PT830479E - A method for increasing the hydrophobicity of printing papers - Google Patents

Abstract

The present invention relates to a method of improving the water repellency of paper in papermaking by virtue of adding prior to web formation to the pulp slurry such a sizing dispersion that contains at least a ketene dimer compound as a hydrophobic sizing agent, and further contains water-soluble colloidal polymer in an amount which is at least 100 % by weight of the hydrophobic sizing agent. The invention is particularly applicable for improving the water repellency of paper containing calcium carbonate as the filler.

Description

DESCRIPTION

METHOD FOR INCREASING PAPER HYDROFOBICITY FOR

PREPARATION The present invention relates to a method of improving the hydrophobicity of paper for printing through internal sizing of the paper. It is a particular object of the invention to improve the hydrophobicity of paper through the use of a ketene dimer compound as a hydrophobicity sizing agent. The purpose of improving hydrophobicity is to give the paper web a degree of sizing which makes the paper compatible with inkjet printing.

The paper strength properties for wetting and penetration are conventionally improved in the paper pulp by means of internal sizing, while in the papermaking process compounds are added in the pulp which increase the hydrophobicity of the paper fibers. Printing paper, which is mainly used as office paper in various types of photocopiers, printers and printing machines, is expected to exhibit high brightness among other properties as well as acceptable stability in use as a filing document. Brightness and file stability properties can be affected by the type of filler used for the paper. A filler compatible with the above-described requirements is precipitated calcium carbonate (PCC). However, there is a problem in using this filler because it requires a neutral or alkaline environment for proper operation. Such a process condition excludes the use of conventional hydrophobic paper size through the resin-alum system. As is known in the art, this drawback is overcome by the use of hydrophobic sizing based on ketene dimer compounds such as alkyl, alkenyl, aryl and alkaryl ketene dimer design.

Such sizing is, however, hampered by other problems particularly in paper weights intended for use in office printing which must be compatible with different types of printer. Notably, in addition to application in inkjet printing, the same paper weight should serve as photocopier paper, laser printer paper, etc. When optimized for the above inkjet use, the base paper must be sized with large quantities of ketene dimer sizing combinations that ultimately cause problems with alternative printer types. In practice, the degree of sizing can reach, e.g., 0.1-0.2% dry mass of fiber in the web.

Over time, ketene dimer compounds have been found to be problematic as a sizing agent because of their tendency to migrate onto the finished paper. Due to such migration, the content of the ketene dimer compound is enriched in the outer layers of the sheet. Migration is made possible because the ketene dimer compound finishing reactions are so slow that the added agents lose their migration ability not before a few days after the sheet finish.

A disadvantageous effect of enrichment on ketene dimer compounds is easier slippage of the sheet surface, i.e., decrease of the surface friction resistance. Reduced friction is particularly detrimental in printing paper and photocopier weights because the lower slip threshold causes handling problems in printers or photocopiers whose paper transfer elements do not provide their intended function in slippery paper weights.

In addition, the aforesaid filler, namely, precipitated calcium carbonate indirectly causes easier slippage of the sheet. This is because it has been found that this filler disrupts the hydrophobic sizing process, whereby larger sizing quantities per unit mass of fiber should be used in comparison to the use of another type of filling.

On the other hand, it has been found that ketene dimer based sizing does not completely bind to the fiber during sheet formation, whereby a fraction of the sizing agent remains in the system and from this fraction a portion is bound later to fiber. When circulating in the system, the sizing compound is subjected to the water hydrolysis effect resulting in a partial decomposition of the sizing compound into the corresponding ketones. Further, a fraction of the size retained in the web will remain unconnected to the fiber, whereby the sizing can undergo hydrolysis by the moisture contained in the web. These phenomena are particularly detrimental in the use of photocopiers where the sheet is subjected to heating in the photocopier, whereby the decomposition of unbound sizing and its migration together with the released moisture 3 of the sheet to the sheet surface are accelerated. As a result, the automatic parts of the copier may become contaminated and the copy result deteriorated. To eliminate these risks, the determination of the residual ketone content contained in the paper weights intended for use in photocopying was instigated.

