Field of the Invention

This invention relates to polyethylene-based hot melt adhesives modified with an aliphatic hydrocarbon modifier for improved hot melt adhesives.

Background of the Invention

Ethylene is known to be polymerizable with many comonomers to form polyethylene copolymers of many different types ranging from hard impact resistant plastics and thermoplastics, to soft elastic films, to hard, rubbery elastomeric tires and the like. Polyethylene can also be blended with other polyolefins to optimize properties.

Ethylene copolymers are also useful as components in adhesives; in particular they can be used in hot melt adhesive compositions, pressure sensitive adhesive compositions, contact adhesive compositions and the like. Typically, tackifiers are added to these ethylene copolymers to give them their adhesive qualities. The strength of the adhesive bond is generally dependent upon the base copoly er and the tackifier used. For example, an ethylene-vinyl acetate copolymer(EVA) blended with a typical non-polar tackifier generally has poor bond strength in comparison with a similar formulation where the EVA was blended with a polar tackifier. Thus, it would be desirable to develop a modifier that when added would increase the bond strength of EVAs blended with non-

polar tackifiers as well as increasing the bond strength of EVAs bonded with polar tackifiers.

Summary of the Invention

This invention relates to a blend of an ethylene copolymer, a tackifier and a modifier. The ethylene copolymer comprises ethylene and one or more polar monomers, preferably esters, acids, alcohols and the like. The modifier comprises a straight or branched chain aliphatic hydrocarbon having one or more polar groups along the aliphatic structure. The polar groups can be one or more acids, alcohols, esters, amides, amines, ketones, aldehydes or mixtures thereof and the like. These blends are then used as adhesives and the like.

Description of Preferred Embodiments

This invention relates generally to ethylene copolymers blended with tackifiers and a modifier to produce adhesives, preferably hot melt adhesives, hot melt pressure sensitive adhesives and pressure sensitive adhesives. The ethylene copolymers which can be used in the blends include ethylene copolymerized with any polar monomer. Examples of polar monomers include, but are not limited to vinyl acids, alcohols, esters, and the like. Preferred examples include alkylmethacrylates, alkylacrylates, alkylmethacrylie acids and alkylacrylic acids. Even more preferable examples of suitable monomers include vinyl acetate, acrylic acid, methacrylic acid, methacrylate, ethylmethacrylate, methylmethacrylate, ethylacrylate and methylacrylate. In another embodiment the ethylene copolymer may be a polymer of ethylene and an alpha olefin, preferably a C ₃ to C ₃ alpha olefin. Examples

include ethylene/hexene, ethylene/butene, and ethylene/octene copolymers and the like.

The polar monomers are typically present in the copolymer at about 1 to about 60 wt.%, preferably 5 to about 50 wt.%, even more preferably about 15 to about 40 wt.%. These copolymers are produced by many processes known in the art and are available commercially in many forms. For example, ethylene vinyl acetate copolymers are produced by high pressure free radical polymerization and can be purchased from Exxon Chemical Company under the ESCORENE ^" trade name.

The tackifiers used in the blends of this invention include any natural or synthetic tackifier. The tackifier may be polar or non-polar, solid or liquid or both. Examples of suitable tackifiers include, but are not limited to, rosins, rosin esters, tall oil rosin esters, linear, branched or cyclic chain aliphatic tackifiers or tackifiers containing mixtures of the straight, branched or cyclic chain aliphatic components, terpenes, or mixtures of the above or the like. Preferred tackifiers include aliphatics and aliphatic mixtures and rosin esters. Specific preferred tackifiers include ECR-372B, a hydrocarbon tackifier comprising mostly various five and nine carbon olefins, diolefins and aromatics in linear cyclic and/or branched forms, Foral 105 and Bevilite 62-107B which are rosin esters. The tackifier may be present in the blend at up to about 80 wt.%, preferably from about 20 to about 60 wt.%, even more preferably from about 40 to about 60 wt.%.

The modifiers that are used in the blends are aliphatic, linear or branched chain hydrocarbons having a polar group or groups attached along the aliphatic structure. The modifiers are typically a C5-C2O/

preferably C10-C15, even more preferably C12-C15 linear or branched chain aliphatic hydrocarbon or blends thereof having one or more similar or different polar groups distributed along the aliphatic structure. The polar groups that can be distributed along the aliphatic structure include acids, alcohols, esters, amides, amines, ketones, aldehydes, acetates, ethers and the like. Preferred examples of polar groups include alcohols, acids and esters.

