Patent Publication Number: US-2010115874-A1

Title: Flooring system including a dry glue

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This PCT application claims priority from U.S. Provisional Application No. 60/701,486, filed Jul. 22, 2005. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     The invention is a flooring system, utilizing a number of flooring elements, and a “dry” (to the touch) glue for maintaining a tight joint between the flooring elements. 
     2. Background of the Invention 
     Wood or laminate flooring has become increasingly popular. As such, many different types of this flooring have been developed. Generally, this type of flooring is assembled by providing a plurality of similar panels, which are interfit or otherwise secured together and which “float” above the subfloor, i.e., the flooring is not mechanically attached to the subfloor. 
     In conventional hardwood or other flooring systems, edges of rectangular boards or planks are often provided with a tongue-and-groove joining system, whereby a first plank has on at least one edge, a protruding tongue, and a second plank, to be installed adjacent and abutting the first plank, has, on at least one side, a groove, which corresponds substantially to the size and shape of the tongue. Thus, in order to install the first board adjacent to the second board, the tongue is inserted into the groove. In some systems, the tongue and groove form a lock, hindering or preventing separation of the boards. 
     Such conventional tongue-and-groove systems are generally installed by relatively moving one panel with respect to the second panel. For example, U.S. Pat. Nos. 6,421,970 and 6,823,638 teach a system whereby the boards are moved relatively horizontally. U.S. Pat. Nos. 6,591,568 and 6,647,690 teach systems whereby assembly can be completed by rotating and/or through a vertical movement. Other examples of tongue-and-groove systems are disclosed by U.S. Pat. Nos. 6,786,019; 6,006,486; 6,862,857; 6,711,869; 6,536,178 (relative vertical movement); U.S. Pat. No. 6,601,359 (relative horizontal or rotational movement); and U.S. Pat. No. 6,865,855. The resulting joint may also have fitting clearances for the drainage of adhesive, if any, such as described by U.S. Pat. No. 6,682,254. Additional components, such as joining profiles, guiding means or resilient members may also be used, for example as taught by U.S. Pat. Nos. 6,729,091; 6,763,643; 6,966,161; 6,920,732; and 6,854,235. Each of the references mentioned in this paragraph is expressly incorporated by reference in its entirety. 
     Additionally, the size and shape of the tongues and grooves varies greatly. For example, U.S. Pat. No. 6,823,638 (herein incorporated by reference in its entirety) teaches a tongue with a groove provided therein and a corresponding groove with a tongue provided therein. 
     Typical flooring elements used in accordance with the present invention are laminate flooring elements, including a core, a decorative surface, and a wear layer. Typical cores include wood, fiberboard, such as high density fiberboard (HDF) or medium density fiberboard (MDF), gypsum, high-density reinforced plaster, plywood, oriented strand board (OSB), cork, bamboo, flaxboard, plastics (e.g., extrudable and/or moldable thermosetting and thermoplastic resins, the latter including high density olefins and PVC), or other structural material, such as metals (e.g., aluminum, copper, brass, alloys thereof and stainless steel) or composites. 
     Such laminate flooring elements generally include a decorative surface. Typical decorative surfaces are formed from one or more patterned paper sheets, impregnated with a resin, and placed atop the core. Many elements also are provided with a surface texture which coincides with the pattern or design of the paper sheets, in order to enhance the realism thereof, as described by U.S. Pat. No. 7,003,364 (herein incorporated by reference in its entirety). However, such decorative surface can be provided by printing directly, on the core material. The uppermost surface of the element most often includes a wear layer, formed by a resinous layer including hard particles to impart resistance against scratching, abrasion, and denting. Such particles are, typically, diamond, silicon carbide, alumina (e.g., alpha-alumina), or ceramics, which can have a Mohs&#39; hardness of at least 6.0. 
     However, in many of these systems, especially floating floors, an adhesive or glue is often used, such that the assembled panels do not separate. Most often, the glue must be separately purchased, and separately applied in a step immediately preceding joining of the panels. 
     Although flooring systems have been commercialized with a “preglue,” wherein the glue or other adhesive is applied at the factory, such systems have drawbacks, and have heretofore required an additional step. Such additional steps typically include application of an external agent (e.g., water or other chemical activating agent, and ultrasonic waves—either immediately before or following installation), or removal of a protective strip, in order to render the preglue in its active state. 
     SUMMARY OF THE INVENTION 
     Thus, the present inventors have developed a flooring system using a “dry” preglue system, which preglue is applied at the factory, which does not require a separate application of an external agent or removal of a protective strip, and/or which additionally provides adhesive properties not found in any commercial system. 
     In one embodiment, the adhesive or components of the adhesive which react with one more other components can be contained in small “microcapsules,” which, under pressure and/or shear, can be ruptured to allow the glue to adhere to the panels. Examples of “microcapsules” are disclosed in U.S. Publication No. 2002-0127374 (herein incorporated by reference in its entirety), and may be organic or inorganic. 
     According to the invention, upon assembly of the panels, and mating of the tongue and groove, the adhesive becomes operative to prevent the panels from separating, by even a small amount. This can be accomplished by rupturing one or more containers, such as the aforementioned microcapsules, containing the glue or precursors thereof. Such containers may also be in the form of one or more tubes containing, e.g., the adhesive material (such as in an encapsulated form therein), separated activators and/or precursors, or two-part systems. Such tubes can be segmented with seals therebetween, such a described by U.S. Pat. No. 7,029,741, herein incorporated by reference in its entirety. 
     In a preferred embodiment, the adhesive, once activated and finally set, will exhibit particular properties. For example, the following properties are preferred: 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Property 
                 Value 
               
               
                   
                   
               
             
            
               
                   
                 Creep Strength 
                 Greater than 10 kN/m 
               
               
                   
                 Tensile Strength 
                 10-15 kN/m 
               
               
                   
                 Storage Stability 
                 Greater than one year 
               
               
                   
                 Hazardous Materials 
                 None 
               
               
                   
                 Initial Tack 
                 Low 
               
               
                   
                 Set Time 
                 10-15 mins 
               
               
                   
                 Odor 
                 Little or none 
               
               
                   
                 Curing Time 
                 Within 24 hours 
               
               
                   
                   
               
            
           
         
       
