Technical Field This invention relates to the bonding of two dissimilar polymeric resin composition surfaces. In a particular embodiment, the invention relates to a process for bonding an epoxy resin matrix reinforced with glass fibers to the surface of a poly(vinyl chloride) pipe thereby the pipe is reinforced and withstands high delaiπinating forces without rupture of the interface bond between the epoxy resin and the poly(vinyl chloride) surface. The invention also relates to the product of this process vhich in a preferred embodiment comprises a pipe.

Background of the Prior Art For seme time, plastic pipe made of one or more layers each of polymeric olefinic chloride resin ("PVC") and epoxy-impregnated glass fibers has been widely used, in the construction and plumbing industries. Light weight and resistance to corrosion have been among the desirable properties of this type of pipe. he pipe conventionally consists of an inner hollow cylinder of PVC σverlayed with a wrapping of epoxy impregnated glass fibers. In seme cases enly a single layer of each material is used; in other cases, however, the first layer of epoxy impregnated glass fibers is σverlayed with a second PVC layer v ich is itself then σverlayed with a second layer of epoxy iπpregnated glass fiber. Any nuπtoer of such multiple alternating layers may be thus built up.

Bending between each pair of dissimilar surfaces of the alternating layers of epoxy impregnated glass fiber and PVC has, however, been a serious problem, often reaching critical dimensions vhere the pipe consists solely of a relatively thin PVC inner cylinder σverlayed with oily one or two layers of an epoxy impregnated glass fiber wrapping. Since PVC and epoxy do not substantially chemically bond with each other, mechanical forces were depended upon to maintain the integrity between the layers of the pipe. However, these mechanical forces were insufficient to withstand the counterv≤ϊEincj

fbrces produced by the fluid pressure within the pipe and the laye of the pipe would become separated or delaminated. This w particularly aggravated it was necessary to cut into the pi as with a conventional pipe joint thereby exposing the interface the cut cross section of the pipe to the full line pressure carri within the pipe.

Pipe manufacturers for some time attempted to overcome t above mentioned problems by seeking various means for creating a stro bond directly between the alternating layers of PVC and epo impregnated glass fiber. Those attempts were substantially hindere however, by the characteristic inertness and chemical resistance PVC and related resins. Since the chemical reactions of tho materials are generally substantially confined to those of degradati in heat σr strong radioactive environments, conventional attempts achieve chemical bends of epoxy resins, directly σr indirectly, PVC or related resins were substantially ineffective and failed overcome the problems noted. Typical of the conventional and/or pri adhesives and surface treatments v ich had heretofore proven to unsatisfactory are those described in U.S. Patents Nbs. 2,815,04 3,002,534 and 3,447,572 as well as British Patent No. 907,763.

Several years ago a process was described in U.S. Pate No. 3,628,991 in ich an acrylonitrile-butadiene-styrene ("ABS") σ polymer dissolved in a mutual solvent for PVC and ABS was applied the surface of the PVC pipe to form a surface solution. The epo impregnated glass fiber layer was then σverwrapped in contact wi this ABS containing surface solution and bonded to the ABS, th approach achieved a notable measure of success in creating satisfactory bond between the PVC inner cylinder ("core") and the epo impregnated glass fiber overwrap. Subsequently, an iπproved process was described in U.

Patent No. Re-29,375 in v ich a defined quantity of a solid epoxy res was incorporated into the ABS containing surface solution. Presen of the solid epoxy resin in the ABS surface solution dramatical improved the ^" bond between the PVC core and the epoxy impregnated gla fiber overwrap layer. This patent also described several other resi vhich could be used for the core material in place of PVC as well two resins (solid themosetting phenolic resins or polyester resin v ich could be used in place of the solid epoxy resin in the A

layer. Critical to the process and products described in this patent, however, was the requirement that the resin incorporated into the butadiene containing layer be chemically the same as the resin used for the fiber glass reinforced overwrap although that resin in the ABS containing layer would normally be in the solid phase ile the same resin in the overwrap would be initially in the liquid phase prior to bonding and curing of the entire coated product.

