| 摘要 |
<p>Cardboard for practice targets - is impregnated to increase brittleness and improve definition of moles formed. The cardboard, consisting of a cellulose material, is made very brittle by chemical impregnating agent. The cellulose material should be short-fibred and free from wood fibres. Suitable impregnants are alkali silicate (Na2SiO3) and pref. also a hardener (Na2SiF6Al2(SO4)3 or acid), or an aminoplastics, e.g. urea-formaldehyde or melamine resin.</p> |
