FI74081C - FOERFARANDE FOER ATT PAOSKYNDA NEUTRALLIMNING. - Google Patents

Description

1 74081

The method accelerates gluing in neutral gluing

The invention relates to a way of speeding up and enhancing sizing in the sizing of a filler-containing paper product with a hydrophobic, cellulose-reactive neutral glue.

The water repellency of the paper, i.e. the degree of hydrophobization, can be increased by various additives. When using a conventional sizing mixture of resin glue and alum, the production of paper products takes place under acidic conditions. The disadvantages of this are, among other things, that the resin adhesive and alum adversely affect the strength properties, brightness and resistance to aging of the paper and that the acidity promotes corrosion. Calcium carbonate cannot be used as a filler because at low pH it would decompose into carbon dioxide and calcium oxide and water-soluble Ca ions would make resin sizing difficult. Em. for these reasons, interest in the manufacture of paper products containing adhesives under neutral and even alkaline conditions has grown strongly. A common feature of suitable synthetic pulp adhesives is that, unlike resin adhesives, they react with cellulose molecules to form a highly permanent, water-repellent or hydrophobic adhesive due to chemical covalent bonds.

"Paper product" as used herein means sheet-like, web-like or molded products made from fibrous cellulosic materials. They also include similar mixtures of cellulose and other material, such as synthetic material or mineral fiber. In addition to the actual cellulose, the "paper product" may contain varying amounts of mechanical or chemimechanical pulp as well as mineral fillers (such as kaolin, talc, CaCO, and TiO).

3 2 2 74081

Neutral adhesives are in the form of an aqueous dispersion, in which case a cationic starch or other cationic compound can be used as a dispersant (see, inter alia, UK 865 727 and 903 496).

Hydrophobic compounds containing groups reactive with cellulose hydroxyls have proven to be good neutral adhesives. Among the synthetic neutral adhesives well known in the art, e.g. long chain fatty acid derivatives of ketene dimers, carboxylic acid anhydrides, organic isocyanates and carbamoyl chloride {FI Publication No. 64,677, U.S. Patent No. 4,279,794 and INSKO 159-81 VIII, p. 17). In addition, fatty acid complexes with chromium or aluminum compounds, long-chain N-substituted aziridine derivatives, long-chain thermoplastic copolymers, and some condensation-type thermosetting resins are mentioned (U.S. Patent 3,575,796).

Synthetic neutral adhesives have e.g. the following advantages: - A neutral or slightly alkaline process gives a paper with better strength properties, stability, aging properties, some printability properties, enhanced effect of optical brighteners and gluing resistance.

- Calcium carbonate can be taken as a filler or a coating scrap containing calcium carbonate can be used. The actual disadvantages in terms of paper quality have not been demonstrated, on the contrary, it has been possible to increase the filler content of the paper when a certain strength level is reached. The pH adjustment of the system is simplified.

- Alkaline grinding has in some cases been found to save energy and favor the development of strength.

- Surface dyeing of the paper product is possible.

- The glue adheres almost completely so the circulating water remains free of glue.

t 3 74081

But synthetic neutral adhesives also have their own disadvantages. Thus - in contrast to conventional resin sizing, the sizing effect, e.g. in the case of ketene dimers, may not be complete until after a few hours or even several days, i.e. the glue matures slowly.

- the formation of glue and foam may occur in the process, as well as e.g. sticking problems. Microbiological activity increases under neutral conditions, - synthetic neutral adhesives most often require cationic retention aids or accelerators which may have adverse effects on sheet formation and other wet end phenomena.

In order to eliminate these disadvantages and to increase the efficiency of gluing, new adhesive-retention agent-accelerator combinations have been invented, as well as more efficient ratios of these components. In general, adhesive dispersions contain cationic starch as a stabilizer. A cationic polymer is used as a retention agent or accelerator for gluing. FI patent publication 64 677, US patent publication 4 279 794 and FI publication publication 677 35 disclose a number of cationic polymers used as retention aids or accelerators, such as cationic starch, mannogalactan, polyethyleneimine, polyamine, polyamide amine, polyamide amine, polyamide -lylamine) and bis-aminopropylpiperazine epihalohydrin, as well as cationic melamine, urea and guanidine formaldehyde resins. It has also been suggested that an anionic polymeric binder be used in addition to the cationic polymeric retention aid (FI-Bulletin 67 735 and TAPPI Notes, 1985 Alkaline Papermaking, page 15).

