FI88734B - HEGBULKIGT KALANDRERAT PAPPER SOM INNEHAOLLER BLAOSAKTIGA PAERLOR OCH FOERFARANDE FOER FRAMSTAELLNING AV DET - Google Patents

Description

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This invention relates to high bulk calendered paper containing blister-like beads and to a method of making the same. Blister-like beads improve the brightness, opacity and softness of the paper and minimize the density of the paper.

Inorganic pigments are usually added to the pulp so that the paper produced has the desired brightness, opacity and printability. The particle size of these inorganic pigments is generally less than one micrometer. However, these inorganic pigments, in particular titanium dioxide, anatase, are dense and can thus increase the weight of the paper to be produced per unit area. In addition, these fine-grained pigments, like many of the other fine-grained components of the paper, permeate the Fourdrinier wire and disappear with the "nol water". Although these losses are minimized by recycling water, recycling comes before a long limit, after which the paper product is damaged, so the losses are real and some of the fines are transported to rivers and. 25 waters, polluting them.

Conventional papermaking processes generally retain only about 65% of the finely divided material fed to the process, including titanium dioxide, clay and carbonates, and the remaining fines pass through the wire and are recovered or not recovered by the recycling methods used. The present invention significantly improves fines retention, generally by increasing the ash content by 7-10 percentage points. The mechanism by which this is accomplished is not entirely .35 clear, but it can be said that improving fines retention is a serious industrial problem that has plagued the paper industry throughout its history.

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Titanium dioxide pigments can be used quite effectively to improve the opacity and brightness properties of different grades of paper, but they are expensive. It should be noted that printing paper is usually finished by calendering, which improves the printability and appearance of the paper 5 for use in books, magazines, etc. Increasing paper density per unit area and postage costs and pigment price are factors that significantly increase titanium dioxide calendering. 10 originally production and operating costs.

To achieve the desired opacity, experiments have been performed in which opaque cellular plastic particles were added to the pulp. These cellular plastic particles were 15 thermoplastics, so they collapsed under the influence of calendering, especially supercalendering, heat and compressive force. The fluff and opacity caused by the plastic particles were lost as the particles collapsed. The compression force used in the calendering is generally at least 26.8 kg / cm and can be as high as 35.7 kg / cm and the temperature at least 37.8 ° C, most usually at least 65.6 ° C. Because these cellular plastic particles lose their volume and opacity enhancing effect when compressed, they have little use in the production of high bulk calendered paper.

This invention is directed to maintaining the brightness and opacity of calendered paper by increasing the thickness of the paper (caliper) and the ability to prevent writing transparency. It is also intended to reduce the need to use inorganic pigments, especially titanium dioxide. As a result, the cost level can be maintained and the density of the calendered paper product can be minimized while maintaining or improving the softness and printability of the paper.

The present invention therefore relates to high bulk calendered paper containing from 2 to 6% by weight of paper of highly crosslinked, titanium dioxide pigmented, polymeric blister-like beads having an average particle size of at least about 5 μζη and at most about 35 μτη, and this calendered paper is characterized by a rice weight of not more than 18.1 kg per rice.

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Thus, according to the invention, all or part of the conventional inorganic pigment to be added to the pulp, such as titanium dioxide, anatase, is replaced by crosslinked, titanium dioxide pigmented, polymer -10 with those vesicular beads having an average particle size between 5-35 μια. The final paper contains at least about 2% by weight of those beads. At a concentration of 2% in very light paper, a small effect can be observed. However, significant practical results require a paper 15 with a rice weight of between 9.0 and 18.1 kg of rice, and the bead content of these papers should be about 3.5-6%, preferably 4-5%, in order to achieve significantly improved practical results. . If the content is less than 3.5%, the effect is difficult to see in papers with the indicated rice weight. If the content is more than 6%, it is not economical to add the beads presented here. Papers with a rice weight of less than 9.0 kg per rice are not the high-quality printing papers referred to in this invention, and papers with a rice weight of more than 18.1 kg per rice have a more difficult to detect effect of .25 fluff.

In order for a calendering operation to produce paper useful as a quality printing paper, the calendering operation must apply a force to the paper such that it breaks most of the beads. This paper is calendered at a pressure of at least about 26.8 kg / cm and at a temperature of at least 37.8 ° C to obtain a calendered paper product suitable as a quality printing paper, and the pigmented blister-like beads used under these conditions increase the paper fluff. Preferred papers to be produced are offset printing papers which are subjected to a pressure of 35.7 to 214.2 kg / cm during the calendering operation, whereby the advantages provided by the present invention are improved at these higher pressures. A pressure of 125.0-214.2 kg / cm is preferred for gravure paper.

