WO1996017029A1

WO1996017029A1 - Hot-melt adhesive compositions

Info

Publication number: WO1996017029A1
Application number: PCT/US1995/015588
Authority: WO
Inventors: William H. Mann; Hugh Cummins; Larry Osterberger
Original assignee: Refac International, Ltd.
Priority date: 1994-12-02
Filing date: 1995-11-30
Publication date: 1996-06-06
Also published as: AU4412696A

Abstract

The compositions include a polyurethane composition component and at least one peptizing agent. The polyurethane component includes a mixture of at least one polyisocyanate, one or more hydroxyl terminated polyol, one or more chain extender, and one or more plasticizer. The peptizing agent reduces the viscosity of the polyurethane hot-melt adhesive composition for use in automated, high-volume operations.

Description

HOT-MELT ADHESIVE COMPOSITIONS

BACKGROUND OF THE INVENTION

1. Field of the Invention:

The present invention relates to hot-melt adhesive compositions and, more particularly, urethane hot-melt adhesive compositions and processes for making the same.

2. Description of the Prior Art: Hot-melt adhesive compositions are well known for use in rapid and efficient bonding of low-strength materials, such as in bookbinding, food cartons, side-seaming of cans, and miscellaneous packaging applications. Typically, hot-melt adhesive compositions are made from thermoplastic materials such as polyethylene, polyvinyl acetate, polyamides, hydrocarbon resins, as well as natural asphalts, bitumens, resinous materials, waxes, and the like. These materials are generally available in solid form, quickly melt upon heating, then set to form a firm bond upon cooling. Because hot-melt compositions can bond materials quickly, they are generally well-suited for use in certain automated operations. Applications for traditional hot-melt adhesive compositions are limited, however, due to their physical properties, primarily their relatively low temperature resistance and strength. Well known hot-melt adhesive compositions are not suitable for automated labeling operations in, for example, the beverage and juice industries which more frequently require labeling to withstand extreme processing, including hot-fill beverages, pasteurization, retort (boiling water environment), extreme cold environments, and the like. In addition to having extreme temperature and moisture resistance, adhesives used in labeling processes should also have high strength, and the ability to adhere to a wide variety of surfaces including aluminum, plastic, paper, glass, and the like. Moreover, it is not unusual for automated labeling operations in, for example, juice, beer, or soda bottling facilities, to apply between 500 and 800 labels per minute. The adhesives, therefore, should also have extremely low viscosities to allow for better flow and movement of the adhesive onto the container surface, thereby providing better adhesion of the label to the substrate, as well as enhanced processability in equipment such as roll coaters, gravure printing rolls for hot-melt materials, spray and fiberizing applicator heads, and the like.

A high temperature, high strength, hot-melt composition, and process for forming the same, is disclosed by Czerwinski et al., in U.S. Patent No. 4,608,418. The polyurethane hot-melt adhesive compositions disclosed include a polyurethane having at least one plasticizer reacted therein. The disclosed reaction mixture includes at least one isocyanate having a functionality less than 2, at least one long chain polyol, at least one chain extender, and at least one plasticizer. Although it is noted that the polyurethane hot-melt compositions could be applied in the molten state, when the compositions have a viscosity (Brookfield viscometer) of less than about 50,000 cps, preferably less than about 25,000 cps, the compositions are still too viscous to use in an automated, high volume, operation for the reasons noted above.

It is also noted that the polyurethane hot-melt compositions, as disclosed by Czerwinski et al., in U.S. Patent No. 4,608,418, provide advantages such as the ability to flow at relatively low temperatures of between about 250°F and about 450°F. In addition, it is stated that these compositions also provide high strength adhesion to many surfaces, stability at elevated temperatures, good heat resistance up to about 350°F, good elastomeric properties, low temperature flexibility, relatively good solvent resistance, good tear resistance, and good impact resistance. It is noted, however, that urethane hot-melt compositions have not been suitable for automated operations, due to their relatively high viscosities. As noted, this problem is most evident in high speed, high volume operations such as labeling, which require faster adhesive flow and movement in, for example, roll-fed systems. To date, all attempts to reduce the viscosity of a polyurethane hot-melt adhesive composition have resulted in reduced physical properties of the adhesive, including the adhesive performance (strength), tensile strength, and temperature resistance. These failed attempts to lower the urethane hot-melt adhesive's viscosity included adding lubricants, plasticizers, waxes and/or other low viscosity resins, and the like.