The laminated product described in the reissue patent has enjoyed a marked success in the market place, being sold o tmercially by J±ins-Manville Corporation under the trademark PERMASTRAN. It has been discovered in service, however, that the pipe is used at low temperatures, such as those on the order of about 0°F (-18°C), the bond formed with the ABS adhesive layer containing the epoxy, phenolic or polyester resin corresponding to the resin in the overwrap has a tendency to weaken and delaminate. Since laminated PVC pipe can frequently be subjected to such temperatures, as vhen it is being shipped or stored outdoors during the winter, it would be very advantageous to have a bonding medium vhich would insure that the PVC core and epoxy, phenolic or polyester impregnated fiber glass overwrap remained firmly and securely laminated.

Brief Suπrπary of the Invention The invention herein is a process for bonding together a first layer ααπprising a -thermoplastic poly(vinyl acetate) , poly (methyl ethacrylate), polystyrene, polybutene, poly(vinyl butyral) σr polymeric olefiniσ chloride resin and a second layer comprising a liquid therπosetting epoxy, j enolic σr polyester resin, >hich layers are substantially chemically unbondable to each other; vtfiich process cαπprises applying to the surface of said first layer a coating consisting essentially of urethane resin in such manner that said coating and said first layer becαne mechanically interengaged at the interface between the two, applying to said coating said second layer in uncured form and thereafter curing said second layer and simultaneously forming a substantially chemical bond between said coating and said second layer, vhereby a laminated product of irrprσved cold temperature integrity and strength is formed.

In one embodiment the first layer comprises PVC and the second layer comprises epoxy iiηsregnated glass fiber. In another embodiment the coating also contai s a butadiene resin. Met_hod _J_y_

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which the bend between the first layer and the coating can be for include surface roughening and/or solvent washing of the first la or forming a surface solution at the interface between the first la and the coating. The invention also comprises a laminated article havin bond between the laminae ich has improved cold temperature integr and strength, said article comprising a first layer containing as principal component a "thermoplastic poly(vinyl acetate) , poly(met methacrylate) , polystyrene, polybutene, poly(vinyl butyral) polymeric olefinic chloride resin and a second layer containing the principal ααπpσnent a the_rmosetting epoxy, phenolic σr polyes resin, said layers being bonded into said laminate by a coat therebetween and in intimate contact therewith, said coating consist essentially of a urethane resin which is mechanically interenga with said first layer and chemically bonded to said second layer.

In one embodiment the first layer ccrrrprises PVC and second layer comprises an epoxy impregnated glass fiber materi In another embodiment the abating also contains a butadiene res Methods by v ich the bond between the first layer and the coating be formed include surface roughening and/or solvent washing of first layer or forming a surface solution at the interface bet the first layer and the coating.

Detailed Description of the Invention This invention is a novel method of bonding two dissim and otherwise unbondable resinous u ti ositions. While the proc of this invention is applicable to bonding any two of the descr classes of materials, the process finds a particularly important in the bonding of alternate layers of PVC and related resins to la of epoxy and related polymeric materials. An important spec application of this process lies in a method for producing plas pipe composed of alternating layers of PVC resin and epoxy impregn glass fiber.

The process of this invention enables strong bonds to formed between layers of dissimilar and otherwise generally unbonda resinous o npυsitions. Pipe produced by the method described he has good integrity and substantial resistance to separation at interfaces within the pipe wall. Where it is necessary to cut σr throuei the pipe wall and expose one αr more of the interfa_ f ^"

the method of this invention can be used quite effectively to seal the cut surface and prevent exposure of the interface to the line pressure within the pipe thereby preventing separation of the pipe wall at that interface. A most important property of pipe produced by the process of this invention is its resistance to delamination even under severe cold temperatures, such as those on the order of about 0°F (-18°C). It has, for instance, been discovered that pipe produced according to the present invention shews bond strength which are frequently twice as great as the best previous laminated pipe, i.e., that produced according to the process of the afore¬ mentioned reissue patent.