Prior art methods for preparing an adhesive emulsion have paid attention to the adhesive composition and the stability of the resulting emulsion. According to TAPPI (TAPPI Notes, Alkaline Paperma- 4 74081 king, TAPPI PRESS, Atlanta, page 15), gluing is started from a pulp slurry to which an aqueous suspension of mineral filler is added. A hydrophobic adhesive and a cationic retention aid are then added simultaneously to the mixed mineral filler slurry. Shortly thereafter, an anionic polymeric binder may be added if desired. In gluing, the glue adheres to both the fibers of the pulp and the filler particles. Because the need for hydrophobization of the filler is less than that of the pulp and because it does not remain entirely in the paper product, i.e. its retention is limited, the filler consumes unnecessarily much adhesive, especially when By increasing the retention of the filler by means of a cationic retention aid, it has thus been possible to reduce adhesive consumption to some extent.

Thus, prior art measures have been able to primarily affect retention and the final sizing result. However, in order to facilitate and speed up the papermaking process, it is important to improve the gluing speed in particular. Despite the fact that the gluing rate has been somewhat improved by the new cationic accelerators according to the prior art, one of the bottlenecks in the process is still the slowness of neutral gluing.

It has now surprisingly been found that treating the filler separately with a cationic polymer before adding the filler to the pulp slurry provides a much faster neutral sizing. Thus, a new, rapid method of neutral sizing paper has been invented, which makes the paper hydrophobic almost immediately, thus greatly facilitating the manufacturing process of the paper product.

The method according to the invention is thus characterized in that the filler is treated in a separate step with a pretreatment agent, which is a cationic polymer, before the filler is added to the fibrous pulp slurry. The purpose is to coat the filler particles with a cationic polymer so that the adhesive does not adhere to them, whereby the adhesion is faster and more efficient.

The cationic agent used in the pretreatment of the filler particles according to the invention, preferably the cationic polymer, may be of a different type or the same type as the retention agent or accelerator used in the neutral sizing. Thus, it may be a cationic polymer such as, for example, cationic or cationized starch; Man-nogalaktaani; melamine, urea or guanidine formaldehyde resin; alkyleenipolyamiinihalohydriinihartsi; amino; disyaanidia-midi-formaldehyde-amine; urea monosubstituted urea resin; polyamine-polyamide polymer; polyacrylamide; sulfonated dimethylol urea resin; aminosulphuric-melamine-formaldehyde resin; polyamiinipolyamidihalohydriinihartsi; cationic polyamine, dicyandiamide formaldehyde resin; a resinous mixture resulting from the reaction of dicyandiamide, ammonium salt, formaldehyde and an acid salt of a water-soluble aminopolyamide; polyethyleneimine; poly (di-allylamino) epihalohydrin; a resin resulting from the reaction of dicyandiamide or cyanamide, bisaminopropylpiperazine and epihalohydrin; or poly (bis-aminopropylpiperazine) epihalohydrin resin. Particularly preferred are the so-called cationic dispersants, which are cationic polymers with significantly lower molecular weights than retention aids. Most preferably, they have a molecular weight of the order of less than 100,000 g / mol. The criterion is that the cationic polymer used in the pretreatment adheres to the filler particles, because according to the invention it is assumed that the filler particles react faster with the adhesive than the pulp fibers, thus slowing down the gluing, so adhesive cationic polymers must be attached to the filler particles.

