Patent Application
20240026168
The present disclosure relates to debonding coating compositions are used as a surface treatment on substrates prior to application of a bonding adhesive, potting adhesive or coating adhesive. The debonding coating provides a debondable surface on which the bonding adhesive can bond and maintain the bonding adhesive's strength and properties. The debonding coating, when exposed to heat, debonds (separates or is easily removed) from the substrate, thus allowing the bonding adhesive overlaid thereon to also separate from the substrate.
Thermally expandable particles (TEPs) have been used to make adhesives debondable. This effort often requires significant effort in reformulating and using only chemistries which are compatible with the TEPs. For example, EP 1141104 B1 discloses the use of heat expandable inorganic particles such as graphite, vermiculite, pearlite, mica, wermlandite, thanmasite and hydrotalcite, which are added to an epoxy resin. When heated the particles expand, allowing the adhesive to debond from a substrate. U.S. Pat. No. 10,800,956 B2 to Henkel AG, discloses a debondable reactive hot melt which contain organic or inorganic salts, which when heated cause the hot melt to melt, allowing debonding from the substrate.
Currently, there is a need for a universal debonding coating which can be used with a variety of different adhesives in a variety of different applications, such as bonding, potting and coating applications and which does not require reformulation due to incompatibility concerns.
In one aspect of the invention, there is provided an adhesive debonding coating composition for thermally debonding a cured adhesive bond-line from a substrate, said debonding coating including:
In another aspect of the invention, there is provided a method of forming debondable adhesion to a substrate which includes:
applying to a surface of said substrate a composition which includes:
In another aspect of the invention there is provided a structure which includes at least one surface, said at least one surface including a cured debonding coating layer in direct contact with said surface and an additional adhesive bonding layer over said debonding coating, wherein said debonding layer includes an adhesive matrix capable of withstanding temperatures greater than about 250° C. and heat expandable microparticles, wherein upon heating the microparticles to a temperature of about 70° to about 250° C., the microparticles expand to cause debonding of the coating and bonding layers from the surface.
In yet another aspect of the invention there is provided a method of forming a debondable adhesion to a substrate which includes:
In yet another aspect of the invention there is provided a heat-debondable adhesive joint which includes:
The present disclosure uses a curable adhesive matrix to form a debondable coating which can be used universally as a pre-coating to render a variety of different adhesive compositions debondable. The debonding coating is be applied to the substrate first to form a debondable interface, followed by application of the bonding adhesive compositions. The debonding coating is cured on the substrate prior to application of the bonding adhesive and does not affect the adhesive properties of the bonding adhesive.
Among the advantages of the present disclosure are: a single coating can be used for a wide variety of adhesive formulations, thereby eliminating the compatibility issues common in the prior art; bonded, potted and coated parts can now easily be maintained and serviced, for example replaced or upgraded by debonding; reclamation of parts is greatly facilitated due to debonding and removal of the recoating and adhesive layers; temporary fixtures can be formed and easily separated; and end of part life can be easily handled by replacement. Additionally, the debonding coatings allow for control of debonding through temperature control.
The debonding coating includes a curable matrix which may be selected from epoxies, silicones, polyurethanes and silicone modified polymers, as well as copolymers and combinations of these polymers. Desirably, the curable matrix is capable of withstanding temperatures greater than the bonding adhesive, for example capable of withstanding temperatures of at least about 250° C.
Non-limiting examples of useful epoxy compositions for use as the debonding coating matrix include two part adhesive compositions having an epoxy resin and a curing (hardening) agent such as a polyamide, which when nixed together cause the epoxy to cure. Examples of useful commercially available epoxy compositions are those sold by the Henkel Corporation, such as Loctite Hysol E-90FL, Loctite Hysol E-120HP, Loctite E-30CL, Loctite E-00CL.
Non-limiting examples of useful silicone compositions for use as the debonding coating matrix include moisture curing, uv curing, uv/moisture curing, heat curing and moisture/heat curing compositions. Combinations of silicone compositions (mixtures and copolymers) may also be employed. Examples of useful commercially available silicone compositions are those sold by the Henkel Corporation, such as Loctite SI 5600, Loctite SI 5607, Loctite 5900 et al.
Non-limiting examples of useful polyurethane compositions for use as the debonding coating matrix include polyurethane compositions, such as 1 part moisture cured polyurethane, 2 part polyurethane, polyurea, and combinations thereof. Examples of useful commercially available polyurethane compositions are those sold by the Henkel Corporation, such as Loctite UK 1351, Loctite UK 1366, Loctite UK U-09FL, Loctite UK U-05FL, Loctite UK 3364. Combination of these polyurethane polymer compositions are useful.
Non-limiting examples of useful silicone-modified polymers compositions for use as the debonding coating matrix include commercially available silicone-modified compositions such as those sold by the Henkel Corporation, such as Loctite MS 939, Loctite MS 930, Loctite MS 9399 and Loctite MS 647. Combination of these silicone-modified polymers compositions are useful.