In particular, when the vesicle-like beads contain titanium -5 dioxide, it can be seen that the calendered paper product is lighter and more translucent in thickness due to the use of the beads. This effect is proportional to the amount used. In addition, it is particularly surprising to notice a significant improvement in print gloss, and this excellent gloss improves the ink retention capacity of the paper.

It has been found that a grade corresponding to calendered paper can also be produced satisfactorily with a lower weight of rice. The term "rice weight" is used in connection with papermaking 15 to describe weight per unit area. Paper of a certain thickness with a lower rice weight has been found to have better opacity and softness with blister-like beads and a smoother surface from the edge of the calendered sheets than a similar paper to which only a mineral pigment such as titanium dioxide has been added.

It is emphasized that the increased fluff provided by this invention is provided by vesicle-like beads having a size of at least 5 μπι, with larger beads producing even better fluff than smaller ones. Beads up to about 35 microns in diameter can be used, but it is recommended to use an average particle size between 8 and 30 μια. The term "vesicle-like" refers to a bead consisting of a plurality of vesicles or cells. The beads considered here consist of an average of at least 5 cells per bead. It appears that a large number of cells per bead prevents the beads from collapsing when the paper containing those beads is compressed with a considerable force of 15 ° as determined by the calendering operation.

Thus, after calendering, the improvement in fluff is about 5-15% when using beads of the above-mentioned size, the improvement in fluff 5 P ft 7 3 4 means the amount of thickness increase in paper of the same weight. If the rice weight of the paper is small, e.g. less than about 15.9 kg per rice (usually 13.6 kg per rice), beads with a particle size of less than about 15 5 μιη will give a better result. In paper with a higher rice weight, e.g. more than 15.9 kg per rice (usually 18.1 kg per rice), beads with an average particle size of more than about 15 μιη give the best result (paper fluff is better preserved in calendering).

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The typical machine calendering conditions studied comprise a vertical compression force between 20.8 and 160.7 kg / cm at a normal papermaking temperature at this process step, i.e., about 65.6 ° C. Calendering temperatures below about 95.3 ° C are generally recommended.

The process for preparing high bulk calendered paper according to the invention is characterized in that a liquid suspension containing carboxyl-functional, highly crosslinked, titanium dioxide pigmented, polymeric vesicle-like beads having an average particle size of at least about 5 μιη and up to about 35 μιη with the material, the beads premixed with a neutralized .25 polycarboxylic acid polymer thickener to reduce the passage of fines through the wire to the zero water, forming a high-bulk paper containing 2-6% by weight of polymeric vesicle-like beads, and calendering said high-bulk paper with a rice weight not exceeding 18.1 kg per rice.

The liquid bead suspension is modified by adding a neutralized polycarboxylic acid polymer, such as ammonia-35a neutralized polyacrylic acid, to thicken the liquid medium, and thus keeping the beads in a stable suspension. It has been observed that when the liquid bead suspension is stabilized as previously described, the papermaking

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process considerably, as the amount of fines passing through the wire into the zero water is reduced. In addition, this operation is particularly effective when an effective amount of anionic retention aid is used in a pulp in which the amount of anionic retention aid is secondary, since normal amounts of retention aid, as used herein, are effective.

It is emphasized that the vesicle-like beads used herein are cross-linked carboxyl-functional beads so that they can contribute to improving fines retention. The presence of titanium dioxide pigmentation in these beads is not required for fines retention, but in the ability of the beads to improve the quality of the calendered paper.

It is interesting to note that the neutralized polycarboxylic acid polymer, which thickens and stabilizes the liquid bead suspension, chemically interacts with the carboxyl functionality of the beads. This is evidenced by the fact that these neutralized polymers are sufficient to stabilize the suspension at a lower viscosity level than other thickeners, so that stabilization is also affected by factors other than the viscosity of the liquid medium alone.

There also appear to be 25 chemical interactions with the anionic retention aid. This is evidenced by the fact that the anionic retention aid is selected and used in a ratio that maximizes retention at the practical level. The amount of neutralized thickener, which is chemically similar to the retention aid and added to the bead suspension, is far too small to significantly contribute to the improvement of retention. It has been thought that the amine or ammonia used to neutralize the carboxyl functionality of the retention aid, the carboxyl functionality of the thickener, and the carboxyl functionality of the beads function to effectively connect the retention aid and the beads. When the retention aid combines with a fine particle that would normally pass through the wire, it results in the retention aid also being able to bind to the bead. This bead 7 b 8 7 5 4 is much larger than a fine particle, which increases the chance that a much larger conglomerate will remain on the wire.

