DE3000367A1 - Paper prodn. with increased dry strength - on machine with closed water circulation using neutral pulp contg. waste paper - Google Patents

Abstract

Prodn. of paper with improved dry strength on paper machines with highly confined or entirely enclosed water circulation involves adding 0.05-5 wt.%, w.r.t. the wt. of the dry fibres, of an agent (I) improving the dry strength to pulp contg. min. 25% waste paper fibres, which is adjusted to pH 6.5-8.5. The pulp pref. consists of pulped and bleached or deinked waste paper. (I) is an acrylamide polymer. (I) is effective, in spite of the (almost) closed water circulation. The paper is suitable for writing, printing and packaging purposes, toilet paper, paper towels etc.

Description

'Process for making paper with improved

Dry strength in the manufacture of paper is increasing Recycled paper used for economic and ecological reasons. Reuse of waste paper ("recycling") has mainly in the production of packaging paper, e.g. corrugated cardboard, which consists almost exclusively of waste paper, has become important. Recently, the use of deinked waste paper, i.e. of printed paper, is gaining ground graphic paper after chemical-mechanical ink removal increasingly important. To reduce wastewater pollution in paper production, Attempts are increasingly being made to keep the water circuits of the paper machine closer to close. As a result, however, a number of substances accumulate originate from the recovered paper used, strong in the water cycle of the paper machine at. These are, for example, lignosulfonates, cellulose and starch degradation products as well as fillers and electrolytes.

The repeated "recycling" of waste paper means that it is reused Cellulose fibers are increasingly damaged, so that the strength properties, E.g. tear length, structure and pick resistance, bursting pressure and GMT value of the produced Papers keep deteriorating.

For this reason, products are being used more and more frequently in paper manufacture, which increase the dry strength of paper. Well-known substances of this type are for example Starch, CMC (carboxymethyl cellulose), mannogalactans, urea and melamine-formaldehyde products and acrylamide-containing polymers. These products improve the Dry strength of paper only in cases in which the water cycle of the paper machine is open is, i.e.

if with fresh water quantities of at least 20 m³ per ton of paper is being worked on. If the water cycle is severely restricted or completely closed of the paper machine are the well-known means of: - increasing the dry strength only slightly effective or completely ineffective.

The object of the invention is to provide a method for producing paper with improved dry strength on paper machines, which are closed with work in an almost closed water cycle.

The object is achieved according to the invention in that at least 25 % of the fibers in the paper stock come from waste paper, the pH value of the paper stock adjusted to 6.5 to 8.5 and the paper stock 0.05 to 5 wt.%, Based on the Weight of the dry fibers, a dry strength agent is added.

According to the method according to the invention, a number of different Paper types produced, e.g. writing and printing paper as well as packaging and hygiene paper.

Packaging papers are, for example, liners, corrugated cardboard, test liners, Wave base paper, Schrenz and cardboard. Hygiene papers include, for example Towel crepe and toilet paper. Graphic papers include newsprint, Gravure and offset printing paper as well as base papers.

The paper stock used for the production of packaging, writing and printing as well as hygiene paper is used, is either 100% fiberized Waste paper or from mixtures of fast waste paper and virgin fiber material, the proportion of waste paper in the mixture being at least 25%. The deployed Virgin pulp can be made from bleached or unbleached sulphite or sulphate pulp or consist of bleached and unbleached wood pulp. The waste paper fibers are specially prepared for the production of hygiene papers and before being reused graphic paper is decolorized or deinked (chemical-mechanical printing ink removal). Both sorted waste paper and corrugated cardboard waste from shops, Daily newspapers, magazines or mixed waste paper from various sources into consideration.

The amount of fresh pulp or wood pulp added to the waste paper depends on the quality of the available waste paper and on the Quality standard of the finished product. With good quality waste paper, you can even do without the addition of pulp or wood pulp at all.

The concentration of fibers in the paper stock suspension is usually low between 0.1 and 4% by weight. The paper stock also contains 0.05 to 5, preferably 0.1 to 1% by weight, based on the weight of the dry fibers, of a dry strength agent for paper. In the process according to the invention, the known dry strength agents can be used used for paper, e.g. native starches, oxidatively or enzymatically degraded Starch, cationized starch, mannogalactans, CMC, urea-formaldehyde or melamine-formaldehyde resins and acrylamide-containing polymers. The starches can be rice, wheat, Trade potato, tapioca or sago starch. The viscosity of the starches is in 5% aqueous solution at a temperature of 50 0C narrower than 200 m.Pas and is preferably in the range from 3 to 100 m.Pas.

