Method for manufacturing a pressure-sensitive adhesive with sufficient moisture permeability and related system

Abstract

A method for foaming an adhesive includes the step of injecting gas into a liquid adhesive to reduce its density. The method also includes the step of mixing the gas-impregnated adhesive to produce a foamed adhesive having numerous small bubbles throughout the adhesive, where at least 80% of the bubbles are 0.005 microns or larger in size. The method then includes the step of curing the foamed adhesive to maintain the size of each bubble formed in the foamed adhesive.

Description

Cross - references and incorporation by reference

[0001] This application claims priority based on U.S. Provisional Patent Application No. 63 / 495,252, "Method of Manufacturing a Pressure - Sensitive Adhesive Having Sufficient Moisture Permeability and Related Systems," filed on April 10, 2023. Further, this application incorporates by reference the entire contents of U.S. Provisional Patent Application No. 63 / 495,252 into this specification.

Background Art

[0002] Architects and engineers agree that buildings must be able to dry. However, commonly used building underlayment materials and membranes can trap condensation and moisture within walls, leading to a decrease in indoor air quality, loss of energy efficiency, and costly damage to buildings. The North American construction industry spends approximately $9 billion annually on repairs and litigation related to building damage caused by water and moisture. New materials used in construction over the past 20 years have been excellent in energy efficiency but poor in ventilation, resulting in claims related to toxic mold exceeding $3 billion. Air leakage from such membranes can increase energy usage by up to 30 - 40% in heating climates and 10 - 15% in cooling climates.

[0003] Appropriate design of the building envelope promotes continuous drying by allowing water vapor to escape. Moisture can penetrate the building envelope through materials or exposure to rain and snow during construction. Additionally, normal occupancy also raises moisture levels. Trapped moisture can cause wood rot, swelling, distortion, metal corrosion, and a decrease in the insulation performance of insulation materials. All of these issues increase the risk of mold, building deterioration, indoor air quality decline, and occupant health and safety risks. In some states, new requirements for improving building energy efficiency increase the likelihood of moisture being trapped when using low - or non - moisture - permeable air barriers.

Summary of the Invention

Problems to be Solved by the Invention

[0004] Current construction practices utilize breathable barrier sheets or membranes to form envelopes covering walls and roofs, controlling moisture movement between the inside and outside of buildings, as well as air movement through the barrier sheets or membranes. Commercially available barrier sheets and membranes typically have adhesive applied to them to secure them to walls or roofs. However, a problem arises in these applications: the adhesives often lack sufficient breathability, trapping large amounts of moisture within the walls, roofs, and buildings.

[0005] To address this issue, many barrier sheets and membranes apply adhesive to only a portion of the entire surface of the barrier sheet or membrane. This results in low moisture permeability in the areas where adhesive is present and high moisture permeability in the other areas where adhesive is absent. In this configuration, the overall moisture permeability of the barrier sheet or membrane is the average of each area. However, in reality, moisture permeability through the barrier sheet or membrane is not uniform, so water vapor trapped beneath the area with adhesive must take a long, difficult detour to escape the barrier sheet or membrane. To address this issue, some barrier sheets and membranes have small areas with adhesive and large areas without adhesive, but this results in reduced overall adhesion to walls and roofs, making them easily detached.

[0006] Another common method to address the challenges arising from the low moisture permeability of adhesives is to foam the adhesive to create bubbles within it, which increase moisture permeability. Typically, this foaming is achieved by blistering the adhesive after it has been applied to a barrier sheet or film. In adhesive blistering, bubbles are created within the adhesive's microstructure by heating it. However, controlling the number and size of bubbles formed by adhesive blistering is difficult, making it challenging to consistently obtain uniformly foamed adhesive.

[0007] Therefore, there is a need for an adhesive that provides moisture permeability of 10 Perm or more while covering the entire surface of the barrier sheet or membrane. [Means for solving the problem]

[0008] In one aspect of the present invention, a method for foaming an adhesive includes injecting gas into a liquid adhesive to reduce the density of the adhesive. The method also includes mixing the gas-impregnated adhesive to produce a foamed adhesive having a large number of small bubbles throughout the adhesive, where at least 80% of the bubbles are 0.005 microns or larger in size. Furthermore, the method includes curing the foamed adhesive to maintain the size of each bubble formed in the foamed adhesive.