In summary, vesicle-like beads used in a liquid suspension thickened with a neutralized polycarboxylic acid polymer to prevent the suspension from precipitating can be effectively retained in the paper along with a larger amount of fines and mineral fillers in the process.

Bead retention is improved by the use of conventional anionic retention aids. The combination of carboxyl-functional crosslinked beads premixed with a neutralized polycarboxylic acid polymer thickener and an anionic retention aid also contributes to improving the retention of all fines in a conventional papermaking process.

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The vesicle-like beads fluff the paper, even if not pigmented, but the pigmented vesicle-like beads withstand the heat and pressure of the calendering operation and, despite their large size (compared to mineral fillers), fluff the calendered paper and maintain the opacity and brightness of the paper while calibrating the paper opacity. At the same time, the amount of titanium dioxide pigment can be considerably reduced. This is surprising. Since there is no need to reduce the amount of titanium dioxide, larger amounts of this pigment can be incorporated into the vesicle-like beads used.

Retention aids which have proved practical in this connection are well known per se and many of them are commercially available. Preferred are copolymers of monoethylene acid and acrylamide and methacrylamide, which generally contain 5-50% acid monomer and the remainder amide monomer. The acid portion of the preferred anionic copolymers 8b'6 / 04 generally consists of either acrylic or methacrylic acid, which is rendered anionic by means of an amine, preferably ammonia. A copolymer containing 20% methacrylic acid and 80% acrylamide is an illustrative anionic retention aid.

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Various anionic resins that can be used as retention aids are discussed in Kirk Othmer's Encyclopedia of Chemical Technology, 3rd Edition, Volume 16, page 804, which states that ordinary fillers, Kool-10, are less than 5 μπι due to their small size. effectively remains on the paper, thus advocating the use of retention aids in the pulp. The beads used here are usually much larger, but their retention on Fourdrinier wire is also improved with the help of standard retention aids.

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Preferred anionic retention aids consist of carboxyl-functional copolymers dispersed in a pulp slurry because they are dissolved in a base, usually ammonia or a volatile amine. The vesicle-like beads used herein consist of a crosslinked polyester resin having unreacted carboxyl groups. These carboxyl groups also combine with the base, as the base is always present during the preparation of the beads.

Polyacrylic acid thickeners are well known substances and have a relatively high molecular weight because they are prepared by polymerization in a liquid emulsion. Acrylic acid or methacrylic acid is usually used, with the selected acid or acid mixture being essentially the sole monomer, although up to 10% of other monoethylenically unsaturated monomers, such as ethyl acrylate, may be present. Up to 2% of a polyethylene monomer such as divinylbenzene or ethylene glycol allyl ether may be present during the copolymerization to increase the molecular weight or to provide limited crosslinking. Ammonia or a volatile amine such as monoethanolamine can be used to neutralize, which thickens the polymer-containing liquid medium. Ammonia is considered the preferred base. Generally, 0.1-9 £ '> 6' / ό 4 2% polyacrylic acid polymer is sufficient for the thickening required (after neutralization) to stabilize a bead suspension containing about 10-50% free water. Exact neutralization is not required. Achieving the desired thickness determines the amount of base to be used.

In the process of the present invention, it is preferable to use a pulp slurry having a pH of 4-6, which is achieved by adding an acid such as sulfuric acid. The reason for this is that the re-10 tension of the fines is greatest in this pH range.

It is interesting to note that anionic retention aids are generally added to or near the headbox to minimize mixing, and this conventional method apparatus is preferably used here as well (blister-like beads are added with retention aids) to achieve good contact between the added anionic groups and the pulp. . More specifically, it is preferred to add the beads and anionic retention aid to the pulp just before the headbox and after pumping and centrifugal filtration presses to minimize shear caused by the anionic retention aid and anionic beads used herein.

In a special comparison using 7.5% titanium dioxide, anatase, in a typical opacitized paper, it was found that a combination of 2.5% titanium dioxide, anatase, and 5% pigmented vesicle-like beads gives a sauna-weighted calendered paper, which is equally strong, fluffier, of similar opacity and softer.A roughly a sauna-like situation follows when using only pigmented vesicle-like beads without titanium dioxide.When using only titanium dioxide-pigmented vesicle-like beads without extra titanium pigment 35 was obtained, the paper was and the surface is softer than the titanium dioxide control.Titanium dioxide pigmented beads are used because the fine pigment on the cell walls of the vesicle-like beads better prevents the beads from collapsing during calendering. - during the ration.

