JP4252442B2 - Paper quality improver - Google Patents

Description

  The present invention relates to an internally added paper quality improver useful for improving the paper quality of a pulp sheet, and a pulp sheet containing the same.

  From the viewpoint of protecting the global environment, it is required to reduce the amount of pulp used. As a result, there is a demand for lighter paper and increased blending of waste paper pulp. However, the paper obtained simply by reducing the amount of pulp in the paper is inferior in quality due to a decrease in opacity due to the thin paper. Further, weight reduction that reduces the amount of pulp in the paper is not desirable because the strength of the paper is lowered, or the paper that requires rigidity such as paperboard is lowered in rigidity. On the other hand, when the blending ratio of the used paper pulp is increased, the paper thickness is lowered and the opacity is lowered due to a decrease in whiteness due to residual ink in the used paper pulp and a decrease in pulp fiber during the recycling process. Therefore, when the amount of pulp in the paper is reduced and the ratio of the used paper pulp is increased, the thickness of the resulting paper is reduced, the strength and rigidity are reduced, and the opacity and whiteness are further reduced.

  Various bulk improvement methods have been attempted in the past for the purpose of preventing thickness reduction due to weight reduction. For example, the production method for reducing the press pressure has a problem that the smoothness is lowered and the printability is inferior. Moreover, using a cross-linked pulp (Patent Document 1), mixing with synthetic fibers (Patent Document 2), filling a filler such as an inorganic substance between pulp fibers (Patent Document 3), and causing voids (Patent Document 4) Although a method can also be mentioned, the recycling of a pulp is impossible or the smoothness of paper is impaired. Moreover, specific alcohol and / or its polyoxyalkylene adduct (Patent Document 5) is known as a bulking agent for paper. Furthermore, in the fatty acid polyamide polyamine type marketed as a bulking agent, although the bulk is improved, the strength and rigidity of the paper are lowered and the paper performance is not sufficient. On the other hand, in order to improve opacity and whiteness, a method of adding a large amount (for example, 5 to 20% by weight) of an inorganic filler such as calcium carbonate, kaolin, or white carbon has been practiced in the art. However, simply adding a large amount of inorganic filler significantly increases the weight of the paper, making it impossible to reduce the weight of the paper.

Further, Patent Document 6 discloses a paper for paper comprising polymer fine particles of an ethylenically unsaturated monomer or diene monomer having a cationic polyvinyl alcohol having a mercapto group as a dispersant as a paper internal additive. An internal additive is disclosed, and Patent Document 7 mainly discloses grafted starch obtained by graft copolymerization with a monomer containing (meth) acrylamide while maintaining the form of starch particles without gelatinizing the starch. Although the additive for papermaking used as a component is disclosed, although the rigidity is improved to some extent, the bulk is hardly improved.
Japanese Patent Laid-Open No. 4-185792 JP-A-3-269199 Japanese Patent Laid-Open No. 3-124895 JP-A-5-230798 WO 98/3730 pamphlet JP-A-8-199079 Japanese Patent Laid-Open No. 11-302992

  An object of the present invention is to provide an internally added paper quality improver that improves the bulk of a pulp sheet and causes little reduction in strength and rigidity.

  The present invention provides an internally added paper quality improver containing an emulsion of a self-emulsifiable polymer composed of a polyester polymer having a hydratable segment, and this internally added paper quality improver on the surface and / or inside of a pulp sheet. An existing pulp sheet is provided.

  By adding the internal additive paper quality improver of the present invention to the pulp slurry at the time of papermaking, the bulk of the pulp sheet can be improved while suppressing a decrease in strength and rigidity of the pulp sheet. Regarding the principle of improving the bulk of the pulp sheet of the present invention, the polymer fine particles in the self-emulsifiable polymer emulsion according to the present invention are stably present in the pulp slurry, and are directly bonded or adsorbed and bonded between the fibers of the pulp. Since these bonded polymer particles melt in the drying process and hydrophobize part of the pulp surface, the interfacial tension between the pulp and aqueous solution increases, and during paper making, there are more voids between the pulps, resulting in a bulky pulp sheet. It is also considered that a bulky pulp sheet can be obtained by controlling the dispersion or partial aggregation state of the pulp. Usually, when a bulky pulp sheet is obtained, there are more voids between the pulps, and the strength of the paper is greatly reduced. However, the self-emulsifiable polymer emulsion of the present invention has polymer fine particles bonded between fibers and pulp. As a result, the quality of the internal paper is improved. As a result, there is little decrease in strength and rigidity despite the increase in bulk, or the strength and rigidity are improved despite the increase in bulk. An agent can be provided.

