ADHESIVE COMPOSITION WITH GLASS SPHERES

Abstract

A new adhesive composition containing glass beads and having unique properties in automotive related applications. The method of making such new adhesive composition.

Claims

1. An adhesive composition comprising 1 to 10 wt. %, based on total weight of the adhesive composition, glass beads; wherein the glass beads have an average diameter of no more than 110 micron meters with 90% of the glass beads having a size distribution between 5 to 200 microns.

2. The adhesive composition of claim 1 further comprises one or more epoxy resins, curing agent, catalyst, fumed silica, one or more tougheners, epoxy silane.

3. The adhesive composition of claim 2 wherein the toughener comprises urethane rubber.

4. The adhesive composition of claim 3 wherein the toughener further comprises at least one of carboxyl terminated butadiene-acrylonitrile (CTBN) epoxy adducts and ethylene/butylenes oxide di block copolymer.

5. The adhesive composition of claim 1 wherein the composition is substantially free of core shell rubber component.

6. The adhesive composition of claim 1 wherein the composition does not contain any added core shell rubber component.

7. The adhesive composition of claim 1 wherein the glass beads are mostly in spherical form.

8. The adhesive composition of claim 1 wherein the glass beads occupy about 10 to 20 volume percent of the composition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0006] The present invention provides an adhesive composition comprising glass beads to improve cohesive failure and other properties of the composition. Like an ordinary base adhesive composition, it will contain such conventional components: epoxy resin(s), curing agent such as dicyandiamide, catalyst such as blocked tertiary amine or urea, fumed silica, tougheners such as urethane rubbers, optionally auxiliary tougheners such as carboxyl terminated butadiene-acrylonitrile (CTBN) epoxy adducts and/or ethylene/butylenes oxide di block copolymer, epoxy silane and other fillers such as calcium carbonate, calcium oxide, calcium metasilicate etc. Instead of using talc and chlorites to maximize T-Peel failure mode and impact performance, glass beads are used without or with lowered amounts of talc and chlorites in the same adhesive compositions. The use of glass beads in the place of traditionally used inorganic fillers not only resulted in better composition performances but also significantly reduced the cost of making adhesive compositions. Some commercial examples of the base adhesive compositions, into which modification can be made with glass beads, include BETAMATE™ Series 1486, 1090G, 1485, 1696, available from The Dow Chemical Company.

[0007] The adhesive composition of the present invention comprises glass beads, preferably hollow spherical glass beads with an average diameter of no more than 110 micron meters, preferably around 50 to 75 microns, and more preferably 60 to 75 microns with 90% of the glass beads having a size distribution between 5 to 200 microns but more preferably between 25 and 105 microns. One commercially available example of the preferred glass beads are Q-Cel™ from Potters Industries Inc. with an average diameter of 75 microns. The particle size distribution shows that 93% is below 125 microns in size, a density of 0.27 g/cc, and an isostatic crush strength of 750 psi. Another example is K25 glass beads available from 3M with an average diameter of 50 micron and 80% of it between 25 and 90 microns, a density of 0.25 g/cc and the isostatic crush strength of 750 psi. The Q-Cel glass beads are reportedly made from normal soda lime borosilicate with a lower melting point of 400° C. The K25 glass beads are reportedly made from the borosilicate glass with a melting temperature of 600° C.

[0008] In a preferred embodiment, glass beads are added while making the base adhesive composition via a simple “add and mix” and in the place of talc and chlorites or with reduced amounts of talc and chlorites typically used for the base adhesive compositions. After addition of the glass beads, the adhesive composition typically will comprise 1 to 10 wt %, preferably 1 to 7 wt % and more preferably 4 to 6 wt %, of the glass beads, all based on the total weight of the adhesive composition. Adhesive compositions with solid glass beads tend to have the same performance as the composition with hollow (hence low density) glass beads, such as K25. In one preferred embodiment, the adhesive composition comprises 10 to 20% in volume of spherical glass beads. In a more preferred embodiment, the adhesive composition comprises 10 to 15% in volume of spherical glass beads. Depending on different applications, some routine adjustment of volume and weight percentage of glass beads in an adhesive composition may be needed with the general guidance as described above.

[0009] While the present invention focused on glass beads, other beads whether solid or hollow, such as ceramic beads, should provide essentially the same benefits to the adhesive composition as glass beads.

[0010] To further improve the desired properties of the adhesive composition, some core shell rubber components may also be added to the adhesive composition but many of the preferred embodiments of the present invention do not contain such core shell rubber component.

EXAMPLES

[0011] The present invention can be further demonstrated with the following non-limiting examples. Sample A is a typical base adhesive composition of BETAMATE™ commercially available from The Dow Chemical Company. The process of making such compositions is known and was disclosed in detail in U.S. Pat. No. 5,278,257, incorporated herein in its entirety. Such typical base composition contains a certain amount of inorganic fillers such as talc and chlorites (e.g., Sierralite™ available from Imerys). Sample B is prepared in a similar manner as Sample A but instead of talc and chlorites, Sample B comprises same weight percentage of glass beads (e.g., Q-Cel from Potters Industries Inc). The difference of Samples A and B are summarized below:

TABLE-US-00001 TABLE 1 Preparation of Samples A B Base Composition 94% 94% Sierralite 252  6% Q-Cel 7028  6% Total wt % 100 100

[0012] Testing Methods and Performance Observations

[0013] The samples were subjected to some mechanical performance tests and the test results are provided below.

Mechanical Testing

[0014] Impact Peel is conducted per ISO11343

[0015] T-Peel Test is conducted per ASTM D 1876

[0016] Failure Mode is conducted visually to gauge the transition from adhesive failure to cohesive failure mode of the applied adhesive to a substrate. The scale is defined as: [0017] 0 100% shiny metal substrate adhesive failure [0018] 1 Practically all adhesive failure [0019] 2 Starting to change to cohesive failure but still in both failure modes [0020] 3 Mixed mode thick and thin cohesive failure [0021] 4 Cohesive failure mostly thick failure mode [0022] 5 Perfect thick cohesive failure through the center of the adhesive

[0023] The results are shown below in Table 2.

TABLE-US-00002 TABLE 2 Testing results of the Samples A B T-Peel, N/mm 5.2 7.0 Failure Mode 2 3 Impact Peel, N/mm 16.6 20.8

[0024] As shown in Table 2, Sample B with glass beads instead of talc and chlorites demonstrated better results in all three tested mechanical properties.