JP2002339294A - Paper strengthening agent for moistening paper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a paper strengthening agent for moistening paper that is a water-soluble blocked urethane polymer and admixed to paper-making stock and deblocked in the drier part of the conventional paper-making machine. SOLUTION: A water-soluble blocked urethane polymer bearing hydrophilic groups and keto oxime-chain terminal-blocked aromatic isocyanate groups is added to the paper-making stock as a moistening paper strengthening agent to form the web and the formed web is dried at a temperature of <=130 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to wet strength agents, and more particularly to wet strength agents of the type added to stocks made into paper in papermaking machines.

[0002]

BACKGROUND OF THE INVENTION In addition to cellulose fibers, paper contains various additives such as fillers, paper strength agents and the like. The wet paper strength enhancer is an additive for enhancing the strength of paper in a wet state, and urea resin, melamine resin, dialdehyde starch, polyethyleneimine, epoxidized polyamide and the like are used.

In recent years, several proposals have been made for using urethane resins for this purpose. JP-A-6
173196 proposes the use of urethane prepolymers containing unblocked isocyanate groups and tertiary amino groups or quaternary ammonium groups as wet strength agents. This is added to the papermaking stock as an aqueous dispersion (emulsion) or applied to the web after papermaking as a sizing agent. In GB2068034A, the isocyanate groups of a urethane prepolymer are blocked with a ketoxime, which is then reacted with a polyfunctional amine to form a urea-bonded, amine-containing blocked urethane prepolymer, which is dissolved in water in the form of an acid salt in papermaking. It is added to stock or applied to the web after papermaking. Applicant's Japanese Patent Laid-Open No. 5
No. 51896 discloses the use of sodium acid sulfite as a blocking agent to make a blocked urethane prepolymer water-soluble, or the reaction with dimethylolpropionic acid when blocking with another blocking agent such as oxime. To block a urethane prepolymer having a hydrophilic group introduced therein. This is added to the web or paper after paper making, by impregnation or the like.

[0004] Urethane prepolymers containing free isocyanate groups are generally unstable in the presence of water.
Blocked urethane prepolymers, on the other hand, require heating for deblocking and are deblocked at the temperatures and times (up to 130 ° C within minutes) encountered in the dryer section of the papermaking machine, especially when added to papermaking stock. There must be.

Accordingly, the present invention relates to the use of a blocked water-soluble urethane prepolymer, which deblocks under conditions normally encountered in the dryer section of a papermaking machine, as a wet strength agent.

[0006]

SUMMARY OF THE INVENTION The present invention provides a wet strength agent comprising a water-soluble blocked urethane prepolymer having a hydrophilic group and a terminal aromatic isocyanate group blocked with a ketoxime.

[0007] The present invention also provides a papermaking method comprising adding the above-mentioned wet strength agent to papermaking stock, forming it on a web, and drying it at a temperature of 130 ° C or less.

Since the aromatic isocyanate groups blocked by the ketoxime are deblocked at the temperature and time encountered in the dryer section of the papermaking machine, paper having high wet strength can be obtained on conventional papermaking machines without the use of special equipment. Paper can be made.

[0009]

DETAILED DESCRIPTION As is well known, urethane prepolymers are prepared by reacting a polyether polyol or a polyester polyol with a polyisocyanate compound in an NCO / OH equivalent ratio excess. Examples of the raw material polyether polyol, polyester polyol and polyisocyanate compound are well known in the field of the polyurethane industry, and any one can be used. Examples of preferred polyol components have a molecular weight of 1,000 to 50,000.
Is a trivalent or higher polyether polyol. This is obtained by using a polyhydric alcohol such as glycerin, trimethylolpropane or pentaerythritol as an initiator and adding an alkylene oxide such as ethylene oxide or propylene oxide in the presence of a basic catalyst.