[Self-emulsifying polymer emulsion]
The self-emulsifying polymer of the present invention is a polyester-based polymer having a hydratable segment and can be present as fine particles in water without using any other emulsifier.

  In the present invention, the hydratable segment is not particularly limited as long as it is a segment having hydratability, and includes, for example, at least one acidic group selected from a carboxyl group, a sulfonic acid group, or a phosphonic acid group or a salt thereof. And those containing a polyoxyalkylene group.

  In the present invention, the polyester polymer is a polyester obtained by polycondensation of a divalent or trivalent acid component and a divalent or higher polyol component, or a divalent or trivalent acid component and a divalent or higher polyol component. And polyester polyamide obtained by polycondensation of aldehyde with an amine derivative.

  The polyester used in the present invention can be produced by subjecting an acid component listed below as a constituent monomer to polycondensation with a polyol component.

Divalent and trivalent carboxylic acids are used as the saturated or unsaturated polyvalent carboxylic acid or acid anhydride thereof as the acid component. For example, phthalic acid, isophthalic acid, terephthalic acid, succinic acid, adipic acid, dimer acid, alkenyl (C ₄ ~C ₂₀₎ succinic acid, cyclohexane dicarboxylic acid, naphthalene dicarboxylic acid, and maleic acid, fumaric acid, tetrahydrophthalic acid, Divalent carboxylic acids such as itaconic acid, citraconic acid and acid anhydrides thereof, and trivalent carboxylic acids such as 1,2,4-benzenetricarboxylic acid and anhydrides thereof, lower alkyl (C ₁ -C ₄ ) esters thereof Is mentioned.

On the other hand, the polyol component is not particularly limited, and ethylene glycol, propylene glycol, 1,4-butanediol, neopentyl glycol, glycerin, pentaerythritol, trimethylolpropane, sorbitol, 1,6-hexanediol, polyethylene glycol, Aliphatic polyols such as polypropylene glycol and polybutylene glycol, or aromatic polyols such as bisphenol A and hydrogenated bisphenol A, and their alkylene (C ₂ -C ₃ ) oxide adducts (addition mole number 2 to 20) Is mentioned.

  In the present invention, the condensation polymerization of the acid component and the polyol component can be performed by a known method, for example, by reacting the acid component and the polyol component at a temperature of 180 to 250 ° C. in an inert gas atmosphere. The end point thereof may be determined by tracking the softening point (Tm), acid value (AV), etc., which are molecular weight indicators.

  The molar ratio between the acid component and the polyol component may be appropriately determined depending on the acid value, weight average molecular weight, glass transition point (Tg) and the like of the target polyester, but the acid component: polyol component = 0. The ratio is preferably 6: 1 to 1.5: 1, and more preferably 0.8: 1 to 1.4: 1.

  In this polycondensation, additives such as an esterification catalyst such as dibutyltin oxide and a polymerization inhibitor such as hydroquinone and t-butylcatechol can be appropriately used.

  The polyester polyamide used in the present invention is produced by a known method, for example, by adding an amine derivative to the component containing the acid component and the polyol used in the production of the polyester and performing condensation polymerization. Can do. Such amine derivatives are not particularly limited, and are polyamines such as ethylenediamine, hexamethylenediamine, diethylenetriamine, and xylylenediamine; aminocarboxylic acids such as methylglycine, trimethylglycine, 6-aminocaproic acid, σ-aminocaprylic acid, and ε-caprolactam. And amino alcohols such as ethanolamine and propanolamine.

  The molar ratio of the acid component, the polyol component and the amine derivative used in the synthesis of the polyester polyamide is appropriately determined according to the acid value, weight average molecular weight, Tg and the like of the polyester polyamide, as in the case of the polyester. do it. The acid value of the obtained polymer can be adjusted, for example, by adjusting the raw material, for example, the acid component / polyol component molar ratio, reaction time, and the like.