[0009] By injecting gas into the adhesive while it is still liquid, and then mixing the gas-impregnated adhesive, numerous small bubbles can be formed within the adhesive's microstructure without heating the adhesive. This makes it possible to make the size of the numerous small bubbles uniform to one another, improving the controllability of bubble size. Furthermore, the numerous small, uniform bubbles in the foamed adhesive make it more permeable to water vapor, improving the Perm value. Here, Perm is a unit that indicates the degree to which water vapor can easily pass through an adhesive, as determined by the methods specified in ASTM E96, E398, and F1249. A higher Perm value indicates higher moisture permeability (or the degree to which water vapor passes through the adhesive). Specifically, a foamed adhesive that is created by injecting gas into the adhesive and then mixing the gas-impregnated adhesive can obtain a Perm value of 50 or higher. The numerous small, uniformly sized bubbles in the foamed adhesive provide a foamed adhesive with higher adhesive strength than blistered adhesives. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 shows a schematic diagram of a system for foaming an adhesive according to one embodiment of the present invention. [Figure 2A]Figure 2A shows a side view of a system for foaming an adhesive according to one embodiment of the present invention. [Figure 2B] Figure 2B shows a front view of a system for foaming an adhesive according to one embodiment of the present invention. [Figure 3] Figure 3 shows an exploded schematic diagram of the mixer of the system shown in Figures 2A and 2B for mixing adhesives according to one embodiment of the present invention. [Figure 4A] Figure 4A shows a perspective view of the stator of the mixer shown in Figure 3 for mixing adhesives according to one embodiment of the present invention. [Figure 4B] Figure 4B shows a perspective view of the rotor of the mixer shown in Figure 3 for mixing adhesives according to one embodiment of the present invention. [Figure 5] Figure 5 shows a cross-sectional view of a portion of the rotor and stator connected in the mixer shown in Figure 3 for mixing adhesive according to one embodiment of the present invention. [Modes for carrying out the invention]

[0011] Figure 1 shows a schematic diagram of a manufacturing process 20 for foaming an adhesive according to one embodiment of the present invention. The manufacturing process 20 includes a step 22 in which gas is injected into the liquid adhesive to generate bubbles within the adhesive and reduce the density of the adhesive, and a subsequent step 24 in which the gas-impregnated adhesive is mixed to complete the formation of bubbles within the adhesive. At this stage, the microstructure of the adhesive contains a large number of small bubbles. After the microstructure of the adhesive is formed, the manufacturing process 20 includes a step 26 in which the adhesive is cured to maintain the size and distribution of each bubble within the microstructure of the adhesive. The foamed adhesive obtained as a result of the manufacturing process 20 has a density range of 15% to 90% of the density of the liquid adhesive before foaming, and its microstructure contains a large number of minute pores (bubbles). In this embodiment, the manufacturing process 20 is carried out as a continuous manufacturing process. In a continuous manufacturing process, gas is injected into the adhesive, and the liquid adhesive flows continuously to the curing process with the gas-impregnated adhesive mixed. In another embodiment, manufacturing step 20 may be carried out as a single manufacturing step. In a single manufacturing step, a predetermined amount of liquid adhesive is held in a container with gas injected into the adhesive. Then, after all the gas has been injected into the adhesive, the entire amount of adhesive is mixed.

[0012] By injecting gas into the adhesive while it is in a liquid state, and then mixing the gas-impregnated adhesive, numerous small bubbles can be formed in the microstructure of the adhesive without requiring heating. This makes the size of the numerous small bubbles more uniform and improves the controllability of the bubble size. The numerous small, uniformly sized bubbles in the foamed adhesive make the foamed adhesive more permeable to water vapor, improving the Perm value (water permeability) of the foamed adhesive. The numerous small, uniformly sized bubbles in the foamed adhesive provide a higher adhesive strength than blistered adhesives.