Further, the use of a polyester polyol as a polyol component is more effective in enhancing wet paper strength. This is produced, for example, by polycondensation of a bifunctional alcohol with a dicarboxylic acid or an acid anhydride thereof.
As bifunctional alcohols, ethylene glycol, 1,
4-butanediol, 1,6-hexanediol, 3-
Polyethers obtained by addition polymerization of ethylene oxide and / or propylene oxide and / or butylene oxide to aliphatic glycols such as methyl-1,5-pentanediol and neopentyl glycol, as well as to these glycols and bifunctional phenols such as bisphenol A It may be a polyol. Examples of dicarboxylic acids and acid anhydrides include adipic acid, terephthalic acid, isophthalic acid, maleic anhydride, sebacic acid and the like. Further, ring-opening polymers of lactones such as ε-caprolactone and ring-opening polymers of cyclic carbonates such as trimethylene carbonate are also included in the polyester polyol.
The trifunctional or higher functional polyester polyol can be produced by using a trifunctional or higher functional polyhydric alcohol such as trimethylolpropane as a part of the alcohol component.

In the present invention, an aromatic polyisocyanate compound is used as at least a part of the raw material polyisocyanate compound. Typical examples include toluene diisocyanate (TDI) and diphenylmethane diisocyanate (MDI). Other polyisocyanates that can be used are aliphatic diisocyanates typified by hexamethylene diisocyanate (HMDI) and alicyclic polycyanates typified by isophorone diisocyanate (IPDI). A dimer of the diisocyanate compound,
Adducts with polyhydric alcohols such as trimers and trimethylolpropane may be used.

In the urethane prepolymer having a terminal aromatic isocyanate group, an aromatic polyisocyanate is used as the whole polyisocyanate component, and the polyol component and N
It is obtained by reacting with a CO / OH equivalent ratio excess (NCO / OH equivalent ratio> 1). In the second method, a non-aromatic polyisocyanate and a polyol component are first converted to NCO / O
This is a two-stage method in which a reaction is performed at an H equivalent ratio of 1 or less to produce a urethane prepolymer having a terminal OH group, and then the OH group-terminated urethane prepolymer is reacted with an aromatic polyisocyanate in an NCO / OH equivalent ratio excess.

A first method for introducing a hydrophilic group is to first produce a urethane prepolymer by reacting a polyol component with a polyisocyanate, and then to form a part of the free isocyanate group and an active group for introducing a hydrophilic group. A step of reacting with a hydrogen compound (hydrophilic group precursor) and blocking the remaining free isocyanate groups with a blocking agent.

The urethane prepolymer produced by the reaction contains at least 2% by weight or more, preferably 5 to 10% by weight, of free isocyanate groups. Part of this isocyanate group is consumed in the reaction with an active hydrogen compound for introducing a hydrophilic group. JP-A-6-171 cited above
No. 96, GB2068034A, JP-A-5-518
No. 96 exemplifies a number of such active hydrogen compounds. Although any such active hydrogen compound may be used, preference is given to aliphatic compounds having an active hydrogen-containing group such as a hydroxyl group or a primary amino group and a tertiary amino group, such as N, N-dimethylethanolamine. ,
N, N-dimethylethylenediamine and the like. Tertiary amino alcohols are preferred. These compounds are bonded to the urethane prepolymer by the reaction between the active hydrogen-containing groups and the isocyanate groups, block the remaining isocyanate groups, and then quaternize the tertiary amino groups bonded with a quaternizing agent. To give a blocked urethane prepolymer of Instead of the quaternization, the tertiary amino group can be neutralized with an appropriate acid to make the salt water-soluble. Most preferably, it is made water-soluble in the form of a quaternary ammonium salt.
The reason is that no acid is required for water solubilization and stocks can be prepared in the neutral to weakly basic region.

[0015] The ratio of the hydrophilic group-introduced active hydrogen compound to the urethane prepolymer must be sufficient to make the prepolymer water-soluble after introduction, but such that free isocyanate remains. This ratio naturally fluctuates depending on the type of the prepolymer raw material polyol and polyisocyanate, the type of hydrophilic group, and the like.
Generally 10-50% of prepolymer isocyanate content
Is equivalent.

A second method for introducing hydrophilic groups involves the inclusion of a polyfunctional tertiary amino alcohol with respect to hydroxyl groups as part of the polyol component during the reaction of the polyol component with the polyisocyanate. Preferred 3
Examples of the lower amino alcohols are N-methyldiethanolamine, N-ethyldiethanolamine and the like, but triethanolamine can also be used. If a bifunctional tertiary amino alcohol is used for the introduction of a hydrophilic group,
When a bifunctional polyol is used as the polymer polyol component, a trifunctional or higher functional low molecular weight polyol such as trimethylolpropane or glycerin can be added to the reaction system to obtain a trifunctional or higher functional urethane prepolymer. In this case, the polyisocyanate compound must have an NCO / OH equivalent ratio excess with respect to the total of all OH groups of all polyol components, that is, polyether polyol, polyester polyol, polyfunctional tertiary amino alcohol, and trifunctional or higher functional low molecular weight polyol. No.