The starches are generally modified by having them in the presence of water with water-soluble cationic polymers or condensates heated to temperatures above the gelatinization temperature of the starch.

The gelatinization temperature is different for each type of starch. This is understood to be the temperature at which some starch grains still have birefringence own, see Ullmanns Enzyclopädie der technischen Chemie, Urban and Schwarzenberg, Munich-Berlin, 1965, Volume 16, page 322. For a cationic modification of Starch is used, for example, copolymers of acrylamide and dialkylaminoalkyl (meth) acrylic esters, water-soluble polymers of alkylene imines, in particular Polyethyleneimines or water-soluble cationic condensation products from alkylene dihalides and polyalkylene polyamines or of halohydrins with polyalkylene polyamines. Based 0.01 to 1.0% by weight of a water-soluble cationic polymer is placed on starch or condensate. Further modification options for the production of cationic Starch are described in the Wochenblatt für Papierfabrikation 18, 690-693 (1978). Cationically and anionically modified starches are available commercially.

Another group of dry strength agents for paper are Polymers containing acrylamide. You can use both homopolymers of acrylamide use as well as copolymers. The homopolymers of acrylamide are not ionic, they can be copolymerized with other non-ionic monomers, modified such as styrene, isobutene, alkyl acrylates, alkyl methacrylates and acrylonitrile be.

However, the acrylamide polymers can also be modified cationically e.g. by combining acrylamide with dialkylamino C1 to C4 acrylates or the corresponding methacrylates copolymerized or by adding polyacrylamide with formaldehyde and pialkylamines to the corresponding Mannich products (dialkylaminomethylacrylamides) implements.

The cationic products can also be modified to the effect that, in addition to acrylamide units and the cationic monomer units, they are styrene or isobutene in copolymerized form.

Anionic polyacrylamides are mainly made by copolymerization of acrylamide with ethylenically unsaturated carboxylic acids, such as acrylic acid, methacrylic acid, Maleic acid or half-esters of maleic acid. Also amphoteric polyacrylamides, which contain both cationic and anionic monomers in copolymerized form, such as Copolymers of acrylamide, diethylaminoethyl acrylate and acrylic acid can be used as Dry strength agents can be used. Dry strength agents for paper based on acrylamide polymers are, for example, from US Pat. No. 2,884,058, U.S. Patent 3,084,093, U.S. Patent 3,840,489, and U.S. Patent 3,875,097.

The acrylamide-containing polymers have a 0.1% strength polymer solution in 5% aqueous saline solution at a temperature of 200C a K value of 50 to 250, preferably 100 to 150.

In the method according to the invention are preferably used as dry strength agents non-ionic and cationic polyacrylamides are used. The dry strength agents are added to the paper stock. The addition is usually made in the machine chest. In principle, however, it can also be used before the mechanical grinding of the fibrous materials or already in the thin stock area between the machine chest and headbox of the paper machine take place. In order to ensure effective dry consolidation of the paper closed Maintaining the water cycle of the paper machine is a control of the pH of the paper stock. The pH of the paper stock should be between 6.5 and 8.5, preferably between 7.0 and 7.5.

To adjust the pH it is necessary to use the paper stock to add a base to the acids obviously contained in the circulating water to neutralize completely or partially. The base used is preferably Caustic soda, ammonia or soda, however, potassium hydroxide, sodium aluminate, milk of lime can also be used and amines such as triethylamine, triethanolamine, or morpholine and others use amines. The best way to set the pH value is during the defibration the raw materials and is checked again in the white water at the paper machine and, if necessary, regulated by additional dosing. The pH of the pulp slurry is continuously tracked during papermaking with the help of a glass electrode.

The parts given in the examples are parts by weight.

The CMT value was determined according to DIN 53143, the dry breaking length according to DIN 43112, Sheet 1, after air conditioning the produced on a laboratory sheet maker Leaves 24 hours at a temperature of 23 0C and a relative humidity determined by 50%. The K value of the polymers was determined according to H. Fikentscher, Cellulosechemie 13, 58-64 and 71-74 (1932), at a temperature of 200C in 5% aqueous saline solutions certainly; where K = k. 103.

