Hot Melt Adhesive Compositions Containing a Polystyrene Resin

The applications identified below disclose and claim compositions similar to those disclosed and claimed herein. The compositions disclosed in these applications differ from the present invention in that the tackifying resin included therein differs from the tackifying resin included in the present invention.

The application Ser. Nos. are 229,204; 229,351; 229,389; 229,390; 229,394; 229,400; and 229,401.

Each of the above applications has been filed of even date herewith.

Hot melt adhesives frequently are employed to prepare laminated structures by bonding two or more laminae together. While many satisfactory hot melt adhesives are available to the art, the art is constantly seeking new compositions having superior performance, or lower cost, or both.

The applicants have discovered hot melt adhesive compositions useful in laminating polar laminae together. The hot melt adhesive compositions of the invention contain three essential components. The first is an alkenyl succinic anhydride. The second is an ethylene copolymer. The third is a tackifying resin selected from a class described infra.

The compositions of the invention contain about 10-30, preferably 15-25, and more especially about 20 weight % of the alkenyl succinic anhydride. The ethylene copolymer is present in the amount of 20-60, preferably 25-50, and more especially about 40 weight % of the composition. The tackifying resin is included in the compositions in the amount of about 10-40, preferably 15-35, and more especially about 25 weight % of the total composition. In the preferred embodiment of the invention, the three named components constitute the entire composition. Optionally, however, the compositions may contain up to about 20 weight % of additional components. An antioxidant of the type conventionally employed with ethylene polymers desirably is included in the compositions.

The alkenyl succinic anhydrides employed in the compositions of the invention are known compounds of the type described in U.S. Pat. No. 4,158,664, whose descriptions are incorporated herein by reference. These compounds are prepared by heating a high molecular weight alpha-olefin containing about 18 or more carbon atoms with maleic anhydride. Their structure is shown below: ##STR1## In the above formula, R is an alkyl group containing at least 15 carbon atoms. Frequently these compounds are prepared from a mixture of alpha-olefins in which each component contains a minimum of about 18 carbon atoms. In this event, R can be expressed as an average value which seldom will be in excess of 49. Preferably R will have an average value of less than 39.

The ethylene copolymers employed in the compositions of the invention will have polymerized therein at least 40 and preferably at least 60 weight % of ethylene, with the balance of the copolymer being one or more polymerized monomers selected from the group consisting of vinyl acetate, acrylic and methacrylic acid, and alkyl esters of acrylic and methacrylic acid. The preferred copolymers will contain 40-90 weight % ethylene with the balance being vinyl acetate. Where the ethylene copolymer contains an alkyl ester of acrylic or methacrylic acid, the alkyl ester preferably will be a methyl or ethyl ester. The ethylene copolymers preferably will have a melt index in the range of about 0.5-200, preferably 1-100, and more especially about 2-20. Methods for preparing such copolymers are well known in the art and certain of such copolymers are commercially available. The tackifying resins employed in the compositions of the invention will be a polystyrene resin having a Ring and Ball softening point of about 25.degree.-125.degree. C., as determined by ASTM E-28-58T. Such polystyrene resins have low molecular weights and are known in the art. Certain of such resins are sold under the trade designation Piccolastic.

As noted supra, in addition to the named components described above, the compositions of the invention may contain up to about 20 weight % of additional components. Such additional components typically are wax-like materials which can modify the melt viscosities of the products of the invention. Suitable materials of this type include (1) low molecular weight, liquid polybutylenes in the molecular weight range of from about 600 to 3000; (2) petroleum waxes such as paraffin wax having a melting point of from about 130.degree.-165.degree. F., and microcrystalline wax having a melting point of from about 140.degree.-200.degree. F.; the latter melting points being determined by ASTM method D 127-60; (3) polyethylene greases having a softening point of from about 80.degree.-100.degree. C., and a hardness value, as determined by ASTM method D-1321, of about 60-120; (4) mineral oil; (5) synthetic waxes made by polymerizing carbon monoxide and hydrogen, such as Fischer-Tropsch wax; and (6) atactic propylene polymers.

The compositions of the invention are solids at room temperature, but have melting points and melt viscosities in a range such that they can be readily applied to appropriate substrates using conventionally employed hot melt techniques and equipment. The compositions, depending upon their precise formulation, have ring and ball softening points within a range of approximately 80.degree. to 105.degree. C. The compositions can be formulated to have viscosities, at 400.degree. F., from as low as about 500 cps to as high as 20,000 cps or more.

A suitable procedure for preparing the hot melt adhesive compositions involves placing the tackifying resin and the alkenyl succinic anhydride in a jacketed mixing kettle (or in a jacketed heavy duty mixer of the Baker-Perkins or Day type for compositions having high viscosities) equipped with a stirrer and thereupon raising the temperature to a range of from about 250.degree. to 400.degree. F., and preferably 300.degree. to 350.degree. F. When the initially charged components have melted, stirring is initiated and the ethylene copolymer then is added. Stirring and heating are continued until a smooth, homogeneous mass is obtained. The resulting hot melt adhesive composition is drawn off and may be used immediately in hot pots; or, it may be melt-extruded into rope form or converted into pellets, rods, cylinders, slugs, or billets depending on the equipment which will be subsequently used to apply the hot melt; or, it may be placed in cooling pans and held in bulk form for later use; or it may be granulated or diced.