Blixt, TR, " Chalk - Calcium Carbonate for the High-Filled Sheet ", Paper presented at the Papermakers Conference 1992 April 5-8, 1992, Nashville, TN, USA, Book 2, pp. 515-520, Tappi Press 1992 describes a papermaking process using PCC as a filler. In the process, alkyl ketene dimer is added to the machine carton at a rate of 0.5 to 2 kg / ton and starch is added to the thick pulp at a rate of 5 kg / ton. EP-A1-0 220 941 discloses a paper sizing composition for internal paper sizing, including ketene dimers as sizing ingredients in a water dispersible encapsulating agent such as starch in an amount of 25 to 100% by mass of the dimer ketene present in the dispersion. US-A-5145522 discloses internal sizing of papers in neutral or alkaline conditions, wherein the ketene dimer sizing is stabilized by a polymeric aluminum compound used in conjunction with a dispersing agent, such as cationic starch being the used starch in an amount of 0.5 to 100% by weight against the ketene dimer used. EP-A-0 610 893 discloses a paper sizing composition. The composition comprises 50 - 99.9 wt% of fully hydrolyzed PVOH and 0.1 - 50 wt% ketene dimer compound (solid / solids). DE-A1-31 04 576 discloses compositions for internal paper sizing using AKD and ASA, and a cationic galactomannan as the protective colloid for these sizing agents, in the amounts of from 0.1 to 1.5 times the reactive sizing agent.

According to the present invention, an essential improvement has now been achieved in overcoming the above-described problem by virtue of a method of improving the inkjet printing capacity of printing paper prepared using precipitated calcium carbonate as a filler, adding before forming the web to the paste a ketene dimer compound, whereby a sizing dispersion containing at least the ketone dimer compound as the hydrophobic sizing agent is used in an amount of 0.1-0.2% dry mass of fiber and additionally contains water soluble colloidal polymer, and wherein the amount of the water soluble colloidal polymer is at least 100% by weight of the hydrophobic sizing agent.

Here, it was first noted that the ketene dimer compound used as a hydrophobic sizing agent is better attached to the fiber, and, secondly, that the precipitated calcium carbonate used as a filler has no essential disrupting effect on the sizing. Due to the latter fact, less amount is required, whereby said lesser amount of the hydrophobic sizing agent may be retained near the fiber in an improved manner until the finishing of the hydrophobic sizing agent has continued at a level that prevents migration. Additionally, it has been found that the invention provides improved ink penetration properties relative to water penetration. This effect is extremely important for the quality of inkjet printing that is becoming increasingly used.

It has been found that the invention is further applicable in cases where the ketene dimer compound employed as a hydrophobic sizing agent in paper sizing is complemented with other conventional hydrophobic sizing agents such as anhydrous alkylated succinic and / or resin.

Particular embodiments of the invention are set forth in the dependent claims. The invention is explained below with the aid of the following examples which elucidate the function of the invention in its different modes of execution.

Example 1

A pilot scale test run was performed, where internal scaling was performed for a paper stock with precipitated calcium carbonate (PCC) added as a filler. The filler (registered name Albacar LO) was used at 22% per mass of dry fiber. The fiber in the basecoat was 75% birch fiber milled at 23 SR ° drainage index and the fiber slurry was adjusted to pH 7. The remainder, 25%, of the fiber was pine fiber also beaten at the drainage index 23 SR ° and fiber slurry also adjusted to pH 7, Raisamyl 135 was added to the slurry as stock starch at the addition rate of 5 kg / ton. The weight of the paper web produced was 80 g / m2. The paper machine was run at 60 m / min resulting in a production rate of 4.08 kg / min. The retention agent used in the process was BMA 590 (colloidal sodium silicate) at an addition rate of 300 g / t of pulp. The paper web was also sized on the surface using Raisamyl 406 LO starch at the 6% solids addition level. The hydrophobic compound used as the sizing agent was alkyl ketene dimer (AKD).

Test runs were performed using the different hydrophobic sizing formulations listed below for internal sizing: 1. Conventional AKD sizing with Raisafob 940, in which the amount of starch-protective colloid addition was not more than 20 mass% sizing. 2. Sizing AKD, addition amount of starch protective colloid 50% by mass of sizing agent. 3. Sizing AKD, addition amount of protective colloid starch 100% by mass of sizing agent. 4. Sizing AKD, addition amount of starch protective colloid 150% by mass of sizing agent. 7 5. AKD sizing, addition amount of starch protective colloid 200% by mass of sizing agent. 6. Sizing AKD, add amount of starch protective colloid 250% by mass of sizing agent. 7. Sizing AKD, addition amount of starch protective colloid 300% by mass of sizing agent. 8. AKD sizing, amount of protective colloid addition using PEI (polymer KK) * in an amount of 200% by weight of sizing agent.