Adhesives useful in the invention are based on hydrophobic, cellulose-reactive adhesives such as long chain ketene dimers, dicarboxylic anhydrides, organic isocyanates and carbamoyl chlorides. These so-called the active ingredients render the paper product hydrophobic by reacting with 6 74081 cellulose in the paper product. The following are some hydrophobic, cellulose-reactive sizing agents which can be advantageously used in the neutral sizing according to the invention.

Alkyl ketene dimers (AKD) have the general formula / r-ch = c = o7 (i) wherein R is a hydrocarbon group such as alkyl of at least 8 carbon atoms, cycloalkyl of at least 6 carbon atoms, aryl, aralkyl or alkaryl. Examples of ketene dimers are octyl, decyl, dodecyl, tetradecyl, hexadecyl, octadecyl, eicosyl, docosyl, tetracosyl, phenyl, benzyl-beta-naphthyl and cyclohexyl ketene dimers, as well as those prepared with ketene dimers. Pasta, naphthenic acid, delta-9,10-decylenic acid, delta-9,10-dodecylenic acid, palmitoleic acid, oleic acid, ricinoleic acid, linseed oil acid, linolenic acid and oleoxy acid, such as those derived from them, as well as those prepared from ketene dimers obtained from coconut oil, babassu oil, palm kernel oil, palm oil, olive oil, peanut oil, rapeseed oil, beef tallow, lard or whale fat. Mixtures of all the above fatty acids with each other can also be used.

Useful acid anhydrides include (A) resin anhydride, cf. U.S. Patent 3,582,464, (B) anhydrides having the structural formula R 1 to C 1 = O

No (II)

R2 - c / = O

7 74081 1 2 wherein R and R may be the same or different saturated or unsaturated hydrocarbon groups which are straight-chain or branched alkyl groups, aromatic-substituted alkyl groups or alkyl-substituted aromatic groups containing 11 to 39 carbon atoms, and (C) -cyclic dicarbyl, of formula 0 4 'R - RO (III) c = o 3. 4

wherein R represents a dimethylem or trimethylene group and R

is a hydrocarbon group containing from 8 to 22 carbon atoms and which is alkyl, alkenyl, aralkyl or aralkenyl. Thus, cyclic anhydrides are substituted succinic or glutaric anhydrides. Typical examples of straight chain anhydrides are myristoyl anhydride, palmitoyl anhydride, oleoyl anhydride and stearoyl anhydride. Typical examples of cyclic anhydrides are isooctadecenyl succinic anhydride, m-hexadecenyl succinic anhydride, octenyl succinic anhydride and octyl glutaric anhydride.

Organic isocyanates are useful when their hydrocarbon chains contain at least 12 carbon atoms, preferably 14 to 36 carbon atoms. Such isocyanates include resin isocyanate, dodecyl isocyanate, octadecyl isocyanate, tetradecyl isocyanate, 6-ethyldecyl isocyanate, 6-phenyldecyl isocyanate, and polyisocyanates such as 1,18-octadecyl diocyanate. isocyanate having one long chain alkyl group per two isocyanate groups which gives the whole molecule its hydrophobic properties.

The formula for carbamoyl chlorides is r1. ° (IV) N - R2 ^ ^ Cl 8 74081 1.2. .

wherein R and R are long chain groups, preferably stearyl groups (INSKO 159-81 Vili).

In general, sizing dispersions contain cationic starch as a stabilizing agent, but other protective colloids well known in the art can also be used, such as cationic water-soluble resins, e.g., the reaction product of aminopolyamine and epichlorohydrin.