It is, therefore, an object of the present invention to provide hot-melt adhesive compositions which can be utilized in high speed, high volume automated operations. It is a further object of the present invention to provide hot-melt adhesive compositions which can be used in automated labeling operations in the beverage and juice industries which is subjected to hot-fill processing, pasteurization, retort, and/or extreme cold environments. It is another object of the present invention to provide polyurethane hot-melt adhesive compositions which have outstanding flow properties. It is -mother object of the present invention to provide polyurethane hot-melt adhesive compositions which have low viscosity, and high strength adhesion properties.

It is still a further object of the present invention to provide polyurethane hot-melt adhesive compositions which have outstanding flow and strength properties, in addition to stability at elevated temperatures, high tensile strength, low temperature flexibility, good solvent resistance, good tear resistance, and good impact resistance.

It is still a further object of the present invention to provide hot-melt adhesive compositions which provide high adhesive strength, low viscosity, low toxicity, little or no odor, and high temperature resistance within a temperature range of between about -40 °F to greater than 200 °F.

Summar of the Invention

Accordingly, the present invention is directed to hot-melt adhesive compositions which can be used in automated, high volume operations, with broad temperature resistance and high strength. The hot-melt adhesive compositions include a polyurethane composition and at least one peptizing agent.

The polyurethane composition component of the present invention is formed from a mixture of one or more polyisocyanate, one or more hydroxyl terminated polyol, one or more chain extender, and one or more plasticizer. These components are initially blended at relatively low temperatures, until the system temperature increases due to exotherm and, after the peak exotherm has been reached, the system is further heated while agitating.

In accordance with the present invention, a peptizing agent is added to the above polyurethane composition, either during the formation of the polyurethane, or during a second operation to the finished polyurethane. If added to the finished polyurethane composition, the peptizing agent is mixed in dry powder, or liquid, form to the urethane. The modified polyurethane can then be either extruded to more fully mix the ingredients in the molten state, or be melted and mixed within the urethane for a given period of time to form the modified hot-melt adhesive. The modified composition is then cooled, by any means known to those skilled in the art, particle reduced, or left in a cooled shape such as blocks or slates prior to packaging, shipping, and/or use.

The peptizing agent, used to modify a standard polyurethane composition, is typically extruded into the composition in an amount up to about 10.0 percent by weight. The peptizing agent, or peptizer, is typically a sulfonated petroleum product and/or mineral oil. It has been found that the present modified polyurethane hot-melt adhesive compositions can be optimally used in high temperature environments, of up to about 350°F, in label processing bottling operations, including hot-fill, pasteurization, and other applications where temperature -4- resistance, either hot or cold, is critical. The present compositions are 100 percent solid thermoplastic urethane hot-melt adhesives that have low enough viscosity to be used in automatic labeling operations. Moreover, the compositions have maintained sufficient physical properties to withstand the rigors of pasteurization and hot-fill processes commonly used in the beverage industry. The adhesives of the present application can also be used outside of the beverage industry in, for example, labeling of aerosol containers and general food containers or packages due to the adhesive's outstanding physical properties. The adhesives can be used to label a wide variety of container sizes and shapes, using a wide variety of label materials, including shrink-film materials, such a polyvinyl chloride and polypropelene. Other objects and features of the present invention will become apparent from the following detailed description.

Detailed Description of the Invention

The present invention is directed to thermoplastic, hot-melt adhesive compositions, and the method of manufacturing the compositions, which include a polyurethane composition and at least one peptizing agent.

The polyurethane composition components of the present invention typically include a mixture of one or more polyisocyanates, one or more hydroxyl terminated polyol, one or more chain extender, and one or more plasticizer. Representative urethane compositions, components thereof, and methods of forming the same, are disclosed by Czerwinski et al., in U.S. Patent No. 4,608,418, and are incorporated herein by reference.

Polyurethanes are well known thermoplastic materials which are obtained by the reaction of diisocyanate with a polyol, or with a combination of a polyol and a short-chain glycol extender. The polyols can be based on polyethers, polyesters, or a combination of both. The physical properties of polyurethanes are derived from their molecular structure and are determined by the choice of building blocks, as well as the atomic interaction between the chains. For example, th melt viscosity depends upon the average molecular weight of the polyurethane, and is influence by chain length and branching. Thermoplastic polyurethanes are viscoelastic, as they behave lik a glassy, brittle solid, an elastic rubber, or a viscous liquid, depending upon the temperature and time scale of measurement.

