer and from 0

80 percent to 50 percent by weight of the sheet of 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

85 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 sheet and the glass mat being fed to the nip of said rolls;

90 (c) positioning said long fiber glass mat within said sheet during impregnation of said mat, whereby said sheet and mat are laminated into a smooth multi-ply product out of the said laminating rolls having a mat-contacting surface provided

95 with a plurality of projections, said long fiber glass mat being positioned within the said sheet by the ends of the said projections.

2. A process according to claim 1, wherein the ends of said projections have reduced

100 configurations.

3. A process according to claim 1 or 2 further comprising laminating a sheet to one face or a respective sheet to both faces of said smooth multi-ply product under heat and pressure, the or

105 each sheet comprising 40% to 100% by weight of the sheet of a synthetic thermoplastic polymer, 0 to 50% by weight of the sheet of a particulate filler and 0 to 45% by weight of the sheet of short glass fibers having an average length of from 0.01 110 to 0.75 inch and arranged generally parallel to the sheet surface.

4. A process according to claim 1 or 2 further comprising laminating a sheet to one face or a respective sheet to both faces of said smooth

115 multi-ply product by assembling the sheet(s) and said smooth multi-ply product, heating the assembly in an oven and stamping the heated assembly with sufficient pressure to laminate the or each sheet to said smooth multi-ply product, 120 the or each sheet comprising 40% to 100% by weight of the sheet of a synthetic thermoplastic polymer, 0 to 50% by weight of the sheet of a particulate filler and 0 to 45% by weight of the sheet of short glass fibers having an average 125 length of from 0.01 to 0.75 inch and arranged generally parallel to the sheet surface.

5. A process according to claim 3 or 4 wherein the face of at least one said sheet which contacts said smooth multi-ply product during lamination

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has an embossed surface containing a plurality of projections.

6. A process according to claim 1 substantially as hereinbefore described with reference to Figure

5 1 of the accompanying drawings.

7. A process according to claim 4 substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.

8. A shaped article which has been produced 10 from a composite laminated sheet prepared by a process as claimed in any one of the preceding claims.

New claims or amendments to claims filed on 11 June 1981.

15 Superseded claim: Claim 1.

New or amended claims:—

1. A process for producing a composite laminated sheet which process comprises:

(a) extruding a sheet comprising from 50 20 percent to 100 percent by weight of the sheet of synthetic thermoplastic polymer and from 0 percent to 50 percent by weight of the sheet of particulate filler, but being essentially free of glass fibers;

25 (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 30 the combined thickness of the sheet and the glass mat being fed to the nip of said rolls;

(c) positioning said long fiber glass mat within said sheet during impregnation of said mat, whereby said sheet and mat are laminated into a 35 smooth multi-ply product, one of the said laminating rolls having a mat-contacting surface provided with a plurality of projections, said long fiber glass mat being positioned within the said sheet by the ends of the said projections.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1981. Published by the Patent Office, 25 Southampton Buildings, London, WC2A 1AY, from which copies may be obtained.