The debonding coating includes the incorporation into the adhesive matrix about 1% to about 60%, or 10% to about 20%; or about 15% to about 30%; or about 30% to about 40%; or about 20% to about 50%; or about 25% to about 60% of heat expandable microparticles. The microparticles desirably are microspheres, which upon the application of a specific temperature, expand within the matrix, causing the cured matrix to debond from the surface of the substrate upon which it was cured.
The amount of heat expandable microparticles present in the matrix may be selected to tailor and control the debonding. For example, a higher amount of microparticles may be required for certain debonding matrices. For flexible coating matrix where expandable particle can readily expand upon heating, the amount of expandable particle needed will be low; on the other end, a hard and brittle coating may also need smaller amount of debondable particles as small amount of expansion is enough to cause crack and delamination from the surface. For tough coating matrix a higher amount of expandable particle is often needed, otherwise after heat expansion the coating may become a foamy but still strong coating. Also, the expansion temperature is also a determining factor in controlling the debonding. It is an aspect of the invention that the debonding coating composition be capable of remaining substantially intact during the curing of the bonding adhesive which is deposited thereon. This require the curing temperature of the bonding adhesive to be lower than the debonding temperature of the coating. Thus, the cured debonding coating composition will be substantially unaffected by the curing temperatures of the bonding adhesive and will also be compatible with the bonding adhesive and not interfere with the adhesive properties of the bonding adhesive.
One particularly useful heat-expandable microsphere is made from polyacrylonitrile shell and a hydrocarbon core, such as those sold under the trade names DUALITE® AND EXPANCEL®. The expandable microspheres may have any expanded size, including from about 5 microns to about 40 microns in diameter. In the presence of heat, the microspheres may increase from about 3 to about 80 times, desirably about 20 to about 80 times, and more desirably about 60 to about 80 times their diameter. The microspheres resemble tiny Ping-Pong balls with a diameter of about 5 to about 40, and consist of a polymer shell that encapsulates a blowing agent. When the microspheres are heated, the blowing agent will increase the pressure at the same time as the polymer shell will become soft and ductile and this causes the microspheres to expand. Once the microspheres are expanded, expanded volume is retained after cooling. Expanded microspheres have a particularly low density (1570 kg/m3). Microspheres also offer other useful features like thermal insulation, sound insulation, increased solar reflection and increased friction on surfaces. The thermal expansion makes it suitable to use as an expanding agent or foaming agent, and it offers a more controlled and uniform foam structure when compared to other foaming agents.
Microspheres may be made from a thermoplastic polymeric shell, which surrounds a core containing a volatile hydrocarbon within. When the microspheres are heated, the hydrocarbon vaporizes and the internal pressure is increased in the microsphere. At the same time, the polymeric shell becomes soft and ductile as it reaches its glass transition temperature (Tg). The microspheres start to expand when the internal pressure of the hydrocarbon gas exceeds the yield strength of the polymer and the decrease in density is substantial since the mass remains the same while the volume increases tremendously. The hydrocarbon works as a blowing agent, and the expansion is controlled by the type and amount of encapsulated blowing agent and the Tg of the polymer. The expansion continues as long as the internal pressure exceeds the yield strength of the polymer shell, or until the shell breaks, or becomes so thin that the hydrocarbon diffuses through the shell, causing the microspheres to decrease in volume.
The microspheres particularly useful in the present invention have a shell that is made of a copolymer of acrylonitrile (ACN), methacrylonitrile (MAN) and methyl acrylate (MA). ACN is the major component and is used because of its excellent barrier properties and chemical resistance, which is due to its semicrystalline structure and high cohesive strength. The barrier properties are very important for the expansion of the microspheres since they determine how much of the blowing agent that is lost through diffusion through the polymer shell which is detrimental for the expansion. MA may be added to lower the Tg and as a result making the shell more ductile. Another way to alter the properties of the polymer shell is to introduce a cross-linker, which decreases the mobility of the polymer chain and increases the Tg. The structure then becomes denser and this will increase the shell's chemical resistance. Cross-linking of the shell is known to have a large effect of the expansion properties, especially on Tmax, the temperature when maximum expansion occurs. The expansion properties of the microspheres can be altered by using different hydrocarbons as blowing agents. The temperature at which the microspheres start to expand is related to the boiling point of the hydrocarbon; a lower boiling point will give a lower expansion temperature and vice versa.
The expandable microspheres have a particular temperature at which they begin to expand Ti (initial expansion temperature) and a second temperature at which they have reached maximum expansion. Microsphere grades are typically sold with specific expansion temperature ranges (Texp), with initial (Ti) and maximum expansion temperatures (Tmax). The initial expansion temperature (Ti) is the typical temperature at which the microspheres start to expand, and the maximum expansion temperature (Tmax) is the temperature at which about 80% of the microspheres have expanded.
