Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-03-15
2004-10-05
Szekely, Peter A. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C525S205000, C525S209000, C525S212000, C525S218000, C525S221000, C428S346000, C428S349000, C428S352000, C428S354000, C428S3550AC
Reexamination Certificate
active
06800680
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to hot-melt adhesive compositions. In particular, hot-melt adhesive blends and methods for their preparation and use are taught by the present invention.
BACKGROUND OF THE INVENTION
Adhesives are often characterized by the form in which they are provided for application. Traditionally, adhesives have been provided in organic solvent for subsequent application. Such adhesives are applied to a substrate and the solvent is then removed. Hot-melt adhesives advantageously reduce or eliminate the use of organic solvents in adhesives and their processing. Hot-melt adhesive systems are essentially 100% solid systems. Usually, such systems have no more than about 5% organic solvents or water, more typically no more than about 3% organic solvents or water. Most typically, such systems are free of organic solvents and water. Advantageously, by reducing the use of organic solvents, special handling concerns associated therewith are also reduced.
Among hot-melt adhesive chemistries, (meth)acrylates (i.e., methacrylates and acrylates) are one of the most prominent. (Meth)acrylates have evolved as a preferred class of adhesives due to their clarity, permanence of properties over time, and versatility of adhesion, to name just a few of the their benefits.
Hot-melt adhesives have a sufficient viscosity upon melting, such that they can be hot-melt processed (e.g., applied to a substrate). By adjusting the processing temperature, the viscosity of the adhesive can be readily tailored for application. For high performance applications (i.e., those requiring relatively strong cohesion, such as shear holding strength), some method of increasing the cohesive strength of applied hot-melt adhesives is often needed (e.g., post-crosslinking or moisture-curing).
For example, energy sources, such as electron beam (e-beam) or ultraviolet (UV) radiation, are commonly used to crosslink adhesives after application. These methods, however, often require an additional processing step and, thus, result in decreased processing efficiency. Furthermore, e-beam is not always desired because it is expensive and can cause damage to some backings when the adhesive is used in a tape. Similarly, UV-radiation has its limitations as a crosslinking energy source. For example, UV-radiation is often not able to be used effectively for crosslinking relatively thick adhesives due to the need for UV-radiation to penetrate throughout the entire thickness of the adhesive. As such, certain fillers and pigments can not be used in adhesives when UV-crosslinking is used because they potentially interfere with penetration of UV-radiation therethrough.
One way to improve cohesive strength of an adhesive is by chemical crosslinking. Such crosslinking involves chemically bridging at least two polymer chains together through bonds (e.g., covalent and ionic bonds). To promote ionic crosslinking, ionic crosslinking agents have been explored. To date, most ionic crosslinking agents include inorganic metal additives. Further detail of particular chemically crosslinked adhesives is provided below.
For example, Japanese Laid-Open Patent Application (Kokai) 54-88,938 to Toyo Ink Mfg. KK discloses a hot-melt adhesive composition comprising a copolymer of a carboxylic acid and a (meth)acrylate and a polymer of an amine compound having an ethylenically unsaturated bond. The amine compounds are used individually or in combination of two or more thereof in a polymer obtained by polymerizing the amine compounds. The amine compound may also be copolymerized with monomers in the carboxylic acid/(meth)acrylate copolymer. It is stated, however, that in this situation, the kind and composition of the amine compound must be carefully controlled so that the resulting copolymer can have both good adhesive strength and good cohesive strength. Furthermore, the production process is liable to be complicated.
Everaerts et al. (U.S. Pat. No. 5,612,136) disclose adhesives comprising a crosslinked copolymer of certain (meth)acrylate esters, certain nitrogen containing basic monomers copolymerizable therewith, optional copolymerizable acidic monomer, and crosslinker.
Lohmann (PCT Publication No. WO 96/05813) teaches preparation of a pressure-sensitive adhesive film having a pressure-sensitive adhesive polyacrylate copolymer with at least 3 mole-% of co-polymerized acrylic acid or methacrylic acid, a polymer containing a basic amino group, and a plasticizer. Exemplified pressure-sensitive adhesives are prepared using organic solvents and coated out of an organic solvent-ethanol.
Guerin et al. (U.S. Pat. No. 4,152,189) disclose polyacrylic hot-melt adhesives prepared by blending from 5 to 95 parts by weight of a first copolymer with from 5 to 95 parts by weight of a second copolymer. Each of the copolymers comprises 0.5 to 15 parts by weight of an ethylenically unsaturated amine, carboxylic acid or sulfonic acid or mixtures thereof.
Desired hot-melt adhesives are those that have the ability to be tailored for a myriad of diverse applications. It is also desired that such hot-melt adhesives are able to meet cohesive strength requirements of certain applications without compromising processing efficiency or tailorability.
SUMMARY OF THE INVENTION
Hot-melt adhesives of the present invention comprise a blend of at least one acidic polymer and at least one basic polymer. Preferably, at least one of the acidic polymer and the basic polymer has hot-melt adhesive properties. Preferably, at least one of the acidic polymer and the basic polymer is a copolymer. Thermally reversible chemical crosslinks allow the adhesive to be easily hot-melt processed, but provide improved cohesive strength to the hot-melt adhesive after its application and cooling.
The acidic polymer is derived from at least one acidic monomer. Preferably, the acidic monomer is selected from ethylenically unsaturated carboxylic acids, ethylenically unsaturated sulfonic acids, ethylenically unsaturated phosphonic acids, and mixtures thereof. Due to their availability, particularly preferred acidic monomers are the ethylenically unsaturated carboxylic acids. When even stronger acids are desired, particularly preferred acidic monomers include the ethylenically unsaturated sulfonic acids and ethylenically unsaturated phosphonic acids.
Preferably, the acidic polymer is a copolymer derived from at least one acidic monomer and at least one non-acidic copolymerizable monomer. In particular embodiments, such acidic copolymers have hot-melt adhesive properties (e.g., pressure-sensitive hot-melt adhesive properties or heat-activatable hot-melt adhesive properties). Other monomers can be copolymerized with the acidic monomers (e.g., basic monomers, vinyl monomers, and (meth)acrylate monomers) as long as the acidic copolymer retains its acidity (i.e., it can still be titrated with a base). More preferably, however, the copolymerizable monomers are essentially free of basic monomers (i.e., the copolymerizable monomers include about 5 wt. % or less of basic monomers, but most preferably, the copolymerizable monomers are free of basic monomers).
Most preferably, the acidic polymer is an acidic (meth)acrylate copolymer. In this embodiment, the acidic (meth)acrylate copolymer is derived from at least one acidic monomer and at least one (meth)acrylate monomer selected from the group consisting of monofunctional unsaturated (meth)acrylate esters of non-tertiary alkyl alcohols, and mixtures thereof, the alkyl groups of which comprise from about 1 to about 20 carbon atoms, preferably about 1 to about 18 carbon atoms, such as those of Formula (I):
wherein R
1
is H or CH
3
, the latter corresponding to where the (meth)acrylate monomer is a methacrylate monomer, and R
2
is a linear, branched, aromatic, or cyclic hydrocarbon group.
The basic polymer is derived from at least one basic monomer. Preferred basic monomers are non-nucleophilic amine-functional monomers, such as those of Formula (II):
wherein
a is 0 or 1;
R is selected from H— and CH
3
—;
X is selected from —O— and —NH—;
Y
Everaerts Albert I.
Sherman Audrey A.
Stark Peter A.
3M Innovative Properties Company
Leon Andrew J.
Szekely Peter A.
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