  The Tg of the polymer used in the present invention is preferably −50 ° C. or more from the viewpoint of maintaining paper strength at room temperature, and the polymer melts / flows at the drying temperature (usually 50 ° C. to 150 ° C.) of the papermaking pulp sheet. From the viewpoint of maintaining the paper strength and the stiffness, 90 ° C. or lower is preferable, and −30 to 80 ° C. is more preferable. In the present specification, Tg was measured by a differential scanning calorimeter, DSC200 (manufactured by Seiko Electronics Co., Ltd.) under a temperature rising condition of 10 ° C./min, and determined by a tangential method.

  The Tm of the polymer used in the present invention is 150, because the polymer can be melted / flowed at the drying temperature (usually 50 ° C. to 150 ° C.) of the paper pulp sheet, and the desired paper strength and rigidity can be maintained. C. or lower is preferable, and 130 C or lower is more preferable. Also, in order to make the polymer easier to melt at the drying temperature, when adding a plasticizer, a large amount of addition is necessary, and if the amount added is too large, the performance of the polymer is impaired, and the stability of the emulsion The amount of the plasticizer is preferably 30 parts by weight or less with respect to 100 parts by weight of the polymer, and Tm is preferably 150 ° C. or less for these reasons. In this specification, Tm is measured with a flow tester CFT-500D (manufactured by Shimadzu Corporation) under a load of 20 kgf (196 N), an orifice diameter of 10 mm, an orifice length of 1 mm, and a temperature rising condition of 3 ° C./min. The temperature at which a half amount flowed out was defined as Tm.

  The acid value of the polymer used in the present invention is preferably 3 mgKOH / g or more from the viewpoint of obtaining a stable aqueous dispersion. For example, when an oil-soluble plasticizer is internally added, the acid value is 3 -100 mgKOH / g is still more preferable, and 10-70 mgKOH / g is especially preferable. In this specification, the acid value was measured according to JIS K 0070.

  The weight average molecular weight (Mw) of the polymer used in the present invention is preferably 500 or more because the strength of the polymer is high and the paper strength and rigidity of the paper-made pulp sheet can be maintained. Since the polymer can be melted at a temperature and the desired paper strength and rigidity can be maintained, it is preferably 50000 or less, more preferably 1000 to 40000.

  Moreover, when the polymer of this invention is polyester polyamide, it is preferable that the amine value (ASTM D2073) of a polymer is 10 mgKOH / g or less.

  In the present invention, when water-soluble polyethylene glycol or the like is used as the polyol component of the constituent monomer of the polymer constituting the self-emulsifiable polymer emulsion, a polyester polymer having a hydratable segment can be obtained.

  Furthermore, it is preferable that at least a part of the carboxyl group or the like present in the polymer constituting the self-emulsifiable polymer emulsion is neutralized, and the neutralization method is not particularly limited. However, when the hydratable segment contains a polyoxyalkylene group, it may be unneutralized or partially neutralized. The neutralizing agent is not particularly limited as long as it can ionize a carboxyl group or the like. Preferably, hydroxides such as alkali metals and alkaline earth metals and various amines are used, and the amount used is a polymer. 0.8-1.4 equivalent is preferable with respect to 1 equivalent of carboxyl groups in it. The neutralizing agent may be used as it is, but may be used after diluting and dissolving in water.

  The self-emulsifiable polymer emulsion in the present invention can be produced by phase inversion emulsification or the like. For example, the polymer and the plasticizer are dissolved in an organic solvent, the water, a surfactant, and the like are added, and then the organic solvent is distilled off and phase-shifted to an aqueous system. Although phase inversion may occur when water is added, it is preferable that phase inversion occurs during the distillation of the organic solvent from the viewpoint of obtaining an aqueous dispersion of a stable polymer. It can also be produced by adding the polymer in a molten state dropwise to a system in which a neutralizing agent, a surfactant or the like has been added or not added to water in advance, and the phase is changed to an aqueous system while stirring the system. .