In general, modifiers comprising linear aliphatic hydrocarbons have been found to be more effective than modifiers of branched aliphatic hydrocarbons. Additional preferred modifiers include linear aliphatics with a polar group attached to the terminus of the aliphatic chain. Examples of modifiers include linear and/or branched octanol, decanol, decanal, tridecanol, tridecanal, n-heptanoic acid, n-nonanoic acid, isooctanoic acid, isotridecanoic acid, neoheptanoic acid, neodecanoic acid, heptanal, heptyl acetate, heptanone, heptyl amine, heptyl amide, heptyl ether, octyl acetate, octanal, octyl acetate, octanone, octyl amine, octyl amide, octyl ether, nonyl acetate, nonanal, nonyl acetate, nonanone, nonyl amine, nonyl amide, nonyl ether, decyl acetate, decanal, decyl acetate, decanone, decyl amine, decyl amide, decyl ether, tridecyl acetate, tridecanal, tridecyl acetate, tridecanone, tridecyl amine, tridecyl amide, tridecyl ether, dodecanol, dodecanoic acid, dodecyl acetate, dodecanone, dodecyl amine, dodecyl amide and dodecyl ether. Preferred modifiers include Exxal L1315, a mixture of C1 ₃ and C15 linear aliphatic alcohols, decyl acetate, tridecyl acetate, and dodecanoic acid.

These modifiers are generally commercially available products and can be purchased from chemical suppliers such as Exxon Chemical Co., Aldrich, Alfa and

the like. Some of the modifiers, such as dodecanoic acid, are naturally occurring compositions and others are the product of oxygenation of a petroleum stream. It is within the skill of one of ordinary skill in the art to make or purchase these compositions.

These modifiers are typically present in the blends of the composition at from about 0.05 to about 20 wt.%, preferably about 1.0 to about 15 wt.%, even more preferably about 2 to about 10 wt.%. Waxes, antioxidants and other additives known in the art may be added to the blends of this invention as optional ingredients. These additives include but are not limited to photostabilizers, antioxidants, ultraviolet stabilizers, fillers, plasticizers, lubricants, coloring agents, lubricants and the like.

Examples of fillers include inorganic fillers such as carbon black, silica, calcium carbonate, talc and clay, and organic fillers include high styrene resin, coumarone-indene resin, phenolic resin, lignin, modified melamine resins and petroleum resins.

Examples of lubricants include petroleum type lubricants such as oils, waxes, paraffins and liquid paraffins; coal tar type lubricants such as coal tar, coal pitch; fatty acid oil type lubricants such as castor oil, linseed oil, rapeseed oil, coconut oil, and tall oil; waxes such as beeswax, carnauba wax and lanolin; fatty acids and fatty acid salts such as licinoleic acid, palmitic acid, barium stearate, calcium stearate and zinc laureate; and synthetic polymeric substances such as petroleum resins.

Examples of plasticizers include hydrocarbon oil, paraffins, aromatic and naphthenic oils, phthalic acid

esters, adipic acid esters, subacic acid esters and phosphoric type plasticizers.

Examples of coloring agents are organic and inorganic pigments, dyes, and inks.

The blends are produced by ordinary methods known in the art for blending ethylene polymers, tackifiers and the like. For example, an ethylene-vinyl acetate copolymer can be placed in a receptacle, heated and stirred. Tackifier can be added to the receptacle and the modifier added to the receptacle so that a uniform dispersion is obtained. Blends of this invention have improved adhesive properties when compared to similar blends lacking the modifier.

The blends of this invention can then be used as adhesives on substrates such as asphalt, cement, metals (including aluminum) , MYLARTM, polymers (including polyolefins such as rubbers, plastics, thermoplastics) , glass, ceramics, wood, paper, rocks, minerals and paint, cardboard, and the like. Preferred examples include polyethylene, polypropylene and aluminum. These adhesives can also be used as a laminate, as a hot melt adhesive, as a pressure sensitive adhesive, as a bookbinding adhesive, as a packaging adhesive, as a structural adhesive, as an automotive adhesive, as a wood adhesive, as an upholstery adhesive, as a structural adhesive and as an adhesive for affixing reflectors to asphalt and the like. Preferred uses include hot melt adhesives, pressure sensitive adhesives and the like.

The following are examples of embodiments of the invention and should not be construed to limit the invention.

