FIELD

This invention relates to friction-activated adhesive formulations and application devices (e.g., glue crayons) for such adhesive formulations.

BACKGROUND

The use of adhesives is commonplace. Commonly used adhesives are available as liquids, semisolid or stick forms, paste, or as solids which must be activated with water, heat, or a solvent for use. Many adhesives use one or more solvents, which, are subject to evaporation resulting in drying out of the composition rendering it unusable. Alternatively, there can be some type of curing mechanism after application to secure a bond.

Many adhesive materials require special storage conditions or packaging, both during distribution, sale, etc., and throughout service life. For example, conventional white glue and glue sticks must be kept tightly sealed or the solvent components thereof can escape, making the adhesive unusable for future applications.

Although solid adhesive sticks of friction-activated adhesive have been known for some time, they have not been sufficiently user-friendly.

Some solid adhesive sticks have poor writability, minimal tack, minimal open (bonding) time, and poor adhesion properties. Other solid adhesive sticks are difficult to apply to surfaces, sometimes requiring the adhesive to be applied to both surfaces being bonded, necessitating rubbing several times with a hard object to ensure bonding, sometimes requiring the use of very high pressures or temperatures to bond (well above what a child or person could apply by simply rubbing with their hand or finger).

U.S. Pat. No. 5,604,268 (Randen et al.) discloses a 100% solids friction-activated adhesive that typically contains a minimum of about 4 parts by weight of a “tackifying monomeric unit having a glass transition temperature (Tg) in the range of about 100° C.” (e.g., Tgin the range of 80° to 110° C.).

The need exists for better friction adhesive formulations that easily apply with minimal writing pressure, produce an even coat of adhesive, and offer both good initial tack and eventual permanence.

SUMMARY

The present invention provides novel friction-activated adhesive formulations that provide surprising improved performance. The present invention also provides application devices for applying such adhesive formulations.

In brief summary, the present invention provides glue crayons comprising semi-crystalline polymers, tackified semi-crystalline polymers, semi-crystalline polymers containing specific pendent macromeric units, semi-crystalline polymers containing high chain length alkyl monomers, semi-crystalline polymers containing both macromeric and high chain length alkyl groups, semi-crystalline polymers containing crystalline additives, and semi-crystalline polymers containing surfactants as described herein.

In some embodiments formulations of the invention are a solid thermoplastic friction-activated adhesive composition comprising, and in some embodiments consisting essentially of, the mixture of:(a) from about 50 to about 100 parts by weight per 100 parts by weight of adhesive composition of a semi-crystalline adhesive polymer and comprises:(1) from about 5 to about 96, typically preferably from about 5 to about 60, parts by weight per 100 parts by weight of adhesive polymer of at least one crystalline monomer having an alkyl carbon length of at least 16, typically up to no more than 50, carbon atoms;(2) from about 4 to about 70, typically preferably from about 12 to about 59, parts by weight per 100 parts by weight of adhesive polymer of at least one non-crystalline monomer having a homopolymer glass transition temperature (Tg) below about 80° C.;(3) 0 to about 70 parts by weight per 100 parts by weight of adhesive polymer of at least one waxy, soft monomer having an average pendant alkyl carbon length of at least 14, typically no more than 50, carbon atoms;(4) 0 to about 10, typically preferably from about 0.5 to about 3, parts by weight per 100 parts by weight of adhesive polymer of at least one monomer having acid or base functionality;(5) 0 to about 40, typically preferably from 0 to about 30, parts by weight per 100 parts by weight of adhesive polymer of at least one functional or non-functional macromer having a melting temperature (Tm) from about 40° C. to about 120° C.;(b) 0 to about 50, typically preferably from about 5 to about 40, parts by weight per 100 parts by weight of adhesive composition of at least one tackifier;(c) 0 to about 50 parts by weight per 100 parts by weight of adhesive composition at least one crystalline additive;(d) 0 to about 50 parts by weight per 100 parts by weight of adhesive composition of at least one filler;(e) 0 to about 30 parts by weight per 100 parts by weight of adhesive composition of at least one oil; and(f) 0 to about 50 parts by weight per 100 parts by weight of adhesive composition of at least one surfactant.

Adhesive formulations of the invention may be used in a variety of application devices. For instance, these adhesive formulations can be molded into the shape of a crayon (or other desired shape, e.g., typically suited for holding by hand), typically with a removable wrapper or covering, and used by hand to deposit effective quantities of adhesive composition onto a substrate. Adhesive formulations of the invention can also be filled into a container, similar to a conventional water-based glue stick (e.g., an outside tube with a progressively advancable elevator), or molded into a desired shape and then placed into an applicator (similar to a pencil style click eraser). These options allow for the best possible application experience for the consumer.

To use the adhesives of the invention, a mass of the adhesive, commonly configured in an application device such as is described herein or similar thereto, is rubbed against a desired adherend substrate.

