Technical Field This invention relates to adhesives and particularly rs-ΪStes to ^" tot melt adhesives. Still more particularly, the instant invention relates to -wax-based hot melt adhesives particularly useful for adhering facings to building products and thermal insulations.

Background of Prior Art

Wax-based hot melt adhesives or coatings have been used for many years. Hot melt adhesives are bonding and coating agents

^• which achieve a solid state and resultant strength by cooling as contrasted with other adhesives which achieve the solid state through evaporation or removal of solvents. Prior to heating, a hot melt adhesive is a thermoplastic, 100% solid material. When heated to approximately 275 to 400°P, the material is brought to a liquid state, and after the heat is removed, it sets usually by simple cooling. Hot melts offer the possibility of instantaneous bonding, especially when joining previously uncemented and often sπcoth irrcermeable surfaces.

When a hot melt adhesive ccmes in close contact with a surface to ^' be bonded, a molecular layer of film at the surface of this substrate immediately attains a temperature approaching that of the hot melt through conductive heat transfer. Rirther more, a high degree of wetting, almost coalescence, of the hot melt coating and the surface material cccurs. Directly afterward, the melt loses heat to substrates disposed on opposite sides of the melt or to a single substrate located on one side of the ooating and to the processing environment on the other side of the coating until a temperature equilibrium is attained. Normally in a hot melt adhesive coating process, the temperature of the entire adhesive substrate

^"" system drops to a point where the melt sets to a solid having adequate cohesive strength for a particular finished product end use.

In short, hot melt adhesives achieve a solid state an resultant strength through cooling, as contrasted with other adhesive which achieve the solid state through evaporation or removal o solvents or through polymerization and/or crosslinking. As has bee noted, hot melts contain no solvents and are 100% thermoplastic.

The ideal hot melt adhesive would be solid at roo temperature and capable of being stored and handled easily withou blocking. Upon heating, it would elt sharply and flow freely. I would be stable even with prolonged heating and able to withstand loc overheating. In liquid-melt form, it could be applied to the wor by nozzle, wheel, wet coating head, or spray. When used fo lamination, its point of solidification would be such that ample tim would be available to close the bond with only m__nimum pressure. O course, bonds accomplished with this ideal hot melt would be stron and the range of materials which it could bond would be wide. Finall the composition of the hot melt would be such that paper product bonded with the adhesive could be reclaimed by some simple process These are general requirements. A quality that might be particularl desirable for αae application could be unimportant for another. I any case, a hot melt adhesive should be in a liquid state at som elevated temperature in order to meet requirements as a hot melt; ye it must set to a cohesive solid state in the anticipated ambien temperature environment of the finished product containing the ho melt adhesive as a component. Hot melt adhesive formulations vary widely depending upo raw materials, intended end use, properties and price considerations Hot melt systems most often oonsist basically of a polymer and diluent. The polymer is the essential ingredient and is the backbon or strength component of the hot melt adhesive. Almost an thermoplastic polymer with adequate resistance to heat degradatio can be used. Examples of practical polymers are polyethylene polyvinylacetate, ethylene-vinyl acetate (EVA) and ethylene-ethy acrylate (EEA) copolymers. Cn the other hand, polyvinyl chloride an nitrocellulose are less practical because of their limited hea stability.

The molten viscosity of a polymer in a given system is proportional to its molecular weight. A hot melt adhesive could be

100% polymer, but there often would be two major drawbacks: limited adhesion and lack of molten properties such as tack, application temperature range and wetting ability.

The polymer as .a component of hot melt adhesives, often produces low viscosity, low strength and poor mechanical properties when its molecular weight is relatively low. -In contrast, a relatively high molecular weight polymer produces high viscosity, high strength and good mechanical properties. Because the properties of the polymer are a dcminant factor in the performance of most hot melt adhesives, it is generally desirable to use relatively high molecular weight polymers in. formulations.