[0013] The density of the foamed adhesive is determined by the amount of gas injected into the liquid adhesive. Therefore, the density of the foamed adhesive can be controlled by controlling the amount of gas injected into the liquid adhesive. Here, the density of the foamed adhesive is defined by the percentage of the density of the liquid adhesive before gas injection. Injecting a small amount of gas into the adhesive results in a slight decrease in the density of the foamed adhesive. Similarly, injecting a large amount of gas into the adhesive results in a significant decrease in the density of the foamed adhesive. The system 30 that performs the manufacturing process 20 (described in more detail with reference to Figures 2A and 2B) includes an injector that injects gas into the adhesive while the adhesive flows through the system 30. For example, in this embodiment and other embodiments, the injector injects air at a flow rate of 0.02 to 0.2 cfm (cubic feet per minute) into the adhesive flowing through the system 30 at a flow rate of 0.5 to 2.0 gpm (gallons per minute). If the injector injects air at a flow rate of 0.2 cfm into the adhesive flowing through system 30 at a flow rate of 0.5 gpm, the density of the foamed adhesive before curing will be approximately 45% of the density of the liquid adhesive before the injector injects the gas into the adhesive. If the injector injects air at a flow rate of 0.02 cfm into the adhesive flowing through system 30 at a flow rate of 2.0 gpm, the density of the foamed adhesive before curing will be approximately 95% of the density of the liquid adhesive before the injector injects the gas into the adhesive. To produce a foamed adhesive with a pre-curing density of 70% of the density of the liquid adhesive before the injector injects the gas into the adhesive, the injector injects air at a flow rate of 0.08 cfm at a flow rate of 1.14 gpm into the liquid adhesive flowing through system 30.

[0014] The gas injected by the injector into the liquid adhesive can be arbitrarily selected. For example, in this embodiment or other embodiments, the gas is air. Air is readily available and does not cause harmful reactions in the liquid adhesive. In another embodiment, other gases, such as carbon dioxide, which are less reactive than diatomic oxygen in air, may be used.

[0015] The microstructure of the foamed adhesive is determined during the mixing of the gas-impregnated adhesive. The gas injected into the adhesive during the injection process forms bubbles that are unevenly distributed throughout the liquid adhesive, and some of the gas injected into the liquid adhesive may coalesce to form larger bubbles. These larger bubbles may be significantly larger than other bubbles formed in the liquid adhesive. Therefore, the microstructure of the adhesive after gas has been injected into the liquid adhesive may have a large variation in bubble size and an uneven distribution throughout the adhesive. To make the bubble size in the adhesive more uniform and to equalize the distribution throughout the adhesive (to determine the microstructure of the adhesive), the gas-impregnated adhesive is mixed by the mixer of system 30 (described in more detail with reference to Figures 2A to 5). The mixer includes a stator and a rotor, and the relative motion of the rotor to the stator applies shear to the gas-impregnated adhesive as it flows through the mixer. The rotational speed of the rotor relative to the stator, and the configuration of the rotor-stator combination, affect the size and distribution of bubbles that determine the microstructure of the foamed adhesive. In a given rotor / stator configuration, when the rotor is rotated at high speed relative to the stator and gas-impregnated adhesive is slowly flowed into the mixer, numerous small bubbles are uniformly distributed within the adhesive. When the rotor is rotated at low speed relative to the stator and gas-impregnated adhesive is slowly flowed into the mixer, numerous larger bubbles are uniformly distributed within the adhesive. When the rotor is rotated at high speed relative to the stator and gas-impregnated adhesive is rapidly flowed into the mixer, numerous small bubbles are not distributed as uniformly within the adhesive as in the slowly flowing adhesive. Similarly, when the rotor is rotated at low speed relative to the stator and gas-impregnated adhesive is rapidly flowed into the mixer, numerous large bubbles are not distributed as uniformly within the adhesive as in the slowly flowing adhesive.