The thermoplastic resin which comprises the principal component of the first layer will be selected frαn the group consisting of poly(vinyl acetate), poly(methyl methacrylate) , polystyrene, poly- butene, poly(vinyl butyral) and the polymeric olefinic chlorides, notably poly(vinylidene chloride) , poly(vinyl chloride) and copolymers thereof. The polymeric olefinic chlorides (which are usually referred to herein collectively as "PVC" resins) are the preferred resins to be used as the first layer of the laminate, particularly v en the laminated article is a pipe. PVC pipe cores are noted for their inertness and stability in the presence of a wide variety of different types of fluids which the pipes may be called upon to transport. The thermoplastic resins useful herein are those which are substantially chemically inert but v ich can form surface solutions with the coatings described below.

The second layer is composed of an initially liquid thermo- setting resin selected frαn the group consisting of epoxy resins, polyester resins and phenolic resins. Of these the epoxy resins are preferred. These resins are reaction products of epoxide compounds with confounds having available hydrogen atoms linked to carbon atoms by oxygen atoms. Exarrples of the latter are the polyhydric phenols and the polyhydric alcohols. A typical epoxy resin useful in this invention is the reaction product of epichlorohydrin and a polyhydric phenol such a bisphenol-A. Other illustrative epoxy resins typically include reaction products of epihalόhydriris and polyhydric alcohols such as ethylene glycol, propylene glycol, trimethylene glycol and the like. Also quite satisfactory in the psrocess of this invention

are the epoxy silanes; these are often used as the binding matrix glass fibers as described, for instance in U.S. Patent No. 3,391,052

Other suitable epoxy resins include the epoxy novolac res such as the epoxy phenol novolac resins. These are basically novo resins vhose phenolic hydroxyl groups have been converted to glyci ethers. Other suitable epoxy resins types include ρ>-amine phe epoxys as well as cyclσaliphatics in tλ ich the epoxide group directly attached to the cycloaliphatic ring and epoxy ethers.

The phenolic resins include those produced by reacting phe with an aldehyde. The cαπtnercial phenols used are phenol, cres xylenols, p>-ter .-butylphenol, p-phenyl-phenol, bisphenols resorcinol. The most important aldehydes are formaldehyde furfural. Preferred among the phenolic resins are those formed by reaction of phenol and formaldehyde. The phenolic resin may be for by either addition or condensation reactions in the presence of eit acid or base.

The polyester resins are formed by the reaction pxDlyfunctional acids or anhydrides and alcohols. A typical polyes resin is prepared by reacting phthallic anhydride or aleiσ anhydr and propylene glycol.

The polyurethanes vtfiich are the basic component of ooating of the present invention are formed by the reaction of a pol with a diisocyanate. Typical among the polyols ich may be used form the polyurethanes of the present invention include those deri from glycerol and sorbitol. Typical of the diisocyanates hich be used are toluene diisocyanate (vhich is usually in the form of mi isαners of toluene diisocyanate) or diphenyl methane diisocyana The reaction to form the polyurethanes is usually catalyzed by ami such as diethylene triamine or dibutyltin ilaurate. In the pres invention the polyurethane resin will be in the solid phase after bond is formed between the coating and the first layer, but will dissolved or dispsersed in a solvent at the time the coating layer applied to the thermoplastic first layer, as will be described below

The ooating may also contain a butadiene resin. This include polybutadiene itself or any of a variety of σopoly ers terpolymers thereof such as butadiene-styrene resin, acrylcnitri butadiene resin, acrylonitrile-butadiene-styrene resin (ABS), mixtu thereof and the like. ,-

Praparation methods for all the resins mentioned in the preceding paragraphs are well known and amply described in the art ^' . Any of the known preparation methods are suitable to prepare the resins for use in this invention. The urethane resin will normally initially be in solid form.