The hot melt adhesive compositions of the invention give very satisfactory results in preparing laminated structures from laminae prepared from resins such as polyamides, acrylonitrile-butadiene-styrene resins, vinyl chloride resins, and wood. The procedural steps for bonding the laminae together are those commonly employed with other hot melt adhesives. The hot melt adhesive is applied to at least one of the surfaces to be bonded. The assembly of touching surfaces then is placed under at least light pressure and cooled to ambient temperature to solidify and set the adhesive. The application temperature of the adhesive is set at a level such that adequate flow is obtained under the applied pressure to obtain a good bond between the surfaces to be bonded.

The following examples are set forth to illustrate more clearly the principles and practice of the invention. Where parts and percentages are set forth, they are on a weight basis unless otherwise noted. As the examples have been transferred directly from our parent application Ser. No. 174,296, filed on July 31, 1980, they also disclose compositions of the type claimed in our related copending applications referred to supra.

Several hot melt adhesive formulations were prepared from (a) an alkenyl succinic anhydride prepared from a C-30+ alpha-olefin* and maleic anhydride by the procedure described in U.S. Pat. No. 4,158,664, (b) a binary copolymer of ethylene and vinyl acetate containing about 18 weight % vinyl acetate and having melt index of 2.5, and (c) a tackifying resin, the chemical identity of which is described in footnotes to Table I. An antioxidant in the amount of 0.5% of the composition was included in each composition to prevent oxidation. Fine particles of the components first were physically admixed at ambient temperature. The physical admixture was then heated to a temperature of about 160.degree. C. with stirring to provide a homogeneous mixture. The compositions of the products, the melt properties of compositions, and the mechanical properties of the compositions are set forth in Table I.

The mechanical properties of the compositions shown in Table I, particularly the tensile properties, are significantly higher than generally similar commercial hot melt adhesives containing microcrystalline waxes in lieu of the alkenyl succinic anhydrides. To demonstrate the magnitude of these differences, controls corresponding to each of the compositions shown in Table I were prepared. The controls were prepared by replacing the alkenyl succinic anhydride of each composition with an equivalent weight of a microcrystalline wax which melts at 180.degree. F. The tensile properties of the compositions identified in Table I and the controls corresponding thereto are shown in Table II.

Laminates were prepared by bonding together sheets of a commercially available ABS resin, a PVC resin, and a nylon resin with adhesive compositions 1A, 1D, 1E, and 1G shown in Table I. In each case, the hot melt adhesive was applied to one surface in an amount to provide substantially 230 grams of adhesive per one square meters of glue line. The adhesive was applied at 400.degree. F. using a Minimatic 400 gun. After the adhesive was applied, the assembly was maintained under a pressure of about 0.5 psi until the assembly cooled to ambient temperature.

Lap shear tensile values were determined on the laminates and the type of failure was noted. The results are shown in Table III, with the type of failure being indicated by the capital letters shown within parentheses following each reported lap shear tensile value. The meanings of the letter designations are:

(A) Denotes total adhesion failure with the entire adhesive layer remaining on one lamina.

(M) Denotes mixed adhesion failure in which some of the adhesive layer remains on both laminae.

(C) Denotes cohesive failure in which both of the laminae, at the glue line, are covered with adhesive. This type of failure indicates that the bond between the adhesive and the laminae is higher than the bulk strength of the adhesive material.

(S) Denotes failure of the laminae substrates with the adhesive bond remaining intact and unbroken.

An additional series of hot melt adhesive formulations were prepared following the procedures described in Example 1, Part A. The compositions of this example differed from the compositions shown in Example 1 in that the ethylene copolymer employed was a binary copolymer of ethylene and vinyl acetate containing 40 weight % vinyl acetate and having a melt index of 7.5. The compositions of the products, the melt properties of the compositions, and the mechanical properties of the compositions are set forth in Table IV.

Laminates were prepared by bonding together sheets of a commercially available ABS resin, a PVC resin, and a nylon resin with adhesive compositions 2-A, 2-B, 2-C, 2-F, and 2-G shown in Table IV. The laminates were prepared in the identical manner described in Example 2. The lap shear tensile values were determined on the laminates and the type of failure was noted. The results are shown in Table V.

An additional series of hot melt adhesive formulations were prepared in the same manner as described in Example 1, Part A. The primary difference in the compositions is that the ethylene copolymer employed therein was a binary copolymer of ethylene and vinyl acetate containing about 60 weight % vinyl acetate and having a melt index of 3.5. The compositions of the products, the melt properties of the composition, and the mechanical properties of the composition are set forth in Table VI.

A series of laminates were prepared from sheets of a commercially available ABS resin, a PVC resin, and a nylon resin with adhesive compositions 3-A, 3-B, and 3-D shown in Table VI. The laminates were prepared in the same manner as described in Example II. Lap shear tensile values were determined on the laminates and the type of failure was noted. The results are shown in Table VII.

Another series of hot melt adhesive formulations were prepared in the manner described in Example 1, Part A. The ethylene copolymer included in the formulations was a binary copolymer of ethylene and methyl acrylate containing about 20 weight % methyl acrylate and having a melt index of 2.0. The compositions of the products, melt properties of the compositions, and the mechanical properties of the compositions are set forth in Table VIII.

Another series of hot melt adhesive formulations were prepared as described in Example 1, Part A. The ethylene copolymer included in the compositions was binary copolymer of ethylene and ethyl acrylate containing about 18% ethyl acrylate and having a melt index of 6.0. The compositions of the product, the melt properties of the compositions, and the mechanical properties of the composition are set forth in Table IX.

Laminates were prepared by bonding together sheets of a commercially available ABS resin, PVC resin, and a nylon resin employing the techniques described in Example 2. The adhesive compositions employed were 4-B, 5-A, 5-B, and 5-C shown in Tables VIII and IX. Lap shear tensile values were determined on the laminates and the type of failure was noted. The results are shown in Table X.