Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
2000-12-20
2003-03-25
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S3550EP, C428S349000, C428S352000, C428S041500, C428S041800, C428S042300, C525S451000, C526S317100, C526S318000, C526S318300, C526S328000, C526S329700, C526S931000, C156S330000
Reexamination Certificate
active
06537659
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to acidic polymer-based PSAs that are thermosettable to provide semi-structural or structural adhesives.
BACKGROUND OF THE INVENTION
When bonding substrates for applications that require particularly high bond strength, it may be desirable to use a PSA (PSA) that can be cured to form a high strength bond, or semi-structural or structural bond. Typically, such PSAs are referred to as thermosettable PSAs. An advantage of thermosettable PSAs is that they can be used to bond surfaces together without the need to clamp, or otherwise hold, the substrates together until the PSA is cured.
For example, see U.S. Pat. No. 5,593,759 (Vargas et al.), where a tape constructed of a core layer of structural adhesive is coated with PSA layers (e.g., acrylic PSAs). The multi-layer bonding tape construction can then be adhesively applied between parts to be bonded. The tape is then cured to form a structural bond. The core layer can be made of various different structural adhesives, such as a partially cured, B-stage structural adhesives or blends of an epoxy-containing material with an acrylate ester resin and hardener. Examples of hardeners include: trichloride amine complexes, boron trifluoride complexes, monoethyl amine, blocked amines, or dicyandiamide and the like. The hardeners are preferably incompatible with the resin at room temperature. It is not always desirable, however, to use a multi-layer adhesive when bonding. Multi-layer adhesives, such as those comprising a core layer coated with PSA layers, often require more complicated preparation procedures as compared to, for example, a single layer bonding adhesive.
Other adhesive systems relying on a combination of epoxy-containing materials and acrylate resins are also known. Similarly, these systems employ a curative, such as an amine-containing compound, which is typically referred to as an epoxy curative. See, for example, PCT Publication Number WO 96/21,704 (Minnesota Mining and Manufacturing Co.) and U.S. Pat. Nos. 4,612,209 (Forgo et al.); 5,011,560 (Nakai et al.); 5,086,088 (Kitano et al.); 5,686,509 (Nakayama et al.); and 5,883,193 (Karim).
It may not always be desirable to use bonding adhesives that include epoxy-containing materials, however. Epoxy-based adhesive systems (i.e., those systems containing epoxy-containing materials as the major component of the adhesive) generally rapidly lose their bond strength at temperatures above their glass transition temperatures as compared to, for example, (meth)acrylate-based adhesive systems (i.e., those systems containing (meth)acrylates as the major component of the adhesive). Furthermore, known adhesive systems comprising epoxy-containing materials are oftentimes brittle and, thus, may prove to be particularly difficult, for example, in effectively bonding irregular (e.g., nonplanar) surfaces or in being used in those applications where a certain degree of flexibility is required, or desired, in the resulting bond. For example, adhesives used in vibration damping articles may benefit from a certain degree of flexibility so as to allow the adhesive to absorb vibrations incident on the article. Other known epoxy-based adhesive systems may also lack moisture resistance, impact strength, or storage stability desired, or required, for a particular application.
As alternatives to epoxy-based adhesive systems, certain references describe crosslinking of (meth)acrylate polymers using amine-containing compounds similar to those described for use in epoxy-based adhesive systems. For example, U.S. Pat. No. 2,925,174 (Stow) describes crosslinking acrylate PSAs using certain polyfunctional polymeric amines. However, the crosslinked compositions are PSAs, which do not have enough bond strength for applications requiring semi-structural or structural bond strengths.
U.S. Pat. No. 5,596,039 (Oishi et al.) describes the use of certain diguanamines prepared from dicyandiamides for thermosetting compositions, including acrylic resins. The resins are purportedly useful in adhesive applications.