     
     In one embodiment, the adhesive, or components thereof, is applied to the entire surface of each of the tongue and groove, but more typically, the adhesive is strategically placed in select locations on the tongue and/or inside the groove. By selecting these application locations, the effectiveness of the adhesive can be maximized. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustrating an embodiment of the invention showing a first-part curative and second-part curative. 
         FIG. 2  is a cutaway perspective view of a substrate having coatings applied according to an embodiment of the invention. 
         FIG. 3  is a side view of an alternative embodiment depicting encapsulated activator showing the second-part curative where catalyst is applied as a lower layer, and where activator is separately microencapsulated. 
         FIG. 4  is an alternative embodiment depicting the second-part curative where activator is a lower layer and catalyst is the middle layer or is in a middle layer. 
         FIG. 5  is an embodiment depicting the second-part curative disposed on opposite sides of the layer with the microcapsules containing monomer and the first-part curative. 
         FIG. 6  illustrates alternate embodiments where the components of the system are coated onto separate surfaces. In version A the capsules with first-part curative are applied to the same surface with catalyst. In version B the catalyst is applied to the surface coated with a second population of capsules encapsulating activator. 
         FIGS. 6 and 7  show a tongue-and-groove system which may be used with the preglue in accordance with the invention. 
         FIG. 8  shows the tongue-and-groove system of  FIG. 6  in its assembled condition. 
         FIG. 9  shows a second tongue-and-groove system which may be used in accordance with the invention. 
         FIG. 10  shows an additional tongue-and-groove system which may be used with the preglue in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Initially, as used throughout the specification and claims, the terms “plank,” board,” and “tiles” mean any type of surface covering material and in any shape. For example, the planks, boards and tiles may be part of a flooring, wall covering, desk, countertop, cabinet, door, vehicle or ceiling component, and can be rectangular, square or have the shape of any other polygon. Although the glue of the invention is particularly designed to be used with laminate flooring materials, the terms “plank,” “board” and “tile” are not so limited. For example, board can convey any type of flooring material, including, plastic, composite materials, hardwood, flaxboard, high density fiber-reinforced plaster, extruded wood, engineered wood, and even ceramic and other non-cellulosic materials. Additionally, the planks may have a decorative upper surface, formed from a material different from that of the remainder of the plank. Typical materials include, laminates (such as foils, plastic sheets, and ceramics (e.g., individual tiles)). 
     Similarly, the term “preglue,” “glue” and “adhesive” as used in the specification and claims, means a substance which can chemically or physically join two, at least tangentially, adjacent surfaces to secure the surfaces together. In some cases, such a substance can be applied during manufacture of the panels. That is to say, before the panels leave the factory, the glue is applied, thus eliminating the need to provide a separate adhesive material just before assembly. Typically, the glue is applied in a non-activated state, such that some later event is needed to convert the preglue into its adhesive state. This invention is particularly directed to a dry preglue, i.e., a glue which is applied at the factory, but does not need the application of an external activator to cause the adhesive effect. Such adhesive effect if preferably achieved by breaking or rupturing a film, such as the wall of a microcapsule or segmented tube. It is additionally considered within the scope of the invention to apply the glue in an activated state, but have a suppressing agent applied thereto, such that the glue has been “de-activated,” awaiting “re-activation” at a later time. 
       FIG. 7  shows a typical tongue-and-groove system which is designed to be assembled horizontally with which the dry preglue of the invention may be used. A first panel  110  is provided with a tongue  112 . The tongue  112  is provided with a retaining element  114 , and a distal surface  116 , as well as an upper surface  118  and a lower surface  120 . Additionally, as shown in  FIG. 7 , the first panel  110  includes a nose  122 , designed to abut an adjacent panel when assembled to form a solid, gap-free surface. 
     A second panel  140  is provided with a groove  141 , a cooperating retaining element  142 , and a proximal surface  144 , as well as upper and lower surfaces,  146  and  148  respectively, and a distal upper surface  150 . 
     Although the retaining elements  114  and  142  are shown as being of a particular construction and at a particular location, such a configuration is shown for convenience only. In other words, the size, shape, type and/or location of the retaining elements  114  and  142  may be altered in any manner without departing from the invention. Thus, the preglue of the invention may be used on any type of tongue-and-groove system known in the art, such as those disclosed in, but not limited to those of, U.S. Pat. No. 6,421,970, No. 6,591,568, No. 6,647,690, and No. 5,823,638 (each of which is hereby incorporated by reference in its entirety). Similarly, there may be multiple retaining elements  114 ,  142 . Moreover, it should be understood that the first panel  110  may be joined to the second panel  140  by, for example, relative horizontal movement, and to a third panel  160  (not shown) by an alternative method, e.g., by relative vertical or rotational movement. 
     Similarly, as the invention utilizes an adhesive material, it is considered within the scope of the invention to eliminate the retaining elements  114  and  142  entirely, thus relying totally upon the adhesive strength of the preglue. Additionally, the retaining elements  114 ,  142  need not be sufficient, alone, to hold the panels  110 ,  140  together when under normal use. 
     For example, as long as the retaining elements  114 ,  142  can maintain the position of the panels  110 ,  140  in their installed positions for at least a short period of time, the preglue of the invention can have enough time to set, to maintain a secure connection, such as a tight joint, of the panels  110 ,  140 . In one embodiment, the locking elements  114 ,  142  can be assembled by human manual pressure, i.e., human muscle power alone, without the need for additional mechanical tools, such as a tapping block and hammer, as is commonly required to assemble locking elements previously known in the art. 
       FIG. 8  shows the first panel  110  and the second panel  140  after assembly. Specifically, the tongue  112  of the first panel  110  is inserted into the groove  141  of the second panel to secure the panels  110 ,  140  together. When assembled, the panels  110 ,  140  meet at least where the top surface  118  of the tongue  112  meets the upper surface  146 , and where the lower surface of the tongue  120  meets the lower surface of the groove  148 , as well as where the nose  122  meets the distal upper surface  150 . In a preferred embodiment, at each of these contact surfaces  200   a - d,  the preglue of the invention functions to hold the panels  110 ,  140  together. However, it is within the scope of the invention to apply the preglue to any number of the contact surfaces  200   a - d,  and in any combination. 
     In addition to the horizontally joined panels as shown in  FIGS. 7 and 8 , the invention is applicable to be used with any assembly method. For example,  FIG. 9  depicts a typical tongue-and-groove system which is designed to be assembled vertically with which the preglue of the invention, and  FIG. 10  depicts a typical tongue-and-groove system which may be assembled through rotational movement with the preglue of the invention. 
     In a preferred embodiment, the dry preglue exhibits specific properties. For example, the creep strength with a gap less than 0.10 mm and a pull rate of 0.02 mm/min is between 1 and 50 kN/m, typically 2-30 kN/m, more typically 7-20 kN/m and preferably 10-15 kN/m. The creep strength can never be too high, and the minimum value is based, in part, on what type of flooring is used. For a typical laminate floor, formed from low or high pressure laminate with a traditional high or medium density fibreboard core, a minimum value should be above 10 kN/m. 
     The creep strength is measured with a gap between the laminate edges being less then 0.10 mm, at a strength of 10-15 kN/m. Normally such joint strength is measured at high piston rate, typically 2 mm/min. However, in an installed floor there are long term forces generated from humidity and temperature changes, and over time this can create gaps between the planks. The reason for applying the adhesive is to increase the strength of the joint, so it can resist these long-term forces. Simulating such the slow forces was performed with a uniaxial machine, such as Lloyd LR50K testing machine (available from AMKTEK, Inc., of Largo, Fla.) with an external extensometer, and the pieces were pulled apart with a joint opening rate of 0.02 mm/min. This pull rate is chosen for practical reasons (it is possible to use other pull rates 0.001-1 mm/min) and that it correlates with previous performed long-term strength tests. In long term strength tests, identical test pieces are hanged with different weights. The weight is increased over time, until the test piece breaks. This could take several weeks. 
     The preglue of the invention also has a particular tensile strength. For example, the tensile strength with a gap less than 0.10 mm and a pull rate of 2 mm/min is between 1 and 50 kN/m, typically 2-30 kN/m, more typically 7-20 kN/m and preferably 10-15 kN/m. The tensile strength is measured in the same way as the creep strength except for the pull rate (2 mm/min). Here, also the gap is important. 
     An important factor in the commercial viability of the preglue is the storage stability after application on planks. In an embodiment, the preglue can maintain its properties for at least 6 months, typically greater than 9 months, and preferably at least as long as one full year, when maintained at a temperature of between 10 and 150° F. (−12-66° C.), irrespective of the relative humidity. The adhesive typically meets the creep strength requirement after one year of having been applied on the board. Temperature and humidity are the important environmental conditions. The capsules typically also withstand normal light, so it is not necessary to pack the planks with special foil, and should also withstand exposure to oxygen and air without the need for any additional materials, such as coatings or packaging. 
     Preferably only non-toxic materials are used. Such non-toxic materials include those materials that are non-hazardous to humans and other animals (both to the skin and mucous membranes), and other, as may be defined by the Occupational Safety &amp; Health Administration of the United States Department of Labor. 
     As used herein, non-toxic may also include hypo-allergenic materials, i.e., materials which do not cause allergic reactions in humans. These materials have little, if any, reaction, when they come in contact with human skin or otherwise contact the human body. 
     The preferred dry preglue has a low initial tack value, which results in little or no adhesion or attraction of dust and other particles. By maintaining a low initial tack value, any negative influence from the presence of dust and other small particles can be significantly reduced if not eliminated. Initial tack, as used throughout this specification and claims, means before the capsules are broken. Such tackiness can be measured via any method, but is typically measured visually. The important thing is that no or little dust or particles adheres to the adhesive before the planks are assembled. The risks with adhesion of dust are that it can be difficult to assemble the planks, create proud edges and the strength of the adhesive can be reduced. 
     In one embodiment, the dry preglue has little or no smell, either before or after activation. Such a condition will be tested at the Swedish National Testing and Research Institute (SP). The important thing is that there is no unpleasant smell from the adhesive during installation and after the installation. Smell is difficult to measure because different people react differently to smells. What SP will do is to measure the volatile components with a method called FLEC (field and laboratory emission cell). The presence or absence of smell or odor can also be measured by human observation. However, in other embodiments of the invention, the release or origination of organic or inorganic odiferous components (such as a mercaptan or other sulfur-containing component) can alert the installer that the dry preglue has been activated. In such circumstances, odiferous substances can be readily identified in minute quantities, e.g., on the order of 100 ppm, 50 ppm or even as low as 10 ppm, could be released or generated. 
     Once the dry preglue has been activated, in preferred embodiments, the glue should not begin to set until the expiration of a predetermined period of time. By providing a predetermined set time of, for example, as long as 45 minutes to one hour, the installer is given an opportunity to assemble the planks, and if needed, remove one or more without destroying them. If, for example, one plank were damaged or was not completely interfit with the adjacent panels, the installer would be able to correct this problem. Practical set times can be between 1 minute and 1 hour, typically between 10 and 45 minutes, and preferably between 10 and 15 minutes. Longer predetermined set times force the installer to avoid putting pressure on the joints until after the set time has expired, and shorter set times negate the ability to disassemble the boards without damage thereto. 
     Once the preglue begins to set, it should achieve its final properties, such as creep strength and tensile strength within a reasonable curing time. Typical curing times can be as long as one week, but are preferably less than 2 days, and most preferably less than 24 hours. 
     The preglue may be applied in any number of manners to the panels. Particular examples of the locations of which the glue may be applied are taught by U.S. Published Application No. 2002-0189747 (incorporated by reference in its entirety), wherein the adhesive is applied to substantially all of each surface of the tongue  112 , other than the distal surface  116 , as well as to substantially all surfaces of the groove  141 , other than the proximal surface  144 . Such capsules typically have a diameter between 1 and 700 μm, more typically between 10 and 100 μm, and preferably between 10 and 50 μm. 
     While it is preferred that the preglue system be spread across the entire length of the edge of the tongue and/or groove, it is considered within the invention to apply the components on substantially less than the entire edge. For example, depending upon the type of locking element being used, it may only be necessary to have the glue system on, 75%, 50%, 25% or even 10% or less of the entire length of the edge. 
     In one embodiment, the preglue system requires (A) a monomer, (B) an initiator, (C) an activator, and (D) a catalyst. In order for the preglue to become fully activated, typically, it is necessary to react each of components (A)-(C) in the presence of (D). Thus, when the panels of the invention leave the factory, at least one component is typically separated from the remainder. Separating can be spatial or can involve isolation of one or more components, such as by microencapsulation. 
     Generally, the system additionally typically includes a binder. One or more of the components, preferably the catalyst, may be contained in the binder. Suitable binders are carriers or vehicles for the microcapsules or non-encapsulated component and can include dried solvents. Examples of binder materials include water-based adhesives or lacquers (e.g., PVAc), solvent based adhesives or lacquers, UV-curing adhesives or lacquer, latex, starch, only solvent and only water. 
     Other optional components include a foaming agent, such as polyols and polyethers with isocyanates which cause the glue to foam or bubble when activated. By utilizing such a foaming agent, the glue can expand in volume to flow and fill interstices or spaces between the planks. This is especially desirable when it is desired to seal the space between the planks immediately below the noses of the planks. 
     The monomer can be any material, which, when exposed one or more other components forms a polymer which can join the boards of the invention. Typical monomers include acrylates, urethanes and epoxies and are preferably 100% solidified and cured by the action of free radicals, cationic reactions and anionic reactions. The catalyst is typically copper, such as a copper solution, e.g., copper chloride in an acetone solvent. 
     The initiator is typically a chemical added to help start the chemical reaction such as polymerization, needed to activate or set the adhesive. Such polymerization may be cross-linking or chain extending. Its action is typically similar to that of a catalyst, except that it is usually consumed in the reaction. In polymer chemistry, an initiator is a chemical compound that initiates a chain reaction. Typically these compounds decompose to form either radical, anionic, or cationic species, which in turn serve as a reactive center for the propagation of chain polymerization. An example of a commonly used radical initiator would be tertiary-butyl hydroperoxide. This is a water soluble compound that, upon mild heating, breaks into two radical species. The initiator is typically a peroxide, such as cumene hydroperoxide. 
     The activator is typically a chemical used to accelerate a reaction or increase chemical activity in another material, for example, to activate the initiator to begin the reaction. A generic example a suitable activators are amines. 
     The adhesive system may be formulated as follows:
         a. Capsule 1:
           i. Monomers (tetrahydrofurfuryl methacrylate and butylene glycol dimethacrylate) and   ii. Initiator (cumene hydroperoxide).   
           b. Capsule 2:
           i. Activator (propyl dihydropyridine).   
           c. The binder contains the catalyst (copper dichloride dihydrate).   d. When the capsules are broken, the activator activates the initiator and then the initiator initiates the polymerization of the monomers and the catalyst catalyzes the polymerization reaction.       

     The various components, as well as binder therefor, can be applied in a number of manners. Typical examples include, vacuum coating, spraying, rolling, brushing, dipping, and electrostatic spraying. When applied, the wet film thickness is typically less than 500 μm, more typically less than 200 μm, and preferably less than 100 μm. However, after activation, the thickness is typically less than 1000 μm, more typically less than 500 μm, and preferably less than 200 μm. 
     The wet film thickness should be less than 1000 μm and, more typically between 300 and 600 μm. The dry film thickness should be less than 800 μm and, typically less than 500 μm, and preferably between 150 and 300 μm. However, after activation, the thickness is typically less than 500 μm, more typically less than 200 μm, and preferably less than 100 μm. 
     It is possible to separate the components by applying the components to both of the panels. However, in order to prevent mixing of the components prematurely, at least one of the components must be separated from the remainder. In one embodiment, components (B)-(D) are applied to one of the tongue or groove, and the monomer is applied to the other of the tongue and groove. Thus, when the tongue and groove are mated, the monomer can contact the activator, catalyst and initiator to activate the glue. Similarly, the components may be separated in any manner, as long as the activation can be prohibited until desired. 
     It is also possible to encapsulate one or more of the components. For example, instead of having one or more components, such as the monomer, separated from the remaining components by being located on a separate panel, one or more components can be encapsulated to prevent mixing until desired. This encapsulation may be organic or inorganic, such as that which is disclosed in U.S. Publication No. 2002-0127374, as well as one or more of melamine, urea and formaldehyde. The capsules, regardless of their size, may also be formed from glass, polymer, gellable colloids and other materials as hereinafter discussed, or another substantially rigid material. In these embodiments, pressure generated by physically joining the boards causes the capsules to rupture. 
     In another embodiment, the capsules are broken by a chemical reaction. For example, the capsule can include a material which, when exposed to a solvent located on the opposite board, will rupture or otherwise open, allowing the escape of the contents contained therein. 
     In one embodiment, the mixing or contact of the various components causes an additional reaction, giving the user some indication that the components have been contacted and that the glue has become activated. The additional reaction is something that can be observed by the user, and need not have any effect on any other property. Such reactions can be smell, color, temperature, turbidity or cloudiness, or any other observable change. 
     The various components may be provided on the boards in a number of manners/locations. For example, as follows.
         a. The components can be separated on the panels, such as components (A)-(C) on one panel and (D) on the second panel. In one embodiment, only the catalyst is provided on the second panel.   b. One or more components can be encapsulated, and at least one is not encapsulated. In this embodiment, the components are maintained apart by their relative encapsulation, rather than by being provided on different panels. Again, more than one component can be provided in a single microcapsule. In one embodiment, components (A), (B) and/or (C) are encapsulated, and (D) is simply applied to the panel. Typically, initiator (B) and activator (C) are not placed in the same capsule. Because the components are inherently separated, the microcapsules and other components all can be provided on one or both boards.   c. One or more of the components can be integral with the board. In other words, one component, such as the catalyst, may be impregnated into the structure of the panel, either only at the edge, or mixed throughout the panel.   d. Multiple microcapsules can be used, wherein the components are maintained separated by being provided in separate microcapsules. Typically, the catalyst is provided in its own microcapsule.   e. A solvent for a microcapsule can be provided in a glass microcapsule. In this embodiment, a solvent for a microcapsule is provided in a glass (or other inert substance which interferes with neither any component nor the final adhesive system) capsule. When the glass capsule is ruptured, typically by physical pressure, the solvent is released, and such solvent is free to act on the microcapsule(s) containing the component(s).   f. The microcapsule(s) can be ruptured by heat or other external forces. In one embodiment, either immediately before the panels are assembled or sometime after assembly, radiation (such as ultrasonic, heat, microwave, electromagnetic, etc.) is applied to rupture the microcapsule(s).       