Notes: *) polyethylene imine

The tests were run using two sizing agent levels, namely by adding the sizing agent (AKD) at 0.1% and 0.2% by dry fiber mass. The starch used as a protective colloid component was Raisamyl 150 EH which is a special degraded starch. The degree of sizing in the prepared papers was tested by measuring the water absorbency of the paper sheets in the Cobb6o test of the sheet surface, while the ink penetration of the sheets was measured using the Schröder test. The brightness of test sheets was also measured.

The test runs gave the following results:

Test n0 / Cobbe test Test Schroder Brightness Amount of [g / m2] (100-> 90%, s) sizing 0.1% 0.2% 0.1% 0.2% [%] 1 78.2 28 , 3 0 10 92.7 2 76.3 28.1 1 11 92.6 3 41.5 26.6 2 15 92.7 4 29.3 20.2 5 135 92.8 5 25.0 18.4 18 248 93.0 6 24.8 18.3 20 253 92.9 7 24.7 7 18.2 21 255 93.0 8 28.8 18.1 21 262 91.1

From the foregoing results it can be seen that at a rate of addition of the sizing agent of 0.1% by dry fiber mass, a sufficient addition rate of the protective colloid component is approx. 200% level by solids mass of hydrophobic sizing agent, whereby this combination provides a Cobbe value of less than 25 g / m 2 which is conventionally considered to represent a sufficient level of sizing. For the largest, 0.2 wt%, rate of addition of the sizing agent, the corresponding water repellency value is achieved using an addition rate of the protective colloid component as low as 100% of the sizing agent solids mass hydrophobic. It has also been found that polyethylene imine (PEI) (Test No. 8) acts as a protective colloid component at the same rate of addition (200%), however, with the penalty that paper brightness is adversely affected particularly in weights made using optical brighteners. The ink penetration property of the paper web is significantly improved up to the addition rate of 200% of the protective colloid component, whereafter this property at higher addition rates remains approximately at the same level as when using PEI.

Example 2

A production scale test run was performed on a thin paper machine yielding paper at 78 g / m 2 basis weight. The paper was prepared using pulp comprised of the 60/40 pine birch fiber rate. The amount of filler added to the base web was at a level of 22% by mass of dry fiber, where 70% of the filler was precipitated calcium carbonate (PCC, Albacar LO) and 30% ground CaC03. The retention system was composed of corn starch and an anionic component (Compozil). The AKD sizing was applied using two different formulations: 1. Raisafob 940, conventional AKD sizing, amount of protective colloid component not exceeding 20% dry mass of sizing material. 2. Raisafob 500, AKD sizing using starch as protective colloid component with an amount increased to 200% dry mass of sizing. The starch added as a protective colloid component was Raisamyl 150 EH.

The test runs were carried out using AKD sizing at 0.12% dry mass of fiber. The tests were run in multiple runs using both previous design formulations under identical conditions given to eliminate random error of the results. The tests are presented in the table below: 11 2 Τ

Run Type Cobb60 east Ink-jet coefficient, black and white Inkjet, test color AKD Schroder friction n ° (100-> 91%, s) side side static side kinetic density time half time medium fade-density (1001) [s] of the ink [s] 77 RF940 21.7 22.2 59 0.79 0.54 1 , 60 9 4 19 10 8 1.08 79 RF940 20.7 21.5 49 0.67 0.50 1.64 11 4 20 10 8 0.98 81 RF940 21.2 20.7 54 0.77 0, 54 1.64 9 6 18 10 8 0.97 84 RF940 20.4 20.6 78 0.75 0.58 1.76 12 4 15 10 8 1.03 87 RF500 19.9 19.8 205 0.76 0.53 1.91 22 2 109 10 8 1.38 89 RF500 19.3 19.0 181 0.75 0.53 1.93 14 2 144 10 8 1.38 91 RF500 19.4 19.2 209 0 , 82 0.57 1.94 21 2 154 10 8 1.42 93 RF500 19.4 19.4 203 0.81 0, 57 1.90 19 2 157 10 8 1.46 95 RF500 19.5 18.9 277 0.78 0.60 1.96 24 2 172 10 8 1.51 as

As is evident from the foregoing results, sizing properties are clearly improved by the use of RF 500 and the coefficient of friction is simultaneously retained at the same level or even improved. Ink-jet printing tests indicate that the use of RF 500 results in positively crimped black-and-white printing results relative to conventional sizing, and at the same time, the color ink-jet printing test remains unchanged, which indicates that the sizing level here is oversupplied for inkjet color printing.