Although pigmented vesicle-like beads are important in the manufacture of calendered paper, the improvement in fines retention in the papermaking process does not appear to require the presence of pigment in the cell walls of the beads, so pigmented beads are not a major factor in the novel process of this invention.

Although excellent properties are achieved without free titanium dioxide, the use of this inorganic pigment, albeit in a smaller amount than usual, is desirable in some cases. In this case, the amount of normal titanium dioxide, anatase, which is about 7.5% in the opacified calendered printing paper can be reduced to 0.5-5%, preferably 1-4%.

Preferred vesicle-like beads are styrene-crosslinked unsaturated polyester resins. These are made into vesicle-like beads according to a known method described in U.S. Patent No. 3,879,314. These vesicle-like beads may vary considerably in size, but are generally on average at least about 5 microns in diameter. For example, beads with an average diameter of 8-30 μιη are easy to manufacture and are fully useful in the present invention. When the size of the beads increases above n.

30 / im, it is more and more difficult to make good quality beads. The beads are generally placed in a liquid suspension and contain about 55-60% water by weight. The suspensions contain more water than the beads can keep dry in the active cake, so the suspensions contain about 15-35% solid beads, in equilibrium with water 35. These are generally thickened with an amount of ammonia-neutralized polyacrylic acid or polymethacrylic acid to obtain a stable suspension, but absolute amounts are not critical, as poorly stable 11 H 8 7 S 4 suspensions are still useful if an additional amount of thickener is allowed.

There are several other patents of interest for the manufacture of vesicle-like beads for use in the present invention, notably U.S. Patent Nos. 3,822,244, 3,923,704 and 3,933,579. The latter patent describes the vesicle-like beads recommended in this application, namely those having the ratio between the diameter of the granule and the average diameter of the 10 vesicles is at least 5: 1, the volume of the vesicle is 5-95% of the volume of the granule and they contain at most 60% by volume of pigment.

The vesicle-like beads used herein have a strongly crosslinked polymeric backbone, preferably consisting of a carboxyl-functional, unsaturated polyester resin crosslinked with an ethylenically unsaturated monomer copolymerizable thereto. Maleate unsaturation has been recommended as the unsaturation of the polyester, with such polyesters being well known per se and will be described later. These polyesters are carboxyl-functional substances and the acid number of the polyester is preferably 10-45 mg KOH / g, more generally 15-25.

The unsaturated monomers used for crosslinking are also well known and water-insoluble monomers, typically represented by styrene and vinyl toluene. Polyesters and monomers are discussed in more detail in U.S. Patent No. 3,879,314, which discloses a process for making vesicle-like beads using water-soluble polyamine. . containing at least three amine groups per molecule and having a dissociation constant in water (pK value) of 8.5-10.5, with diethyltriamine being a typical representative. The polyamine is used in a concentration corresponding to 0.3 to 1.4 amine groups per 35 polyester carboxyl groups. 35-45% unsaturated polyester with 55-65% styrene is recommended for crosslinking. The beads are usually used without drying and contain a lot of water and the amines used to make them.

The invention is described below, in which it should be noted that the parts and ratios are given in units of weight, unless otherwise stated.

The pigmented vesicle-like beads of this invention are described in U.S. Patent No. 3,879,314, issued April 22, 1975, cf. in particular Example II. By working according to Example II and using a polyester containing 18% phthalic anhydride, 37% maleic anhydride and 45% propylene glycol dissolved in styrene to form a solution containing 41.8% polyester, titanium dioxide, anatase, pigmented vesicular beads containing 43.2% pigment. Polyester is a carboxyl functional product and this carboxyl functionality exists in large part in salt form together with the amines used to make the beads. These beads 20 have an average size of 25 μια and contain an average of more than 10 cells per bead.

These beads are added to a pulp of 39.9 kg of softwood pulp, 60.0 kg of hardwood pulp, 20.0 kg of clay, 2.3 kg of calcined clay and 1.5 kg of alum mixed with water to give a mixture of 1892.7 dm3 , to which 300 ml of concentrated sulfuric acid are added to keep the pH between 4.5 and 6.5. This pulp slurry is modified to contain 4-6% vesicle-like beads and 1.5% titanium dioxide, anatase, by dry weight of the pulp 30, after which the pulp slurry is pumped into the headbox through a valve where its dry matter content decreases by 2.5%: respectively.

