Use of ultrafine calcium carbonate particles in papermaking

Abstract

 A process for the production of paper by introducing a suspension of ultrafine calcium carbonate particles to a fiber-containing suspension. A method for improving the dewatering of a paper-making suspension containing at least one cationic polymer.

Description

[0001] The present invention relates to the use of a precipitated calcium carbonate (PCC) suspension, and in particular, a suspension of ultrafine PCC particles, in papermaking. The present invention also relates to an improved method for dewatering and an improved process for the production of paper.

[0002] It is well known to use colloidal silica, such as that associated with the various Compozil® systems, in the production of paper to obtain improved retention and dewatering.

[0003] Here, a suspension comprising ultrafine PCC particles is utilized in the manner analogous to the previously employed colloidal silica. It has been surprisingly discovered that these suspensions can provide, in combination with agents such as cationic polymers, a substantial improvement of the retention and dewatering in the production of paper. The improvements in dewatering can, for example, allow the speed of the papermaking machine to be increased. Accordingly, the economics of the papermaking process can be substantially improved.

[0004] Although not wishing to be bound by an particle theory, it is believed that the primary function of the PCC particles is the ability to provide a desired charge, e.g., typically a negative charge, thereby enhancing the charge characteristics of the system.

[0005] To this end, one aspect of the invention relates to a suspension of ultrafine PCC particles. By "ultrafine" it is meant particles having a mean particle size of less than 200nm, preferably less than 100 nm with particles sized on the order of 25-75 nm being suitable. For example, the PCC suspension according to the present invention can comprise ultrafine PCC particles such as those available from Solvay SA under the SOCAL® trademark. Specific examples of such ultrafine particles are illustrated in the following chart:

[0006] In view of their size, the ultrafine particles employed in the present invention typically have a higher surface area and a higher charge density which make them particularly suitable for use in the invention.

[0007] The ultrafine particles can be employed in an aqueous suspension in an amount suitable to provide the desired dewatering improvement. In this regard, it may be desirable to provide as high as concentration of the particles as possible subject to issues such as the manufacturing conditions, the maximum concentration at which the suspension would remain fluid and pourable without excessive settling. One example of a suitable suspension includes about 10 % by weight of the ultrafine particles in an aqueous suspension.

[0008] The suspension can be produced by techniques recognized in the art and need not be described in detail here.

[0009] As mentioned above, the suspensions according to the present invention can be used as a replacement for colloidal silica in paper-making processes. Insofar as paper-making processes are well recognized in the art, they need not be described in detail. However, for sake of completeness, the inventors offer the following remarks regarding the paper-making suspensions that are suitable for the present invention.

[0010] The present invention can employ a variety of paper-making suspensions containing a variety of cellulose-containing fibers. The suspensions should typically contain a suitable amount of fibers to provide the desired consistency at the various points of the paper making process. For example, the consistency of the fiber in thick stock can typically be on the order of 3%, of thin stock on the order of 0.5 to 1 % and later, at the drying section, at least about 50 percent by weight of such fibers, based on dry material. Such amounts are well recognized in this field.

[0011] The components can for example be used for suspensions of fibers from chemical pulp, such as sulphate and sulphite pulp, thermomechanical pulp, refiner pulp or groundwood pulp from both hardwood and softwood and can also be used for suspensions based on recycled fibers. The suspension can also contain mineral fillers, such as for example kaolin, titanium dioxide, gypsum, chalk and talcum.

[0012] Finally, it is noted that the terms "paper" and "paper-making" as used herein do of course not include solely paper and its production but also other cellulose fiber containing products in sheet or web form such as pulp sheets, board and cardboard and their production.

[0013] As discussed above, one or more cationic polymer(s) are employed in the paper-making suspension. The cationic polymers suitable for use in the invention include natural, e.g. based on carbohydrates, and synthetic polymers. Examples of suitable polymers include cationic starch, cationic guar gum, cationic acrylamide based polymers, cationic polyethyleneimines, polyamidoamines and poly(diallyldimethyl ammonium chloride). The polymers can be used singly or in combination with each other.

[0014] The amount of polymer is to a high degree dependent on the type of this and other effects desired from this. For synthetic polymers at least 0.01 kg polymer per ton, calculated as dry on dry fibers and optional fillers are usually used. Suitably amounts of from 0.01 to 3 and preferably from 0.03 to 2 kg per ton are used. For polymers based on carbohydrates, such as cationic starch and cationic guar gum, typically, amounts of at least 0.1 kg/ton, calculated as dry on dry fibers and optional fillers, are used. Suitably these are used in amounts of from 0.5 to 30 kg/ton and preferably from 1 to 15 kg/ton.

[0015] The other significant component of the paper-making suspension is the PCC suspension. The amount of PCC suspension employed in the context of the present invention can vary within wide limits depending on, among other things, the type of suspension being employed.