     The present invention teaches an improved adhesive composition especially suited for forming high strength dry-to-the-touch structural adhesives. The adhesive composition of the invention, in some embodiments, is a thin layer flowable adhesive providing a dry-to-the-touch adhesive providing high strength when joining interference fit components. At least one of the adhesive constituents flows into contact with the other constituents of the adhesive composition to form a high strength structural adhesive. 
     In a preferred embodiment a flowable monomer is encapsulated together with initiator, as described by U.S. Provisional Application No. 60/______, titled Encapsulated Structural Adhesive, filed Jul. 22, 2005 (Atty. Docket No. 6595) in the name of Sandra Jacqueline Guinebretiere et al., herein incorporated by reference in its entirety. A flowable activator can be separately encapsulated or positioned in a binder material, matrix or carrier for the adhesive composition. For convenience herein, all such materials are referred to as binder or binders herein. Upon capsule rupture, the flowable components of monomer, initiator and activator flow into reactive contact with each other and a catalyst forming a high strength adhesive. 
     The present invention in various embodiments teaches an encapsulated curable adhesive composition comprising a two part curative, e.g., activator and curative. The curative consists substantially of a first-part curative of a preferably peroxy initiator, and a second-part curative. Other additives can also be present such as rheology modifiers, pigments, fragrances, odor-masking agents, fillers, colorants and plasticizers. In one embodiment, a first population of polymeric microcapsules encases the initiator and monomer which is reactive with the second-part curative. The second-part curative is also of two parts or two components. The capsules encase both the first-part curative and the monomer thereby forming a monomer and initiator (first-part curative) blend. The polymeric microcapsules are substantially impermeable to both parts of the curative. The monomer is selected from flowable (meth)acrylate esters, epoxy(meth)acrylate and urethane(meth)acrylate esters. For convenience the term “(meth)acrylate” is to be understood as used herein and in the claims as referring to both the acrylate and methacrylate versions of the specified monomer. However, the encapsulated monomer and initiator blend is a free flowing liquid having a viscosity of less than 500 milliPascal-second (Cp) (Centipoise). The term “monomer” in the specification and claims should be understood as being defined for purposes hereof to include monomers and oligomers thereof and blends of monomers and oligomers provided the requisite viscosity parameters of the resultant blend are met. The monomer preferably has a Tg of 35° C. or less or is blended with monomers to have a resultant Tg of less than 35° C. The second-part curative comprises a catalyst and activator. The second-part curative is preferably external to the polymeric microcapsules containing monomer and initiator disposed on the substrate to be joined, or in a binder or carrier for the system, or on the outside of the microcapsules. Alternatively, the activator of the second-part curative is separately encapsulated or positioned in a binder material, matrix or carrier for the adhesive composition. The catalyst is typically external to the microcapsules, and can be in the binder or carrier or applied as a first coating to a substrate which is over coated with the balance of the components of the structural adhesive. Optionally, the catalyst may be separately encapsulated or positioned in a binder material, matrix or carrier for the adhesive composition. 
     An encapsulated curable adhesive composition is taught for forming high strength structural adhesives. In the majority of embodiments, these structural adhesives are able to be fashioned as dry-to-the-touch coatings before activation. 
     The encapsulated curable adhesive composition comprises a two part curative comprised of a first-part curative and a second-part curative. The first-part curative is an initiator material. The second-part curative is a catalyst and an activator. The adhesive composition includes a first population of polymeric microcapsules encapsulating a monomer reactive with the two part curative when “complete,” meaning that the initiator, catalyst and activator have all come together, enabling reactive contact. The internal contents or core of the first population of microcapsules includes a flowable monomer or monomers reactive with the two part curative. Prior to encapsulation, the monomer is blended with the first-part curative forming a blend of the monomer and initiator. This blend of monomer and first-part curative forms the core of the first population of microcapsules. The second-part curative comprises catalyst preferably a water soluble catalyst such as a copper metal salt, and an activator. A binder material is also provided to retain the population of microcapsules and two-part curative in proximity such as when coated on a substrate to be joined. Preferably the activator is separately encapsulated forming a second population of microcapsules. 
     The monomer is preferably selected from difunctional acrylates, methacrylate esters, epoxyacrylate esters, epoxyacrylates, urethane acrylate esters, and melamine acrylate monomers and oligomers. More preferably the monomer is a difunctional methacrylate ester or difunctional urethane acrylate ester. Blends of any of the foregoing are possible. 
     Blends of difunctional methacrylate esters together with monofunctional acrylate esters are also particularly useful. 
     The monomer and the initiator blend is selected to be a free flowing liquid, meaning a viscosity of less than 500 centipoise. The monomer and initiator blend has a viscosity of less than 500 centipoise (Cp), (at room temperature 25° C. unless otherwise indicated). Centipoise is equivalent to milliPascal-second units (milliPascal-second). Viscosity parameters herein are understood as measured at 25° C. unless otherwise indicated. Similarly, the activator is preferably separately encapsulated and also selected to be a free flowing liquid. 
     Preferably the viscosity of the monomer is less than 100, and even more preferably less than about 7 Cp (milliPascal-second); and the viscosity of the monomer and initiator blend is preferably less than 25 Cp, and more preferably less than 10 Cp. 
     Most preferably the viscosity of the monomer and initiator blend is less than 5 Cp (milliPascal-second). A convenient way to measure viscosity is by use of a viscometer such as Brookfield, Model LVF. 
     The aspect of achieving a free flowing liquid of the monomer (or monomers) and initiator which forms the internal phase or core of the first population of microcapsules can be accomplished by blending monomers of high viscosity with from 0 to 99 weight percent a lower viscosity monomer. For illustration, melamine acrylate having a viscosity of 1500 Cp can be blended or in essence, diluted, with tetrahydrofurfuryl(meth)acrylate and hexanediol dimethacrylate (viscosity&lt;15 Cp) in sufficient weight percent or ratio to achieve a blend with the initiator that is well below 500 Cp (milliPascal-second) making the blend useful as a free flowing liquid in the invention. The useful ratios of such blends to achieve the desirable viscosity of less than 500 Cp can be readily ascertained by the skilled artisan by blending different proportions of viscous and non-viscous monomers. 
     Similarly the activator is selected to be a free flowing liquid, and preferably has a viscosity of less than 500 Cp at room temperature, and more preferably less than 100 Cp, and most preferably less than 10 Cp. 
     The monomer or blend of monomers is selected to have a Tg of 35° C. or less, more preferably less than 25° C., and most preferably less than 10° C. In certain applications a Tg of 1° C. or less is preferable. Similar to the technique for blending high viscosity monomers with lower viscosity monomers, blending of high Tg monomers with lower Tg monomers can also be done to achieve a resultant Tg for the monomer blend of 35° C. or less. Table 1 lists a variety of monomers along with their Tg values and viscosity. Table 1 lists a variety of monomers available from commercial suppliers such as Sartomer (Exton, Pa.) and others. Various monomers and oligomers are available commercially that either have the requisite viscosity and Tg values, or which can be blended together to achieve the requisite viscosity and Tg. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Monomer 
                 Tg C. 
                 Mw 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                   
                   
                 viscosity Cps 
               
               
                   
                   
                   
                 25° C. or 
               
               
                   
                   
                   
                 milliPascal- 
               
               
                   
                   
                   
                 second 
               
               
                 2-phenoxyethyl acrylate 
                 5 
                 192 
                 12 
               
               
                 tridecyl acrylate 
                 −55 
                 255 
                 7 
               
               
                 difunctional aliphatic urethane acrylate 
                   
                   
                 3000@60 C. 
               
               
                 urethane diacrylate oligomer 
                 −37 
                   
                 9975@60 C. 
               
               
                 urethane diacrylate oligomer 
                   
                   
                  660@60 C. 
               
               
                 1.6 hexanediol diacrylate 
                 43 
                 226 
                 9 
               
               
                 ethoxylated (4) bisphenol diacrylate 
                 60 
                 512 
                 1080 
               
               
                 caprolactone acrylate 
                 −53 
                 344 
                 80 
               
               
                 urethane dimethacrylate 
                 25 
                   
                 1740@60 C. 
               
               
                 trimethylolpropane trimethacrylate 
                 27 
                 338 
                 44 
               
               
                 tetrahydrofurfuryl methacrylate 
                 23 
                 170 
                 5 
               
               
                 tetrahydrofurfuryl acrylate 
                 −15 
                 156 
                 6 
               
               
                 tripropylene glycol diacrylate 
                 62 
                 300 
                 15 
               
               
                 1,6 hexanediol dimethacrylate 
                 30 
                 254 
                 8 
               
               
                 polyethyleneglycol dimethacrylate 
                   
                 330 
                 15 
               
               
                 1,3 butylene glycol dimethacrylate 
                 29 
                 226 
                 8 
               
               
                 ethoxylated (2) bisphenol A dimethacrylate 
                   
                 452 
                 1082 
               
               
                 ethoxylated (10) bisphenol A dimethacrylate 
                 −1 
                 808 
                 410 
               
               
                 caprolactone modified neopentylglycol hydroxypivalate 
                   
                 540 
                  70-140 
               
               
                 diacrylate 
               
               
                 caprolactone modified neopentylglycol hydroxypivalate 
                   
                 768 
                 200-300 
               
               
                 diacrylate 
               
               
                 melamine acrylate 
                   
                   
                 1500 
               
               
                 aromatique polyether urethane diacrylate oligomer 
                 −40 
                   
                 3195@60 C. 
               
               
                 TMPTA trimethylolpropane triacrylate 
                 62 
                 296 
                 106 
               
               
                 isodecyl acrylate 
                 −60 
                 212 
                 5 
               
               
                 caprolactone acrylate 
                 −53 
                 344 
                 80 
               
               
                 ethoxylated bisphenol A diacrylate 
                 60 
                 512 
                 1080 
               
               
                 pentaerythritol tetraacrylate 
                 103 
                 298 
                 520 
               
               
                 ethoxylated trimethylolpropane triacrylate 
                 103 
                 428 
                 60 
               
               
                 polypropylene glycol monomethacrylate 
                   
                 405 
                 35 
               
               
                 propoxylated trimethylolpropane triacrylate 
                 −15 
                 470 
                 90 
               
               
                 polybutadiene dimethacrylate 80%/HexaneDiol DiAcrylate ester 
                 −75 
                   
                  890@60 C. 
               
               
                 20% 
               
               
                 low viscosity polyester acrylate oligomer 
                 1 
                   
                 630 
               
               
                 polyester acrylate oligomer 
                 21 
                   
                 7700 
               
               
                 epoxy acrylate oligomer 
                 62 
                   
                  250@60 C. 
               