In order to form the coating of -the present invention, the urethane resin is first dissolved or dispersed in ccraninuted form in a solvent. It is preferred that the urethane be dissolved in order to obtain the optimum bond. Typical solvents which may be used include tetrahydrofuran, methyl ethyl ketone, cyclohexanone, methylene chloride, acetone, ethyl acetate, iscphorone and the like. When the coating also contains a butadiene resin it is preferred that the ^' solvent be a mutual one for both the urethane and the butadiene resins. Similarly, if the mechanical interengagement of the coating and the first layer is to be obtained by means of formation of a surface solution at the interface thereof, it is preferred that the solvent also be a mutual solvent for the thermoplastic resin in the first layer as well as for the urethane and the thermoplastic resin.

The second layer containing the thermosetting resin impregnated glass fiber, in which the thermosetting resin is initially in liquid form, may if desired also ααntain a curing agent for the thermosetting resin. Typical curing agents are described in the aforementioned reissue patent.

The exact composition and concentration of the components in the first ^• and second resinous layers are not critical. Each component will be selected prijπarily because of the particular properties desired in the finished article. Thus in a typical pipe composition the PVC core cylinder will be composed essentially all (i.e., usually about 90% σr greater) of PVC with a small amount of conventional additive materials such as stabilizers, antioxidants, colorants, etc. Similarly, the typical overwrap layer of epoxy impregnated glass fiber will consist of a range of concentrations of continuous filament glass fibers in an epoxy matrix and may also- include materials such as σolorants, antioxidants, stabilizers, curing agents, etc. in small amounts. The various concentrations of epoxy and glass will depend en the properties desired in the finished pipe. In these cases, as in all others involving the various materials ich may be in the first and/cr second resinous layers, there is muc -«ri r ^' ^?

art describing the various materials and their properties. Th skilled in the art will have no difficulty selecting suita compositions frαn the prior art for use in the process of t invention. For the purpose of this invention, therefore, the first second resinous layers are considered suitable if they are generally bσndable to each other and if they each contain respective thermoplastic and thermosetting resins as princi components. "Principal component" as used herein is defined to m a component hich is present in sufficient quantity so as to contrib substantially to the bonding process of this invention. Generally t will mean that the particular cαπponent will comprise 40% to 50% more by weight, up to 100% by weight, of the particular polyme composition being considered. Such a component may, however, present in a aπaller concentration if the other components relatively inert and/or the component in question provides a ma part of the bonding function. Thus, for instance, in an ep impregnated glass fiber layer, the epoxy resin may vary over wide ra en concentrations and yet be considered a principal component for other important component in the system, glass fiber, is inert does not participate in the bonding process. It is, of cour important that a "principal component" be present in sufficient amo to materially participate in the bonding function; small σr tr amounts of a component vhich provide only a small amount of bond are not considered to be within the scope of this invention.

The novel coating layer initially contains two princi components: the urethane resin and a solvent which is a mutual solv for both the thermoplastic and for the urethane resin. The ureth resin is initially in solid form and is either dissolved or disper in the solvent. During the process herein the solvent will evapora leaving a solid urethane coating interengaged with the thermoplas substrate. If desired, the coating may also contain a butadiene res in vhich case the solvent is usually also a mutual solvent for butadiene resin. When a butadiene resin is present, the urethane butadiene resins will be present in a butadiene: rethane resin wei ratio of up to 85:15, preferably in a range of 20:80 to 80:20, more preferably in approximately equal amounts. If desired, coating may also contain a quantity of a thermosetting resin of

sa e chemical type as the thermosetting epoxy, phenolic or polyester resin of the second layer. The thermosetting resin will, be incorporated into the coating in a manner and quantity analogous to that described in the reissue patent. In this case preferably the mutual solvent for the thermoplastic, butadiene and urethane resins will also be a solvent for the thermosetting resin.

