RADIATION SENSITIVE ADHESIVE

Abstract: So that a radiation sensitive adhesive can be used in confined spaces, adhesive-compatible radiation-scattering particles are added to the adhesive. Preferably, the adhesive is ultraviolet light curable and the particles are glass beads about 45 microns in diameter, mixed in about equal amounts by weight.

Description: RADIATION SENSITIVE ADHESIVE This invention relates to radiation sensitive adhesives. It is known that radiation sensitive adhesives allow a relatively long time during which the parts to be attached can be position-adjusted, and that after such adjustment has been accurately accomplished, the adhesive can be activated by radiation -- in a manner which is certain not to disturb the critical relative positions of the parts. The IBM Technical Disclosure Bulletin of December 1977, at page 2609, describes the formulation of one such adhesive, which is activated by ultraviolet light. A problem arises where the adhesive is between parts which render the bulk of the adhesive inaccessible to direct application of the sensitising radiation. Heretofore, it has been considered inappropriate to use radiation sensitive glues or adhesives in certain environments, and more specifically, radiation sensitive glues or adhesives have been recommended for use only in those situations where the glue or adhesive could be full-surface illuminated as the glue or adhesive was activated. Without such total illumination of the glue or adhesive, the resulting bond between the parts was likely to suffer deterioration with time, in that surfaces not illuminated would either not cure at all or cure at a different rate to the remainder. If the glue or adhesive did totally cure, dimensional changes were likely to result. As a result, the utility of this class of adhesive was limited. An object of the present invention is to extend the utility of radiation sensitive adhesives to situations where the parts to be glued or secured leave some, but not all, of the adhesive exposed for activating radiation after the parts have been brought to their final desired relative positions. Another object of the present invention is to extend the utility of radiation sensitive adhesives by the addition of light-scattering particles, these particles serving the dual purposes of providing full illumination of the glue or adhesive by activating radiation which impacts less than the full surface; and providing a bodying effect to the glue or adhesive, which bodying effect increases the viscosity of the glue or adhesive. This increase in viscosity reduces the propensity of the glue or adhesive to run, and provides the property of being able to bridge a gap between the two members to be glued or adhered. The present invention is particularly applicable to commarcially available radiation sensitive adhesives, such as Dymax 628T brand (a product of American Chemical and Engineering Corp.) and Speedbonder 352 brand (a product of the Loctite Corp.). Automated assembly of parts dictates the use of fast-curing, low shrinkage, dimensionally stable adhesives. An exemplary use is the attachment of a head button to the accessing arm of a flexible data-recording disk drive, such as described in application 83100920.4 (EP-A- ). However, the present invention is not limited to this application, but is of general utility. Acrylic structural adhesives which cure with ultra-violet light are well suited for this purpose. However, the need critically to adjust the position of the head button often results in a gap between the head button and the accessing arm. An exemplary gap is 0.9mum. Also, the construction and arrangement of the head button/accessing arm does not always leave the full surface available for direct application of the ultraviolet source. Thus the two characteristics above referred to are particularly useful. In an embodiment of the present invention, a radiation sensitive adhesive, such as DYMAX 628T or SPEEDBONDER 352 is modified by the addition of glass beads, about 45 microns in diameter. Equal weights of adhesive and glass beads are used. The method of mixing the beads and adhesive is not critical, provided the beads are quite uniformly distributed throughout the bulk of the adhesive. Preferably, the glass beads are first surface-treated with a silane coupling agent which is compatible with the polymer of the adhesive. These pretreated particles stay better in suspension during storage of the adhesive. The new and unusual results achieved by the present invention are demonstrated by the following test results. Disk drive head and accessing arm components were held with a gap of 1.5 millimetres therebetween. Adhesive in the amount of 0.03 grammes was applied at two 180 -spaced areas in this gap. The exposed glue was subjected to a 15-second burst of high intensity ultraviolet light as provided by a 350-watt mercury arc lamp. The samples were at the focal point of a long-focus lens, some 0.3048m (12 inches) away. The following forces were required to separate the parts. The data represents an average of three replicate tests. Adhesive Breaking Force Ibs. kg (1) DYMAX 628T 6.5 2.9484 (2) DYMAX 628T, with glass beads, equal amounts 16.5 7.4844 by weight (3) Speedbonder 352 8.2 3.71952 (4) Speedbonder 352, with glass beads, equal 13.7 6.21432 amounts by weight As shown, substantial improvement in bond strength occurs with the addition of the glass beads. Visual inspection of the dark area of the broken bonds for inspection of the dark area of the broken bonds for adhesives (1) and (3) showed uncured adhesive in the areas which did not receive direct radiation from the ultraviolet source. Adhesives (2) and (4) did not show this phenomenon because the glass beads operate to distribute or scatter the ultraviolet radiation inside the bond, by internal reflection. Other light scattering particles, which are compatible with the adhesive or glue, will perform the same results. By distributing radiation, in the form of ultraviolet light, throughout the adhesive, the light scattering particles, in the form of glass beads, enable the adhesive to be cured substantially uniformly between two bodies, non-transparent to the curing radiation.

Claims: CLAIMS 1 A radiation sensitive adhesive characterised by the addition of adhesive-compatible radiation-scattering particles to the adhesive. 2 An adhesive according to claim 1, in which, prior to addition, the particles are treated with an adhesive-compatible surface treating agent. 3 An adhesive according to claim 1 or 2, in which the particles are about 45 microns in diameter. 4 An adhesive according to claim 1, 2 or 3, in which the adhesive is curable by ultraviolet light. 5 An adhesive according to any preceding claim, in which the particles are glass beads. 6 An adhesive according to claim 5, in which the glass beads are pretreated with an adhesive-compatible silane coupling agent. 7 An adhesive according to any preceding claim in which the adhesive and particles are mixed in about equal amounts by weight. 8 An adhesive according to any preceding claim, in which the adhesive is an acrylic structured adhesive. 9 A method of bonding two spaced members, comprising the steps of positioning the two members with a gap therebetween, closing the gap with a radiation sensitive adhesive which includes radiation-scattering particles which increase the body or viscosity of the adhesive, and flooding the exposed portions of the adhesive with activating radiation. 10 A method according to claim 9, in which the adhesive is one according to any of claims 1 to 8. 11 A method according to claim 9 or 10, in which the two members are a magnetic head and a mount for the head.

Inventors: LEGG, RODERICK EUGENE, QUIST, FREDERICK FENN, JR., SCHWANDER, JEFFREY DARRELL, SIMSON, LOWELL MARR
Applicants: INTERNATIONAL BUSINESS MACHINES CORPORATION
Application year: 1983
Main classification: C09J3
IPC codes: C09J5, C09J11, C09J4, G03F7, G11B5