Example 3

A production scale test run was carried out in which the following sizing formulations were compared: 1. Raisafob 940 AKD sizing, addition amount of starch protective colloid not exceeding 20% by mass of sizing agent. 2. Raisafob 500 sizing AKD, addition amount of protective colloid starch 200% bulk sizing agent. The paper prepared here was an intended office paper for multiple uses. Production target values for paper quality were established as follows: residual ketone content less than 0.4 mg / g (for use in photocopying), black density 13 higher than 1.2 in B / W printing on printers ink jet and combination of black density greater than 0.75 in color printing.

Test run conditions:

Paper quality:

Office paper (multiple uses)

Base weight: 80 g / m2

Baseline web composition: 70% birch fiber at 23 ° SR drainage index 30% pine fiber at 23 ° SR drainage index

Filling:

Precipitated calcium carbonate (PCC)

Retention system:

Two component formulation (polymer + bentonite) Surface sizing:

Starch Raisamyl 408 + 1.5 kg of styrene acrylate polymer / ton of pulp solids

Paper machine speed: 980 m / min

Addition rate of AKD: 1 kg of AKD / ton of pulp solids, or alternatively, 1.4 kg of AKD / ton of pulp solids Test Results: 14

Sizing agent [kg / ton] Cobb60 [g / m2] Penetration of ink HST 80 [%, S] Residual ketone [mg / g] Black density, B / W printing, felt side Black density, . color, felt side RF 940 1 25 80 0.41 1.02 0.64 RF 940 1.4 23 153 0.68 1.22 0.82 RF 500 1.4 21 238 0.27 1.38 0, 90

As is evident from the foregoing results, the sizing properties are clearly improved by the use of RF 500. In addition, the residual ketone content remains below the set target value. Also, the target density values set for ink jet printing are exceeded. Instead, using the RF sizing formulation 940 with a low protective colloid content, it is not possible to find the upper limit established for the residual ketone content. Thus, the paper prepared in this process is not suitable for use in the intended copier. If the rate of addition of sizing is reduced to a level of 1 kg / ton of pulp solids, the RF sizing formulation 940 may find marginally the level set for the maximum permissible residual ketone content, however, with no meet required ink penetration criteria.

It has been found that the invention is additionally suitable for use in such paper sizing applications in which a fraction of the hydrophobic sizing agent is composed, in addition to AKD, in addition to another suitable sizing agent for water repellency improvement such as anhydrous alkenyl succinic acid (ASA). However, since ASA sizing formulations do not impart hydrophobic properties as effective as those of AKD sizing formulations, they should be used in greater amounts to achieve comparable inkjet printing qualities. Because of the staining problems caused by the required high ASA sizing rates in papermaking, this sizing approach seems less favored. However, due to the use of an ASA sizing formulation in the present application would give a low content of residual ketone in finished finished paper, which is a definite benefit when using the paper in photocopiers. The well-known problem properties of this sizing agent require that the sizing raw materials be prepared in the immediate vicinity of the papermaking process. In the following example, the behavior of this type of sizing formulation is described.

Example 4

A production scale test run was carried out to compare the behavior of the following sizing formulations: 1. Raisafob 500 sizing AKD, addition amount of starch protective colloid 200 mass% of the ketene dimer. 2. Raisafob MF ASA scaling, dispersed in Raisamyl 135 starch reserve at an ASA / starch ratio of 1: 2.

3. Raisafob 500 + Raisafob MF sizing AKD plus Raisafob MF, added separately. 4. New scaling formulation formulation size AKD / Raisafob 500 + ASA scattering dispersed in the AKD / ASA ratio of 50/50. The paper prepared here was an intended office paper for multiple uses. Production target values for paper quality were established as follows: ketone content less than 0.4 mg / g (for use in photocopying), black density greater than 1.2 in B / W printing on jet printers of ink and black density combination of more than 0.75 in color printing.