  As said organic solvent, C3-C8 ketone solvents, such as acetone, methyl ethyl ketone, and diethyl ketone, C4-C8 ether solvents, such as tetrahydrofuran, etc. are preferable, and acetone, methyl ethyl ketone, and tetrahydrofuran are more preferable. As the usage-amount of an organic solvent, it is preferable that it is 100-600 weight part of organic solvents with respect to 100 weight part of polymers used for the self-emulsifiable polymer emulsion of this invention. Moreover, it is preferable that the usage-amount of the said water is 100-1000 weight part with respect to 100 weight part of polymers used for the self-emulsifiable polymer emulsion of this invention. In this case, surfactants such as acetylene glycol compounds, various anions and nonions in water, especially higher alcohol sulfates, polyoxyethylene alkyl ether sulfates, dialkyl sulfosuccinates, β-naphthalene sulfonate formalin condensate salts, etc. Further, it is preferable to add about 1 to 20 parts by weight with respect to 100 parts by weight of the polymer because the average particle diameter of the polymer fine particles can be reduced and the polymer concentration can be increased.

  The organic solvent is preferably distilled off, for example, at 25 to 70 ° C. under reduced pressure. The content of the organic solvent is preferably 1% by weight or less, more preferably 0.1% by weight or less in the polymer emulsion. It is preferable to adjust to. Moreover, it is more preferable to adjust the pH of the obtained treatment liquid to 5 to 10. The above-mentioned neutralizing agent etc. can be used for pH adjustment.

  When the self-emulsifiable polymer emulsion has a polyoxyalkylene group, it can be obtained in substantially the same manner as in the case of the self-emulsifiable polymer emulsion, except that no organic solvent is used and no neutralizer is used. it can. In addition, in order to perform phase inversion emulsification more smoothly, it is also effective to heat a polymer and water beforehand.

  Examples of water used in the polymer emulsion include ion-exchanged water, tap water, and distilled water, but are not particularly limited as long as the desired effects in the present invention are not inhibited. The content is adjusted so that the total amount becomes 100% by weight when the components other than water are contained.

  Specifically, the self-emulsifying polymer emulsion of the present invention is an aqueous dispersion of a polymer obtained by dispersing the polymer in water, and is suitably used as the paper quality improver of the present invention.

  The content of the polymer contained in the self-emulsifiable polymer emulsion is preferably 10 to 60% by weight, more preferably 20 to 50% by weight in the self-emulsifiable polymer emulsion. The content of water used in the self-emulsifiable polymer emulsion is adjusted to 100% by weight in total with the components other than water of the self-emulsifiable polymer emulsion.

  In addition, the average particle size of the polymer in the polymer emulsion adjusts the molecular weight, acid value, degree of neutralization, etc. of the polymer, dissolves the polymer in an organic solvent, and adds water, and a surfactant as necessary. In addition, the organic solvent can be removed by distilling off the organic solvent, and the phase can be appropriately adjusted by changing the phase inversion emulsification conditions and the like.

  Further, when the polymer contains a polyalkylene group as a hydratable segment, the hydrophilic part of the resulting polymer, that is, by adjusting the molecular weight, molar ratio, etc. of the hydratable segment such as polyethylene glycol, and / or the polymer In addition to adjusting the molecular weight, acid value, degree of neutralization, etc., adding a surfactant, etc., if necessary, performing a phase inversion to an aqueous system, and adjusting as appropriate by changing the phase inversion emulsification conditions, etc. be able to.

  The average particle size of the polymer in the self-emulsifiable polymer emulsion of the present invention is preferably 0.01 to 10 μm, more preferably 0.02 to 5 μm, from the viewpoint of obtaining good dispersibility. In the present specification, the average particle diameter of the polymer was measured with a laser diffraction / scattering particle size distribution analyzer LA-910 (manufactured by Horiba, Ltd.), and the median diameter was used.

[Internal paper quality improver]
The internal additive paper quality improver of the present invention contains the self-emulsifying polymer emulsion according to the present invention as described above, and further includes, for example, plasticizers such as diallyl phthalate, known surfactants, colorants, and additives. Etc. can be contained as long as expression of a desired effect in the present invention is not inhibited.

  The internal additive paper quality improver of the present invention can be prepared by mixing components such as the plasticizer, surfactant, colorant and additive in advance, or when preparing a self-emulsifiable polymer emulsion. To prepare a preparation.

