1. Field of the Invention
The present invention relates to a method for recycling of old corrugated container (OCC) using flotation and kneading treatment and more particularly, to a method for recycling of OCC, wherein OCC is treated with flotation and kneading treatment, and thereby removing fines and ink spots in the recycled pulp and improving the strength and drainage properties. As a result, it can be recycled similar to the expensive virgin unbleached kraft pulp.
2. Description of the Prior Art
The total paper production of Republic of Korea amounted to 8 million tons in 1997, and hence Korea became one of the top 10 largest production countries in the world. The production of the base paper for corrugated board essential for packaging goods accounts for more than 30% of the total paper production. Corrugated board used for packaging of goods, plays an important role in transfer and protection of goods, and improves the value of goods. So, it is an important packaging paper in the aspect of strength and appearance both. The base paper of corrugated board is; mainly manufactured from Korean old corrugated container (KOCC), and thus the recycling rate of KOCC is very high. However, KOCC used as main source material for the manufacture of corrugated board is already printed. Also, various printed matters other than corrugated board are contained in the waste paper, and since deinking has not been performed in the previous recycling process, the accumulation of ink is deepened as the recycling is repeated. Accordingly, since there remained ink spots cannot be removed by dyeing treatment in the recycling procedure, the base paper of the recycled corrugated board are distinguished apparently from the high-quality base paper of corrugated board, composed of unbleached kraft pulp, without spots.
The recycled pulp of OCC has the disadvantage of deteriorated appearance due to ink spots and poor drainage in papermaking and weak strength due to the high fines content. Currently used KOCC has the fines content more than half of the total paper compositions because of the repeated recycling treatments. And, the formation of fines is accelerated much more due to the hornification of fiber as the recycling treatment is repeated. Generally, fines refer to inorganic materials and fine fibers smaller than 75 .mu.m, and they have been the main cause of the declination of productivity because they interfere draining of wet web in papermaking of the base paper.
However, the problem of drainage deterioration in papermaking due to the fines could not be settled by the conventional recycling treatment technique using KOCC as main source material. In addition, it was impossible to pulverize mechanically the said ink spots because the drainage deterioration due to the formation of fines hindered the sufficient treatment of hornified OCC pulp.
Although the technology comprising cleaning OCC with screen or cleaner, fractionating of long and short fiber portions, and improving the paper strength bad selectively disintegrating the long fiber portions, has been applied in developed countries [Bliss T., Pulp and Paper, 88, 104 (1987); Clark L. E. and lannazzi F. D., Tappi, 57, 59 (1974)], the said technology is only suitable for high quality OCC comprising good quality of unbleached kraft pulp and neutral sulfite semichemical pulp. The strength of the base paper of the corrugated board can not be improved, in case low-quality OCC, having more fines content than long fiber portions, is used for main material of the corrugated board, as in Korea.
For this reason, high-quality base paper for corrugated board with excellent: strength and without spots has been imported until now, and recently the imported amount of high quality base paper of corrugated board has increased rapidly from166,000 tons in 1995 to 193,000 tons in 1996 with the improvement of standard of living [Pulp & Paper International, 39, 65 (1997)]. As mentioned above, there was no alternative other than using 100%-imported unbleached kraft pulp as source material, and KOCC could not be used with the conventional technology. Actually, in 1996, the total quantity of unbleached kraft pulp imported for the manufacture of kraft paper and various corrugated board amounted to 270,000 tons [Pulp & Paper International, 39, 65 (1997)]. Accordingly, there is a serious demand for the development of new technology which improves the productivity, enhances the strength, removes ink spots in OCC, and reproduces to high-quality corrugated board by improving the drainage property of KOCC with high fines content.