| 摘要 |
A cover layer, for example applied to a carrier sleeve (3), is volume compressible by being formed as a unitary seamless cover layer (3) of foamed or expanded or blown material resulting in micropores or microcells of less than 0.01 mm, with a percentage of closed or individual cells to total cells being greater than 50%. This cover layer will have a bounce-back or rebound elasticity of greater than 95% and preferably has a thickness of between about 1 to 5 mm. It may be covered with a polyurethane or rubber based outer cover layer of, for example, about less than 0.5 mm thickness. The cover layer is applied by providing a base substance which is made thixotropic, stirring it and applying it in liquid form as a spiral stripe on a rotating and axially moving cylinder (5), the material being free foaming and curing as it is being applied, and when still in spreadable and somewhat flowable condition to form a uniform seamless cover layer which includes individual, unconnected micropores or microcells. Additives such as talcum, and suitable selection of curing agents or activators and inhibitors, as well as blowing agents can control the size and eventual density of the material.
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