[0016] Referring further to Figure 1, the microstructure of the foam adhesive may contain any number of pores (bubbles) of any size. For example, in this embodiment and other embodiments, the microstructure of the foam adhesive may contain a large number of small pores, each of which is substantially the same size as the others. More specifically, the microstructure may contain pores of size 0.005 microns or larger, and more specifically, pores in the size range of 0.005 to 50 microns. A similar microstructure is disclosed in U.S. Patent No. 11,186,985, owned by VaproShield LLC and issued to Bess et al., which is incorporated herein by reference. The large number of micropores allows the adhesive to provide sufficient moisture permeability without impairing its ability to bond building films to wall and roof substrates.

[0017] Referring further to Figure 1, after the gas-impregnated adhesive's microstructure is established by the mixer of system 30, the adhesive is cured to stabilize and fix the established microstructure. For example, in this embodiment and other embodiments, the adhesive is applied to the release liner and dried in stage 26. During this drying, the drying rate of the adhesive may be increased by heating, but in this embodiment and other embodiments, the amount of heating is not such that blistering occurs in the adhesive. Alternatively, heating is performed rapidly to raise the temperature of the adhesive in a short time and fix the microstructure established in mixing stage 24. In another embodiment, drying may be performed without heating. During the curing process, the adhesive is applied to the release liner to a predetermined thickness according to the final application of the foamed adhesive.

[0018] Referring further to Figure 1, once the foam adhesive has cured, it can be applied to any desired structure depending on the end use. For example, in this embodiment and other embodiments, the end use of the adhesive is applied to a membrane used as part of the envelope of a wall or roof that is constructed on a number of substrates. The membrane protects the substrates and other components from external environmental factors such as rain and moisture, which can damage such components by penetrating and being absorbed. Furthermore, the membrane protects the substrates and other components by allowing water vapor trapped inside the building to escape to the external environment. The composition of the membrane may be arbitrary, and for example, in this embodiment and other embodiments, the membrane includes the fabrics disclosed in the aforementioned U.S. Patents owned by VaproShield LLC, U.S. Patent No. 11,525,265 granted to Johnson et al., and U.S. Patent No. 11,512,473 granted to Johnson et al. Each of these U.S. Patents is owned by VaproShield LLC and is incorporated herein by special reference. More specifically, the membrane may be a nonwoven polyester fabric with a basis weight ranging from 60 grams per square meter (gsm) to 160 gsm. The thickness of the foam adhesive applied to the membrane may range from 1.5 millimeters to 150 millimeters, depending on the desired total permeability obtained from the membrane and the adhesive strength of the adhesive. Generally, the thicker the adhesive relative to a given microstructure, the stronger the adhesive strength and the lower the water vapor permeability or transmittance (Perm value).

[0019] Referring further to FIG. 1, the manufacturing process 20 can be utilized for the foaming of any desired adhesive. For example, in this embodiment and other embodiments, the adhesive is an acrylic pressure-sensitive adhesive. More specifically, the adhesive includes a polyacrylic resin and is disclosed in detail in U.S. Patent No. 10,899,107 granted to Bess and U.S. Patent No. 11,485,112 granted to Bess et al. Each U.S. patent is owned by VaproShield LLC and is hereby incorporated by reference into the present application. In this embodiment and other embodiments, the acrylic pressure-sensitive adhesive has a specific gravity of 1.1 in a liquid state before gas injection. Specific gravity is the value obtained by dividing the density of the adhesive by the density of water. When foamed by the manufacturing process 20, a foamed adhesive with a thickness of 4 millimeters and at least 50 Perm of tackiness is obtained. Specific gravity is the ratio of the density of the adhesive to the density of water. When the specific gravity is 1.1, the adhesive is denser than water. When the adhesive is foamed using the manufacturing process 20, the adhesive becomes a foamed adhesive with a thickness of 4 millimeters and at least 50 Perm of tackiness.

[0020] FIGS. 2A and 2B show diagrams of a system 30 for foaming an adhesive according to an embodiment of the present invention. FIG. 2A shows a side view of the system 30. FIG. 2B shows a front view of the system 30.