EXAMPLES

In the examples below, a series of hot melt adhesives (HMA) based on an ethylene-vinyl acetate comprising 28 wt.% vinyl acetate was formulated using various tackifiers and modifiers. Formulations were prepared in stainless steel beakers at a temperature of about 150 degrees C with a blanket of nitrogen covering the materials. Once the components had melted in the quiescent state, a propeller type stirrer that just touched the top of the materials was used to mix them. Stirring was continued for 30 minutes after visual inspection indicated that a homogeneous blend had been achieved.

Each of the HMA formulations was laid out to form a thin film suitable for bonding. The HMA was heated to 150 degrees C in an oven then laid out on release paper using the 0.006 inch channel of an eight path applicator. The resulting film had a thickness of about 0.005 inch. The HMA films were used to bond cast films of polypropylene 0.004" thick. Seals were made in a hot press heated to 150 degrees C, the adhesive being sandwiched between polypropylene film using a pressure of approximately 100 psi for 10 seconds.

Molding plates of aluminum 1/32" thick were used to separate the polypropylene film from the platens of the press. After sealing, the bonds were quenched between water cooled platens at approximately 25 degrees C using a pressure of approximately 100 psi. For the purposes of T-peel testing, 0.5" strips were cut from the bonded sandwich of polypropylene film and HMA. Test pieces were allowed to age for a minimum of 48 hours prior to evaluating the strength of the bond.

T-peel, a measure of adhesive strength, testing was carried out at room temperature on an Instron 4505

testing frame with an extension rate of 2"/min and a sampling rate of 2 points/sec. In the case of adhesives exhibiting only slip/stick failure, (slip/stick is erratic adhesive failure and/or widely fluctuating peel force) the T-peel strength was taken as the average of the peaks on the force/deformation plot. In cases where both smooth peel and slip/stick were exhibited by the same sample, the average value of the smooth peel regions was taken as the T-peel strength. For each HMA formulation five samples were tested and the results averaged.

EXAMPLE 1

In the following experiments, the EVA was present at 40 weight percent with the modifier being added at the expense of the tackifier. These data show that linear acids and alcohols are more effective as bond strength enhancers than their branched counterparts. In the case of acids, the more highly branched neo acids are less effective than the iso acids. Various blends and testing results are listed in Table 1 below. C13/C15 is a mixture of C13 and C15 straight chain alcohols. ECR-372B is a hydrocarbon tackifier comprising mostly various five and nine carbon olefins, diolefins and aromatics in straight, cyclic and/or branched forms, Foral 105 and Bevilite 62-107 are rosin esters.

Modifier Viscosity @ 10 T-peel Failure type (%) RPM strength (lb/in)

11,100 0.8 Adhesive s/s

2.5 9,400 1.5 Adhesive smooth

5 8,630 2.3 Adhesive smooth 7.5 7,400 3.0 Adhesive smooth

5 9,600 2.6 Adhesive s/s *

3.8 10,200 1.0 Adhesive s/s 8.25 11,000 0.3 ' Adhesive s/s ι-3 2.5 9,670 1.9 Adhesive smooth tr 5.0 7,400 1.9 Adhesive smooth (D 7.5 6,630 2.2 Adhesive smooth 2.9 9,080 2.2 Adhesive smooth 5.8 7,130 3.8 Adhesive smooth 8.7 6,250 4.1 Adhesive smooth

9.5 Cohesive smooth

6.9 6,220 0.5 Adhesive s/s 3.5 10,000 1.4 Adhesive smooth 4.2 8,320 1.5 Adhesive smooth 5.4 8,200 2.6 Adhesive smooth

*s/s = slip/stick Example 2

The effect of bonding pressure on T-peel strength of certain hot melt adhesives was determined. The procedures set out in Example 1 were followed. An ethylene-vinyl acetate copolymer containing 28% vinyl acetate was blended with ECR372B which is a hydrocarbon tackifier comprising mostly various five and nine carbon olefins, diolefins and aromatics in straight, cyclic and/or branched forms, Foral 105 and Bevilite 62-107 are rosin esters and various modifiers. The blends and the T-peel strengths at 100-200 psi are reported in Table 2. TABLE 2

As is apparent from the foregoing description, the materials prepared and procedures followed relate to specific embodiments of the broad invention. It is apparent from the foregoing general description and the specific embodiments that, while forms of the invention have been illustrated and described, various modifications can be made without departing from the spirit and scope of this invention. Accordingly, it is not intended that the invention be limited thereby.