Synthetic so-called neutral adhesives often require a cationic retention aid to initially attach to the fibers and possibly an accelerator may be used to accelerate the sizing reaction. Such retention aids or accelerators include cationic polymers such as cationic starch; cationic mannogalactan; melamine-niformalyylihartsit; urea-formaldehyde resins; guanidine forma lyylihartsit; alkylene polyamine-halohydriinihartsit; The amino-sit; dicyandiamide-formaldehyde-amine polymers; urea mono-substituted urea resins; polyamine-polyamide polymers; cationic polyacrylamide; sulfonated dimethylol urea resins; amino-sulfuric acid-melamine-formaldehyde resins; cellulose swelling amine oxide; polyamiinipolyamidihalohydriinihartsit; cationic polyamine; disyaanidiamidiformaldehydihartsit; a resinous mixture resulting from the reaction of dicyandiamide, ammonium salt, formaldehyde and an acid salt of a water-soluble aminopolyamide; polyethylene imii-ni; poly (diallylamino) epihalohydrin; a resin resulting from the reaction of dicyandiamide or cyanamide, bis-aminopropylpiperazine and epihalohydrin; and poly (bisaminopropylpiperazine) epihalohydrin resin. The cationic retention aid is generally very high molecular weight; its molecular weight can be up to the order of 10 g / mol. In addition to the cationic retention aid or accelerator, an anionic polymeric binder can also be used.

The method according to the invention differs from the neutral gluing method according to the prior art in that the filler is treated separately with a pretreatment agent before the filler is added to the fibrous pulp slurry. First, a slurry of a filler, preferably a mineral filler, is prepared by mixing, the slurry being considerably more concentrated than the pulp slurry. The slurry is then mixed with a pretreatment agent, which is preferably a cationic polymer, more preferably a cationic polymer intended as a dispersant, which has a molecular weight significantly lower than that of conventional retention aids. The preferred amount of pretreatment agent is 0.05 to 10.0%, preferably 0.1 to 1.0% by weight of the filler. The mixed filler slurry containing the cationic pretreatment agent is poured into a machine bed with a finished, prior art fibrous pulp slurry. A hydrophobic neutral adhesive, preferably a dispersion of the above-mentioned ketene dimer derivative, acid anhydride, isocyanate or carbamoyl chloride, most preferably the former, and a cationic retention aid, which may be one of the above-mentioned cationic polymers, are then added to the slurry in a known manner. The preferred amount of neutral adhesive is 0.01 to 1.0% (active ingredient), more preferably 0.04 to 0.20% of the total dry weight of the paper product. The preferred amount of retention aid is 100 to 500 g / t of dry paper product if the retention aid is polyacrylamide.

eXAMPLES

The following are examples of how the invention may be practiced.

The pretreatment of the filler with the cationic polymer was performed as follows. The filler slurry was made by mixing commercial filler calcium carbonate (Faxekalk) with water to form about 10% slurry, although under factory conditions considerably higher dry matter contents of the slurry can and should be used. After stirring for about 5 minutes, the slurry was complete. The indicated amount of pretreatment agent was then added to the filler slurry, which was a cationic polyacrylamide-based dispersant (Fennodispo K 91), a cationic resin remover (Fennodispo K 92), a strongly cationic pulp starch (Posenyl 51265), or a cationic polyacrylic acid (Posenyl 51265). After the addition of the pretreatment agent, stirring was continued for another 15,74081 for about 15 minutes. The mixed, pretreatment-treated filler slurry was fed to a machine pan prepared with about 2% pulp slurry. The cellulose used contained 40% bleached pine cellulose, 25 SR and 60% bleached birch cellulose, o 25 SR. The filler dosage was 22% of the total solids, which, taking into account the retention, became the filler content of the paper about 20%. The retention was very good because it was a very slow-running test paper machine (speed 6 m / min).

The indicated amount of alkyl ketene dimer glue (AKD glue) and so much cationic retention aid based on very high molecular weight polyacrylamide (Fennopol K304) were added to the mixture that it was about 230 g / t dry paper product. The glue was added to the so-called. expansion vessel and retention aid in wire water.

In prior art comparative experiments, pretreatment was either omitted or replaced by adding a mixture of AKD adhesive and prior art accelerator to the filler-containing wood pulp slurry instead of AKD adhesive. The prior art accelerators used in the comparative experiments were cationic urea-formaldehyde resin (UF accelerator) and cationic dicyandiamide resin (DCD accelerator).

AKD glue was produced in two types, the so-called cardboard glue and fine paper glue.

