Pagewidth inkjet printhead assembly having a composite support structure

1. A pagewidth inkjet printhead assembly that comprises

an elongate support structure of a composite material; and

a plurality of printhead modules mounted on and along the support structure, the composite material being configured so that a coefficient of thermal expansion of the elongate support structure is substantially the same as that of the printhead modules, wherein the support structure comprises a beam formed from two distinct materials, each material provided in segments, the segments of each material alternating along the length of the structure and being bonded to one another end to end.

2. A pagewidth inkjet printer as claimed in claim 1 , in which a coefficient of thermal expansion of one material is greater than that of silicon and a coefficient of thermal expansion of the other material is less than that of silicon.

3. A pagewidth inkjet printhead assembly as claimed in claim 2 , wherein the elongate support structure is a laminar beam with any odd number of longitudinally extending layers of at least two different materials wherein layers of the same material are symmetrically disposed about the central layer.

4. A pagewidth inkjet printhead assembly as claimed in claim 3 , in which the laminar beam has three longitudinally extending layers where two outer layers are a first material and a central layer is a second material.

5. A pagewidth inkjet printhead assembly as claimed in claim 1 , in which combined lengths of adjacent segments between mounting positions of the printhead modules define a pitch and a coefficient of thermal expansion across each pitch is substantially equal to that of a printhead module supported on that pitch.