Regardless of whether the introduction of the hydrophilic group or its precursor group is carried out by either of the above-mentioned methods, the urethane polymer having an aromatic free isocyanate group at the end can convert the free isocyanate group remaining before water-solubilization into ketoxime. Must block. Typical examples of ketoximes that can be used for this purpose are aliphatic ketoximes such as butanone oxime (methylethyl ketoxime) and cycloaliphatic ketoximes such as cyclohexanone oxime.

After completion of the blocking, the precursor (tertiary amino group) of the hydrophilic group is finally quaternized with a quaternizing agent such as dimethyl sulfate or diethyl sulfate, or neutralized with an appropriate acid. To obtain a wet paper strength enhancer of the present invention.

The wet paper strength enhancer of the present invention can be applied to the web after papermaking by a method such as application to a paper web like a sizing agent, but it is added to papermaking stock together with other additives such as filler. It is suitable to be added to paper made through a wire section, a press section, a dryer section and the like by a conventional method. In the dryer section of a papermaking machine, the paper is heated and dried between rows of cylinders, which are typically heated to a maximum of 130 ° C. The paper strength agent of the present invention is sufficiently deblocked under this heating condition, and the regenerated urethane prepolymer serves as a binder to strengthen the bond between paper fibers.

The amount of the paper strength enhancer of the present invention depends greatly on the desired paper quality with respect to the paper strength and can vary from 0.1 to 5% of the dry weight of the fiber (pulp). In special cases, more than 5% by weight can be added.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below by way of an embodiment which simulates an actual papermaking process. In these, "parts" and "%" are based on weight unless otherwise specified.

Example 1 Polyester polyol having an average molecular weight of 1,000 (copolymerized 1,4-butanediol and adipic acid) 150
Parts, polyethylene glycol 50 having an average molecular weight of 1000
Parts, 5 parts of trimethylolpropane, 20 parts of N-methyldiethanolamine and 143 parts of p-MDI were reacted at 40 ° C. for 60 minutes to obtain a urethane prepolymer having a free isocyanate group content of 3% (calculated from the charged amount). The temperature of the system was lowered to 30 ° C., 25 parts of butanone oxime was added, and the mixture was reacted at 50 ° C. for 60 minutes. After confirming the disappearance of the free isocyanate group, 56.5 parts of diethyl sulfate was added, a quaternization reaction was carried out at 55 ° C. for 30 minutes, and the mixture was diluted with 1750 parts of water to obtain a light brown transparent heat having a solid content of 20%. A reactive blocked urethane prepolymer aqueous solution was obtained.

Example 2 Polyester polyol having an average molecular weight of 1,000 (copolymerized 1,4-butanediol and adipic acid) 100
Parts, polyethylene glycol 10 having an average molecular weight of 1000
0 parts, 5 parts of trimethylolpropane, 20 parts of N-methyldiethanolamine, and 143 parts of p-MDI at 40 ° C.
And free isocyanate group content 3%
A urethane prepolymer (calculated from the charged amount) was obtained. The temperature of the system was lowered to 30 ° C., 25 parts of butanone oxime was added, and the mixture was reacted at 50 ° C. for 60 minutes. After confirming the disappearance of the free isocyanate group, the temperature was lowered to 40 ° C., neutralized with 24 parts of acetic acid, stirred for 30 minutes, diluted with 1500 parts of water, and a light brown transparent heat-reactive block having a solid content of 20%. An aqueous urethane prepolymer solution was obtained.