The paper made from this pulp slurry had a rice weight of between 16.8 and 18.1 kg of rice and was calendered at a pressure of either 26.8 or 160.7 kg / cm 3 at a temperature of about 65.6 ° C. Compared to a similar pulp containing 6.5% titanium dioxide, anatase, it was found that the thickness of the calendered paper increased by 5-15% at all rice weights and at both bead content levels of 4% and 6%.

The prepared paper, both without beads and with beads, was treated in a conventional manner in an adhesive press, after which it was calendered under the above-mentioned conditions to obtain a finished paper which was tested. The paper containing pigmented vesicle-like beads was thicker and more opaque than ordinary titanium dioxide-dipigmented paper. This confirms that the present invention provides a lighter weight and equally opaque printing paper.

The vesicle-like beads in the form of an ammonia-neutralized polyacrylic acid-thickened, stable liquid suspension can be added together with an anionic retention aid consisting of a copolymer of 20% methacrylic acid and 80% acrylamide in an amount of 1% by weight of solid. These are added to the pulp together with water to dilute the pulp to the desired dry matter content immediately before the headbox to prevent cutting. Compared to the use of an anionic retention aid alone, it can be seen that a significantly smaller amount of fines passes through the wire, which can be seen as a decrease in the zeta potential of zero water. With respect to the ash content, it can be seen that the normal retention obtained by comparing the theoretical and actual ash content increases from about 67-68% to 76-77% when this fact is examined in the light of the present invention.

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Claims (10)

14 Ö8 734 A high bulk calendered paper containing from 2 to 6% by weight of paper of highly crosslinked titanium dioxide pigmented polymeric vesicle beads having an average particle size of at least about 5 μπι and at most about 35 μm, characterized in that said calendered the rice weight of the paper shall not exceed 18.1 kg per rice. High bulk calendered paper according to claim 1, characterized in that the amount of blister-like beads in the paper is at least about 3.5%, that the paper has a rice weight of at least about 9.0 kg per rice to obtain high quality printing paper, and that the blister-like beads The average particle size of 15 is between 10 and 30 μπι. High bulk calendered paper according to claim 2, characterized in that the number of beads labeled in the paper is about 4-5%, that they contain an average of at least 5 cells per bead, that the grain diameter of the vesicle-like beads and the average vesicle diameter the ratio is at least 5: 1 and that the volume of the blister is 5-95% of the volume of the granule and contains pigment up to 60% of the volume. 25 High bulk calendered paper according to claim 3, characterized in that the polymeric body of the beads consists of a carboxyl-functional unsaturated polyester resin crosslinked by copolymerization with an ethylenically unsaturated monomer, and that the vesicle-like beads are added to the pulp slurry and added to the pulp slurry. High bulk calendered paper according to Claim 4, characterized in that 35 to 45% of the maleate-unsaturated polyester are crosslinked with 55 to 65% of styrene and in that the polyester has an acid number of 10 to 45 mg KOH / g. is 88734 The high bulk calendered paper of claim 1, wherein the paper is calendered at a compression pressure of at least about 26.8 kg / cm 3 and a temperature of at least about 37.8 ° C. 5 High bulk calendered paper according to claim 1, characterized in that the calendering pressure is between 125.1 and 214.4 kg / cm 3 and the calendering temperature is at least about 65.6 ° C. 10 High bulk calendered printing paper according to claim 6, characterized in that the amount of titanium dioxide, anatase, which is not present in said beads is 1 to 4%. A method of making high bulk calendered paper according to claim 1, characterized in that the liquid suspension containing carboxyl-functional, highly crosslinked, titanium dioxide pigmented polymeric vesicle beads having an average particle size of at least about 5 μχα and at most about 35 μπι. adding to the pulp slurry together with the anionic retention aid the beads premixed with the neutralized polycarboxylic acid polymer thickener to reduce the passage of fines through the wire to the zero water, forming a high bulk paper containing 2-6% by weight of said high blister-like beads, paper to form a calendered paper product having a rice weight of 30 or less per 18.1 kg of rice. Process according to Claim 9, characterized in that the carboxyl-functional polymeric material of the vesicle-like beads has an acid number of 10 to 45 mg KOH / g, the anionic retention aid is a copolymer of acrylamide with 5 to 50% of monoethylenically unsaturated carboxylic acid, the thickener is polyacrylic acid that the anionic retention aid and thickener are neutralized with ammonia. 88734 BC 5 Patentkrav