               
                 polyester acrylate oligomer 
                 −19 
                   
                 28 
               
               
                 polyester acrylate oligomer 
                 42 
                   
                 65 
               
               
                 polyester acrylate oligomer 
                 −45 
                   
                 150 
               
               
                 polyester acrylate oligomer 
                 −22 
                   
                 180 
               
               
                 bisphenol A base epoxy acrylate 
                 60 
                   
                 2150@65 C. 
               
               
                   
                   
                   
                 viscosity cps 
               
               
                   
                   
                   
                 25 C. 
               
               
                 epoxy acrylate blended with SR351 
                   
                   
                 800 
               
               
                 aromatic urethane acrylate 
                 50 
                   
                  700@60 C. 
               
               
                 aliphatic urethane acrylate 
                 27 
                   
                 660@60 C., 
               
               
                   
                   
                   
                 10080@25 C. 
               
               
                 urethane acrylate 
                 −47 
                   
                 4155@60 
               
               
                 low viscosity diacrylate oilgomer 
                 26 
                   
                 1000 
               
               
                 aliphatic polyester base urethane diacrylate 
                 −38 
                   
                 58250@60 C.  
               
               
                 polybutadiene dimethacrylate 
                 −39 
                   
                 4125@60 C. 
               
               
                 aliphatic urethane acrylate 
                 30 
                   
                 60000@60 C.  
               
               
                 methacrylated polybutadiene 
                   
                 6000 
                 65000@45 C.  
               
               
                 methacrylated polybutadiene, UV curable resin, soluble in water 
                   
                 3200 
                 25000 
               
               
                 epoxidized soy bean oil acrylate 
                 −22 
                   
                 25100 
               
               
                 trifunctional urethane acrylate 
                 43 
                   
                 156000, 
               
               
                   
                   
                   
                 2800@60 C. 
               
               
                 aromatic urethane acrylate 
                 30 
                   
                 15000@60 C.  
               
               
                 aromatic polyester based urethane diacrylate 
                   
                   
                 8900 
               
               
                 polyester acrylate oligomer 
                 −20 
                   
                 52000 
               
               
                 polyester acrylate oligomer, water soluble for UV wood coating 
                   
                   
                 11000E@60 C.    
               
               
                 polyester acrylate oligomer 
                 35 
                   
                 85000 
               
               
                 aromatic urethane acrylate 
                 35 
                   
                 58000 
               
               
                 aliphatic urethane acrylate 
                 22 
                   
                 6190@60 C. 
               
               
                 polybutadiene dimethacrylate 80%/HDODA 20% 
                 −75 
                   
                  890@60 C. 
               
               
                 polyester acrylate oligomer 
                 21 
                   
                 7700 
               
               
                 epoxy acrylate oligomer 
                 62 
                   
                  250@60 C. 
               
               
                 polyester acrylate oligomer 
                 42 
                   
                 65 
               
               
                 aromatic urethane acrylate 
                 50 
                   
                  700@60 C. 
               
               
                 urethane acrylate 
                 −47 
                   
                 4155@60 
               
               
                 caprolactone modified neopentylglycol hydroxypivalate 
                   
                 768 
                 200-300 
               
               
                 diacrylate 
               
               
                 urethane dimethacrylate 
                 25 
                   
                 1740@60 C. 
               
               
                 melamine acrylate 
                   
                   
                 1500 
               
               
                 bisphenol A base epoxy acrylate 
                 60 
                   
                 2150@65 C. 
               
               
                 urethane dimethacrylate 
                 25 
                   
                 1740@60 C. 
               
               
                 caprolactone modified neopentylglycol hydroxypivalate 
                   
                 768 
                 200-300 
               
               
                 diacrylate 
               
               
                 polybutadiene dimethacrylate 80%/HexaneDiol DiAcrylate ester 
                 −75 
                   
                  890@60 C. 
               
               
                 20% 
               
               
                 polyester acrylate oligomer 
                 21 
                   
                 7700 
               
               
                 epoxy acrylate oligomer 
                 62 
                   
                  250@60 C. 
               
               
                 polyester acrylate oligomer 
                 42 
                   
                 65 
               
               
                 bisphenol A base epoxy acrylate 
                 60 
                   
                 2150@65 C. 
               
               
                 aromatic urethane acrylate 
                 50 
                   
                  700@60 C. 
               
               
                 urethane acrylate 
                 −47 
                   
                 4155@60  
               
               
                   
               
            
           
         
       
     
     Viscosity of the internal phase of the capsules is adjustable by blending monomers. In this table the internal phase contains: activator DPC 3% by weight in the monomers or initiator CHP 5% by weight in the monomers), M corresponds to THFA/HDDMA 50/50. 
     
       
         
           
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                 Viscosity (cps, 25° C.) 
               
               
                   
                 Brookfield model LVF, 
               
               
                 Monomers in the internal phase 
                 spindle 2, 60 rpm 
               
               
                   
               
             
            
               
                 Melamine acrylate oligomer (Doresco 
                 15 
               
               
                 UV75° C., 1500 cps)/M 50/50 
               
               
                 Bisphenol A base epoxy acrylate (CN120, 
                 25 
               
               
                 2150 cps @ 65° C.)/M 40/60 
               
               
                 Urethane dimethacrylate (CN1963, 1740 cps 
                 53 
               
               
                 @ 65° C.)/M 50/50 
               
               
                 Polybutadiene (Ricon 130, 750 cps)/M 
                 25 
               
               
                 50/50 
               
               
                   
               
            
           
         
       
     
     The viscocity of the internal phase is preferably lower than 100 cps. CN120 and CN1963 are products of Sartomer (Exton, Pa.). Doresco™ is a trademark of Lubrizol, Wickliffe, Ohio. DPC is diphenyl carbazone. CHP is cumene hydroperoxide. M corresponds to tetrahydrofurural methacrylate (THFA) blended with hexane diol dimethacrylate (HDDMA) in a 50/50 percent ratio by weight. 
     
       
         
           
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                 Activator + diluent 
                   
                   
               
               
                 monofunctional + difunctional 
               
               
                 monomer 
                 Resultant Viscosity 
                 Resultant Tg 
               
               
                   
               
             
            
               
                 Hexanedioldimethacrylate + 
                 &lt;500 Cp 
                 &lt;35° C. 
               
               
                 tetrahydrofurfural methacrylate 
               
               
                 and 3,5-1,2-dihydro-1-phenyl-2- 
               
               
                 pyropylpyridine 
               
               
                   
               
            
           
         
       
     