[0021] As previously described in connection with FIG. 1, the system 30 includes an injector 32, a mixer 34, a controller 36, and a pump 38. The injector 32 injects gas into the liquid adhesive flowing through the system 30 to generate bubbles in the adhesive. The mixer 34 mixes the gas-impregnated adhesive to complete or finish the formation of bubbles in the adhesive. The controller 36 controls the flow rates of the gas and the liquid adhesive, as well as the mixing speed of the mixer. And the pump 38 pumps the adhesive into the system 30.

[0022] The mixer 34 may be any desired mixer capable of causing shear in the gas-impregnated adhesive, making the bubbles generated in the adhesive more uniform in size, and uniformly distributing the bubbles throughout the adhesive. For example, in this embodiment and other embodiments, the mixer 34 (described in more detail in relation to Figures 3 to 5) includes a rotor having a number of teeth (described in relation to Figures 3 and 4B) and a stator having a number of teeth (described in relation to Figures 3 and 4A). The stator is arranged such that the teeth of the rotor move in close proximity to the teeth of the stator as the rotor moves relative to the stator. As the gas-impregnated adhesive flows through the mixer 34, the adhesive flows between the teeth of the rotor and the teeth of the stator (described in relation to Figure 5). As the gas-impregnated adhesive flows through the mixer and the rotor moves relative to the stator, the teeth of the rotor and the teeth of the stator shear the adhesive. The amount of shear applied to the adhesive depends on the speed at which the rotor teeth move relative to the teeth of the stator. In this embodiment and other embodiments, the rotor and stator each have a center, and are positioned relative to each other such that a single axis extends perpendicularly through both centers. A motor 39 powers the mixer, rotating the rotor relative to the stator at approximately 700 revolutions per minute (rpm). As the gas-impregnated adhesive flows through the mixer 34, the adhesive first flows along the periphery of the rotor. Then, as the adhesive flows toward the centers of the rotor and stator, it flows between the teeth of the rotor and the teeth of the stator. The gas-impregnated adhesive then passes through the center of the rotor and is discharged from the mixer 34.

[0023] Referring further to FIGS. 2A and 2B, injector 32 can be any desired injector that can insert gas into the flow of the adhesive as the adhesive flows through system 30. For example, in this embodiment and other embodiments, injector 32 includes a valve (not shown) that has a hollow tube (not shown) extending from an outlet, and the hollow tube is disposed in the adhesive flowing through tube 40. The gas injected into the adhesive flows from tank 42 to injector 32 via line 44. The valve that controls the flow of gas through injector 32 may be located within or near tank 42 or near the outlet of the tube disposed in the flow of the adhesive. In this embodiment and other embodiments, controller 36 may open the valve and keep it open to supply a stable gas flow into the flowing adhesive. In other embodiments, controller 36 may sequentially open and close the valve to supply a pulsed gas flow into the flowing adhesive.

[0024] Controller 36 can be any desired controller that can control the mixing speed of the mixer and the flow rates of the gas and the liquid adhesive. For example, in this embodiment and other embodiments, controller 36 includes a control circuit with a user interface that enables programming of the desired adhesive flow rate, the desired amount of gas injected into the adhesive, and the mixing speed of mixer 34. Further, controller 36 includes sensors that monitor the flow rates of the adhesive and the gas and the mixing speed of mixer 34, and if one or more of these desired speeds unexpectedly change, controller 36 may notify the operator of system 30 and / or return the one or more speeds to the desired speeds. More specifically, controller 36 includes a mass flow sensor 46 that detects the flow rate of the liquid adhesive and a pressure sensor that detects the gas pressure within tank 42, and controller 36 can use these to determine the flow rate of the gas injected into the adhesive.

[0025] Referring further to Figures 2A and 2B, the pump 38 may be any desired pump capable of transferring liquid adhesive with a specific gravity of 1.01 to 1.3 into the system 30. For example, in this embodiment and other embodiments, the pump 38 has a reciprocating piston 48 driven by an electric motor 50, an inlet 52 through which the liquid adhesive flows into the pump 38, and an outlet 54 through which the liquid adhesive flows out of the pump 38. The motor 50 and the reciprocating piston 48 are sized and configured to transfer the liquid adhesive through the system 30 at a flow rate in the range of 0.5 to 2.0 gpm.