Polyacrylonitrile (PAN), also known as polyvinyl cyanide and Creslan 61, is a synthetic, semicrystalline organic polymer resin, with the linear formula (C3H3N)n. Though it is thermoplastic, it does not melt under normal conditions. It degrades before melting. It melts above 300° C. if the heating rates are 50 degrees per minute or above. Almost all PAN resins are copolymers made from mixtures of monomers with acrylonitrile as the main monomer. It is a versatile polymer used to produce large variety of products including ultra filtration membranes, hollow fibers for reverse osmosis, fibers for textiles, oxidized PAN fibers. PAN is a component repeat unit in several important copolymers, such as styrene-acrylonitrile (SAN) and acrylonitrile butadiene styrene (ABS) plastic.
The debondable coating compositions of the present disclosure include the following characteristics:
The debondable coating compositions of the present invention optionally may further include any plasticizers, tackifiers, humectants, fillers, pigments, dyes, stabilizers, rheology modifiers, polyvinyl alcohols, preservatives, e.g., antioxidant, biocide; and mixtures thereof. These components can be included in an amount of from about 0.05% to about 15% by weight of the debondable coating compositions.
Useful bonding adhesives may be selected from any adhesive composition which is capable of bonding to the debonding coating composition. Non-limiting examples of classes of bonding adhesives include acrylic-based adhesives, epoxy adhesives, polyurethane (PU) adhesives, silicone-modified adhesives, cyanoacrylate adhesives, hot-melt adhesives, copolymeric adhesives such as PU/acrylics, epoxy/acrylics, silicone/acrylics, and combinations of these adhesives. The limitation with respect to the selection of the bonding adhesive is that the bonding adhesive's curing temperature cannot be higher than the debondable coating's debondable temperature. When a higher curing temperature is required, then a higher temperature debondable coating should be used (e.g., coating with higher temperature expanding particles).
The debondable coating compositions may be used in adhesive bonding applications as show in
Also as described herein, the bonding adhesive 20 may be selected from any adhesive composition which is capable of bonding to the debonding coating and includes acrylic-based adhesives, epoxy adhesives, polyurethane (PU) adhesives, silicone-modified adhesives, cyanoacrylate adhesives, hot-melt adhesives, copolymeric adhesives such as PU/acrylics, epoxy/acrylics, silicone/acrylics, and combinations of these adhesives. The adhesive should not be an adhesive requiring a curing temperature above the debonding temperature of the debondable coating. Ideally the debonding coating strength at service temperature range should be higher than the bonding adhesive strength, so that the user will not encounter unexpected bond failure.
Debonding coating thicknesses may range from about 1 mil (0.00254 cm) to about 20 mils (0.0508 cm), or about 2 mils (0.00508 cm) to about 10 mils (0.0254 cm), or about 3 mils (0.00762 cm) to about 5 mils (0.0127 cm), depending on the substrate and chosen application.
An inventive debonding coating composition was formulated by mixing 20% by weight of polymeric microspheres (Commercially available as Expancel® 031 DU 40) into a commercially available epoxy composition, Loctite E-120H, which is a fast setting industrial grade epoxy resin designed to cure at room temperature. This epoxy has particular use for bonding, potting or encapsulating a variety of substrates, including plastic, metal, glass, wood and ceramic substrates. The inventive debonding coating composition was applied to aluminum lapshears (1″×½″), with some lapshear pairs having the coating on both of the lapshears to be mated, and other lapshear pairs having the debonding coating on only one of the lapshears to be mated. The debonding coating compositions were allowed to cure at room temperature.
Subsequent to the curing of the debonding coating, a commercially available silicone adhesive composition (Loctite SI 5600), also referred to herein as the “bonding adhesive, was applied over the debonding coating and the lapshears were then mated and allowed to cure. Once the silicone adhesive was fully cured, some of the lapshears were pulled at room temperature, and others were pulled after heating under relatively mild temperatures (30 minutes at 150° C.) and the tensile strengths recorded in pounds per square inch (psi).
An inventive debonding coating composition was formulated by mixing 20% by weight of polymeric microspheres (Commercially available as Expancel® 031 DU 40) into a commercially available epoxy composition, Loctite E-90-F, which is a fast setting industrial grade epoxy resin designed to cure at room temperature. The inventive debonding coating composition was applied to lapshears as a pre-coating prior to application of the bonding adhesive (silicone) and allowed to cure. Some of the lapshears received the debonding coating only on one of the mating lapshears, and other lapshears received the debonding coating on both of the mating surfaces of the lapshears.
Subsequent to curing of the debonding coating, commercially available silicone adhesive composition (Loctite SI 5600) was applied over the debonding coating and allowed to cure. The lapshears were pulled both at room temperature, as well as at under relatively mild heating (30 minutes at 150° C.), and the strengths recorded in pounds per square inch (psi).
| Number | Date | Country | |
|---|---|---|---|
| 63172812 | Apr 2021 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/US2022/023789 | Apr 2022 | US |
| Child | 18372238 | US |