Example 1 For the production of cardboard, a fiber suspension is first used made by making a mixture of c70% corrugated cardboard waste and 30% mixed waste paper suspended in water that comes from the closed cycle comes from a paper machine. The consistency of the pulp slurry becomes 0.5% set. The freeness of the fibers was 500SR. The fiber slurry had a pH of 5.0. The pulp suspension was divided into four equal parts and processed into sheets with a basis weight of 120 g / m2 under the following conditions: a) stock suspension pH 5.0, no additive b) stock suspension as in a) + 0.3%, related on dry fiber, a copolymer of 75% acrylamide and 25% diethylaminoethyl acrylate with a K value of 150 c) stock suspension according to a), however, by adding sodium hydroxide solution pH 7.0 adjusted d) Example according to the invention, pulp suspension as c) + 0.3%, based on dry fiber, the copolymer of 75% acrylamide and 25% Diethylamnoethyl acrylate with a K value of 150 In Table 1 is the CMT value and the Dry tear length given for the sheets obtained in tests a) to d) became. Experiment d) is an example according to the invention.

Table 1 Test CMT value dry tear As% long (m) a) 156 3100 4.5 b) 170 3200 7.5 c) 160 3100 5.0 191 3500 7.9 Example 2 Off 100% mixed waste paper is a 0.5 aqueous pulp suspension using produced by water, which is the closed water cycle of a paper machine was taken. The pH of the pulp suspension was 6.0. As a dry strength agent a copolymer of acrylamide and styrene was used, its production in Example 1 of U.S. Patent 3,840,489 is given. The pulp suspension was in divided into four equal parts and one each for the production of paper sheets Weight per unit area of 120 g / m2 is used. Experiments a) to c) are comparative examples. The following fiber suspensions were used in the individual tests: a) Pulp suspension pH 6.0, no further additive b) as a), but 0.3% of that described above Copolymer of acrylamide and styrene, based on the weight of the dry Fibers e) pulp suspension as in a), but increasing the pH value by adding sodium hydroxide solution 7.5 set d) Example according to the invention, pulp suspension as c), but in addition another 0.3%, based on dry fiber, of the acrylamide copolymer and styrene.

For the sheets obtained in tests a) to d), the CMT value was the bursting pressure and the ash content are determined. The results are given in Table 2.

Table 2 Test OMT 30 burst pressure (kpa) Ash (%) a) 117 160 7.2 b) 124 162 7.0 c) 120 158 8.5 d) 154 184 1: 0.5 Example 3 A 0.7% aqueous pulp suspension, those made from 50% deinked waste paper (newspapers, magazines) and 50% wood pulp and water produced from the closed water cycle of a paper machine was divided into four equal parts. As a means of increasing dry strength this printing paper became a cationic starch in the case of experiments b) and d) used by reacting starch with ß-diethylaminoäthylchlorldhydrochlorid according to Example 1 of US Pat. No. 2,813,093. Experiments a) to c) are Comparative experiments, experiment d) is an example according to the invention. There were each Sheets made with a basis weight of 60 g / m2. The following stock suspensions were used: Experiment a) Stock suspension from the circulating water of a paper machine with a pH value of 5.0 Experiment b) pulp suspension as in experiment a), however an additional 0.3%, based on solid fiber, of the cationic starch test c) pulp suspension according to experiment a), but by adding sodium hydroxide solution to one pH adjusted to 7.5 Experiment d) stock suspension as in Experiment c), but an additional 0.3% by weight, based on dry fiber, the above cationic starch.

Dry tear length> pick resistance (determined according to the Dennison wax test and the ash content of the obtained paper sheets are shown in Table 3.

Table 3 Test dry tear length (m) Pick resistance ash (%) (Dennison points) a) 2,600 6 8.1 b) 2,800 8 8.5 c) 2,700 7 8.0 d) 3,000 10 9.2

Claims (3)

Claims 1. Process for the production of paper with improved y Dry strength on paper machines that are severely restricted or completely enclosed Water cycle work, characterized in that at least 25% of the fibers of the paper stock come from waste paper, the pH value of the paper stock to 6.5 to 8.5 adjusted and the paper stock 0.05 to 5 total, based on the weight of the dry fibers, a dry strength agent can be added. 2 .. The method according to claim 1, characterized in that the paper stock consists of shredded and discolored or deinked waste paper. 3. The method according to claims 1 and 2, characterized in that that acrylamide polymers are used as dry strength agents.