Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2001-08-31
2003-06-03
Foelak, Morton (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S178000
Reexamination Certificate
active
06573309
ABSTRACT:
This application claims priority from International application PCT/EP00/01474, filed Feb. 23, 2000, and German application DE 19909270.2, filed Mar. 3, 1999.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention pertains to reduced tack foamable compositions based on epoxy resins. More specifically, particular combinations of epoxy resins containing solid epoxy resins are utilized to obtain putties which are sufficiently low in surface tackiness to be readily handled, yet are pliable enough to be shaped to conform to non-planar surfaces.
2. Discussion of the Related Art
It is known that a number of industries, e.g., the automobile industry, require parts that are both strong and light-weight. One attempt to achieve this balance between strength and minimal weight provides for hollow metal parts. However, hollow metal parts are easily distorted. Accordingly, it is also known that the presence of structural foam in the cavities of the hollow parts can improve the strength and stiffness of such parts.
Generally, such foams comprise a thermosettable resin such as an epoxy resin, a blowing agent and a filler. Preferably, these foams have a density of about 20-40 lb/ft
3
(about 0.30 to about 0.65 g/cc) and are able to withstand heat in excess of 175° C., more preferably in excess of 200° C. Optional ingredients include accelerators, curing agents, processing aids, stabilizers, colorants, and UV absorbers.
Specific formulas for structural foam vary widely and are widely found. For example, U.S. Pat. No. 5,575,526 teaches several resin-based structural foams including Formula 2, which contains 54.5% EPON 828 epoxy resin, 7.5% HALOXY 62 epoxy diluent, 6.1% DER 732 flexible epoxy, 2.0% EXPANCEL 551DU blowing agent, 8.8% MICROS microspheres, 17.7% 3M K20 microspheres and 3.4% DI-CY dicyandiamide curing agent. U.S. Pat. No. 5,755,486 discloses thermally expandable resin-based materials containing, for example, epoxy resin, acrylonitrile-butadiene rubber, calcium carbonate, carbon black, fumed silica, glass spheres, curing agent, accelerator, and blowing agent. Structural foams such as, e.g., Terocore® (a product of Henkel Surface Technologies), are now used in a variety of industries.
One recurrent problem with many of the structural foam formulations of this type that have been developed to date has been their relatively high degree of tack.
In many of the end-use applications in which structural foams are employed, a desired quantity of the structural foam in its uncured, unfoamed state must be placed on or near the surface of a metal part. Said surface may be somewhat difficult to access due to its proximity to other surfaces, thus often requiring the foamable composition to be applied manually. It will typically be desirable to have the foamable composition be sufficiently pliable or dough-like in consistency so that it may be easily shaped and otherwise manipulated to approximately follow the contours of the surface to which it is being applied.
Certain known structural foam formulations provide excellent strength and other physical properties when foamed and cured, yet are somewhat difficult to work with due to their pronounced “stickiness” prior to curing. The uncured formulation thus often does not separate cleanly from the hands or gloves of the operator who is applying the formulation to the structural member or the like into which the formulation is to be incorporated as a composite. A similar problem exists where tools or other machinery are utilized in the application of the foamable formulation. Residue from the uncured formulation consequently tends to build up on the application instruments being used, requiring periodic disposal or cleaning. Besides wasting a portion of the foamable formulation, productivity suffers due to the cleaning time required. It would therefore be very desirable to modify the properties of such foamable compositions in order to lower the surface tackiness, without significantly affecting either the pliability of the composition or its performance when foamed and cured.
SUMMARY OF THE INVENTION
It has now been surprisingly discovered that the excessive tackiness problems encountered in previously known structural foam formulations based on liquid and/or semi-solid epoxy resins may be effectively alleviated through the use of solid epoxy resins. The dough or putty thereby obtained may stil be easily formed into any desired configuration, yet leaves little or no residue on the instruments (e.g., hands, gloves, tools) used for such manipulation. Reduced tack foamable compositions thus are provided which comprise one or more base epoxy resins selected from the group consisting of liquid epoxy resins and semi-solid epoxy resins, one or more blowing agents, and one or more curatives, and an amount of one or more solid epoxy resins effective to reduce the surface tackiness of the foamable composition as compared to the surface tackiness of an analogeous foamable composition which does not contain any solid epoxy resin. Such compositions when foamed and cured furnish structural foams having excellent physical properties, including high strength and heat resistance.
DETAILED DESCRIPTION OF THE INVENTION
Preferred foam formulations contain about 35 weight percent to about 85 weight percent total of epoxy resins, about 5 weight percent to about 60 weight percent of fillers (preferably, including about 5 weight percent to about 50 weight percent hollow glass microspheres), about 0.1 weight percent to about 5 weight percent of one or more blowing agents, and about 0.1 weight percent to about 10 weight percent of one or more curatives. The foamable composition may also contain varying amounts of other additives such as blowing agent accelerators (activators), adhesion promoters (coupling agents), toughening/flexibilizing agents, thixotropic/rheological control agents, colorants and/or stabilizers. It is particularly advantageous to select formulation components which, when mixed together, provide a foamable dough of putty-like consistency which can be readily molded or shaped into any desired configuration prior to foaming and curing. At the same time, the dough should not exhibit a significant degree of cold flow. That is, the dough should essentially retain its shape over an extended period of time at ambient temperatures.
DETAILED DESCRIPTION OF THE INVENTION
Selection of the epoxy resins to be utilized is critical to the present invention. As a base epoxy resin, one or more liquid and/or semi-solid epoxy resins are employed. One or more solid epoxy resins are combined with the base epoxy resin to modify the surface tack of the foamable composition thereby obtained, as will be described in more detail hereinafter. Characterization herein of the physical form of a particular epoxy resin (i.e., “liquid”, “semi-solid”, “solid”) is in reference to its form at approximately room temperature (i.e., about 25° C.). Semi-solid epoxy resins are those epoxy resins which are neither completely solid nor completely liquid at room temperature.
Generally speaking, epoxy resins are those thermosettable resins having an average of more than one (preferably, about two or more) epoxy groups per molecule.
Epoxy resins are well-known in the art and are described, for example, in the chapter entitled “Epoxy Resins” in the Second Edition of the
Encyclopedia of Polymer Science and Engineering
, Volume 6, pp. 322-382 (1986). Exemplary epoxy resins include polyglycidyl ethers obtained by reacting polyhydric phenols such as bisphenol A, bisphenol F, bisphenol AD, catechol, or resorcinol, or polyhydric aliphatic alcohols such as glycerin, sorbitol, pentaerythritol, trime thylol propane and polyalkylene glycols with haloepoxides such as epichlorohydrin; glycidylether esters obtained by reacting hydroxycarboxylic acids such as p-hydroxybenzoic acid or beta-hydroxy naphthoic acid with epichlorohydrin or the like; polyglycidyl esters obtained by reacting polycarboxylic acids such as phthalic acid, tetrahydrophthalic acid or terephthalic acid with epichlorohydrin or the lik
Muenz Xaver
Reitenbach Dirk
Foelak Morton
Harper Stephen D.
Henkel Teroson GmbH
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