The urethane coating may be interengaged with the thermoplastic substrate (i.e., the first resinous layer) in different ways. In a preferred method, the substrate is first sanded to roughen the surface and the solvent containing the urethane is then sprayed or painted onto the roughened surface. When the solvent subsequently evaporates or is heated to volatilize it, the solid urethane resin left is found to have filled the myriad of minute "valleys" created in the substrate surface by the sanding, thus effecting a firm mechanical interlock of the coating and the substrate.

Alternatively, the substrate can be solvent washed with one of the aforementioned solvents, preferably methyl ethyl ketone or tetrahydrofuran when the substrate is PVC. Solvent washing to roughen the surface may also be combined with sanding, but is not preferred because solvent washing appears to "fill in" the "valleys" created by sanding to seme extent, thus making the subsequent urethane/ substrate bond less strong.

In yet another embodiment, the u ethane-containing mutual solvent can be worked into the outer surface of the substrate in a quantity sufficient to dissolve the outer surface portion of the thermoplastic layer and to form a surface solution of that portion with the coating. Care should be taken, however, that the quantity of coating used is not so great as to dissolve a major portion of the first layer and thereby to weaken σr materially change the properties of that composition.

Those skilled in the art of adhesion and bonding will be well aware of the p cper amount of ooating to be used en a particular resin composition substrate to achieve a good bond without seriously diminishing the desirable properties of the substrate. The quantity of coating is such as normally to penetrate the surface of the first polymeric resin composition to a depth of about 0.5 to about 8 mils (0.01 to 0.20 πrn) and to form a coating thickness of up to about 15

ils (0.38 mm). Seme data suggest that the thicker coatings give mo consistent results.

The coated first layer is then heated to a teπperature 100°F to 200°F (37°C to 93°C) , preferably 100°F to 150 (37°C to 65 ^σ C), and held for about 1 to 16 hours. This heati serves to precondition the first layer and coating for the final curi step. The volatile solvent is driven off, leaving the urethane res present as a solid forming the adhesive coating layer. In most cas the surface is not tacky after this heating so that the coated fir layer (such as a pipe) may readily be handled and oonveyed to t location at vhich the overwrap is to be applied. In addition, th heating step causes the first layer to undergo shrinkage if t particular thermoplastic resin has a tendency to shrink in the presen of heat. This prevents differential shrinkage frc occurring in t subsequent heat curing step after the overwrap has been applied a significantly reduces the possibility that the final laminated produ will become delaminated during final curing or that undue delaminati stresses will be built up in the bonding adhesive.

Following this heat preconditioning the second lay consisting of the the_ι__mosetting resin impregnated glass fiber applied to and placed in contact with the solid surface of the dri and solidified ooating. The thermosetting resin will be in substantially liquid and uncured state. The concentration of t thermosetting resin in the second layer may, as noted above, vary ov quite a wide range, particularly vhere the layer also αontains ine materials such as glass fibers. The layer may be sprayed, painte wiped σr otherwise applied to the hardened surface of the ooatin preferably in liquid form. In a preferred embodiment the layer in the form of resin impregnated filaments which are layed σr wrap en or around the substrate and surface solution. Thus, v en pipe to be formed by the process of this invention the inner cylinder (e. the PVC oore) is first coated on its cuter surface with the sσlvat urethane coating. Thereafter following heating of the solvated coati and inner cylinder, and the resultant solidifying of the uretha coating and mechanical interengagement of the coating and t thermoplastic substrate, epoxy impregnated fiber glass filame attaining epoxy in the form of a relatively viscous, uncured liqui

^■ ^

are wrapped continuously and tightly around the cylinder bringing the epoxy into intimate contact with the solid coating surface.