The second component of hot melt adhesives is the diluent system. The diluent system makes it possible to utilize the properties of the polymer. It is usually a blend of materials such as wax, plasticizer, tackifying or plasticizing resin like wood rosin or rosin esters, stabilizers and sometimes inert pigments or extenders.

The diluent system provies a variety of effects. It is the vehicle for the polymer thereby lowering the viscosity of the hot melt and iteking it more convenient to apply. It enhances the wetting ability and adhesive strength of the polymer. It provides molten tack and tack range. It contributes barrier properties and gloss and provides a means of making the polymer rigid or flexible. The diluent for a hot melt remains in the system when a hot melt is applied and is not dissipated or absorbed. Any hot melt bond reflects the composite properties of all its components, including the diluent. If in the interests of πachinablility and low cost, lower molecular weight polymers are used cαribined with a high percentage of diluents, the effectiveness of a polymer in imparting its characteristics to a hot melt adhesive is reduced. The desirable polymer properties of toughness, heat resistance and low temperature flexibility are di_m_i_nished almost in direct proportion to the molecular -weight and concentration of the polymer.

-4- Prior art wax-based hot melt adhesives particularly usefu for adhering facings to building products and thermal insulations ar usually characterized by their high cost. Typically the hot mel adhesives that are based en low cost ingredients either do not provid a moisture vapor barrier and/or do not provide sufficient bondin strength. At times kraft_ facings for building products and therma insulations have been coated with an asphalt based pound to provid bonding and vapor barrier requirements. However, su h a feeing i characterized by its tendency ^" to block (e.g., for a layer of coate feeing to stick to the layer below it) and potental environmenta problems associated with the application of the asphalt coating o the use of the coated feeing. The asphalt compounds of the past ar thus not appropriate for certain applications.

Certain large carpet manufacturers utilize EVA based ho melt adhesives which include a high percentage of fillers, i.e., u to 60% by weight in order to reduce costs. However, these EVA base adhesives do not provide a moisture vapor barrier which is especiall necessary in coating kraft paper for use in bonding fecings ont insulations at the manufacturing location. An example of barrier properties, especially for the froze food field, is found in ethylene-vinyl acetate blends with petroleu waxes. These coatings which usually have good gloss and hea sealability are specifically designed as barrier coatings. However here the primary desired features are coating properties and estheti properties with less emphasis on an ability to bond a variety o substrates, molten tack, tack range or strength characterisitics.

Prior art hot melt and asphalt based adhesives have definite "tack" or stickiness at rocm temperature. When these hav been used to coat sheet materials which are cαrmonly rolled for stora or shipment (and are therefore hereinafter referred to as "roll goods it has been necessary to take steps to prevent the sticky adhesiv on one layer of the roll from adhering to the sheet which forms th next layer of the roll. Such means have included incorporating pape separators as part of the roll and/or dusting the sheet surface wit

materials such as talc, or coating the obverse side of the facing with a release agent. This, of course, adds substantial additional fabrication and material costs as well as incorporating into the roll goods materials such as separating paper and talc which are not needed for the end use of the roll goods and therefore must be removed and discarded by the user.

In many instances, the hot melt adhesives which are applied to sheets to form adhesive jacketing materials which are used as vapor barrier facings for building materials and thermal insulations, are installed outdoors or in other environments where they are subjected to humidity and/or low temperatures with resultant cold cracking. This cold cracking often caused hot melt adhesives to be rejected for use in many applications viere they would otherwise have been quite suitable. Brief Surπrπary of the Invention