[Pulp sheet]
As a method for producing a pulp sheet in the present invention, a known method is used. By using the above-mentioned self-emulsifiable polymer emulsion as a paper quality improver, a pulp sheet having a paper quality improver added therein can be obtained. The addition amount of the internal additive paper quality improver of the present invention is preferably 0.05 parts by weight or more from the viewpoint of the paper quality improvement effect with respect to 100 parts by weight of pulp in terms of solid content, from the viewpoint of maintaining the original performance of the pulp sheet. 20 parts by weight or less is preferable. More preferably, it is 0.1-10 weight part. Even when such a small amount is added, it is possible to improve the bulk of the pulp sheet and to obtain a pulp sheet with little decrease in strength and rigidity despite the increase in bulk.

  Further, in addition to the above-mentioned polymer, another polymer may be appropriately used as the internal paper quality improver of the present invention as long as the desired effect in the present invention is not inhibited.

  The internally added paper quality improver of the present invention is added at any point before the paper making process (internal addition). It is added before the papermaking process where a thin liquid of pulp raw material is filtered to form a paper layer as it travels over the wire mesh, and is used as a pulper, refiner, etc., a disintegrator, a beating machine, a machine chest, a head box, and white water. Although it may be added to a tank such as a tank or piping connected to these facilities, a place where it can be uniformly blended with a pulp raw material, such as a refiner, a machine chest, or a head box, is desirable.

  In the production of the pulp sheet in the present invention, a sizing agent, a filler, a yield improver, a drainage improver, a paper strength improver, and the like, which are used in general paper making, may be added. In particular, in order for the paper quality improver of the present invention to exhibit its function, it is important to fix to pulp, and therefore, an agent that promotes fixing can be used. Examples of such agents include aluminum sulfate, cationized starch, compounds having an acrylamide group, polyethyleneimine, and the like. The amount of the agent that promotes fixing is preferably 0.001 to 5 parts by weight with respect to 100 parts by weight of the pulp.

  The pulp sheet obtained by using the internally added paper quality improver of the present invention has a bulk up rate of 2% or more, a paper strength maintenance rate of 85% or more, and a stiffness maintenance rate of 85% or more compared to the additive-free sheet. Preferably there is.

  The pulp sheet obtained using the internally added paper quality improver of the present invention is a newspaper paper in the item classification described in the Paper Pulp Technology Handbook (issued by the Paper Pulp Technology Association, pages 455-460, 1992), It is suitably used for non-coated printing paper, finely coated printing paper, coated printing paper, information paper, cardboard paper, white paperboard, packaging paper, or other paper or paperboard.

  In the following production examples and examples, “%” and “part” represent “% by weight” and “part by weight” unless otherwise specified.

Production Example 1
An average of 2.2 mol of propylene oxide adduct of bisphenol A (indicated as BPA-P2) 3561 g (10 mol), 1207 g (10.4 mol) of fumaric acid, 0.31 g of hydroquinone and 8.5 g of dibutyltin oxide under a nitrogen stream For 4 hours at 160 ° C. Then, after heating up to 200 degreeC, it was made to react under normal pressure for 1 hour under the reduced pressure of 9.33 kPa, and polyester resin (1) was obtained.

Production Examples 2-7
Using the acid component and glycol component shown in Table 1, polyester resins (2) to (7) were obtained in the same manner as in Production Example 1.

  Tg, Tm and AV of the obtained polyester resins (1) to (7) were measured by the above method. The results are shown in Table 1.

note)
* 1: Acid component ・ FA: phthalic acid, manufactured by Wako Pure Chemical Industries, Ltd. ・ TPA: terephthalic acid, manufactured by Wako Pure Chemical Industries, Ltd. ・ AdA: adipic acid, manufactured by Wako Pure Chemical Industries, Ltd. ・ TMA: 1, 2 , 4-Benzenetricarboxylic acid, manufactured by Wako Pure Chemical Industries, Ltd.
* 2: Glycol component • BPA-P2: bisphenol A propylene oxide average 2.2 mol adduct, manufactured by Kao Corporation • BPA-P16: bisphenol A propylene oxide average 16 mol adduct, manufactured by Kao Corporation • BPA- E2: Bisphenol A ethylene oxide average 2.2 mol adduct, manufactured by Kao Corporation PEG # 1540: polyethylene glycol, molecular weight 1540, manufactured by Wako Pure Chemical Industries, Ltd. PEG # 1000: polyethylene glycol, molecular weight 1000, Wako Pure Yakuhin Manufacturing Example 8
300 g of polyester resin (1) and 45 g of diallyl phthalate (DAP) (15% with respect to the resin component) were dissolved in 540 g of methyl ethyl ketone. Next, dimethylethanolamine was neutralized by adding 1.1 times the amount necessary to neutralize the remaining carboxyl groups, 750 g of ion-exchanged water was added with stirring, and methyl ethyl ketone was distilled off at 40 ° C. under reduced pressure. The water was adjusted to obtain a self-emulsifiable polyester emulsion (1).