[0016] In the context of the present invention, the weight ratio of cationic polymer(s) to PCC is typically based on the charge characteristics of the system. The other primary factor relates to the economics of the system. It is particularly suitable where the ratio of polymer to PCC in suspension is not less than 10, more preferably not less than 20.

[0017] However, it is important to note that a wide range of amounts for the PCC suspension employed is capable of providing the dewatering advantages that can be associated with the present invention.

[0018] The paper-making suspensions employed in the present invention can include one or more conventional paper additives such as hydrophobing agents, dry strength agents, wet strength agents etc. Such additives are suitable for, but not significant to, the present invention.

[0019] Examples of suitable additive include aluminum compounds that can be employed in combination with the PCC suspension and cationic polymers, since it has been found that aluminum compounds may provide a further improvement of retention and dewatering. Any known aluminum compound for use in papermaking can be used, for example alum, polyaluminium compounds, aluminates, aluminum chloride and aluminum nitrate. The polyaluminium compounds can for example be polyaluminium chlorides, polyaluminium sulphates and polyaluminium compounds containing both chloride and sulphate ions. The polyaluminium compounds can also contain other anions than chloride ions, for example anions from sulphuric acid, phosphoric acid, organic acids such as citric acid and oxalic acid.

[0020] In addition, while the cationic polymer(s) are typically added prior to the PCC suspension, processes employing a reversed order of addition are not outside the scope of this invention.

[0021] Upon adding the PCC suspension to the fiber-containing suspension, the process includes the forming and dewatering of the fiber-containing suspension on a wire to form paper. In this regard, techniques and devices for forming and dewatering the paper-making suspension are well-recognized in the art and need not be described in detail here. It is noted that the PCC suspension can be effectively employed over the entire pH range of 4 to 10 in papermaking, with 4.5 to 8.5 being typically preferred.

[0022] The invention is further illustrated in the following examples which, however, are not intended to limit the same.

Example 1- Comparison of Ultrafine PCC Suspension to Compozil®

Components:

[0023] Compozil® : used directly as so ld.
   SOCAL® U3: A 10% suspension of SOCAL® U3 was employed.
   (Stirring speed 1500 rpm, small dissolver)
   9854: 10 ml of a 1% hot suspension of starch in a magnetic stirrer was produced (regulation M1).

Production of the paper material:

[0024] The thick material became on a concentration of ~7.0 g/l by addition of deionized water
   opposed. The setting of the concentration occurs about the regulation of the whole retention
   (Regulation P.5.). Next, salt, NaCl, was added to reach a conductivity of 1.2 M / cms.

[0025] Afterwards this material became in proportions of 1000 ml.

[0026] The accordingly necessary amount of strength paste was added, and became these servings, the mixture was then treated by means of a DFS 03 mixer and drained.

Determination of the Drainage Time

[0027] From the mixer, 1000 ml material strength mixture was emptied into the funnel of the DFS03 (for the draining time intended) and was stirred with 500 rpm. After 60s the mixer stopped, and at the same moment, the cone of the moving chamber was raised. The amount of the filtrate resulted was taken up in dependence at the moment. The maximum filtrate amount amounted to 400 gs. The filtration occurred about the Riegler-standard metal sieve.

Material concentrations:

[0028] Samples employing SOCAL®U3: 6.51 gs / I
   Samples employing Compozil®: 6.84 gs / I

[0029] Table I illustrates that the results for SOCAL®U3 while, Table II show the results for Compozil ® in tabular form.

Drainage time for the product SOCAL® U3.

[0030] Like it is to be seen clear it could by means of mixing Starch: SOCAL® U3 (1.5 rel. %:0,1 rel. %, to the paper material concentration) the drainage time can be reduced by two-thirds.

[0031] By employing 0.1 ml from a 10% suspension, the drainage time was comparably to that associated with the addition of 0.1 ml Compozil ®.

[0032] An effect shows the ability of the SOCAL®U3 to decrease drainage time, where an aid, such as starch, has been previously added. Without the presence of starch, the Compozil® showed only a minor improvement in the drainage time. With the addition of starch, the reduction in drainage time was, indeed, only 0.1 and 0.7%. Increasing amounts actually led to a lengthening of the drainage time.

Claims

1. A process for the production of paper, comprising the steps of:

(a) providing a fiber-containing suspension containing cellulose fibers, and optional fillers;

(b) introducing at least one cationic polymer into the fiber-containing suspension, and

(c) introducing at least one PCC suspension comprising ultrafine PCC particles to the fiber-containing suspension, and

(d) forming and dewatering the fiber-containing suspension.

2. A method for improving the dewatering of a paper-making suspension comprising the addition of a PCC suspension comprising ultrafine PCC particles to a paper-making suspension containing at least one cationic polymer.

3. The use of a PCC suspension comprising ultrafine PCC particles as a substitute for colloidal silica as a dewatering agent in the formation of paper from a paper-making suspension.