電子線照射の紙質に及ぼす影響

抄録

Low energy electron beam irradiating instruments are applied for surface treatment and paint cure because of their compactness compared with corresponding high energy instruments. As electron beam has higher transmittance than UV light, it is supposed to be suitable for high-speed curing of relatively thick ink film such as intaglio ink film.
However, electron beam irradiation causes degradation of organic high-polymer induced by radical reaction, involving the main chain scission and crosslinking reaction of the polymer. In the case of paper, electron beam irradiation decreases degree of polymerization of cellulose and sheet strength.
In this paper the effects of electron beam irradiation on the physical and chemical properties of handsheets were studied.
Following results were obtained.
(1) The fiber strength of the handsheets, given by the wet zero-span breaking length, decreased with electron beam irradiation, while the fiber bonding strengths, as given by Pulmac B factor, wet breaking length and Young's modulus, increased. Besides, the microphotographs of the fractured areas of the handsheets showed that the sheet fracture pattern shifted from the inter-fiber bond breakage mode to the fiber breakage mode.
(2) The contributions of the fiber strength and fiber bonding strength to the double folds and tensile strength were determined by multiple regression analysis using the equation T=kF^aB^bL^c (T : Physical property of handsheet, F : Fiber strength, B : Fiber bonding strength, L : Fiber length, k, a, b, c : Parameter). It was found that the decreases of double folds and tensile strength caused by electron beam irradiation are mainly attributed to the decrease of fiber strength.
(3) The GPC analysis of the irradiated handsheets showed that the decrease of fiber strength is caused by the decrease of degree of polymerization of cellulose.
(4) With high dose of irradiation different kinds of pulp sheets showed similar values of probability of main chain scission, while with low dose of irradiation each pulp sheet showed different value of that.
(5) Amount of chemical groups such as aldehyde and carboxyl groups and copper number of the handsheets increased with irradiation.