The present invention provides a low-cost, highly-filled, wax-based hot melt adhesive especially useful for coating and/or adhering facings to building prcducts and thermal insulations. A hot melt adhesive blend of the present invention consists essentially of, in parts by weight, up to 25 parts of a paraffin wax, 10 to 30 parts of a modifying hydrocarbon resin, 1 to 20 parts of an elastomeric copolymer, and 20 to 35 parts of an ultra-fine ground inorganic filler material. Preferably, the components of the present invention also include up to 25 parts of a microcrystalline wax. The low cost hot melt coating and adhesive of the present invention is suitable for coating and laminating paper and is amenable to application as a continuous film. Furthermore, the hot melt blend of the present invention is characterized by its low cost caused by the use of a high percentage of filler, excellent moisture vapor transmission ratio (MVTR) , satisfactory bonding and strength properties, taclcLng at high temperatures, nonblocking of coated surfaces and cold cracking resistance. Lastly, the hot melt blend of the present invention allows bonded paper products to be reclaimed by a simple process.

In particularly preferred embodiments, the paraffin wax wil be a fully refined paraffin wax with a melting point (ASTM D87 between the limits of 135 to 150°F, the mcdifying hydrocarbon resi will be a low molecular weight, thermoplastic hydrocarbon resin, th elastα eric copolymer will be an ethylene-vinyl acetate copolymer res and the inert inorganic filler will be ultra fine ground limestone Furthermore, the microcrystalline wax or dark micro wax will be partially refined paraffin wax (petrolatum) .

Detailed Description of the Preferred Embodiments The first major component of the composition or blend o the present invention is a high melt point paraffin wax. This wil normally be a wax with a melt point on the order of 135°F or higher preferably in the range of about 135 to 150°F (57.22 to 65.56°C) Particularly preferred are fully refined paraffin waxes having mel points of approximately 143°F (61.7°C). The paraffin wax wil be nominally present as 15 parts to by weight of the total compositio or blend, with a preferred range of up to about 25 parts by weigh The product which has been found particularly useful in the blend of the present invention is a Hi test paraffin wax which provide relatively high melting point properties and is sold under the produc name of "Paraffin Wax Cede 1087" by Boler Petroleum Company, Wayne Pennsylvani .

While the Hi test paraffin has been noted to have a meltin point lying between 135 to 150°F, this temperature range is merel one vhich has been found most suitable for the blend of the presen invention. It should be noted therefore that the higher temperatur ranges are better for purposes of application although the cost the paraffin increases with a concomitant increase in the cost the blend. The -temperature range for the melting point of the test paraffin should be based en the end use of the product, but fo coating and for laminating paper products such as kraf paper, kra paper to paper, kraft liner board to paper and paper to paper, a in the present invention, the temperatures specified above are quit

^" appropriate.

Also present in the composition will be a modifying hydrocarbon resin. The flaked, solid resins produced mainly frcm aromatic monomers are suggested for use in the present invention. The resin color is not important; consequently a low-cost resin may be utilized. The material functions as a tackifier and with the paraffin wax serves to wet out large proportions of an inert filler which is used in the presently disclosed blend. The inert filler is an ultra-fine ground inert inorganic filler material and will be more fully described, infra. The hydrocarbon resin will normally be present as from 10 to 30 parts by weight of the composition and preferably about 16-20 parts by weight. One material which has been found to be particularly preferable is sold by Hercules, Inc., Wilmington, Delaware under the trade name of "Picccmer XX100 BHT" resin. A suitable substitute has also been found to be sold by Hercules Inc. under the trade names of "Terate 131" or "Terate 303." The modifying hydrocarbon resin serves several functions but should be primarily characterized as the type of resin which could be used to "wet-out" large proportions of pigments or completely encapsulate the ultra-fine inert inorganic filler material and which exhibits hot tack at elevated temperatures. The ability to wet-out and completely encapsulate the small particles of the inert filler allows a bond to be created between the other components of the blend so that the inert filler becomes an intricate component of the blend. This intricate blending or bonding allows high levels of the inert inorganic filler to be added to the blend of the hot melt adhesive thereby substantially lowering its cost while allowing it to still achieve a good vapor barrier.