U.S. Pat. No. 4,404,246 (Charbonneau et al.) describes a PSA tape having an adhesive layer of a copolymer of alkyl acrylate and an acid, and a small amount of a lower-alkoxylated amino formaldehyde condensate as a latent crosslinking agent. After the tape has been applied and heated to crosslink the adhesive, the resultant bonds have outstanding resistance to peel forces combined with good resistance to shear forces, especially at elevated temperatures.
However, the lower-alkoxylated amino formaldehyde described in this reference contains tertiary amines and the lower-alkoxylated amino formaldehyde is used in amounts within the range of about 0.1-0.8% by weight of the copolymer. Furthermore, the adhesive must be heated moderately, such as at 120° C. for 30 minutes, to crosslink (i.e., cure) the adhesive. The more heat that is required during a process, however, the more energy must be expended, resulting in processes that take longer and cost more.
Similarly, see U.S. Pat. No. 4,396,675 (Groff). Again, the alkoxylated crosslinking agent contains tertiary amines. The crosslinking agent is used in amounts of about 0.1 to about 10 percent by weight of the copolymer, preferably 1 to 5 percent. Groff states that amounts above 10 percent would not enhance crosslinking and might detract from the adhesive properties of the tape.
Depending on the application and type of substrate being bonded, the use of moderate to high temperatures for curing the adhesive may also be problematic. This may be the case, for example, when heat-sensitive substrates are to be bonded. Heat-sensitive substrates include relatively low softening point or melting temperature plastics, such as polycarbonate, polyethylene terephthalate polyester, polymethyl methacrylate, and certain polyolefins, as well as substrates, such as electronic circuit boards, having heat-sensitive components attached thereto.
Other compositions comprising (meth)acrylates and amine-containing compounds are also known. For example, aqueous coating compositions comprising dicyandiamide dissolved in an aqueous solution of a salt of a copolymer of an unsaturated carboxylic acid monomer and a hydroxylalkyl (meth)acrylate monomer are disclosed in U.S. Pat. No. 4,045,399 (Suzuki et al.). Also see German Patent Publication Numbers DE 3634780 and DE 3726956 (both to Kruger). Furthermore, see Czechoslovakian Patent Number 227 514. However, when drying the aqueous coating compositions to remove water from the system, the coating compositions may become cured. Therefore, intermediate thermosettable adhesives may not be possible when using such aqueous systems and coating methods described therein. Furthermore, types and amounts of components used in aqueous systems must be carefully selected so as to be soluble in water, limiting formulation latitude.
Vulcanizable acrylic rubber compounds comprising dicyandiamide are described in Japanese Patent Publication Numbers JP 61-076542; JP 61-278554; and JP 61-1103957. Powder coating compositions comprising acrylic polymers and dicyandiamide are described in Japanese Patent Publication Number 51-057723.
Alternative thermosettable PSAs are desired. Such compositions would be particularly useful for bonding substrates without the need to clamp, or otherwise hold, the substrates together until the PSA is cured. It would also be desirable for the PSAs to be capable of being cured to form high bond strength adhesives, such as semi-structural or structural bond adhesives.
SUMMARY OF THE INVENTION
Thermosettable PSA (PSA) compositions of the invention comprise a major proportion of the adhesive component of at least one acidic polymer and at least one amine-containing compound capable of reacting with acidic functional groups on the acidic polymer to cure the thermosettable PSA composition into a thermoset adhesive. The thermosettable PSA compositions are particularly useful for forming semi-structural or structural bonds.
In one embodiment, the thermosettable PSA composition comprise
Karim Naimul
Khandpur Ashish Kumar
Salnikov Dmitriy
3M Innovative Properties Company
Dawson Robert
Keehan Christopher
Pribnow Scott R.
LandOfFree
Acidic polymer-based thermosettable PSAs, methods of their... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Acidic polymer-based thermosettable PSAs, methods of their..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Acidic polymer-based thermosettable PSAs, methods of their... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3026206