     Table 3 is another example of blending of monomers to achieve a resultant viscosity of less than 500 Cp and resultant Tg of less than 35° C. 
     The monomer and initiator blend is a free flowing liquid which is encapsulated and comes into reactive contact with both parts of the two part curative when the capsules are fractured. 
     Reactive contact of the monomer and first-part curative with the second-part curative is effected by fracturing, shearing, crushing, or otherwise breaking or degrading the microcapsules so that the free flowing monomer and first-part curative comes into contact with the second-part curative. Mixing occurs through flow of the free flowing monomer and initiator from the capsule interior and flow of activator from the capsule interior upon application of pressure or relative movement of the substrates such as when an interference fit is affected. Common interference fit assemblies include threads on bolts, mortise and tenon, and various snap-fit assemblies or tongue and groove assemblies and couplers. 
     The monomers useful in the invention are difunctional acrylate esters, difunctional methacrylate esters and difunctional polyurethane acrylate esters and epoxy acrylates stable in the presence of initiator. Monomers shall be understood as including oligomers thereof. Optionally, an inhibitor such as hydroquinone can be added to the monomer and initiator blend in the capsules to prevent premature polymerization. 
     The initiator (first-part of the two-part curative) is blended with the monomer and preferably forms the internal or core contents of the first population of polymeric microcapsules. Optionally the initiator can be separately encapsulated though the preferred embodiment herein is a blending of the monomer and initiator and encapsulation of the blend. 
     Useful monomers in the invention are di- and poly-functional acrylate esters, difunctional (meth)acrylate esters, polyfunctional (meth)acrylate esters, difunctional urethane acrylate esters, polyfunctional urethane acrylate esters and polyfunctional and difunctional epoxy acrylate monomers and oligomers used alone or in combination as blends. In alternate embodiments, optionally, the di- and polyfunctional acrylates, methacrylates, urethane acrylates, and epoxy acrylates are further blended with monofunctional acrylates, methacrylates, urethane acrylates and epoxy acrylates. 
     In one form of the embodiments, the encapsulated curable adhesive composition is assembled as a two part system. The curative is of two parts. The first-part curative is a free radical initiator, preferably a peroxy initiator. The initiator is preferably encapsulated together with the monomer. Alternatively the initiator may be separately encapsulated. 
     A typical and preferred example of the initiator is cumene hydroperoxide. More particularly, the free radical initiator needs to be soluble or dispersible in the monomers and oligomers. The free radical initiator can be selected from the group of initiators comprising an azo initiator, peroxide, dialkyl peroxide, alkyl peroxide, peroxyester, peroxycarbonate, peroxyketone and peroxydicarbonate. The free radical initiator can be selected from 2,2′-azobis(isobutylnitrile), 2,2′-azobis(2,4-dimethylpentanenitrile), 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis(2-methylpropanenitrile), 2,2′-azobis(methylbutyronitrile), 1,1′-azobis(cyclohexanecarbonitrile), 1,1′-azobis(cyanocyclohexane), benzoyl peroxide, decanoyl peroxide; lauroyl peroxide; benzoyl peroxide, di(n-propyl)peroxydicarbonate, di(sec-butyl)peroxydicarbonate, di(2-ethylhexyl)peroxydicarbonate, 1,1-dimethyl-3-hydroxybutyl peroxyneodecanoate, α-cumyl peroxyneoheptanoate, t-amyl peroxyneodecanoate, t-butyl peroxyneodecanoate, t-amyl peroxypivalate, t-butyl peroxypivalate, 2,5-dimethyl 2,5-di(2-ethylhexanoyl peroxy)hexane, t-amyl peroxy-2-ethyl-hexanoate, t-butyl peroxy-2-ethylhexanoate, t-butyl peroxyacetate, di-t-amyl peroxyacetate, t-butyl peroxide, di-t-amyl peroxide, 2,5-dimethyl-2,5-di-(t-butylperoxy)hexane-3, cumene hydroperoxide, 1,1-di-(t-butylperoxy)-3,3,5-trimethyl-cyclohexane, 1,1-di-(t-butylperoxy)-cyclohexane, 1,1-di-(t-amylperoxy)-cyclohexane, ethyl-3,3-di-(t-butylperoxy)-butyrate, t-amyl perbenzoate, t-butyl perbenzoate and ethyl 3,3-di-(t-amylperoxy)-butyrate. 
     The initiator is employed at an amount of 10 percent or less by weight in the core of the capsules and more preferably from about 3 to 5 percent by weight, and most preferably 0.1 to 5 percent by weight (based on weight of the internal phase or core of the capsules). 
     The monomers desirably crosslink in contact with both parts of the two part adhesive. Preferably, the first-part curative is blended with the monomer and encapsulated together with the monomer forming a first population of microcapsules. In one embodiment the second-part curative is positioned external to the microcapsules, for example, on the outside of the capsule wall, on a substrate to be joined, in a carrier, or a binder, with all such placements of the second curative being deemed external to the first population polymeric capsules. The second curative could also be separately encapsulated forming a second population of microcapsules. 
     The monomers for example can be selected from the group of monomers and oligomers consisting of alkene glycol dimethacrylate, alkyl dimethacrylate, alkyldiol dimethacrylate, alkoxy alkanol diacrylate, trialkanol triacrylate, alkoxy(alkoxy) n  alkyl triacrylate, alkoxy(alkoxy) n  alkyl dimethacrylate, aralkyl dimethacrylate, cycloalkyl dimethacrylate, alkoxy dimethacrylate, bicycloalkyl dimethacrylate, cycloalkoxy dimethacrylate, alkene glycol diacrylate, alkyl diacrylate, alkyldiol diacrylate, alkoxy alkanol dimethacrylate, trialkanol trimethacrylate, alkoxy(alkoxy) n  alkyl trimethacrylate, alkoxy(alkoxy) n  alkyl diacrylate, aralkyl diacrylate, cycloalkyl diacrylate, alkoxy diacrylate, bicycloalkyl diacrylate, cycloalkoxy diacrylate, wherein the alkyl and alkene moieties are of 1 to 16 carbons, the cycloalkyl moieties are of 4 to 8 carbons, n is an integer from 1 to 6. Aromatic polyether urethane(meth)acrylates, aliphatic polyester, aliphatic urethane acrylate including alkyl, alkenyl or aryl substituted or unsubstituted urethane acrylates and epoxy acrylates can also be advantageously employed. 
     More specifically, by way of illustration and not limitation, the monomers can be selected from any of hexyl dimethacrylate; triethylene glycol dimethacrylate; ethylene glycol dimethacrylate; tetraethylene glycol dimethacrylate; polyethylene glycol dimethacrylate; 1,3 butylene glycol diacrylate; 1,4-butanediol dimethacrylate; 1,4-butanediol diacrylate; diethylene glycol diacrylate; diethylene glycol dimethacrylate; 1,6 hexanediol diacrylate; 1,6 hexanediol dimethacrylate; neopentyl glycol diacrylate; neopentyl glycol dimethacrylate, polyethylene glycol diacrylate; tetraethylene glycol diacrylate; triethylene glycol diacrylate; 1,3 butylene glycol dimethacrylate; tripropylene glycol diacrylate; ethoxylated bisphenol diacrylate; ethoxylated bisphenol dimethyacrylate; dipropylene glycol diacrylate; alkoxylated hexanediol diacrylate; alkoxylated cyclohexane dimethanol diacrylate; propoxylated neopentyl glycol diacrylate, trimethylolpropane trimethacrylate; trimethylolpropane triacrylate, pentaerythritol triacrylate, ethoxylated trimethylolpropane triacrylate, propoxylated trimethylolpropane triacrylate, propoxylated glyceryl triacrylate, ditrimethylolpropane tetraacrylate, dipentaerythritol pentaacrylate, ethoxylated pentaerythritol tetraacrylate, and the like, and mixtures thereof. 
     Monofunctional acrylates, methacrylates and urethane acrylates, urethane methacrylates for blending with the monomer include, by way of illustration and not limitation, monomers and oligomers of alkyl acrylate, aralkyl acrylate, cycloalkyl acrylate, alkoxy acrylate, cycloalkoxy acrylate, bicycloalkyl acrylate, alkoxy(alkoxy) n  acrylate, alkyl methacrylate, polyalkene(meth)acrylate, aralkyl methacrylate, cycloalkyl methacrylate, alkoxy methacrylate, bicycloalkyl methacrylate, cycloalkoxy methacrylate, and alkoxy (alkoxy)methacrylate. The alkyl moieties should be selected preferably of 1 to 16 carbons, the cycloalkyl moieties from 4 to 8 carbons, and n is an integer from 1 to 6. 
     More particularly the monofunctional acrylates, methacrylate or urethane acrylates or methacrylates can be selected from n-pentyl acrylate, 2-methyl butyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, n-decyl acrylate, n-dodecyl acrylate, lauryl methacrylate, lauryl acrylate, 2-ethylhexyl methacrylate, n-octyl methacrylate, iso-octyl acrylate, iso-octyl methacrylate, isononyl acrylate, isodecyl acrylate, 2-ethoxyethyl methacrylate; butyl diglycol methacrylate; tetrahydrofurfuryl acrylate; tetrahydrofurfurylmethacrylate; furfuryl methacrylate 2-phenoxyethyl acrylate, isohexyl acrylate; tridecyl acrylate; tridecyl methacrylate; ethoxylated nonyl phenol acrylate and the like and mixtures thereof. 
     The catalyst is an organic acid or a salt of a transition metal or a metal ion. The catalyst optionally can be separately encapsulated. Preferred are copper salts such as copper chloride. Organo copper salts can also be advantageously employed such as copper acetyl acetonate and copper ethyl hexanoate. Optionally the catalyst such as copper salts can be encapsulated with the activator, or optionally even separately encapsulated. 
     The catalyst is used at about less than 2 percent and more preferably 0.2 to 1 wt. percent (based on weight of the reactive constituents making up the adhesive). 
     An activator, preferably separately encapsulated is included. Useful activators to be used in combination with the catalyst and first population of microcapsules include ferrocene, butyl ferrocene, diethylferrocene, amino rhodanine, diphenyl carbazone, diphenyl carbazide, dithizone, guaiazulene. 
     More particularly, the activator is an organonitrogen compound such as tertiary amine, amide and imide compounds, aliphatic amines, aldehyde amines, aromatic amines. Specific examples include, without limitation, acetylphenyl hydrazine, diphenyl carbazide, diphenyl carbazone, dithizone, propyl dihydropyrridine, acetaldehyde-benzylamine, butyraldehyde aniline, benzylamine, various dialkyl amines such as dialkylamine, aniline, toluidine, hexamethylene tetramine, polyethyleneimine, aminorhodanine, tetramethylthiourea, mercaptobenzothiazole, and the like. 
     The activators are used at preferably less than 10 percent by weight, and more preferably from 1 to 5 percent by weight of the reactive adhesive composition (excluding weight of binder and wall material). 
     Microcapsules are obtained by providing an aqueous mixture containing a colloidal dispersion of hydrophilic wall-forming material and monomers with initiator. 
     High shear agitation is applied to the aqueous mixture to achieve a particle size of the core material of about 0.1 to 250μ (250 microns), preferably 0.1 to 100 microns and more preferably 0.1 to 50 microns. Smaller capsules of 10μ or less can be produced for specialized applications. 
     Common microencapsulation processes can be viewed as a series of steps. First, the core material which is to be encapsulated is emulsified or dispersed in a suitable dispersion medium. This medium is preferably aqueous but involves the formation of a polymer rich phase. Most frequently, this medium is a solution of the intended capsule wall material. The solvent characteristics of the medium are changed such as to cause phase separation of the wall material. The wall material is thereby contained in a liquid phase which is also dispersed in the same medium as the intended capsule core material. The liquid wall material phase deposits itself as a continuous coating about the dispersed droplets of the internal phase or capsule core material. The wall material is then solidified. This process is commonly known as coacervation. 
     Gelatin or gelatin-containing microcapsule wall material is well known. The teachings of the phase separation processes, or coacervation processes which are described in U.S. Pat. Nos. 2,800,457 and 2,800,458 are incorporated herein by reference. Uses of such capsules are described in U.S. Pat. No. 2,730,456. 
     In-situ polymerization, microcapsule walls are formed from materials present in a discontinuous phase. Thus, the wall forming materials dispersed into the discontinuous phase polymerize and migrate outward to the interface between the discontinuous and continuous phases, resulting in the formation of microcapsule wall. Known techniques of in-situ polymerization include free radical polymerization and the incorporation of reactive polyisocyanates and polyol compounds within the discontinuous phase. 
     More recent processes of microencapsulation involve, and preferred herein, are the polymerization of urea and formaldehyde, monomeric or low molecular weight polymers of dimethylol urea or methylated dimethylol urea, melamine and formaldehyde, monomeric or low molecular weight polymers of methylol melamine or methylated methylol melamine, as taught in U.S. Pat. No. 4,552,811 incorporated herein by reference. These materials are dispersed in an aqueous vehicle and the reaction is conducted in the presence of acrylic acid-alkyl acrylate copolymers. The microcapsule can be formed from materials comprising gellable colloids, carboxymethyl cellulose, gelatin, gelatin-gum arabic, methylated methylol melamine resin, melamine formaldehyde, dimethylol urea, urea formaldehyde, methylol melamine, methylated dimethyl urea, a gelatin anionic polymer, alkyl acrylate-acrylic acid copolymer or other commonly-used polymeric materials used in coacervation. 
     The invention is not limited to one manner of microencapsulation. Processes of microencapsulation are now well known in the art. U.S. Pat. Nos. 2,730,456, 2,800,457; and 2,800,458 describe methods for capsule formation. Other useful methods for microcapsule manufacture are: U.S. Pat. Nos. 4,001,140; 4,081,376 and 4,089,802 describing a reaction between urea and formaldehyde; U.S. Pat. No. 4,100,103 describing reaction between melamine and formaldehyde; British Pat. No. 2,062,570 describing a process for producing microcapsules having walls produced by polymerization of melamine and formaldehyde in the presence of a styrenesulfonic acid. Microcapsules are also taught in U.S. Pat. Nos. 2,730,457 and 4,197,346. The more preferred process for forming microcapsules are from urea-formaldehyde resin and/or melamine formaldehyde resin as disclosed in U.S. Pat. Nos. 4,001,140; 4,081,376, 4,089,802; 4,100,103; 4,105,823; 4,444,699 or most preferably alkyl acrylate-acrylic acid copolymer capsules as taught in U.S. Pat. No. 4,552,811. Each patent described is incorporated herein by reference to the extent each provides guidance regarding microencapsulation processes and materials. 
     Preferably the capsules employed are from 0.1 to 100 microns, preferably 1 to 50 microns, more preferably less than 40, and most preferably less than 30 microns. Other sizes are possible for specific applications. 
     The first step in the encapsulation process is the preparation of the discrete droplets or domains of the monomer in the dispersion medium. Preferably the initiator is blended first with the monomer. Where such materials are in solution or liquid form and the encapsulation is to be by way of, e.g., coacervation, interfacial polymerization, etc., the dispersion medium solution or liquid containing the monomer and initiator is subjected to high shear mixing or agitation to create a suspension, emulsion or colloidal system of discrete domains of the monomers and initiator blend of the requisite size. The catalyst of the second-part curative can be incorporated into a solid binder or substantially solid carrier, and the carrier or binder may be ground and sorted to a desired particle size. A film forming binder or carrier is preferred through solvent solubilized solids can also be employed. The activator of the second-part curative is preferably in separate microcapsules. 
     A useful microencapsulation technique is coacervation wherein the material to be encapsulated (monomer and first-part curative) is dispersed or emulsified in a liquid solution of the material to be used as the wall material. The solution is perturbed to cause a phase separation of the wall material, or at least a portion thereof, from the solvent with all or some of the wall material coating the dispersed material to be encapsulated. In this process, the wall forming material may directly separate out onto the emulsified or dispersed core material or it may form its own emulsion with the droplets of the wall material subsequently depositing on the droplets of the core material. In either case, the liquid wall material deposits itself as a continuous coating about the dispersed droplets of the internal phase or capsule core material of monomers and initiator and the wall material is then solidified. Solution perturbation can be any that affects the solubility of the wall material including changes in temperature and addition of another solvent, including, for example, the addition of a non-solvent for the wall material. It should be readily understood by those skilled in the art that the foregoing may be accompanied by a pH shift with wall materials such as gelatin to promote the phase separation in the wall formation step, as taught in Green (U.S. Pat. Nos. 2,800,457 and 2,800,458, incorporated herein by reference). 