Cardboard glue was prepared as follows. 2 parts by weight of cationic starch (e.g. Posamyl E6) are slurried in 100 parts by weight of water and the mixture is stirred for about 30 minutes at 95 ° C.

o The starch solution is cooled to 65 ° C, mixed with 10 parts by weight of ketene dimer and the pH is adjusted to 2-3 with sulfuric acid. The mixture is emulsified with a rotor / stator type emulsifier (e.g. Ultra-Turrax, Jank & Kunkel KG) for about 10 minutes and cooled to room temperature.

I: 11 74081

Fine paper glue was prepared as follows. The adhesive premix is prepared in the same way as cardboard adhesive. After emulsification, the adhesive was passed twice through a high-pressure homogenizer (pressure difference 400 bar).

Adhesives according to the invention and the prior art were subjected to adhesive tests by determining Cobb values and performing a drip test as well as an HST test.

The Cobb value, i.e. the water absorption of the paper, refers to the amount of water that is absorbed by either surface of the paper in a given time from a 1 cm high water column evenly covering it.

Since sizing is intended to increase the hydrophobicity of the paper, it follows that the lower the Cobb value, the better the sizing result. The Cobb method is described in more detail in SCAN-B 12:64. According to its principle, air-conditioned specimens are weighed both before and after they have been placed in contact with water under certain conditions. Before the latter weighing, the excess water is removed by squeezing the test pieces between the blotting papers with a brass roll of specified size and weight. In the case of Cobb values, the water absorption time used is also reported as a subscript. Thus, Cobb and Cobb mean that the water 60 60 absorption time has been 30 and 60 seconds, respectively.

According to the drip test, a drop of water is placed on the surface of the paper and the time it takes for the drop to absorb inside the paper is measured. Since it is a question of the absorption time, it follows that the higher the reading, the better the bonding. It is important for the papermaking process to achieve hydrophobicity as quickly as possible. Thus, the drip test is measured immediately after the paper is finished and Cobb after 10 minutes. These values describe the so-called instant-gluing, ie how fast the gluing matures (develops). The value of Cobb 60 for 1 week is measured after one week of natural maturation, °. .

(23 C 50% RH). The Cobb value describes the final gluing 60.

74081 12 In the HST (Hercules Sizing Tester) test, ink is poured on the top surface of the paper and the time taken for the light reflection reading from the bottom surface of the paper to fall to 80% of the original reflection is counted. The experiment is described in more detail in the standard TAPPI T 530 pm-83. Since sizing is intended to increase the hydrophobicity of the paper, it follows that the higher the HST value, the better the sizing result.

The following table shows the measurement results. It appears that the accelerated gluing method according to the invention, in which the filler is separately treated with a cationic polymer before the filler is added to the wood pulp slurry, provides a much faster and better neutral gluing.

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Claims (7)

A method for accelerating and enhancing sizing by gluing a filler-containing paper product with a hydrophobic, cellulose-reactive neutral glue, characterized in that the filler is treated in a separate step with a pretreatment agent which is a cationic additive, preferably a cationic polymer, before adding the filler to the fiber. Process according to Claim 1, characterized in that a cationic polymer suitable for dispersion and having a molecular weight substantially lower than the molecular weight of the cationic polymers optionally used for retention is used as the filler pretreatment agent. Process according to Claim 1 or 2, characterized in that a pretreatment agent of 0.05 to 1.0%, preferably 0.1 to 1.0% by weight of the filler is used in the treatment of the filler. Process according to one of the preceding claims, characterized in that a long-chain ketene dimer is used as the hydrophobic neutral adhesive which is reactive with cellulose. Process according to one of the preceding claims, characterized in that 0.01 to 1.30% (active ingredient), most preferably 0.04 to 0.20%, by dry weight of the paper product, which is reactive with cellulose, is used. Process according to one of the preceding claims, characterized in that the filler to be treated is a mineral filler, preferably calcium carbonate. Method according to one of the preceding claims, characterized in that the filler to be treated is added to the fibrous pulp slurry in an amount of about 10 to 50% of the dry weight of the paper product.