[0026] Figures 3, 4A, and 4B each show an example of the mixer 34 of the system 30 shown in Figures 2A and 2B. Figure 3 shows an exploded schematic of the mixer 34 of the system 30 shown in Figures 2A and 2B, which mixes an adhesive according to one embodiment of the present invention. Figure 4A shows the stator of the mixer 34 according to one embodiment of the present invention. Figure 4B shows the rotor of the mixer 34 according to one embodiment of the present invention. As described in relation to Figures 2A and 2B, the movement of the rotor relative to the stator shears the gas-injected liquid adhesive as the adhesive flows through the mixer 34.

[0027] In this embodiment and other embodiments, the mixer 34 includes a rotor 58, a stator 60, an inlet 62, and an outlet 64. The rotor 58 includes a number of teeth 66 (also shown in Figure 4B, but only four are referenced for clarity). The stator 60 also includes a number of teeth 68 (also shown in Figure 4A, but only four are referenced for clarity). These are configured such that the centers of the rotor 58 and stator 60 are located on the axis 70, and the rotor 58 and stator 60 are collinear. The gas-impregnated adhesive enters the mixer 34 through the inlet 62 and then flows through the housing 72 toward the periphery of the rotor 58. The gas-impregnated adhesive then passes through a passage 74 between the housing 72 and the periphery of the rotor 58 and enters the interface where the rotor teeth 66 mesh with the stator teeth 68. The gas-impregnated adhesive then flows toward the center of the stator 60 and passes through another passage 76 leading to the outlet 64. The nut 78 is screwed onto the bolt 80, detachably connecting the housing 72 to the stator 60 and maintaining the state in which the teeth 66 of the rotor 58 are engaged with the teeth 68 of the stator. The nut 82 is screwed onto the drive shaft of the motor 39 (Figures 2A and 2B), detachably connecting the rotor 58 to the motor 39, so that when the motor 39 rotates the drive shaft, the rotor 58 also rotates.

[0028] Figure 5 shows a partial cross-sectional view of a rotor 58 and stator 60 coupled in the mixer 34 shown in Figure 3, according to one embodiment of the present invention. When coupled, the teeth 66 and 68 mesh with each other, forming an interface through which the gas-impregnated adhesive flows, and the teeth 66 and 68 shear the adhesive. More specifically, as the rotor 58 rotates around the axis 70 in the direction of arrow 84, the teeth 66 move relative to the teeth 68. Then, as the gas-impregnated adhesive flows in the direction of arrow 86, the adhesive passes through the gap between the teeth 66 and 68. Because the rotor teeth 66 move relative to the stator teeth 68, the portion of the adhesive in contact with the side surface of the teeth 66 is sheared or displaced relative to the portion of the adhesive not in contact with the side surface of the teeth. To emphasize the shearing as the adhesive flows between the teeth 66 and 68, the portion of the adhesive in contact with the side surface of the stator teeth 68 is prevented from moving together with the portion of the adhesive in contact with the side surface of the rotor teeth 66. As the gas-impregnated adhesive moves from the periphery of the rotor 58 to the passage 76 in the center of the stator 60, the adhesive flows between multiple sets of teeth 66 and 68, and thus undergoes multiple shearing forces. These shearing forces in the gas-impregnated adhesive break down large bubbles in the adhesive into numerous smaller bubbles, which then spread throughout the adhesive, creating a more uniformly distributed network of small bubbles. Subsequently, the adhesive hardens, fixing the size and distribution of the bubble voids and creating a microstructure containing numerous small, dispersed pores within the adhesive.