Another component of the present invention will be an elastomeric copolymer which improves both the blend's tensile properties and cold crack resistance at low temperatures. Suitable for this use are ethylene-vinyl acetate (EVA) or ethylene-ethyl acrylate copolymers (EEA). These components will be present as 1 to 20 parts by weight and preferably 1 to 8 parts by weight of the ccmposition or blend in order to control the cost of the blend. The EVA or EEA adds to the elastomeric strength properties of the blend.

-3- Furthermore, the EVA/EEA components make the blends of the prese invention more viscous and more pressure sensitive at elevat temperatures. lastly, the blends are made more flexible and le crystalline through the use of these copolymers. Still another component and one of the components whi allows the present blend .to be cost effective and inexpensive the applications noted above, will be an ultra fine ground, iner inorganic filler. This will be present in amounts frcm 20 to 85 par by weight and preferably, in order to sharply reduce blend cost, to 85 parts by weight. A material which has been found to satisfactory as the inert, inorganic filler material is ultra fi ground limestone or calcium carbonate. The ultra fine grou limestone preferably should have a residue of less than or equal .01% on a 325 mesh screen as measured using the testing method defin in ASIM D1199. Suitable substitutes for the calcium carbonate m be selected frcm the group consisting essentially of ultra fine grou clay, glass, perlite, other carbonates and silicas.

Preferably, another major component which may form a pa of the present invention is a microcrystalline paraffin wax or da micro wax which is less crystalline than the Hi test paraffin a tends to make the blends of the present invention more plastic, le brittle, more suitable for laminating as its proportion increas and lowers the cold crack temperature of the blends. When the amou of paraffin wax is reduced, the amount of micro wax used may increased proportionally. Adhesive properties for laminating increa in the present invention as the amount of micro wax increases a the amount of paraffin wax decreases. A variety of useful dark mic waxes are available cαimercially but a dark micro wax which has be found suitable in the present invention is sold under the produ name of "PS050" by Moore and Monger, Inc., Fairfield, Connecticu Normally, dark micro wax may be present up to about 25 parts by weig and nominally about 5 parts by weight.

The hot melt adhesive composition or blend of the prese -invention remains stable with the additions of 20 to 50 parts p

millions of an antioxidant such as EOT at temperatures on the order of 200°F to 350°F for extended periods of time that are substantially longer than 72 hours. The material is not tacky or adherent after application and cooling and can be described as a hard material. However, it can be readily reactivated by heating the substrate. Thus, it is ideally suited as an adhesive for roll goods • since it is applied hot,, cooled to form a hardened material prior to rolling and the rolled material can be shipped and stored easily for indefinite periods of time and be readily reactivated by the end user at the appropriate time without blocking.

Also, the hot melt adhesive generates no objectionable or harmful quantities of smoke. The hot melt composition also allows bonded paper products to be reclaimed by a simple process in which the products are recycled in a beater box and reused on a cylinder board machine. The blends of the present invention are less expensive than prior art adhesives of the hot irelt type (wherein good bonding and a good moisture vapor barrier are requirements) because of the high degree of filling utilizing the ultra-fine ground inert, inorganic fillers. The expense of the blends is also reduced through the use of inexpensive grades of modifying hydrocarbon resins and micro- crystalline wax.

The blend, when used as a coating on substrates, acts as a moisture barrier and has excellent elastcmeric cohesive properties such as tensile strength, shear strength, etc. The blend also exhibits a good moisture vapor transmission ratio (MVTR) in part because the Hi test paraffin is rejected or exuded from the exposed surface layer of the blend when the blend, used as a coating, cools. As is well known, wax itself provides a good moisture barrier so that when the blend is cooled, the Hi test paraffin is exuded frcm the coating and provides an additional coating. This exudation phenomenon takes place each time the blend is melted and subsequently cooled. The exudation of the Hi test paraffin wax takes place despite the fact that the blend is highly filled with an ultra-fine ground inert

inorganic material. This is apparently due to the feet that t modifying hydrocarbon resin which encapsulates the filler materi becomes less miscible with paraffin as the blend temperature drops This unique blend of wax, resin and elastomer copolymer th effectively wets out the filler while simultaneously achieving desir blend properties.