Test run conditions:

Paper quality:

Office paper (multiple uses)

Base mass: 80 g / m2 17

Baseline web composition: 70% birch fiber at 23 SR ° drainage index 30% pine fiber at 23 SR ° drainage index

Filling:

Precipitated calcium carbonate (PCC) at a level of 20% by mass of dry fiber

Retention system:

Two-component formulation (polymer + bentonite) Surface Dimensioning:

Starch Raisamyl 408 + 1.5 kg of styrene acrylate polymer / ton of pulp solids

Paper machine speed: 980m / min

AKD addition rate: 1.4 kg / ton (as AKD, pulp solids RF500)

ASA addition rate: 1.4 kg / ton (MF MF)

AKD / ASA addition rate: 0.7 kg + 0.7 kg / ton (RF500 and RF MF, using separate additions)

New sizing formulation: 0.7 kg + 0.7 kg / ton (ASA dispersed in RF500 product)

Test Results: 18

Sizing agent Cobb60 [g / m2] Penetration of ink HST 80 [%, s] Residual ketone [mg / g] Black density, B / W printing, felt side Black density, . color, felt side RF 500 1.4 22 24 0.29 1.32 1.06 RF MF 1.4 23 122 0 1.14 0.58 RF 500 + RF MF 0.7 + 0.7 22 173 0 , 15 1.18 0.78 New formulation 0.7 + 0.7 21 208 0.15 1.21 0.86

As is evident from the foregoing results, the established requirements for the compatibility of prepared paper with inkjet printing are not achieved using only ASA sizing. Notably, the paper exhibits zero residual ketone content. The new type of sizing formulation combination is capable of meeting the established requirements for both photocopier and inkjet printing. The results also show the effect of ASA hydrolysis on the sizing efficiency when ASA is dispersed in heated stock starch and then added separately. As for inkjet printing, here again the new sizing formulation gives better density values than those achieved using only ASA.

In a manner similar to combining with ASA sizing, the akd dispersion based on Raisafob 500 can be combined with resin sizing. In general, the resin imparts good friction properties and does not make the paper slippery as is typically the case when using only AKD sizing. 5/5/2007

Claims (12)

A method of improving the ink jet printing of printing paper fabricated using precipitated calcium carbonate as a filler, adding before the formation of the web to the pulp a ketene dimer compound, characterized in that a scattering dispersion which contains at least the ketene dimer compound as a hydrophobic sizing agent in an amount of 0.1-0.2% dry fiber mass and additionally contains water soluble colloidal polymer, and wherein the amount of the water-soluble colloidal polymer water is at least 100% by weight of the hydrophobic sizing agent. A method as defined in claim 1, characterized in that a scattering dispersion in which the amount of the colloidal polymer is in the range of approx. 150-250% by weight of the hydrophobic sizing agent. A method as defined in claim 1, characterized in that a scattering dispersion containing at least one additional sizing agent selected from the group consisting of anhydrous alkenyl succinic acid and resin is used. A method as defined in any one of claims 1 to 3, characterized in that said water soluble colloidal polymer is selected from the group of compounds comprising: starches, carboxymethylcellulose, ethyl cellulose, polyacrylamides, polyethyleneimines, polyesters, polyethers, polyamides, alcohols polyvinyl alcohol, gelatin, tristearate, gum arabic, sugars or a mixture thereof. 1 A method as defined in claim 4, characterized in that said water soluble colloidal polymer is a low viscosity amphoteric starch. A method as defined in claim 3, wherein the further sizing component is an anhydrous alkenyl succinic acid in an amount of 20-70%, advantageously 30-50%, by weight of the ketene dimer. A method as defined in claim 3, characterized in that the further sizing component is strengthened resin. A method as defined in claims 3 or 7, characterized in that the further dimensioning component is resin in an amount of approx. 20-50% by mass of the ketene dimer compound. A method as defined in any one of claims 1 to 8, characterized in that the sizing dispersion additionally contains a surfactant compound, a biocidal agent and / or a pH control agent. A method as defined in claim 7 or 8, characterized in that the sizing dispersion contains 2-15% by weight of aluminum sulfate of said colloidal polymer. A method as defined in any one of claims 1 to 10, characterized in that said ketene dimer compound is selected from the group of ketene alkyl, alkenyl, aryl and alkaryl dimers. 2 A method as defined in any one of claims 1 to 11, characterized in that the content of said hydrophobic sizing agent in the sizing dispersion is approx. 1-15 wt.%, Advantageously 6-15 wt. %. 5/3/07 3