     In coacervation encapsulation, the material to be coated is typically a liquid and is emulsified in the solvent to form droplets which are then coated with the wall material. Oftentimes it is advantageous to also employ an emulsification agent to assist with the emulsification of the carrier materials or precursors thereof. Preferred emulsification agents that can be used are amphiphilic, that is, they contain both hydrophilic and hydrophobic groups in the same molecule. Exemplary emulsification agents include, but are not limited to, partially hydrolyzed polyvinyl alcohol, starch derivatives, cellulose derivatives, polyacrylamide, and the like. A preferred emulsification agent for use in the invention is partially hydrolyzed polyvinyl alcohol or polyacrylic acid. Polyacrylic acid used as a stabilizer with polyamide wall material was particularly preferable. In a preferred method, high shear agitation is provided to the aqueous mixture to achieve a droplet size of less than about 250 microns, preferably less than 100 microns. 
     The conditions for encapsulation will vary based upon the choice of the material used for the capsule wall. Suitable materials for the capsule walls include natural materials such as gelatin, gum arabic, starches, shellac, and rosin, polymers such as polyvinyl alcohol, polyethylene, polypropylene, polystyrene, polyacrylamides, polyethers, polyesters, polyamides, polybutadiene, polyisoprene, silicones, epoxies, polyurethanes, formaldehyde resins such as reaction products of formaldehyde with phenols, urea, and melamine, and copolymers such as polyurethane copolyethers. Alkylacrylate-acrylic acid copolymer is a preferred wall material. 
     Dyes, pigments, fillers, plasticizers, binding agents, and other additives can be incorporated in the microcapsule wall or applied to the microcapsule wall surface. One important parameter to keep in mind when formulating wall materials is permeability. Generally, the wall material should have low permeability, at least with respect to the material to be encapsulated. No or low permeability of the capsule wall is particularly important with respect to the second-part curative in the binder or external to the capsules so as to prevent loss of the curative and premature polymerization of the curable composition. Likewise, it may be important for the microcapsule wall to be impermeable or of low permeability to the curable component of the curable composition so as to prevent any ingress of the same of external materials. Dependent upon the encapsulated material, it may also be desirable to formulate the wall material to have low permeability to certain gases such as oxygen or low permeability to liquids such as water or solvents such as toluene or tetrahydrofuran. The requisite permeation rates will vary for each system, but can be met by judicious choice of the wall material and by degree of crosslinking of the wall material. Generally, as crosslinking increases, the permeation rate decreases. 
     The microcapsule walls can comprise less than 15 percent and preferably from 5 to 10 percent by weight of the encapsulated components. 
     Optionally the microcapsules with monomer and first-part curative, and the second-part curative metal catalyst are dispersed in a binder or adhered to a surface by the binder. The second-part curative activator is separately microencapsulated and also dispersed in the binder or adhered to a surface by the binder. It is to be understood in this context that there are two populations of microcapsules. The first population of microcapsule includes the first-part curative (initiator) with monomer as the capsule core contents. The second-part curative comprises catalyst external to the microcapsules and a second population of microcapsules with activator, preferably a hydrophobic activator. The binder could constitute a carrier material for the capsules. Preferably the binder is a polymeric material or selected from almost any adherent material and preferably selected from binder materials such as polyvinylalcohol, starches, modified starches, gelatin, hydroxyl ethylcellulose, methyl cellulose, methyl-hydroxypropyl cellulose, or selected from many film forming materials such as carboxylated polyvinyl alcohols, polyacrylates, urethanes, polyvinylacetates, vinyl acetate ethylene copolymers, carboxylated vinyl acetate, polystyrene, or various film forming latexes. The binder is preferably used in an amount sufficient to hold the adhesive constituents or capsules onto the substrate but less than an amount that would interfere with adhesion of the formed adhesive when the capsules are ruptured and the contents come into reactive contact. 
     Various additives such as rheology modifiers, rheology aids, tackifiers, plasticizers, rubberized particles, styrene-butadiene rubber lattices, lubricants, toners, coloring agents, can be optionally employed. 
     Optionally, as an alternative embodiment the binder material can be selected to be UV curable binders include materials such as those curable using electron beam, UV radiation or visible light, such as acrylated monomers or oligomers of acrylated epoxy resins, acrylated urethanes and polyester acrylates and acrylated monomers including monoacrylated, multiacrylated monomers, and thermally curable resins such as phenolic resins, urea/formaldehyde resins and epoxy resins, as well as mixtures of such resins. The curing mechanism through UV light can be employed with or without the assistance of an additional thermal cure mechanism. In the context of this application it is understood that the term “radiation curable” embraces the use of visible light, or ultraviolet (UV) light, and electron functions and radiation cure functions can be provided by different functionalities in the same molecule. 
     If UV cure of the binder is desired, generally any UV-curable binder may be chosen. Examples of suitable binders also include unsaturated polyester resin and alkyl resins, unsaturated melamine formaldehyde resins, polybutadiene resins, and unsaturated compounds such as (meth)acrylates and allyl compounds. 
     Examples of UV-curable polyesters include polycondensation products from unsaturated di- or polycarboxylic acids or derivatives thereof, for instance: maleic acid, maleic anhydride and/or fumaric acid, and polyols such as ethylene glycol, 1,2-propane diol, diethylene glycol, hexane diol, glycerol, trimethylol propane or pentaerythritol. These polyesters can be blended with ethylenically unsaturated monomeric compounds, such as methacrylic compounds and vinyl compounds, including acrylate compounds and allyl compounds. 
     Illustrative UV curable (meth)acrylates and allyl compounds include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate; (meth)acrylic esters of aliphatic diols and/or polyols, for instance: ethylene diacrylate, trimethylol propane triacrylate and pentaerythritol tetraacrylate; hydroxyl(meth)acrylates such as hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl methacrylate, 4-hydroxybutyl acrylate and pentaerythritol triacrylate and allyl compounds such as diallyl phthalate, diallyl maleate, triallyl isocyanurate and ethylene glycol diallyl ether. 
     A desirable UV binder is urethane acrylate resin, more particularly at least one isocyanate group-containing adduct of (a) an acrylic or methacrylic hydroxyl ester having 5 to 20 carbons atoms and (b) a polyisocyanate having 4 to 44 carbon atoms and 2 to 4 isocyanate groups. As examples of suitable isocyanate compounds may be mentioned hexamethylene diisocyanate, 2,2,4-trimethylhexane-1,6-diisocyanate, 2,4,4-trimethylhexane-1,6-diisocyanate, and cyclohexyl-1,4-diisocyanate, or the adduct of hexamethylene diisocyanate. 
     Suitable photoinitiators include for example: aromatic carbonyl compounds such as benzyl, benzyl dimethyl ketal, acetophenone, substituted acetophenones, thioxanthone chlorothioxanthone and preferably benzophenone. Optionally, use may be made of compounds such as aromatic azo compounds and compounds such as benzoin and ethers thereof, such as the methyl ether, the ethyl ether, the propyl ether and the t-butyl ether. Mixtures of photoinitiators may also be used. 
     The photoinitiator is usually present in an amount of 0.05 to 10% by weight, based on the UV-curable binder. Some free radical polymerizations are inhibited by oxygen and may require provision of an inert atmosphere. Microencapsulation of components can help to restrict oxygen contact. 
     Preferably the binder in a UV reactive system is a reactive oligomer or prepolymer which polymerizes when subjected to UV radiation in the presence of a suitable initiator. An optional component of the binder can be commonly employed diluents which modify the cure rate and, for example, the viscosity of the uncured composition. The binder must be capable of adhering to the substrate on curing, but it should of course also wet or adhere to the substrate before curing. 
     The following is an illustrative example of a UV curable binder. CN monomers are products of Sartomer (Exton, Pa.): CN550 (amine modified polyether acrylate oligomer) 53.2% by weight; CN501 (amine modified polyether acrylate oligomer) 22.8%; CN976 (aromatic urethane diacrylate) 20%; CN385 (benzophenone) 2%; and Irgacure 184 (photoinitiator) 2% (Ciba Specialty Chemicals). Viscosity at 25° C. is about 2000 mPa. 
     The components of the second-part curative preferably are water soluble or water dispersible and are preferably external to the capsules. The components that are hydrophobic or oil soluble are preferably internal to the capsules. Most preferably the activator is selected to be hydrophobic and is separately encapsulated in a second population of microcapsules, separate and distinct from the first population of microcapsules encapsulating the monomer and first curative comprising initiator. 
     The second-part curative comprises a catalyst and activator. The second-part curative is external to the first population of polymeric microcapsules, on the outside capsule wall, or in the binder. In one embodiment, the monomer is a difunctional methacrylate, and the monomer can include in addition a monofunctional methacrylate, such as furfuryl methacrylate. The difunctional methacrylate is preferably butylene glycol dimethacrylate, or hexane diol dimethacrylate. 
     Looking now at the drawings,  FIG. 1  depicts an embodiment according to the invention. Monomer, and initiator which is the first-part curative, form the core of microcapsules 1, referred to herein as the first population of microcapsules. Catalyst  2 A, a metallic salt or organic acid or metal ion, is shown outside of microcapsules  1 . Sizes are exaggerated. 
     Activator  2 B such as a tertiary amine, imide or amide can be separately encapsulated to form a second population of microcapsules. The microcapsule  5  for activator  2 B in  FIG. 1  is depicted using dotted lines since the encapsulation is optional. Other optional configurations for activator  2 B include the arrangement of  FIG. 4  wherein activator  2 B is shown dispersed in a binder material  4 ′ or carrier. The binder materials  4 ,  4 ′, and  4 ″ can be the same or different binders. The binder can constitute a matrix material or foam that temporarily isolates activator  2 B from catalyst  2 A. 
     An alternative arrangement with larger partial separation of catalyst  2 A from activator  2 B is depicted in  FIG. 5 . The binder materials  4 ,  4 ′ and  4 ″ can each be the same or different binders. 
       FIG. 2  illustrates the curable composition of the invention as a coating onto substrate  3  which can be any relatively rigid material such as glass, hardwood, fiberboard, plywood, oriented strandboard (OSB), chipboard, fiberglass, polymeric, natural or synthetic, composites such as fibers dispersed in various matrices such as resins, metals, or ceramics. The substrate should be selected to be receptive to the adhesive composition and should be tested for forming strong bonding with the adhesive composition. Medium-density fiberboard (MDF) and high-density fiberboard are suitable examples of fiberboard. 
     In  FIG. 2  catalyst  2 A and activator  2 B are shown dispersed in binder materials  4  and  4 ′ respectively. Microcapsules  1  with monomer and initiator core are shown adhered to binder material  4 ′. 
     Dimensions are exaggerated in the drawings. The quantity of the binder is exaggerated and can be optionally limited to that quantity necessary to adhere the components of the adhesive system. It is therefore not always necessary to envelope the catalyst or activator, especially if these constituents are separately encapsulated. 
       FIG. 3  is an alternative embodiment wherein microcapsules  1  containing monomer and the first-part curative are dispersed in binder material  4 ′ overcoated over lower binder material layer  4 . The binder materials can be the same or different. Microcapsules  1  containing monomer and the first-part curative form a first population of microcapsules. A second population of microcapsule  5  is (shown smaller in size and ellipsoid in shape for purposes of illustration. Size selection is optional and can be selected to be larger than the first population of microcapsules). The second population of microcapsules contain activator  2 B within the core. 
     In  FIG. 3 , as a further alternative, the capsules  1 , activator  2 B, catalysts  2 A can optionally be uniformly or chaotically dispersed in a single binder material  4  forming a single layer adhesive coating. The single layer adhesive coating is often preferable and most economic. 
     In  FIG. 4  microcapsules  1  contain monomer and the first-part curative. The second-part curative of catalyst  2 A and activator  2 B is illustrated as dispersed in separate layers of binder material  4  and  4 ′. Binder materials  4 ,  4 ′ and  4 ″ can be the same or different in each layer. Microcapsules  1  are shown in the top binder layer  4 ″. Alternatively, microcapsules  1  can be dispersed throughout any of the binder material layers. 
     In  FIG. 4  activator  2 B is a lower layer and catalyst  2 A forms a middle layer or is dispersed in a binder  4 . 
     In  FIG. 5  the second-part curative is disposed on opposite sides of the binder layer with microcapsules containing monomer and the first-part curative. Catalyst  2 A is depicted below capsules  1 , and activator  2 B is illustrated applied as an overcoat on the opposite side of capsules  1  in binder  4 ″. Optionally binder  4 ″ can be omitted if adherence via binders  4 ′ and  4  is sufficient to hold capsules  1 , activator  2 B and catalyst  2 A in place. 
       FIG. 6  illustrates alternative embodiments A and B where the components of the adhesive system are coated onto separate surfaces  6  and  7 . Surfaces  6  and  7  can take the form of a variety of mating or interlocking configurations such as the thread surfaces of a bolt and nut, mortise and tenon, dovetail, interlocking tongue and groove, snap-lock parts, male and female couplers, and various other configurations bringing at least two surfaces into proximate contact. Surfaces  6  and  7  can include a tab and corresponding recess, detent, friction fit or other mechanical interlock to facilitate holding the surfaces in place until the adhesive cures or sets. The adhesive system of the invention provides a dry-to-the-touch adhesive that can facilitate more permanent joining and assembly. 
     In  FIG. 6  version A capsules  1  with first-part curative are shown applied to at least one face of surface  7 . Catalyst  2 A is also shown applied along with the first population of capsules  1 . 
     A second population of capsules  5  encapsulating activator  2 B are applied to at least one face of surface  6 . 
     In  FIG. 6 , an alternative embodiment is also illustrated as version B wherein the catalyst  2 A is applied to a face of surface  6  with the second population of capsules  5  which encapsulate activator  2 B. Sufficient binder (not shown) should be utilized to adhere capsules  1  and  5  and catalyst  2 A to hold them in position until the capsules are ruptured. This allows the free flowing liquid contents of the capsules to come into reactive contact such that the first-part curative and second-part curative can react with the monomer forming the structural adhesive. 
     As a yet further alternative embodiment, capsules  1  and  5  can be applied with binder to one or the same surface, and a catalyst  2 A can be applied to a mating surface. All such variations are within the scope of the invention. 
     The examples herein are considered to illustrate the invention and should not be considered as limiting. In the examples all parts or proportions are by weight and all measurements are in the metric system, unless otherwise indicated. 
     EXAMPLE 1  
     Preparation of Microcapsules Containing 5% Initiator in Internal Phase 
     The composition of the capsules is as follows: 
     