Example 3 Polyester polyol having an average molecular weight of 1,000 (copolymerized 1,4-butanediol and adipic acid) 150
Parts, polyethylene glycol 50 having an average molecular weight of 1000
Part, 5 parts of trimethylolpropane, 20 parts of N-methyldiethanolamine and 69.3 parts of HMDI were reacted at 60 ° C. for 120 minutes to obtain a free isocyanate group content of 0%.
(Calculated from the charged amount) to obtain a urethane prepolymer having terminal hydroxyl groups. Subsequently, 39.6 parts of p-MDI was added and reacted at 40 ° C. for 60 minutes to obtain a terminal MDI-type urethane prepolymer having a free isocyanate group content of 3.4% (calculated from the charged amount). Further, the temperature of the system was lowered to 30 ° C., and 25 parts of butanone oxime was added.
Minutes. After confirming the disappearance of the free isocyanate group, 46.2 parts of dimethyl sulfate was added, a quaternization reaction was carried out at 55 ° C. for 30 minutes, and the mixture was diluted with 1600 parts of water to give a light brown transparent heat having a solid content of 20%. A reactive blocked urethane prepolymer aqueous solution was obtained.

Example 4 Polyester polyol having an average molecular weight of 1,000 (copolymerized 1,4-butanediol and adipic acid) 110
Parts, polyethylene glycol 90 having an average molecular weight of 1000
Parts, 5 parts of trimethylolpropane, 20 parts of N-methyldiethanolamine and 21.7 parts of IPDI at 80 ° C. for 120 minutes to give a free isocyanate group content of 0%.
(Calculated from the charged amount) to obtain a urethane prepolymer having terminal hydroxyl groups. Subsequently, 27.6 parts of 2,4-TDI was added and reacted at 40 ° C. for 60 minutes to obtain a terminal TDI type urethane prepolymer having a free isocyanate group content of 4.1% (calculated from the charged amount). In addition, the temperature of the system is
Then, 34.5 parts of cyclohexanone oxime was added and reacted at 50 ° C. for 60 minutes. After confirming the disappearance of the free isocyanate group, 46.2 parts of dimethyl sulfate was added, a quaternization reaction was performed at 55 ° C. for 30 minutes, and the mixture was diluted with 1250 parts of water to obtain a light brown transparent heat having a solid content of 20%. A reactive blocked urethane prepolymer aqueous solution was obtained.

Comparative Example 1 Polyester polyol having an average molecular weight of 1,000 (copolymerized 1,4-butanediol and adipic acid) 150
Parts, polyethylene glycol 50 having an average molecular weight of 1000
Parts, 5 parts of trimethylolpropane, 20 parts of N-methyldiethanolamine and 143 parts of p-MDI were reacted at 40 ° C. for 60 minutes to obtain a urethane prepolymer having a free isocyanate group content of 3% (calculated from the charged amount). The temperature of the system was lowered to 30 ° C., 63.9 parts of nonylphenol was added, and the mixture was reacted at 50 ° C. for 60 minutes. After confirming the disappearance of the free isocyanate group, 56.5 parts of diethyl sulfate was added, a quaternization reaction was carried out at 55 ° C. for 30 minutes, and the mixture was diluted with 1670 parts of water to obtain a light brown transparent heat having a solid content of 20%. A reactive blocked urethane prepolymer aqueous solution was obtained.

Comparative Example 2 Polyester polyol having an average molecular weight of 1,000 (copolymerized 1,4-butanediol and adipic acid) 150
Parts, polyethylene glycol 50 having an average molecular weight of 1000
Parts, 5 parts of trimethylolpropane, 20 parts of N-methyldiethanolamine and 96 parts of HMDI at 50 ° C. for 10 parts.
Reaction for 0 minutes, free isocyanate group content 3.5%
A urethane prepolymer (calculated from the charged amount) was obtained. The temperature of the system was lowered to 30 ° C., 25 parts of butanone oxime was added, and the mixture was reacted at 50 ° C. for 60 minutes. After confirming the disappearance of the free isocyanate group, 56.5 parts of diethyl sulfate was added, a quaternization reaction was performed at 55 ° C. for 30 minutes, and the mixture was diluted with 1300 parts of water to give a transparent thermal reaction having a solid content of 20%. A mold blocked urethane prepolymer aqueous solution was obtained.

Paper Making Test The paper making test was carried out according to JIS P 8209-1961.

NBKP (softwood sulphate pulp)
3 g was cut into about 3 cm squares, immersed in 1668.7 g of water overnight, defibrated with a standard disintegrator for 3 hours, pulp concentration 7.5%, freeness 527 mL (Canadian Standard Freeness,
(20 ° C., 0.3%) pulp slurry.

