Filler for paper-making and neutral paper-making process by the use thereof

Claim 1

A filler composition for paper-making comprising 100 weight parts of particles of heavy calcium carobnate and at least 0.1 weight parts of a particle composition consisting of particles meeeting the requirements (A), (B) and (C): (A) the zeta potential (Suspension concentration 1,000 ppm in pure water, measuring temperature 20° C.) is negative; (B) the particle size "d" of the particle composition resulting from dispersion for 10 minutes of a 10 weight % aqueous suspension of said particle composition by ultrasonic dispersing means measured by the use of the standard sieve and micro-sieve of JIS Z8801 is 10 μm<d≦150 μm; (C) the specific surface area S (cm 2 /g) of the particles of said particle composition measured by the BBT method is within the range shown by the formula S>100,000/D ρ (1) wherein D=Average particle size (μm) of the composition ρ=Specific gravity of the composition D being measured by the following method, wherein a 10 weight % aqueous suspension of said suspension of the particle composite: is further dispersed for 10 minutes by ultrasonic dispersion means and then is passed through a 125 μm (119 mesh) sieve, the sifted portion is then passed through a 100 μm (149 meash) sieve and thereafter the same procedure is repeated with sieves of 75 μm (200 mesh), 45 μm (330 mesh) and 22 μm (580 mesh) in this order, the portion which has passed the 22 μm sieve is diluted with water to a 0.5 weight % aqueous suspension, which is then passed through a micro-sieve of 15 μm and the 7 classified portions having been trapped by said respective sieves and micro-sieve and having passed said micro-sieve of 15 μm are dried and weighted, the weight % against the total weight of each portion or class is determined, the mean value for the particle size of each class is set as listed in the Table 1 below, and the value D is caluculated by the formula 2 below, TABLE 1 ______________________________________ Dry Mean particle size Class weight (%) (μm) ______________________________________ 125 μm n.pass W.sub.1 d.sub.1 = 135.0 125 μm pass - 100 μm n.pass W.sub.2 d.sub.2 = 112.5 100 μm pass - 75 μm n.pass W.sub.3 d.sub.3 = 87.5 75 μm pass - 45 μm n.pass W.sub.4 d.sub.4 = 60.0 45 μm pass - 22 μm n.pass W.sub.5 d.sub.5 = 33.5 22 μm pass - 15 μm n.pass W.sub.6 d.sub.6 = 18.5 15 μm pass.sup. W.sub.7 d.sub.7 = 12.5 ______________________________________ D=Σwi/Σ(wi/di) (2) and ρ being measured by the method in JIS K 5101 "Pigment dispersing method."