Production Examples 9-13
Self-emulsification is achieved by phase inversion emulsification in the same manner as in Production Example 8 using the polyester resin, neutralizing agent (1.1 times the amount necessary to neutralize residual carboxyl groups) and plasticizer shown in Table 2. Polyester emulsions (2) to (6) were obtained.

Production Example 14
280 g of a preheated polyester resin (7) at about 100 ° C. was dispersed in 820 g of preheated 70 ° C. water to obtain a self-emulsifiable polyester emulsion (7).

  The average particle size of the self-emulsifiable polyester emulsions (1) to (7) obtained above is measured by the above method, and the solid content concentration is measured by an infrared moisture meter (Kett, Infrared Moisture Determination Balance, FD-240). And measured at 150 ° C. for 20 minutes under heating conditions. The results are shown in Table 2.

note)
* 1: Neutralizer ・ DMEA: Dimethylethanolamine, Wako Pure Chemical Industries, Ltd. ・ TEA: Triethanolamine, Wako Pure Chemical Industries, Ltd. ・ NaOH: Sodium hydroxide, Wako Pure Chemical Industries, Ltd.
* 2: Plasticizer / DAP: diallyl phthalate, manufactured by Wako Pure Chemical Industries, Ltd. Comparative Production Example 1 (cationic polystyrene emulsion)
In accordance with JP-A-8-199079, Example 3, using as a protective colloid a mercapto-modified polyvinyl alcohol having a mercapto group at its terminal (M-115, manufactured by Kuraray Co., Ltd., complete saponification, polymerization degree 1500) As an emulsion, styrene and hydroxypropyltrimethylammonium chloride methacrylate (cationic monomer) were used to obtain an emulsion having a solid content concentration of 41.5% and an average particle size of 4.35 μm.

Examples 1-8 and Comparative Examples 1-8
<Pulp raw material>
As a pulp raw material, virgin pulp was used in which LBKP (hardwood bleached pulp) was disaggregated and beaten with a beater at 25 ° C. to give a 1% LBKP slurry. The Canadian standard freeness (JIS P 8121) of this product was 450 ml.

<Paper making method>
The virgin pulp slurry was weighed so that the pulp basis weight of the pulp sheet after papermaking was 70 g / m ² ± 1 g / m ² and adjusted to pH 4.5 with aluminum sulfate. Next, as shown in Tables 3 and 4, the internal additive paper quality improver (self-emulsifiable polyester emulsions (1) to (7)) of the present invention or a comparative additive is added in an effective amount of 0.5 per 100 parts of pulp. Add 1 part internally, and if necessary, add fixing agent (cato308) and sizing agent (AKD) in the amounts shown in Table 3, and make paper with 80-mesh wire (area 625 cm ² ) with a square tappi paper machine. A wet sheet was obtained. Two sheets of filter paper (270 mm square) having a basis weight of 320 g / m ² were stacked on the wet sheet, and a coating plate was further stacked thereon to perform coaching, and then the wet sheet was taken out. Next, the wet sheet was sandwiched between two filter papers and pressed at 55 g / cm ² for 5 minutes. After pressing, it was dried for 2 minutes at 105 ° C. using a mirror dryer. The dried pulp sheet was conditioned at 23 ° C. and 50% humidity for 1 day, and then the paper bulk up rate, paper strength, stiffness, and sizing degree were measured by the following methods. The papermaking is 5 sheets each, and the measured value is an average of 10 times / paper. The results are shown in Tables 3 and 4.