       
         
           
               
               
               
               
             
               
                   
               
             
            
               
                 Internal Phase (IP) 
                 Hexanedioldimethacrylate, 
                 156.9 
                 g 
               
               
                   
                 Tetrahydrofurfuryl methacrylate, 
                 17.4 
                 g 
               
               
                   
                 Cumene hydroperoxide (CHP) 
                 9.2 
                 g 
               
               
                 1 st  Water Phase: 
                 Deionized water, 
                 112 
                 g 
               
               
                   
                 Acrylic acid butyl acrylate copolymer, 
                 17.5 
                 g 
               
               
                   
                 5% NaOH aqueous solution 
                 14.1 
                 g 
               
               
                   
                 methoxymethyl methylol melamine 
                 2.9 
                 g 
               
               
                 2 nd  Water Phase 
                 Deionized water 
                 33.0 
                 g 
               
               
                   
                 Polyacrylic acid 
                 6.1 
                 g 
               
               
                   
                 Methoxymethyl methylol melamine 
                 17.4 
                 g 
               
               
                   
               
            
           
         
       
     
     A procedure for preparing microcapsules is as follows. The 1 st  Water Phase was prepared according to the composition as listed above, and pH of the aqueous solution was adjusted to 5.82 with 5% sodium hydroxide solution, and maintaining the temperature of the solution at 65° C. Then the premixed internal phase was pre-heated to 65° C. was pre-emulsified into the 1 st  Water Phase by high shear agitation at 800 rpm to form an emulsion and then milled at 1700 rpm with a high shear milling blade until an emulsion droplet size of 14 μm was obtained as analyzed by a Model 780 Accusizer. Thereafter, the 2 nd  Water Phase was added to the emulsion along with 2.2 grams of sodium sulfate. The emulsion was mixed and maintained at 65° C. for 8 hrs. An average capsule size of 14.8 μm was obtained. 
     EXAMPLE  
     Preparation of Microcapsules Containing 2.5% Initiator in Internal Phase 
     The composition of and the procedures for preparing the microcapsules are the same as in Example 1 except for the following: 
     
       
         
           
               
               
               
             
               
                   
               
             
            
               
                 Internal Phase (IP) 
                 Hexanedioldimethacrylate, 
                 161.0 g  
               
               
                   
                 Tetrahydrofurfuryl methacrylate, 
                 17.9 g 
               
               
                   
                 Cumene hydroperoxide (CHP) 
                 4.58 g 
               
               
                   
               
            
           
         
       
     
     EXAMPLE 3  
     Preparation of Microcapsules Containing 1.5% Initiator in Internal Phase 
     The composition of and the procedures for preparing the microcapsules are the same as in Example 1 except for the following: 
     
       
         
           
               
               
               
             
               
                   
               
             
            
               
                 Internal Phase (IP) 
                 Hexanedioldimethacrylate, 
                 162.6 g  
               
               
                   
                 Tetrahydrofurfuryl methacrylate, 
                 18.1 g 
               
               
                   
                 Cumene hydroperoxide (CHP) 
                 2.75 g 
               
               
                   
               
            
           
         
       
     
     EXAMPLE 4  
     Preparation of Microcapsules Containing 5% Initiator in Internal Phase 
     The composition of and the procedures for preparing the microcapsules are the same as in Example 1 except for the following: 
     
       
         
           
               
               
               
               
             
               
                   
               
             
            
               
                 1 st  Water Phase: 
                 Deionized water, 
                 112 
                 g 
               
               
                   
                 Acrylic acid butyl acrylate copolymer, 
                 9.1 
                 g 
               
               
                   
                 5% NaOH aqueous solution 
                 14.1 
                 g 
               
               
                   
                 methoxymethyl methylol melamine 
                 2.9 
                 g 
               
               
                 2 nd  Water Phase 
                 Deionized water 
                 33.0 
                 g 
               
               
                   
                 Polyacrylic acid 
                 6.1 
                 g 
               
               
                   
                 Methoxymethyl methylol melamine 
                 8.8 
                 g 
               
               
                   
               
            
           
         
       
     
     EXAMPLE 5 
     Preparation of Microcapsules Containing 5% Initiator in Internal Phase 
     The composition of and the procedures for preparing the microcapsules are the same as in Example 1 except for the following: 
     
       
         
           
               
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Internal Phase (IP) 
                 Hexanedioldimethacrylate, 
                 139.5 g 
               
               
                   
                   
                 Tetrahydrofurfuryl methacrylate, 
                  34.8 g 
               
               
                   
                   
                 Cumene hydroperoxide (CHP) 
                  9.2 g 
               
               
                   
                   
               
            
           
         
       
     
     EXAMPLE 6  
     Preparation of Microcapsules Containing 1% Activator in Internal Phase 
     The composition of the capsules is as follows: 
     
       
         
           
               
               
               
               
             
               
                   
               
             
            
               
                 Internal Phase (IP) 
                 Hexanedioldimethacrylate, 
                 163.5 
                 g 
               
               
                   
                 Tetrahydrofurfuryl methacrylate, 
                 18.2 
                 g 
               
               
                   
                 3,5-diethyl-1,2-dihydro-1-phenyl- 
                 1.83 
                 g (1%) 
               
               
                   
                 2-pyropyl pyridine, 
               
               
                 1 st  Water Phase: 
                 Deionized water, 
                 112 
                 g 
               
               
                   
                 Acrylic acid butyl acrylate 
                 17.8 
                 g 
               
               
                   
                 copolymer, 
               
               
                   
                 5% NaOH aqueous solution 
                 13.6 
                 g 
               
               
                   
                 methoxymethyl methylol melamine 
                 2.9 
                 g 
               
               
                 2 nd  Water Phase 
                 Deionized water 
                 32.0 
                 g 
               
               
                   
                 Polyacrylic acid 
                 6.1 
                 g 
               
               
                   
                 Methoxymethyl methylol 
                 17.2 
                 g 
               
               
                   
                 melamine 
               
               
                   
               
            
           
         
       
     
     A procedure for preparing microcapsules is as follows. The 1 st  Water Phase was prepared according to the composition as listed above, and pH of the aqueous solution was adjusted to 5.82 with 5% sodium hydroxide solution, and temperature of the solution was maintained at 65° C. Then the premixed internal phase pre-heated to 65° C. was emulsified into the 1 st  Water Phase by mixing at 700 rpm to form an emulsion, and then milled at 1700 rpm with a high shear milling blade. After milling for 15 min, the 2 nd  Water Phase was added to the emulsion along with 2.2 grams of sodium sulfate. The emulsion was mixed and maintained at 65° C. for 8 hrs. An average capsule size of 15.4 μm was obtained as analyzed by a Model 780 Accusizer. 
     EXAMPLE 7 
     Preparation of Microcapsules Containing 5% Activator in Internal Phase 
     The composition of the capsules is as follows: 
     
       
         
           
               
               
               
               
             
               
                   
               
             
            
               
                 Internal Phase (IP) 
                 Hexanedioldimethacrylate, 
                 108 
                 g 
               
               
                   
                 Tetrahydrofurfuryl methacrylate, 
                 12 
                 g 
               
               
                   
                 3,5-diethyl-1,2-dihydro-1-phenyl- 
                 6 
                 g (5%) 
               
               
                   
                 2-pyropyl pyridine, 
               
               
                 1 st  Water Phase: 
                 Deionized water, 
                 104 
                 g 
               
               
                   
                 Acrylic acid butyl acrylate 
                 18 
                 g 
               
               
                   
                 copolymer, 
               
               
                   
                 5% NaOH aqueous solution 
                 14 
                 g 
               
               
                   
                 methoxymethyl methylol melamine 
                 3.0 
                 g 
               
               
                 2 nd  Water Phase 
                 Deionized water 
                 32.0 
                 g 
               
               
                   
                 Polyacrylic acid 
                 6.0 
                 g 
               
               
                   
                 Methoxymethyl methylol 
                 17.7 
                 g 
               
               
                   
                 melamine 
               
               
                   
               
            
           
         
       
     
     A procedure for preparing microcapsules is as follows. The 1 st  Water Phase was prepared according to the composition as listed above, and pH of the aqueous solution was adjusted to 5.82 with 5% sodium hydroxide solution, and temperature of the solution was maintained at 65° C. Then the premixed internal phase pre-heated to 65° C. was emulsified into the 1 st  Water Phase by a mixer at 700 rpm to form an emulsion, and then milled at 1500 rpm with a high shear milling blade until an emulsion droplet size of 14 μm was obtained as analyzed by a Model 780 Accusizer. Thereafter, the 2 nd  Water Phase was added to the emulsion along with 2.3 grams of sodium sulfate. The emulsion was mixed and maintained at 65° C. for 8 hrs. An average capsule size of 15.4 μm was obtained. 
     EXAMPLE 8  
     Preparation of Microcapsules Containing Only Activator in Internal Phase 
     The composition of the capsules is as follows: 
     
       
         
           
               
               
               
             
               
                   
               
             
            
               
                 Internal Phase (IP) 
                 3,5-diethyl-1,2-dihydro-1-phenyl-2- 
                  183 g 
               
               
                   
                 pyropyl pyridine, 
               
               
                 1 st  Water Phase: 
                 Deionized water, 
                  112 g 
               
               
                   
                 Acrylic acid butyl acrylate copolymer, 
                 17.8 g 
               
               
                   
                 5% NaOH aqueous solution 
                 13.6 g 
               
               
                   
                 methoxymethyl methylol melamine 
                  2.9 g 
               
               
                 2 nd  Water Phase 
                 Deionized water 
                 32.0 g 
               
               
                   
                 Polyacrylic acid 
                  6.1 g 
               
               
                   
                 Methoxymethyl methylol melamine 
                 17.2 g 
               
               
                   
               
            
           
         
       
     