[0029] Generally, in the mixer 34 of this embodiment, the size of the bubbles in the gas-impregnated adhesive is influenced by the gap between the rotor teeth 66 and the stator teeth 68, and the speed at which the teeth 66 move relative to the teeth 68. The smaller the gap between the teeth 66 and teeth 68, the smaller the bubbles in the adhesive. Also, the faster the speed at which the teeth 66 move relative to the teeth 68, the smaller the bubbles in the adhesive. Since the rotor 58 rotates around the shaft 70, the speed of the rotor teeth 66 relative to the stator teeth 68 depends on the distance of the teeth 66 from the shaft 70. Teeth 66 adjacent to the periphery of the rotor move faster than teeth 66 closer to the shaft 70, and teeth 66 adjacent to the passage 76 in the center of the stator 60 move the slowest. Furthermore, in the mixer 34 of this embodiment, the distribution of bubbles in the entire gas-impregnated adhesive depends on the number of rows of teeth 66 and teeth 68. The more rows there are, the more of the gas-impregnated adhesive flowing through the mixer 34 is exposed to the shearing action of teeth 66 and 68, resulting in a more uniform distribution of air bubbles throughout the adhesive.

[0030] The foregoing description is provided to enable those skilled in the art to practice and utilize the present invention. Various modifications of this embodiment will be readily apparent to those skilled in the art, and the general principles described herein are applicable to other embodiments and uses without departing from the spirit and scope of the invention. Accordingly, the present invention is not intended to be limited to the embodiments shown, but rather to be given the broadest scope consistent with the principles and features disclosed herein.

Claims

1. A method for foaming adhesive, A step of injecting gas into a liquid adhesive to reduce the density of the adhesive, A step of mixing the gas-impregnated adhesive to produce a foamed adhesive having numerous small bubbles throughout the adhesive, wherein at least 80% of the bubbles are 0.005 microns or larger in size. A step of curing the foamed adhesive to maintain the size of each bubble formed in the foamed adhesive, Methods that include...

2. The adhesive is an acrylic pressure-sensitive adhesive. The method according to claim 1.

3. The specific gravity of the adhesive is 1.

1. The method according to claim 1.

4. Injecting the gas into the adhesive includes injecting air. The method according to claim 1.

5. Injecting the gas into the adhesive is The process involves injecting the gas through a nozzle located inside the chamber while the adhesive is flowing through the chamber. The method according to claim 1.

6. The gas is injected at a rate of 0.2 to 0.02 cubic feet per minute. The method according to claim 5.

7. The adhesive flows through the chamber at a rate of 0.5 to 2.0 gallons per minute. The method according to claim 5.

8. The gas is injected into the adhesive at a rate of 0.08 cubic feet per minute. The adhesive flows through the chamber at a rate of 1.14 gallons per minute. The method according to claim 5.

9. Mixing the adhesive impregnated with the aforementioned gas is This includes shearing the adhesive between the stator and rotor of the mixer. The method according to claim 1.

10. Mixing the adhesive impregnated with the aforementioned gas is Pumping the gas-impregnated adhesive through a mixer having a stator and a rotor so that the gas-impregnated adhesive flows between the teeth of the stator and the teeth of the rotor, With the gas-impregnated adhesive flowing between the teeth of the stator and the teeth of the rotor, the rotor of the mixer is moved relative to the stator such that the teeth of the rotor pass near the teeth of the stator and shear the gas-impregnated adhesive. including, The method according to claim 1.

11. The relative density of the foamed adhesive before curing is 0.45 to 0.95 times that of the liquid adhesive before gas injection. The method according to claim 1.

12. The relative density of the foamed adhesive before curing is 0.7 relative to the density of the liquid adhesive before gas injection. The method according to claim 1.

13. Curing the foamed adhesive includes heating the foamed adhesive. The method according to claim 1.

14. The process further includes holding the foam adhesive before curing it. The method according to claim 1.

15. The process further includes applying the foam adhesive to the substrate before curing the adhesive. The method according to claim 1.

16. By mixing the gas-impregnated adhesive, a foamed adhesive is produced, which generates a large number of small bubbles throughout the adhesive. At least 80% of the bubbles are in the size range of 0.005 to 50 microns. The method according to claim 1.

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