Following application of the outer second layer, the thermo¬ plastic resin is cured by conventional curing means. Generally this involves heating the entire assemblage so as to thermally cure the thermosetting resin. The heat applied ^" will, of course, be kept sufficiently low such that other resins in the entire assemblage as well as any fillers or additives or other materials vhich may be present will not be detrimentally affected. Such curing techniques are well known to those skilled in the art and need not be exeπplified here. It has been found that for σcmpositions exemplified below, cure temperatures of about 130°F to about 180°F (54°C to 82°C) maintained for about 0.5 to 16 hours produced entirely satisfactory bonds. Curing of the second or overwrap layer may be expedited by incorporation into the layer of a quantity of curing agent for the thermosetting resin.

The following will illustrate the present invention. In an experimental trial at a ccπmercial pipe plant, samples of pipe made according to the process of U.S. Patent Re-29,375 were compared to pipe made under identical conditions with the exception that urethane was substituted for epoxy in the coating layer. The underlying substrate material was a PVC pipe core and the overwrap was a glass fiber reinforced epoxy resin. The PVC core surfaces were cleaned by washing with methyl ethyl ketone and/or by flap sanding. Both thin (2-4 mils; 0.05-0.10 ππi) and thick (10-12 mils; 0.25-0.30 urn) saπples were evaluated. Also the effect of cleaning of the PVC surface was evaluated by making a few samples in vhich the surface was not cleaned prior to incorporation of the coating layer. Inspection of the pipe saπples after production indicated that all sairples in which the PVC core had been cleaned were of good quality σr better, while the bonds of the uncleaned samples were uniformly poor. The urethane used was a product designated "Adiprene L-167" available ccπmercially frcm the DuPcnt Company. In some cases the coating was sprayed onto the PVC core with ccπmercial spray equipment and in other cases it was hand- painted onto the core. Impact testing using the method of ASTM D-244 produced the results shown in the following Table. In both cases the test felling weight ("tup") was "Tip C."

TABLE I

Test Pipe Urethane Coating ASTM D-2444 Impact

No. Temp.,°F Application Thickness,rails Impact,Ft/lbs Improveme

1 72 Spray 10-12 165 22%

2 72 Spray 2-4 165 22%

3 72 Hand n.m. 150 11%

4 72 Control - 135 -

5 0 Spray 10-12 150 100%

6 0 Spray 2-4 90 20%

7 0 Hand n.m. 105 40%

8 0 Control _ 75 — n.m. — not measured

It will be inπiediately evident from these data that t materials made in accordance with the present invention are a uniformly stronger than the bonds obtained in the control materi made in accordance with the reissue patent process. The improveme is particularly marked at low temperatures (0°F; -18°C) and t thicker the coating the stronger the bond. Data from tests made the same time indicated that all samples of both the control materi and the material of this invention in vhich the PVC core had be cleaned prior to coating application readily passed the water press burst test.

In each case the urethane material contai ed a convention amount of a curative material and both were dissolved in a solve (ethyl acetate) .

In another experiment test samples made according to t process of the reissue patent with epoxy were compared to sampl similarly formed using "Estane 5716" (trademark) fully reacted uretha resin available cαr ercially frcm B.F. Goodrich Chemical Co. Resul are described in Table II below.

Table II

Material Shear Strength, psi

"Estane 5716" urethane alone 1060

+ ABS 1660

+ epoxy 1380

+ epoxy + ABS 1630

In a subsequent test in vhich "Estane 5713" (trademark) fully cured urethane resin (available ccπmercially from B.F. Goodrich Chemical Co.) was used in place of the aforementioned "Estane 5716" (trademark) resin because of the former's higher heat resistance, the cold temperature (0°F, -1S°C) ASTM D-2444 impact strength was found to be about three times greater than an epxoxy-containing material made according to the reissue patent disclosure.

Statement of Industrial Application The invention herein is applicable to the bonding of any wo dissimilar and chemically unbondable resinous materials. It is particularly applicable to the formation of laminated materials such as laminated pipe.