The pulp slurry was added to 594 g of water by adding 400 g of the pulp slurry and 6 g (corresponding to 1% of the dry weight of the pulp) of the blocked water-soluble urethane prepolymer solutions of Examples and Comparative Examples which had been previously adjusted to a solid content of 5%. Concentration 3
% And stock.

32 g of the stock thus prepared was fractionated, paper-made by a sheet machine, and applied to a press machine (3.5 g / m ² × 5 minutes) at 20 ° C. and 65% RH.
And air-dried overnight at 120 ° C x 5 minutes.
Paper was formed on test paper having a basis weight of 50 g / m ² . This was cut into a piece of paper having a length of 11 cm and a width of 1.5 cm, attached to an autograph standard tensile tester at a distance between chucks of 5 cm, and the central portion was wetted with a brush to measure the tensile strength. No blanket control was added to the blank control. As Comparative Example 3, 6 g of a commercially available polyamide epichlorohydrin resin wet strength agent was added as a 5% aqueous dispersion to a stock having a pulp concentration of 3%. Table 1 shows the results.

Table 1 量 Wet paper strength enhancer addition amount (%) Wet Tensile (pulp strength in stock (Kg / cm) as pure content based on dry weight) ─────────────────────────────── {Example 1 1 1.23 Example 2 1 0.75 Example 3 1 1.18 Example 4 1 0.92} ─────────────── Blank control 0 0.24 Comparative example 1 1 0.14 Comparative example 2 1 0.15 Comparative example 3 1 0.80 ──────────────────────────

From the above results, it is apparent that the wet strength agent of the present invention has at least a performance comparable to that of a conventionally used polyamide epichlorohydrin resin wet strength agent. On the other hand, the paper strength enhancer of Comparative Example 1 does not cause deblocking under the above heat treatment (drying) conditions, so that almost no wet paper strength enhancing effect is recognized similarly to the blank control. Further, it can be seen that the paper strength enhancer of Comparative Example 2 has insufficient deblocking under the above heat treatment conditions because the blocked terminal isocyanate group is an aliphatic isocyanate group, and therefore does not enhance wet paper strength. Therefore, they are not suitable for wet paper strength agents of the type added in the stock preparation process.

Continuing on the front page (72) Inventor Naofumi Saiuchi 1814 Miyake, Oji-shi, Yasu-cho, Yasu-gun, Shiga Prefecture (72) Inventor Shigehiro Kouchi 1346 East-Relief, Anju-cho, Ikoma-gun, Nara Prefecture (72) Inventor Takeshi Miyamura Minami, Kameoka, Kyoto 1-6-15, Azaleagaoka Sakuradai F-term (reference) 4L055 AA02 AC06 AG85 AH17 BD10 EA20 EA32 FA13

Claims (8)

[Claims] 1. A wet paper strength agent comprising a water-soluble blocked urethane prepolymer having a hydrophilic group and a terminal aromatic isocyanate group blocked with a ketoxime. 2. The wet strength agent according to claim 1, wherein the ketoxime is an oxime of an aliphatic or alicyclic ketone. 3. The wet paper strength enhancer according to claim 1, wherein said hydrophilic group is a quaternary ammonium group or an acid-neutralized tertiary amino group. 4. The quaternary ammonium group or acid neutralizer 3
The tertiary amino group is introduced by introducing a polyol having a tertiary amino group as a part of the polyol component into the urethane prepolymer chain through a urethane bond, and quaternizing the tertiary amino group or neutralizing with an acid. The wet paper strength enhancer of claim 3. 5. The urethane prepolymer comprises a polyol component containing a polyether polyol and / or a polyester polyol and NCO of an organic polyisocyanate.
2. The wet strength agent according to claim 1, wherein the organic polyisocyanate which is a reaction product having a / OH equivalent ratio> 1 and provides at least a terminal isocyanate group is an aromatic polyisocyanate. 6. The method of claim 1, wherein the wet strength agent is added to a papermaking stock and formed into a web.
A papermaking method comprising drying at a temperature of 0 ° C. or less. 7. The method according to claim 6, wherein the amount of the wet strength agent added is 0.1 to 5.0% based on the weight of the fiber in the stock. 8. A wet strength paper obtained by the paper making method according to claim 6.