Adhesives and methods of forming adhesives

Abstract

The present invention relates to specially formulated adhesives and methods for preparing such adhesives. The present invention also relates to composites and materials formed from such adhesives. More specifically, the present invention is concerned with specially formulated adhesives comprising phenolic resins.

Claims

1. A method of increasing the heat resistance of a substrate bonded to an adhesive comprising applying the adhesive to a substrate such that the adhesive bonds to the substrate, and wherein the adhesive comprises: (i) 1 part by weight of a phenolic resin; (ii) 2 to 4 parts by weight of a transition metal hydroxide and/or aluminium hydroxide; and mixing components (i) and (ii), wherein the mixing is conducted in the presence of 0.2 to 1 parts by weight, relative to the phenolic resin, of a viscosity controlling agent, and further comprising the step of applying the adhesive to the substrate such that the adhesive bonds to the substrate.

2. A method according to claim 1, wherein the adhesive comprises from 2.5 to 3.5 parts by weight of the metal hydroxide.

3. A method according to claim 1, wherein the adhesive comprises from 0.4 to 0.9 parts by weight of the viscosity controlling agent, wherein the viscosity controlling agent can be a liquid.

4. A method according to claim 1, wherein the metal hydroxide comprises particles having a particle size distribution with a D90 from 50 to 70 ?m, and/or a D50 from 15 to 35 ?m, and/or a D10 from 1 to 10 ?m.

5. A method according to claim 1, wherein the metal of the metal hydroxide is selected from one or more of scandium, vanadium, chromium, manganese, iron, cobalt and aluminum.

6. A method according to claim 1, wherein the metal hydroxide and/or aluminum hydroxide is of the formula M(OH).sub.3, wherein M is a metal.

7. A method according to claim 1, wherein the adhesive further comprises fibers.

8. A method according to claim 1, wherein the adhesive has a viscosity of from 200 to 10,000 mPas at 20? C. as measured according to the standard method ISO 3219:1993.

9. A method according to claim 1, wherein the adhesive comprises a catalyst in an amount of less than 2 wt. % relative to the content of phenolic resin.

10. A method according to claim 1, wherein the adhesive is substantially free of catalyst.

11. A method according to claim 1, further comprising the step of causing or allowing the adhesive to at least partially set.

12. A method according to claim 11, wherein the step of causing or allowing the adhesive to at least partially set comprises heating the adhesive to a suitable temperature.

13. A method according to claim 12, wherein the adhesive is heated to a temperature of at least 50? C.

14. A method according to claim 12, wherein the adhesive is heated for at least one minute.

15. A method according to claim 1, wherein the substrate is in the form of a sheet.

16. A method according to claim 15, wherein the adhesive is distributed in a layer on a surface of the sheet.

17. A method according to claim 1, wherein the substrate comprises a metal.

18. A method according to claim 17, wherein the substrate comprises aluminum.

19. A method according to claim 1, further comprising the step of applying a second substrate to the adhesive so that the adhesive additionally bonds to the second substrate.

20. A method of increasing the heat resistance of a substrate bonded to an adhesive comprising applying the adhesive to a substrate such that the adhesive bonds to the substrate, and wherein the adhesive comprises: (i) 1 part by weight of a phenolic resin; (ii) 2 to 4 parts by weight of a transition metal hydroxide and/or aluminium hydroxide; and mixing components (i) and (ii), wherein the mixing is conducted in the presence of 0.2 to 1 parts by weight, relative to the phenolic resin, of a viscosity controlling agent, wherein the adhesive is substantially free of catalyst.

Description

EXAMPLE 1: PREPARATION OF ADHESIVE

(1) An adhesive was formed according to the composition shown in Table 1 by use of a mechanical mixer until such time that the components appeared to be homogeneously combined.

(2) The phenolic resole resin use was an aqueous resole resin having a dry weight of 74-77% and less than 0.1% free formaldehyde obtained from Satef H?ttenes-Albertus as LACFEN ES 81 LF.

(3) The Al(OH).sub.3 is a ground aluminium hydroxide having 99.60% Al(OH).sub.3 content, d10 of 3.5 ?m, d50 of 23.0 ?m, and d90 of 57.0 ?m obtained from CellMark chemicals as ATH G200.

(4) TABLE-US-00001 TABLE 1 Relative amount Aqueous phenolic resole 100 resin Grey sand 160 Al(OH).sub.3 220 Water 28 Black iron oxide 2 Glass fibres (chops) 200

EXAMPLE 2

(5) The adhesive of Example 1 was applied to an aluminium sheet having a thickness of greater than 0.5 mm and the adhesive was cured.

(6) The composite was heated using a blowtorch flame (producing a temperature of around 1150? C.) applied to the surface of the aluminium sheet. After 10 to 15 minutes of heating, there was some melting of the aluminium in the local region where the flame was applied. However, the sheet as a whole substantially maintained its structural integrity and remained intact as a single piece bonded to the adhesive. The area affected by melting was, on average, confined to an area of about a 4 cm radius around the centre of the position at which the flame was applied. Even after more than 30 minutes heating, a layer of aluminium remained unmelted between the flame and the adhesive.

EXAMPLE 3

(7) Two aluminium sheets, each having a thickness of less than 0.5 mm, were bonded together by a layer of the adhesive of Example 1. The adhesive was then cured.

(8) The composite was heated as described in Example 2. The area of the first aluminium sheet directly in contact with the flame underwent some melting in the region in which the flame was applied. However, the composite as a whole substantially maintained its structural integrity and the second aluminium sheet did not distort or melt even after more than 30 minutes of heating.

EXAMPLE 4

(9) Two sheets of typical kitchen aluminium foil were attached together by a layer of the adhesive of Example 1 and were coated with the adhesive, which was subsequently cured.

(10) The composite was heated was heated as described in Example 2. The composite maintained structural integrity without breakage. The aluminium in the composite was found to be intact.

EXAMPLE 5

(11) Aluminium shavings were immersed in the adhesive of Example 1 and the adhesive was cured.

(12) This composite was heated as described in Example 2 for more than 30 minutes. There was no structural failure or burning of the composite during this heating.

(13) When aluminium shavings were applied only to the surface of a layer of the adhesive, during the same heating for 30 minutes, the composite did not yield. However, upon cooling of the composite, the area in which the flame was applied was less structurally strong than for the composite having shavings immersed in the adhesive.

EXAMPLE 6

(14) A layer of aluminium powder was deposited on front and rear surfaces of a layer of the adhesive of Example 1, and the adhesive was cured.

(15) When the composite was heated as described in Example 2, results similar to Example 5 were obtained, except that the area directly heated by the flame appeared stronger in comparison. The temperature of the composite where the flame was applied was around 1000? C., and the opposite surface of the composite has a temperature of about 400? C.

COMPARATIVE EXAMPLE 1: HEAT TREATMENT OF SUBSTRATE

(16) When the same heating as in Example 2 is applied to the second sheet of aluminium of Example 3, after it is removed from the adhesive, the aluminium sheet was found to melt and distort rapidly.

(17) The above examples demonstrate that the adhesive of the present invention advantageously allows substrates to maintain structural integrity under heating with a flame at high temperatures. As demonstrated by Comparative Example 1, in the absence of the adhesive, the aluminium substrate rapidly melts and deforms, which contrasts with the results of Example 3, where the structural integrity of the aluminum and composite was maintained.