<Bulk up rate>
The tightness is obtained according to JIS P8118, and the bulk up rate is calculated by the following equation. The smaller the tension is, the higher the bulk is, and the difference of 0.02 in the tension is sufficiently recognized as a significant difference. The larger the bulk up rate, the higher the bulk, and the difference in the bulk up rate of 2% is sufficiently recognized as a significant difference.

Bulk up rate (%) = [(1 / tensity of paper containing agent-added-1 / tensity of paper without additive) / (1 / tensity of paper without additive)] × 100
<Paper strength maintenance rate>
The burst strength (JIS P8112 method) is obtained and calculated by the following formula. The greater the paper strength maintenance rate, the higher the paper strength, and the difference in paper strength maintenance rate of 5% is sufficiently recognized as a significant difference.

Paper strength maintenance rate (%) = (Burst strength of paper containing agent / burst strength of paper without additive) × 100
<Stiffness maintenance factor>
Clark stiffness (according to JIS P8143 method) is obtained and calculated by the following equation. The greater the stiffness maintenance factor, the higher the stiffness, and the difference of 5% stiffness maintenance rate is fully recognized as a significant difference.

Rigidity retention rate (%) = (Clark stiffness of paper with added agent / Clark stiffness of paper without additive) × 100
<Size>
Measurement was performed based on the Stekk human method (JIS P8122).

* 1: Solid content per 100 parts of pulp
* 2: Additive ・ cat308: Cationized starch, manufactured by Nissho Chemical Co., Ltd. ・ AKD: Alkyl ketene dimer, SKS-293F, manufactured by Arakawa Chemical Co., Ltd. ・ Polyacrylamide: Polystron 356, manufactured by Arakawa Chemical Co., Ltd. -PVA (GL-05): polyvinyl alcohol, partial saponification, polymerization degree 500, manufactured by Nippon Synthetic Chemical Co., Ltd.-CMC (FT-3): manufactured by Nippon Paper Chemicals Co., Ltd.-Lauryl alcohol ethylene oxide 6 mol adduct : Emulgen 106, manufactured by Kao Corporation From the results of Tables 3 and 4, the bulkiness of the paper was improved by adding the internal additive paper quality improver comprising the self-emulsifiable polyester emulsion of the present invention into the pulp slurry during papermaking. Obtaining a pulp sheet that has little decrease in strength and rigidity despite improvement, or has improved strength and rigidity despite improvement in bulk I bet it has been found that can be.

Furthermore, it can be seen that the size performance of the internally added paper quality improver of the present invention is improved when used in combination with a neutral sizing agent (alkyl ketene dimer) as compared with a neutral sizing agent added system.

Claims (8)

A carboxyl group or segment containing at least one of its salts, and the segment comprising a polyoxyalkylene group, the weight average molecular weight contains an emulsion of a polyester-based polymer is from 1,000 to 40,000, to improve the bulk of the pulp sheet In addition, an internally added paper quality improver that suppresses the decrease in strength and rigidity. The internal additive paper quality improver according to claim 1, wherein the average particle size of the polymer in the polyester polymer emulsion is 0.01 to 10 µm. The internal paper quality improvement according to claim 1 or 2, wherein the polyester polymer is obtained by condensation polymerization of a divalent or trivalent acid component and a divalent or higher polyol component having a polyoxyalkylene group. Agent. The internal paper quality according to claim 3, wherein the divalent or trivalent acid component is at least one selected from the group consisting of phthalic acid, terephthalic acid, adipic acid and 1,2,4-benzenetricarboxylic acid. Improver. A dihydric or higher polyol component having a polyoxyalkylene group is bisphenol A alkylene (C ₂ ~ C _Three 5) The internally added paper quality improver according to claim 3 or 4, which is at least one selected from the group consisting of an oxide adduct (added mole number 2 to 20) and polyethylene glycol. The molar ratio of the divalent or trivalent acid component and the dihydric or higher polyol component having a polyoxyalkylene group is acid component: polyol component = 0.6: 1 to 1.5: 1. The internal additive paper quality improver according to any one of -5. A pulp sheet in which the internal paper quality improver according to any one of claims 1 to 6 is present on the surface and inside of the pulp sheet. The pulp sheet according to claim 7 , wherein 0.05 to 20 parts by weight of the internally added paper quality improver is present in terms of solid content with respect to 100 parts by weight of the pulp.