Finally, the adhesive blend is blendable at a temperatu of about 315°F and can be applied in manufacture over a temperatu range of 200°F to 400°F by conventional hot melt coati techniques. Application of the hot melt adhesive to sheets such facing substrates and the like can be accomplished by convention slot coaters vjhich form a thin continuous film of adhesive on moving sheet of substrate. Most preferably, the coating or adhesi is applied using a conventional doctored hot roll coater.

While the adhesive of the present invention may also applied in discrete units such as dots or strips to a substrate, will be understood that the material of this invention cannot, applied in discrete units, serve as a vapor barrier since there a voids between the discrete units. However, the blends still impa cold crack resistance, hot tack upon reactivation, and provide a l blend cost.

The following are four examples of particular combinatio of components that have worked well utilizing the concepts describ above. The components are listed as parts by weight.

Example 1 Component Parts

Hi Test Paraffin 15 "Piccα er XX100 EHT" ¹ 20 "Elvax 250" ² 5 "Camel Wite" ³ 60

1. "Piccomer XX100 BHT", a tradamarked proprietary product of Hercules Incorporated.

2. "Elvax 250", a trademarked proprietary product of E.I. duPcnt de Nemours & Co. 3. "Camel Wite", a ccπtnercial product of H.T. Campbell Sons'

Co.

Example 2

Component Parts

Hi Test Paraffin 15 "Piccomer XX100 BHT" 16

"Elvax 250" 4

"Camel Wite" 60

Dark Micro Wax 5

Exaiτple 3

Component Parts

Hi Test Para fin 15

"Terate 131" or Terate 303" ⁴ 16

"Elvax 250" 4 "Camel Wite" 60

Dark Micro Wax 5

4. "Terate 131" and "Terate 303" are trademarked proprietary products of Hercules Incorporated.

Example 4 Component Parts

Hi Test Paraffin 15

"Piccomer XXL00 BHT" 16

Union Carbide "(18%) EEA" ⁵ 4

"Camel Wite" 60 Dark Micro Wax 5

5. "(18%) EEA", a trademarked proprietary product of the Union Carbide Corporation

The products utilizing these formulations were applied t a foil/kraft facing material using cαxmercial coating equipment apply the adhesive as a coating spread across the facing sheet. T sheet containing the coating was rolled after the adhesive had αoole _ using conventinal rolling equipment. It was later found to be readil capable of being unrolled without any significant tearing or adhesi of the adhesive to adjacent layers of feeing. Thereafter, the unroll facing was applied to glass fiber thermal insulation by heating t facing to reactivate the hot melt adhesive and adhering the faci to the glass fiber while the adhesive was still hot. ΪSo subseque delamination occurred.

The blend illustrated as Example 1 was not as flexible the other examples due to the fact that Dark Micro wax was not prese which tends to allow the blends to be more flexible despite repeat flexure. Example 1 would thus not be as flexible after more tha one or two flexures as the other examples.

The blend illustrated as Example 2 is the preferred ble for laminating facing materials to building products and fiber glas insulations and has been found to be inexpensive, highly mixabl non-bloc3Lng at .storage temperatures of up to about 130°F, and ha an excellent MVTR. Furthermore, Example 2 has shown an ability accept and hold the inert filler material in suspension using onl low shear rate prcpellor type dispersers despite being highly filled.

Exaπple 3 illustrates that "Terate 131" or "Terate 303" m be substituted for "Piccomer XX100 BHT", which is used as the prefer modifying hydrocarbon resin in the present invention. Example 4 ten to illustrate the equivalence of an EEA formulation with the preferr EVA formulation of Example 2.