     A procedure for preparing microcapsules is as follows. The 1 st  Water Phase was prepared according to the composition as listed above, and pH of the aqueous solution was adjusted to 5.82 with 5% sodium hydroxide solution, and temperature of the solution was maintained at 65° C. Then the premixed internal phase pre-heated to 65° C. was emulsified into the 1 st  Water Phase by a mixer at 700 rpm to form an emulsion, and then milled at 1500 rpm with a high shear milling blade. After milling for 15 mins, the 2 nd  Water Phase was added to the emulsion along with 2.2 grams of sodium sulfate. The emulsion was mixed and maintained at 65° C. for 8 hours. An average capsule size of 16.4 μm was obtained as analyzed by a Model 780 Accusizer. 
     EXAMPLE 9 
     Preparation of Microcapsules Containing 5% Activator in Internal Phase 
     The composition of and the procedures for preparing the microcapsules are the same as in Example 7 except for the following: 
     
       
         
           
               
               
               
             
               
                   
               
             
            
               
                 1 st  Water Phase: 
                 Deionized water, 
                 112 g  
               
               
                   
                 Acrylic acid butyl acrylate copolymer, 
                 9.1 g 
               
               
                   
                 5% NaOH aqueous solution 
                 14.1 g  
               
               
                   
                 methoxymethyl methylol melamine 
                 2.9 g 
               
               
                 2 nd  Water Phase 
                 Deionized water 
                 33.0 g  
               
               
                   
                 Polyacrylic acid 
                 6.1 g 
               
               
                   
                 Methoxymethyl methylol melamine 
                 8.8 g 
               
               
                   
               
            
           
         
       
     
     EXAMPLE 10 
     Preparation of Microcapsules Containing Only Activator in Internal Phase 
       
     
       
         
           
               
               
               
               
             
               
                   
               
             
            
               
                 Internal Phase: 
                 PDHP (3,5-diethyl-1,2-dihydro-1-phenyl- 
                 290 
                 g 
               
               
                   
                 2-pyropyl pyridine) 
               
               
                 Water Phase I 
                 water 
                 230.4 
                 g 
               
               
                   
                 Acrylic acid butyl acrylate copolymer 
                 3.0 
                 g 
               
               
                   
                 5% NaOH 
                 22.1 
               
               
                   
                 methoxymethyl methylol melamine 
                 4.8 
                 g 
               
               
                 Water Phase II 
                 water 
                 126 
                 g 
               
               
                   
                 Polyacrylic acid 
                 10.1 
                 g 
               
               
                   
                 Methoxymethyl methylol melamine 
                 29.5 
                 g 
               
               
                   
               
            
           
         
       
     
     A general procedure of capsule manufacture is described. 290 grams of 3,5-diethyl-1,2-dihydro-1-phenyl-2-pyropyl pyridine (PDHP) is selected as an internal phase. 
     A first water phase is prepared of 230.4 grams water 3 grams of acrylic acid butylacrylate copolymer, and 4.8 grams methoxymethyl methylol melamine. pH is adjusted to 5.68 with 5% NaOH. 
     A second water phase is prepared of 126 grams of water, 10.1 grams polyacrylic acid, and 29.5 grams methoxymethyl methylol melamine. 
     Water phase I is maintained at 65° C. with stirring (500 rpms). The internal phase is added and stirring increased to blend at high speed to achieve an emulsion size of 27.1 μm. 
     The second water phase is added along with 3.8 grams Na 2 SO 4  and the mixture heated for 8 hours at 65° C. Capsules of approximately 26 μm. size are obtained. 
     EXAMPLE 11 
     Adhesive Coating Formulation 
     Capsules containing initiator and capsules containing activator were mixed with catalyst and binders, and were coated on cellulosic substrate made of high density fiber boards. Alternatively catalyst may be pre-applied on the substrate, mixed in the liquid coating formulation, or applied in both. The binder used was a vinyl acetate-ethylene copolymer latex. After the coating was dried, two pieces of substrate with the coating applied using a snap-fit tongue and groove assembly were mated together, and the compression fit exerted sufficient shear force to break the capsules in the coating, resulting in reactive contact among initiator, activator, monomers and catalyst. Table 4 shows the bonding strength tested with an EJA Materials Tester (Thwin-Albert Company). 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Bonding strength with different adhesive formulations 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                 Capsule 
                   
                   
                   
                   
               
               
                   
                   
                   
                 Ratio of 
                   
                   
                 Copper 
               
               
                   
                 Initiator 
                 Activator 
                 Initiator to 
                   
                 Copper 
                 in slurry 
                 Strength 
               
               
                 Test # 
                 Capsules 
                 Capsules 
                 Activator 
                 Binder (%) 
                 pre-coat 
                 (ppm) 
                 (N) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 1 
                 Example 1 
                 Example 7 
                 1/1 
                 0 
                 Yes 
                 740 
                 0 
               
               
                 2 
                 Example 1 
                 Example 7 
                 1/1 
                 0 
                 Yes 
                 1480 
                 0 
               
               
                 3 
                 Example 1 
                 Example 7 
                 1/1 
                 5 
                 Yes 
                 740 
                 89 
               
               
                 4 
                 Example 1 
                 Example 7 
                 1/1 
                 5 
                 Yes 
                 1480 
                 519 
               
               
                 5 
                 Example 1 
                 Example 7 
                 1/1 
                 5 
                 No 
                 4400 
                 510 
               
               
                 6 
                 Example 4 
                 Example 9 
                 1/1 
                 0 
                 Yes 
                 1480 
                 396 
               
               
                 7 
                 Example 4 
                 Example 9 
                 1/1 
                 5 
                 Yes 
                 1480 
                 670 
               
               
                 8 
                 Example 1 
                 Example 6 
                 1/2 
                 0 
                 No 
                 1480 
                 0 
               
               
                 9 
                 Example 1 
                 Example 6 
                 1/2 
                 0 
                 Yes 
                 1480 
                 869 
               
               
                 10 
                 Example 1 
                 Example 6 
                 1/2 
                 5 
                 Yes 
                 1480 
                 921 
               
               
                 11 
                 Example 1 
                 Example 8 
                  1/99 
                 5 
                 Yes 
                 1480 
                 719 
               
               
                 12 
                 Example 1 
                 Example 8 
                  5/95 
                 5 
                 Yes 
                 1480 
                 284 
               
               
                 13 
                 Example 1 
                 Example 8 
                 10/90 
                 5 
                 Yes 
                 1480 
                 191 
               
               
                 14 
                 Example 2 
                 Example 8 
                  1/99 
                 5 
                 Yes 
                 1480 
                 633 
               
               
                 15 
                 Example 3 
                 Example 8 
                  1/99 
                 5 
                 Yes 
                 1480 
                 636 
               
               
                 16 
                 Example 5 
                 Example 10 
                  1/99 
                 5 
                 No 
                 4400 
                 950 
               
               
                   
               
            
           
         
       
     
     EXAMPLE 12 
     Initiator and Activator Capsules Coated on Separate Substrates 
     Capsules containing initiator and capsules containing activator may be separately formulated with other coating components, such as catalyst and binders. In the following table, these were coated on separate substrates to be bonded. Table 5 shows bonding strength tested with an EJA Materials Tester (Thwin-Albert Company). 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Bonding strength for capsules coated on separate substrates 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                 Capsule 
                   
                   
                   
                   
               
               
                   
                   
                   
                 Ratio of 
                   
                   
                 Copper 
                 Strength 
               
               
                   
                 Initiator 
                 Activator 
                 Initiator to 
                 Binder 
                 Copper 
                 in slurry 
                 (N) 
               
               
                 Test # 
                 Capsules 
                 Capsules 
                 Activator 
                 (%) 
                 pre-coat 
                 (ppm) 
                 (Newtons) 
               
               
                   
               
               
                 1 
                 Example 1 
                 Example 7 
                 1/1 
                 0 
                 Yes 
                 1480 
                 156 
               
               
                 2 
                 Example 1 
                 Example 7 
                 1/1 
                 5 
                 Yes 
                 1480 
                 442 
               
               
                 3 
                 Example 1 
                 Example 6 
                 1/2 
                 0 
                 Yes 
                 1480 
                 772 
               
               
                 4 
                 Example 1 
                 Example 6 
                 1/2 
                 5 
                 Yes 
                 1480 
                 961 
               
               
                 5 
                 Example 1 
                 Example 8 
                  1/99 
                 5 
                 Yes 
                 1480 
                 896 
               
               
                 6 
                 Example 5 
                 Example 10 
                  1/99 
                 5 
                 No 
                 4400 
                 966 
               
               
                   
               
            
           
         
       
     
     EXAMPLE 13 
     Different Binders 
     Many different kinds of binder materials can be used in the coating formulation. They should be able to hold capsules and other components of the coating in place, and has no adverse effect on bonding strength. The following binders were tested: 
     A—Vinyl acetate-ethylene copolymer 
     B—Acrylic latex 
     C—Carboxylated vinyl acetate resin 
     D—Polyvinyl acetate 
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 Bonding strength with different binders 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                 Capsule 
                   
                   
                   
                   
               
               
                   
                   
                   
                 Ratio of 
                   
                   
                 Copper 
               
               
                   
                 Initiator 
                 Activator 
                 Initiator to 
                   
                 Copper 
                 in slurry 
                 Strength 
               
               
                 Binders 
                 Capsules 
                 Capsules 
                 Activator 
                 Binder (%) 
                 pre-coat 
                 (ppm) 
                 (N) 
               
               
                   
               
               
                 A 
                 Example 1 
                 Example 7 
                 1/1 
                 5 
                 Yes 
                 1480 
                 790 
               
               
                 B 
                 Example 1 
                 Example 7 
                 1/1 
                 5 
                 Yes 
                 1480 
                 595 
               
               
                 C 
                 Example 1 
                 Example 7 
                 1/1 
                 5 
                 Yes 
                 1480 
                 775 
               
               
                 D 
                 Example 1 
                 Example 7 
                 1/1 
                 5 
                 Yes 
                 1480 
                 560 
               
               
                   
               
            
           
         
       
     
     EXAMPLE 14  
     Viscosity of monomer blends as the internal phase of capsules. M corresponds to THFA/HDDMA 50/50 ratio 
     
       
         
           
               
               
             
               
                   
               
               
                   
                 Viscosity (cps. 25° C.) 
               
               
                   
                 Brookfield model LVF, spindle 2, 
               
               
                 Monomers in the internal phase 
                 60 rpm 
               
               
                   
               
             
            
               
                 Melamine acyrlate oligomer (Doresco 
                 Approx. 15 
               
               
                 UV75° C., 1500 cps)/M 50/50 ratio 
               
               
                 Bisphenol A base epoxy acrylate 
                 Approx. 25 
               
               
                 (CN120, 2150 cps @ 65° C.)/ 
               
               
                 M 40/60 ratio 
               
               
                 Urethane dimethacrylate (CN 1963, 
                 Approx. 53 
               
               
                 1740 cps@65° C.)/M 50/50 ratio 
               
               
                 Polybutadiene (Ricon 130, 750 cps)/ 
                 Approx. 25 
               
               
                 M 50/50 ratio 
               
               
                   
               
            
           
         
       
     
     The above blends can contain up to 5% by weight of DPC activator or CHP initiator. HDDMA is hexanediol dimethacrylate. THFA is tetrahydrofurfuryl methacrylate. 
     CN polymers and Ricon™ are trademarks of Sartomer (Exton, Pa.). Doresco™ is a trademark of Lubrizol (Wickliffe, Ohio). CHP is cumene hydroperoxide; DPC is diphenyl carbazone; CN120 is bisphenol epoxy acrylate. 
     As used herein, “Mw” means molecular weight average, unless otherwise noted to the contrary. 
     Although the flooring system has been described with reference to multiple floor boards, it is considered within the invention to use the dry preglue system as described herein on any surface of a molding, such transition moldings, end moldings, T-moldings, carpet reducers, hard surface reducers, quarter round moldings, wall base moldings or shoe moldings, as described, for example, in U.S. Pat. No. 6,8660,074, herein incorporated by reference in its entirety.