The polyurethane compositions of the present invention are based on essentially stoichiometric amounts of a diisocyanate having a functionality of 2.2 or less. If the functionality exceeds 2.2, a less preferred thermosetting material results. A wide variety of polyisocyanate reactants can be used in the present compositions, including aromatic, aliphatic, cycloaliphatic, or aralkyl polyisocyanates. It is noted that toluene diisocyanate (TDI), and 4,4-diphenyl methane diisocyanate (MDI) are the most widely used isocyanates in the manufacture of urethane polymers. Of these, it is most preferred to use an MDI, such as

Mondur® XP 744, a polyisocyanate prepolymer based on MDI (a registered trademark of Miles, Inc., Pittsburgh, PA). Other commercial materials of this type include, for example, Isonate® 143L MDI (a registered trademark of Upjohn Company, Kalamazoo, MI).

In addition to the polyisocyanate, as noted above, either polyether polyols or polyester polyols are used in the polyurethane composition. Relatively high molecular weight, substantially linear polyhydroxyl compounds, are preferred. The molecular weight is typically between about 500 and about 5,000; most preferably, between about 800 and about 3,000. As noted in U.S. Patent No. 4,608,418, mixtures of the relatively high molecular weight polyhydroxyl compounds may also be used in polyurethane compositions. An example of a polyol useful in the present polyurethane compositions is Tone® polyester polyol, having a molecular weight of between about 530 and about 3,000 (a registered trademark of Union Carbide Chemicals and Plastics Co., Inc., Danbury, CT).

In addition to the polyols, polyurethane compositions may also include chain extending agents. These compounds carry, per molecule, at least two active hydrogen atoms, and preferably have a molecular weight of between about 50 and about 500. These compounds react with the isocyanate groups of the prepolymer, formed between the polyol and isocyanate, and build up high molecular weight polyurethanes by linking several isocyanate prepolymer molecules. The chain extending agents are well known to those in the art and include, for example, ethylene glycol, propanediol, butanediol, hexanediol, and the like. The compositions of the present invention can use almost any readily available chain extending agent. Typically, the chain extender is 1,4 butanediol, for example, available from BASF Chemicals, Parsippany, NJ.

A plasticizer is also typically added to the polyurethane composition, to both facilitate processing and increase the flexibility and toughness of the final product by internal modification of the polymer molecule. Plasticizers are well known, and include nonvolatile organic liquids and low-melting solids, for example, phthalate, adipate, sebacate esters, and benzoate esters, polyols, such as ethylene glycol and its derivatives, tricresyl phosphate, caster oil, and the like. A preferred plasticizer is Benzoflex® benzoate ester plasticizer (a registered trademark of Velsicol Chemical Corporation, Rosemont, IL).

Other useful thermoplastic materials may be added to the above-noted polyurethane compositions to impart any of a variety of characteristics including color, additional flexibility, rigidity, adhesive properties, and the like. These materials include phenolic resins, acrylic resins, epoxy resins, rosins, and the like. Typically, these thermoplastic resin materials can be dissolved in the plasticizer, and be blended into the polyurethane composition. One such material, Sylvatac® resin, a glycerol ester of highly stable monomeric rosin acids, has been used as a tackifier with more traditional hot-melt adhesives in packaging and book binding applications (a registered trademark of Arizona Chemical Company, Panama City, FL).

As noted in U.S. Patent No. 4,608,418, a catalyst may or may not be used in the polyurethane compositions. Catalysts, such as tertiary amines, are typically used in the polyurethane formation process by, for example, adjusting the reaction speed and/or temperatures. Lastly, it is noted that the formulation of the polyurethane composition component used in the present hot-melt adhesives can be performed in either a batch or continuous process.

It has been found that standard polyurethane compositions, based upon the above-noted components, have a molten state viscosity that is too high for practical application in, for example, automated operations such as a roll-fed labeler. As noted above, an adhesive which can be applied by a labeler to a container, such as an aluminum beer can, that would allow for the label to be transferred onto the can before filling and be able to withstand a pasteurization process (with temperatures up to between about 170°F and 180°F) is desired. Moreover, it is desired for an adhesive to be used in, for example, heat shrinking labeling applications, wherein the adhesive has sufficient heat resistant properties to hold the label material (typically made from polypropelene, polyethylene, polyvinyl chloride, polystyrene, and the like) in place while further operations are performed on the film label. As noted, currently available hot-melt adhesives fail in one or more of the desired properties, by having insufficient temperature resistance (hot or cold), and/or not having a low enough viscosity to allow their use in automated, high volume, operations.

