Pressure-sensitive adhesive containing acicular silica particles crosslinked with polyfunctional aziridines

Abstract

An adhesive composition comprising an emulsion polymer which comprises a (meth)acrylate copolymer, and acicular silica particles, crosslinked by a polyfunctional aziridine crosslinking agent is described.

Description

Background technique

[0001] Pressure sensitive adhesives (PSAs) are known to have properties including: (1) dry tack and persistent tack, (2) adhesion under no more than finger pressure, (3) sufficient adhesion to adherends ability, and (4) sufficient adhesive strength to enable clean removal from the adherend. Materials that have been found to function well as PSAs include polymers designed and formulated to exhibit the requisite viscoelasticity, resulting in a desired balance of tack, peel adhesion, and shear holding power. PSAs are characterized as being generally viscous at room temperature (eg, 20°C). PSAs do not include compositions simply because they are sticky or capable of adhering to certain surfaces.

[0002] U.S. Patent No. Re. 24,906 (Ulrich) discloses a pressure sensitive adhesive tape whose adhesive layer comprises acrylate and a copolymerizable monomer (such as acrylic acid) , which is described in the patent as an "acrylic pressure sensitive adhesive tape"...

Examples

example

[0118] These examples are for illustrative purposes only and are not meant to limit the scope of the appended claims. All parts, percentages, ratios, etc. in the examples, as well as in the remainder of the specification, are by weight unless otherwise indicated.

[0119] Acronym

[0120] abbreviation or trade name

illustrate

PSA-1

Acrylic emulsion adhesive with a pH of 4.3 (FASTBOND

49), commercially available from 3M Company (St. Paul, MN).

PSA-2

ROBOND PS-90, pH 9 Acrylic Emulsion Bonding

commercially available from Rohm & Haas (Philadelphia, PA)

have to.

PSA-3

Latex binder, prepared as described in Synthesis Example 1 below.

PFAZ 322

Triaziridine crosslinker, available from Bayer Materials Science

Commercially available from LLC (Pittsburgh, PA).

SNOWTEX UP

Silica particles from Nissan Chemical Industries

Ltd. (Chiba-Prefecture, Japan).

RHODACA...

Synthetic example 1

[0126] Synthesis Example 1: Preparation of PSA-3

[0127] To a 1 liter stainless steel Waring blender vessel was added 360 grams of deionized water, 8 grams of RHODACAL DS-10, 1.0 grams of lithium hydroxide, 1.2 grams of triethanolamine, 344 grams of 2-octyl acrylate (2-OA) , 15 grams of acrylic acid (AA) and 15 grams of methyl methacrylate (MMA). Homogenize the contents using a mixer set on low speed for 2 minutes, then pour into a 2 liter resin flask equipped with a thermometer, mechanical stirrer with Teflon impeller, condenser and nitrogen inlet. Next, 0.8 g of potassium persulfate was added. The reaction mixture was stirred at 250 rpm and heated to 62°C under a nitrogen blanket. Stirring and a nitrogen blanket were maintained throughout the reaction. After the peak exotherm at about 90°C, 82 grams of deionized water were added. The interval was maintained at 75°C for 4 hours, cooled and filtered through cheesecloth to provide a latex binder at 47.3% solids, a Brookf...

example 1 and comparative example C3

[0133] PSA-1 was blended with various concentrations of SNOWTEX UP. Binder solutions were prepared with and without PFAZ 322 as shown in Table 1. The samples without PFAZ 322 are Comparative Examples C3A-C3C. A comparative sample was also prepared from Comparative Example C2. The peel adhesion and shear strength of the tapes made from these adhesive emulsions were measured as described in the Test Methods above. The listed weight percentages are calculated relative to dry polymer. Comparative Example C8 is listed to show the effect of the polyfunctional aziridine crosslinker in the absence of acicular nanoparticles.

[0134] Table 1

[0135] sample

[0136] The data in Table 1 show that the combination of aziridine crosslinker and silica nanoparticles produced the adhesive with the highest shear value.

Background technique

[0001] Pressure sensitive adhesives (PSAs) are known to have properties including: (1) dry tack and persistent tack, (2) adhesion under no more than finger pressure, (3) sufficient adhesion to adherends ability, and (4) sufficient adhesive strength to enable clean removal from the adherend. Materials that have been found to function well as PSAs include polymers designed and formulated to exhibit the requisite viscoelasticity, resulting in a desired balance of tack, peel adhesion, and shear holding power. PSAs are characterized as being generally viscous at room temperature (eg, 20°C). PSAs do not include compositions simply because they are sticky or capable of adhering to certain surfaces.

[0002] U.S. Patent No. Re. 24,906 (Ulrich) discloses a pressure sensitive adhesive tape whose adhesive layer comprises acrylate and a copolymerizable monomer (such as acrylic acid) , which is described in the patent as an "acrylic pressure sensitive adhesive tape"...

Examples

example

[0118] These examples are for illustrative purposes only and are not meant to limit the scope of the appended claims. All parts, percentages, ratios, etc. in the examples, as well as in the remainder of the specification, are by weight unless otherwise indicated.

[0119] Acronym

[0120] abbreviation or trade name

illustrate

PSA-1

Acrylic emulsion adhesive with a pH of 4.3 (FASTBOND

49), commercially available from 3M Company (St. Paul, MN).

PSA-2

ROBOND PS-90, pH 9 Acrylic Emulsion Bonding

commercially available from Rohm & Haas (Philadelphia, PA)

have to.

PSA-3

Latex binder, prepared as described in Synthesis Example 1 below.

PFAZ 322

Triaziridine crosslinker, available from Bayer Materials Science

Commercially available from LLC (Pittsburgh, PA).

SNOWTEX UP

Silica particles from Nissan Chemical Industries

Ltd. (Chiba-Prefecture, Japan).

RHODACA...

Synthetic example 1

[0126] Synthesis Example 1: Preparation of PSA-3

[0127] To a 1 liter stainless steel Waring blender vessel was added 360 grams of deionized water, 8 grams of RHODACAL DS-10, 1.0 grams of lithium hydroxide, 1.2 grams of triethanolamine, 344 grams of 2-octyl acrylate (2-OA) , 15 grams of acrylic acid (AA) and 15 grams of methyl methacrylate (MMA). Homogenize the contents using a mixer set on low speed for 2 minutes, then pour into a 2 liter resin flask equipped with a thermometer, mechanical stirrer with Teflon impeller, condenser and nitrogen inlet. Next, 0.8 g of potassium persulfate was added. The reaction mixture was stirred at 250 rpm and heated to 62°C under a nitrogen blanket. Stirring and a nitrogen blanket were maintained throughout the reaction. After the peak exotherm at about 90°C, 82 grams of deionized water were added. The interval was maintained at 75°C for 4 hours, cooled and filtered through cheesecloth to provide a latex binder at 47.3% solids, a Brookf...

example 1 and comparative example C3

[0133] PSA-1 was blended with various concentrations of SNOWTEX UP. Binder solutions were prepared with and without PFAZ 322 as shown in Table 1. The samples without PFAZ 322 are Comparative Examples C3A-C3C. A comparative sample was also prepared from Comparative Example C2. The peel adhesion and shear strength of the tapes made from these adhesive emulsions were measured as described in the Test Methods above. The listed weight percentages are calculated relative to dry polymer. Comparative Example C8 is listed to show the effect of the polyfunctional aziridine crosslinker in the absence of acicular nanoparticles.

[0134] Table 1

[0135] sample

[0136] The data in Table 1 show that the combination of aziridine crosslinker and silica nanoparticles produced the adhesive with the highest shear value.