A PROCESS FOR THE SIZING OF PAPER

Abstract: An aluminium hydroxychloride having the general formula Al n (OH) m Cl 3n-m , wherein m is a number smaller than 3n and the ratio is at least 2, preferably 5, for use as a size precipitant in paper making.

Description: The present invention relates to a process for the sizing of paper and more specifically for the precipitating step of the resin sizes. In the so-called paper sizing, colophony based sizes, added to the fiber pulp in aqueous suspension, are precipitated by addition of a water solution of aluminium sulphate. Such a technology is however affected from several problems and drawbacks such as: - incrustations of calcium sulphate are formed on the walls of the sizing tank; algae are developed and foams are formed; - the effluent waters are polluted; - there is a corrosive action. In the past alternative processes were proposed in which aluminium hydroxychlorides are used instead of the aluminium sulphate. Particularly, in the German patent No. 363,668 the use of the non polymeric salt having formula Al2(OH)5 Cl is disclosed. The Austrian patent No. 356,511 discloses and claims the use of aluminium polyhydroxychloride, substantially free from sulphate ions, having the formula: EMI1.1 wherein n is?/ 2. By using this precipitating agent the problem of the incrustation formation is done away with. The main purpose of the present invention is that of providing a process by which the paper sizing is improved. Another purpose of the present invention is that of providing a process permitting the acidifying step of the fiber suspension to be avoided, this step being used in most paper manufacturing plants before the addition of the precipitating agent, thus achieving a saving and a simplification of the process apart from the substantial elimination of the corrosion phenomena. It has been found and is the subject of the present invention that these purposes are achieved by a process for the paper sizing, of the type in which the aqueous fiber suspension, added with the sizing agent is supplemented with a precipitating agent consisting of an aluminium polyhydroxychloride, characterized in that said polymeric aluminium hydroxychloride has the highest Cl/OH ratio consistent with the general formula: Al (OH) Cl n m 3n-m specifically a Cl/OH ratio of at least 2. According to the preferred embodiment of the process of the invention the precipitating agent is an aluminium polyhdroxychloride having the formula (Al2OHCl) since in this case any recourse to a previous acidifying of the aqueous fiber suspension is eliminated. For the preparation of the aluminium polyhydroxychloride useful for the process of the invention, besided directly obtaining the compound with the desired CL/OH ratio, the commercially available aluminium polyhydrochloride can be used, the correction to the optimum value of the Cl/OH ratio and thus of the chlorine content being carried out by admixing with hydrogen chloride. The process of the invention has been compared with that using aluminium sulphate in the case of paper pulp for the preparation of extensible kraft paper having a weight of 78 g/sq.m., the pulp comprising 20% of raw cellulose and 80% of waste paper pulp. The pulp was added with 11% of conventional size; in the first case 4.4% of aqueous solution of aluminium sulphate was added, whereas in the second case 1.8% of aqueous solution of aluminium polyhydroxychloride having a C1/OH ratio of 5:1 was used. In the following table the physical and mechanical properties of the resulting paper are reported: Aluminium aluminium sulphate polyhydroxychloride average tensile strenght (kg) 4.73 5.32 average tearing lenght (m) 4.049 4.548 average elongation (%) 5.8 6.8 bursting strenht (Kg/sq.cm.) 3.42 3.56 In both cases the sizing is optimum, but it will be noted that the physical and mechanical properties are r@markably and unforeseably improved and, morevoer, the amount of precipitating agent to the added to the suspension of fibers and sizing agent is relevantly reduced,

Claims: CLAIMS 1. A process for the paper sizing, of the type in which an aqueous suspension of fibers and sizing agent is added with aluminium polyhydroxychloride characterized in that said aluminium polyhydroxychloride having general formula Al (OH) Cl n m 3n-m has a Cl/OH ratio of about 2:1 2. A process according to claim 1, characterized in that said aluminium polyhydroxychloride has a Cl/OH ratio of 5:1.

Inventors: SPINA, NICOLA
Applicants: PRODECO S.P.A.
Application year: 1982
Main classification: D21H3
IPC codes: C01F7, D21H17