A polyurethane hot-melt adhesive composition, as referred to above, and disclosed in U.S. Patent No. 4,608,418 (which is incorporated by reference), has been successful in securing labels on containers prior to filling with hot material up to about 250°F. The labeled container has then been cooled after filling, as is commonly found in the industry. Moreover, the polyurethane -7- hot-melt adhesive compositions have been used in pasteurization processes, wherein the labeled container passes through the entire process, from filling at about 34 °F to pasteurization temperatures as high as about 180°F, to cooling to room temperature. Pasteurization times and temperatures vary, but the polyurethane hot-melt adhesive compositions have passed the extremes found in the industry.

The polyurethane hot-melt adhesive compositions disclosed have been modified for use in high volume, in automated operations. The polyurethane hot-melt adhesive compositions of the present invention incorporate a small weight percent of a peptizing agent to the compositions to modify the adhesive's Theological properties. These materials, normally associated with the rubber processing industry, typically reduce the viscosity of polyurethane adhesive compositions and allow the adhesive to more readily flow, allowing the adhesive to be applied in automated labeling operations in a controlled manner, without sacrificing the physical and adhesive properties of the polyurethane. Peptizing agents, or peptizers, are most typically used with other rubber-processing chemicals to reduce the viscosity of rubber and permit easier processing thereof. When milled into rubber, they cause chain scission, with a consequent lowering of the molecular weight. These materials include sulfonated petroleum products and mineral oils, typically in an inert carrier. Petroleum sulfonates are available in liquid form and as dry powders. In particular, these forms are available as Leegen® rubber plasticizer (powder), and Vanplast® anti-corrosive agent (liquid) (registered trademarks of R.T. Vanderbilt Company, Inc., Norwalk, CT). Typically, up to about 10.0 percent, by weight, of the peptizing agent can be added to the polyurethane hot-melt adhesive composition to reduce the viscosity within the range necessary for use in automated systems which may include, for example, roll coaters, gravure printing rolls for hot-melt materials, spray and fiberizing applicator heads, and the like. It has not been determined whether more than about 10.0 percent, by weight, of the peptizer has any detrimental effects on the adhesive's physical properties. Preferably, however, the peptizing agent makes up between about 0.25 and about 2.0 percent, by weight, of the compositions of the present invention. As noted, the peptizing agents can be added to the polyurethane hot-melt adhesive compositions while they are in the molten state, either before or after all of the components have been blended together. Alternatively, the peptizing agent can be added as a dry blend (or mix) with the polyurethane hot-melt adhesive in particle reduced form, and then be extruded to fully mix the ingredients in the molten state. The finished modified compositions are then cooled, by means known in the art. They can then be particle reduced by, for example, -8- pelletizing, prill manufacturing, cryogenic granulating, and the like, before packaging, shipment, and/or use.

The present invention will be further illustrated by the following example which is intended to be illustrative in nature and is not to be construed as limiting the scope of the invention.

Example

The preparation and performance of the thermoplastic, hot-melt adhesive compositions of the present invention were examined.

The compositions were formulated by first charging a moisture and air-free reactor with a plasticizer and a polyol, Benzoflex® plasticizer (Velsicol Chemical), and TONE® 260 polyester polyol (Union Carbide Chemicals). Then, under a nitrogen blanket, the components were heated to about 380 °F. A thermoplastic resin material, such as Sylvatac® 80N tackifying resin (Arizona Chemical), and a chain extender (1,4 butanediol) were then added to the reactor. When the process temperature reached about 200 °F, a polyisocyanate, Mondur® XP 744 MDI (Miles, Inc.), was added and the heater temperature was raised to about 480 °F. At this point, an exotherm raised the process temperature from about 200 °F to about 320 °F. When the process temperature reached about 350°F, the temperature setting of the heater was reduced to about 410°F, and the reaction temperature was maintained at a temperature of between about 350°F to about 360°F for a period of about 3 hours. The viscosity of the polyurethane composition was monitored, and a discharge viscosity was measured to be in the range of between about 5,000 and about 6,000 cps. The composition was then modified by adding a peptizing agent (powder), Leegen® rubber plasticizer (R.T. Vanderbilt). The peptizing agent was mixed with the polyurethane composition, and the blend was extruded in an extruder to further fully mix the ingredients in the molten state. The modified hot-melt adhesive composition was then cooled.