The frictional heat generated during application melts the polymers in the adhesive formulation so as to result in transfer of adhesive from the adhesive body to the surface of the adherend, resulting in formation of a tacky adhesive deposit thereon. Functional glue crayons that are both writable and will deposit a fugitive, tacky adhesive can be prepared from the base semi-crystalline and the tackified semi-crystalline polymers. Functional glue crayons with improved temperature storage stability can be prepared from those semi-crystalline polymers containing the higher chain length alkyl groups and from those polymers containing the crystalline additives. Functional glue crayons with improved writability and improved temperature stability can be prepared from those semi-crystalline polymers containing the macromeric groups and more preferably from those semi-crystalline polymers which contain both the macromeric groups and the higher chain length alkyl groups. In addition specific crystalline additives can be added to the tackified semi-crystalline adhesives and the macromer semi-crystalline adhesives to obtain similar improved temperature stability. Glue crayons that are both functional and have higher temperature stabilities provide a significant improvement over the crayons in the background literature.

The invention also provides glue crayons comprising, and in some embodiments, consisting essentially of, such compositions. Such glue crayons offer excellent storage and handling stability.

Adhesives of the invention can be used in numerous formats, typically in the form of an adhesive crayon. Illustrative advantages of adhesives and glue crayons of the invention include long term stability, i.e., no tendency to dry out or cure over time, reduced tendency to wrinkle paper as compared to many commercial glue sticks and white glues, no requirement for a special applicator, and enhanced precision of adhesive delivery even by hand application.

Advantageously, glue crayons of the present invention form secure bonds but do not dry out or require barrier type packaging to prevent loss of components that could lead to detrimental product performance. Furthermore, with such properties, minimal and less wasteful packaging options are available. An additional benefit is the solid form of the stick which prevents dripping and spilling and accidental application, which is common with the current forms of liquid adhesive. Another advantage of glue crayons of the invention is that the properties of the composition are such that a youngster can readily draw or write with the glue crayon.

Glue crayons of present invention are particularly useful in school, home and office markets as a method to deliver a controlled quantity of an adhesive to a specific application site/area for light-duty, adhesion tasks with paper, cardboard, wood, craft materials, etc. The glue crayon formulations of the present invention provide an improvement over the art by providing good writability (easy application), good tackiness (finger tack), good instant adhesion (quick stick), good open time (time to form bond), and require low application pressures (simple rubbing with the hand or finger) to form a bond.

Other advantages of the present invention over many commercially available alternatives include: (1) no volatile organic solvent problems, such as flammability, toxicity and odor; (2) when not in use and in particular, uncapped, no dry out like the water-based glue sticks; (3) instant tack, that is, there is no waiting period for the adhesive to “dry” after application; (4) no paper substrate cockling that is sometimes seen with the aqueous based, glue stick adhesives; (5) no expensive containers required; and (6) ease of use by adults and children, alike.

A major distinction between the glue crayons disclosed in U.S. Pat. No. 5,604,268 (Randen et al.) and those of the invention relates to composition of the adhesive polymer, in particular, incorporation of a non-crystalline monomer there. The reference teaches that it is critical to that the adhesive polymer comprise at least one non-crystalline monomer with a homopolymer Tgin the range of about 100° C., i.e., from about 80° C. to about 110° C. Surprisingly, we have found that high performing glue crayons can be made without using such a component, using relatively lower Tgmaterials instead. That this is surprising is highlighted by the disclosure of the reference where such high Tgmonomer is taught to act as a tackifying monomer, increasing the overall Tgand modulus enough to provide decent adhesion. We have found that this can be achieved even without that component, so long as there is some non-crystalline component to disrupt the crystallinity provided by all the other monomers. By using such lower Tgmaterials instead, formulations of the invention can be made with reduced cost, and increased synthetic flexibility, with the final composition provide improved writability as compared to otherwise similar formulations in accordance with the teaching of the reference.

Key and Glossary

For the following defined terms, these definitions shall be applied, unless a different definition is given in the claims or elsewhere in this specification.

The term “crystalline monomer” means a monomer whose homopolymer has a melting temperature (Tm) of from about 45° C. to about 68° C.

The term “macromer” means a low molecular weight polymer which may or may not contain telechelic functionality.

The term “open time” is the time period that the applied adhesive remains tacky enough to form a bond with another substrate.

The term “polymer” includes polymers, copolymers (e.g., polymers formed using two or more different monomers), oligomers and combinations thereof, as well as polymers, oligomers, or copolymers that can be formed in a miscible blend by, for example, coextrusion or reaction, including transesterification. Both block and random copolymers are included, unless indicated otherwise.

The term “solid” means materials that are substantially self-supporting at room temperature (i.e., 20° C. to 25° C.) such that if left at rest they will retain their shape without deforming or flowing.

The term “tacky” means sticky to the touch.

The term “telechelic” means a polymer or prepolymer containing one or more function end groups that have the capacity for selective reaction to form bonds with another molecule and the functionality of a telechelic polymer or prepolymer is equal to the number of such end groups.

The term “waxy” means monomers whose homopolymer has a Tmfrom about 25 to about 44° C.

The term “writability” refers to the ease of deposition of the adhesive onto a substrate.

Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about”. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings of the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviations found in their respective testing measurements.

Weight percent, percent by weight, % by weight, and the like are synonyms that refer to the concentration of a substance as the weight of that substance divided by the weight of the composition or indicated component thereof and multiplied by 100.

The recitation of numerical ranges by endpoints includes all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5). As used in this specification and the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the content clearly dictates otherwise. Thus, for example, reference to a composition containing “a compound” includes a mixture of two or more compounds. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.

