Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-05-08
2003-01-28
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
active
06512043
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates generally to structural acrylic/methacrylic adhesives and more particularly to acrylic/methacrylic adhesives used for construction purposes or for the assembly of large objects.
Many products, ranging from car parts to boats to truck cabs and other structures are made by bonding various sheets (panels) of material, such as fiberglass, with adhesives. For example, U.S. Pat. Nos. 4,942,201 and 4,714,730, assigned to ITW of Glenview, Ill., the contents of which are incorporated herein by reference, describe adhesives made with methacrylate and acrylate based adhesives together with various other additives and ingredients for use in the construction of large objects.
Available adhesives have exhibited certain inadequacies in their potential application to various construction and manufacturing methods. For example, it is often desirable to apply the adhesive to a first surface of a substrate, for example a panel, and permit the adhesive to remain “open” and uncured for working times longer than one hour or more before the panel is assembled to another structure. “Working time” is thus the time where the adhesive compound can effectively be applied to one or more substrate. For example, during the construction of large boats, panels to be assembled could be 30 feet or longer and the bead, typically applied in a serpentine fashion, would be even longer. It is therefore necessary for the beginning of the bead to remain workable until it is time to assemble the panel, even if it takes a considerable amount of time to finish applying the bead and position the panel. This period of time, between the time when the adhesive is applied to a first substrate and when that first substrate can be pressed to a second substrate and positioned in place, to assemble the first substrate to the second substrate, will be referred to herein as “working time”.
It is also desirable for adhesives to exhibit excellent cure properties, even when applied to cross sections well above {fraction (1/16)} of an inch. For example, when large panels are fastened to structures with adhesive, the gap between the two members can vary in thickness. Gaps in a pair of adhered 20-50 foot panels can be 1 inch or more. Adhesives that are applied to this thickness generate considerable heat while curing. Adhesives with short cure times also can generate considerable heat. However, it is undesirable for the adhesive to generate so much heat that it boils during curing, because bubbles can form, thereby reducing structural integrity of the bonded assembly and composition.
It is also desirable for adhesives to cure over a wide range of temperatures, including cold temperatures below 65° F. and hot temperatures over 80 or 90° F., such as 95° F., that one might experience when building boats in southern Florida. Thus, it is desirable for adhesive to cure at cold temperatures, yet remain open for sufficiently long times at hot temperatures.
Available adhesives have exhibited other inadequacies. For example, many state of the art adhesives can “slide” down a vertical or inclined surface or in the case of overhanging overhead surfaces, fall off. This phenomenon is particularly troublesome on certain substrates, when a long working time is needed or when a large bead is run. This sliding phenomenon has interfered with the use of methacrylate and acrylate adhesives for structural bonding of large members in vertical or overhanging positions, particularly when adhering long objects and panels formed of glass fiber reinforced unsaturated polyester type materials. This can interfere with construction times and can in certain instances, and make the use of adhesives undesirable or impossible without complicating the manufacturing process or varying materials of construction.
Accordingly, it is desirable to provide a new adhesive which overcomes the drawbacks of the prior art.
SUMMARY OF THE INVENTION
Generally speaking, in accordance with the invention, a two-part adhesive comprising an adhesive part and an activator part is provided. The adhesive part comprises acrylic and/or methacrylic monomers, and advantageously further comprises toughening agents, impact modifiers including graft co-polymer (core-shell and non core-shell) impact modifiers, carboxylic acids, reducing agents, inhibitors, retarders and chain transfer agents. The activator part comprises initiators, a carrier and thickening agents. Advantageous reducing agent components include anilines, toluidines, substituted anilines and substituted toluidines. These reducing agents are particularly useful when used in conjunction with a peroxide initiator, such as a dibenzoyl peroxide initiator. Adhesives in accordance with the invention can achieve working times of 40 to 80 minutes or longer at 95° F.
Accordingly, it is an object of the invention to provide improved adhesives having advantageous properties and performance characteristics.
Other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the constructions, compositions and articles which possess the characteristics, properties and relations of elements, all as exemplified in the detailed disclosure hereinafter set forth.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention is directed to structural adhesive compositions that can be used in various bonding applications, which have long working times, non-sag performance and acceptably low slide, so that they can be used to adhere large objects in an inclined, vertical or even overhead configuration. The invention is also directed to adhesive compositions which do not exhibit boil problems, even when relatively large beads of up to one inch or more in cross sectional diameter are applied.
The invention results in part from maintaining an advantageous balance between elastomeric polymer toughening agents and core-shell structured polymer impact modifiers to provide a combination of a high bonding strength, high impact strength, high tensile strength and high elongation of the cured adhesive, to develop an adhesive with selected advantageous physical characteristics. Consideration of the solvating power of the materials can lead to improved resistance to sagging and sliding. Selection of materials with due consideration of boiling points and the cure profile can resolve problems associated with boiling during curing.
It is believed that sliding results from the solvating properties of an adhesive with the substrate to which it is applied. This can be particularly problematic when the substrate is a polymer material, such as glass fiber reinforced unsaturated polyester. Thus, by identifying and reducing or eliminating ingredients with a high solvating power, anti-sliding performance can be improved.
Boiling problems can be addressed by identifying and reducing or eliminating the amount of ingredients with low boiling points and substituting ingredients with higher boiling points, while regulating the maximum heat generated during cure, through proper selection and proportion of ingredients. Preferred embodiments of the invention comprise acrylic or methacrylic monomers and one or more of the ingredients set forth below in Table 1.
Adhesives are advantageously provided in a two-part system, comprising what can be referred to as an adhesive part, portion or component and an activator part, portion or component. The two components are combined prior to application and should be formulated to promote relatively long working times. Otherwise, the adhesive will harden before the full bead is applied for the two parts to be adhered in proper contacting relationship and proper adhesion might not be achieved.
A preferred composition of the adhesive portion of a two-part adhesive in connection with preferred embodiments of the invention, is set forth below in Table 1.
TABLE 1
Composition of Adhesive Part
Range, % by wt,
Component
Acceptable
Preferred
Most Preferred
(Meth)Acrylate monomer(s)
55-75
58-68
60-65
Carboxylic acid(s)
Gosiewski Donald
Wang Xiaobin
Cain Edward J.
Illinois Tool Works Inc.
Pitney Hardin Kipp & Szuch LLP
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