A variety of formulations were produced to evaluate the effect of the addition of the peptizing agent on the polyurethane composition. Table I lists the components of the composition, by weight percent. The viscosity of each formulation was measured, and the results are also presented in Table I. Table I

II III IV YI

wt. % wt. % wt, % wt, % wt, % wt. %

1 ,4 Butanediol 5.83 5.78 5.5 6.12 6.06 5.77

Benzoflex® 988SG 21.85 21.63 20.61 18.06 17.89 17.03

Mondur® XP744 27.87 27.59 26.29 29.22 28.94 27.56

Sylvatac® 80N 12.41 12.28 11.7 13.01 12.88 12.27

Tone® 0260 32.04 31.71 30.22 33.59 33.27 31.69

Leegen® 1.01 0.96 0.96 0.92

Benzoflex® 352 4.72 4.76

Viscosity (cps) 2000 1000 900 3000 1500 1300

Based on the above results, it is apparent that the addition of a peptizing agent (Leegen® rubber plasticizer) significantly reduces the viscosity of a polyurethane hot-melt adhesive composition. Formulations II, III, V, and VI, which included between about 0.92 and about 1.01 percent of the peptizing agent, by weight, had viscosities reduced by up to 50%, and flow properties enhanced, without lessening their adhesive properties (particularly tensile strength and temperature resistance). This combination of properties in the modified compositions makes them particularly suitable for automated, high-volume labeling processes where the labeled container will be exposed to high temperature environments (for example, hot-filling, and/or pasteurization).

It was also noted that the viscosity-lowering effect of the peptizing agent can be enhanced by the further addition of a plasticizer (Benzoflex® 352 plasticizer), as in formulations III and VI. The use of a plasticizer, such as Benzoflex® 352 plasticizer, without a peptizing agent was also evaluated; and, although the viscosities of polyurethane hot-melt adhesive compositions were reduced, the physical properties (particularly, the tensile strength and melt range of the adhesives) of the compositions were also lowered. It is, therefore, preferred to include a peptizing agent (with or without an additional plasticizer) in the polyurethane hot-melt adhesive compositions to provide outstanding flow and strength properties.

Although particular embodiments of the invention have been described in detail for purposes of illustration, various modifications may be made without departing from the spirit and scope of the invention. For example, addition of the peptizing agent can occur during the processing of the polyurethane composition. In addition, other types of, or additional, additives may be used in the polyurethane composition component of the invention. The modified hot-melt adhesive compositions can be used in a wide variety of processing equipment applications. Also, the peptizing agents of the present invention may be used with other thermoplastic adhesives, other thermosetting adhesives, and other thermoplastic urethane adhesives. Accordingly, the invention is not to be limited except as by the appended claims.

Claims

1. A thermoplastic, hot-melt adhesive composition, comprising: a polyurethane composition; and at least one peptizing agent.

2. The composition as claimed in claim 1, wherein the polyurethane composition includes one or more polyisocyanate.

3. The composition as claimed in claim 2, wherein the polyisocyanate is 4,4-diphenyl methane diisocyanate.

4. The composition as claimed in claim 2, wherein the polyurethane composition further includes one or more hydroxyl terminated polyol.

5. The composition as claimed in claim 4, wherein the polyol is a polyether polyol.

6. The composition as claimed in claim 4, wherein the polyol is a polyester polyol.

7. The composition as claimed in claim 6, wherein the polyester polyol has a molecular weight of between about 500 and about 5,000.

8. The composition as claimed in claim 4, wherein the polyurethane composition further includes one or more chain extender.

9. The composition as claimed in claim 8, wherein the chain extender is 1 ,4 butanediol.

10. The composition as claimed in claim 8, wherein the polyurethane composition further includes one or more plasticizer.

1 1. The composition as claimed in claim 1 , wherein the peptizing agent is selected from the group consisting of sulfonated mineral oil, sulfonated petroleum products, and mixtures thereof.

12. The composition as claimed in claim 1, wherein the composition has a viscosity of less than about 2000 cps.

13. The composition as claimed in claim 12, wherein the composition has a viscosity of between about 900 cps and about 1500 cps.