JP2002115198A - Wet paper-strengthening agent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wet paper-strengthening agent which is added to a paper- making stock in a neutral to basic region and comprises a blocked water-soluble urethane prepolymer whose blocking groups are removed in an existing paper machine. SOLUTION: This wet paper-strengthening agent comprising a water-soluble blocked urethane prepolymer having hydroxy groups and blocked isocyanate groups, characterized by using a phenol compound having an electron-attracting group at the ortho or para position as a blocking agent.

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 the urethane prepolymer are blocked with a ketoxime, which is then reacted with a polyfunctional amine to form an amine-linked blocked urethane prepolymer, which is dissolved in water in the form of an acid salt and added to the papermaking stock. Or applied to the web after papermaking. Japanese Patent Application Laid-Open No. 5-51896 of the present applicant
The publication discloses the use of sodium acid sulfite as a blocking agent to make the blocked urethane prepolymer water-soluble, or when blocking with another blocking agent such as an oxime, for example, a hydrophilic reaction by reaction with dimethylolpropionic acid. It is disclosed that the urethane prepolymer introduced with a group is blocked. 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. Blocking with oxime does not deblock under these conditions.

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]

The present invention uses phenols having an electron withdrawing group at the ortho or para position as a blocking agent for a blocked water-soluble urethane prepolymer used as a wet paper strength enhancer. Since the blocking agent is deblocked at a lower temperature than the oxime, it can be added to stock on conventional papermaking machines without special equipment and used to produce paper with high wet strength.

Therefore, the present invention is characterized by comprising a water-soluble blocked urethane prepolymer having a hydrophilic group and a blocked isocyanate group, wherein the blocking agent is a phenol having an electron withdrawing group at the ortho or para position. Provide a wet strength agent.

A preferred specific example of the blocking agent is p-
Hydroxybenzoic acid and its esters; salicylic acid and its esters. These are preservatives and pharmaceutical raw materials that are recognized as food additives, and are highly safe for the human body. Therefore, it is considered that even if these deblocked compounds remain on the paper, it is safe, and even if they are contained in the wastewater from the factory, there is little adverse effect on the ecosystem.

[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.

As the other raw material, a polyisocyanate which is non-yellowing, that is, contains no aromatic ring, is preferred. Examples thereof are aliphatic diisocyanates typified by hexamethylene diisocyanate, alicyclic diisocyanates typified by isophorone diisocyanate, and dimers, trimers and adducts thereof with polyhydric alcohols such as trimethylolpropane.

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

The urethane prepolymer produced by the reaction contains at least 2% by weight, 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 group and the isocyanate group, 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.

The ratio of the hydrophilic group-introducing active compound to the urethane prepolymer should be sufficient to make the prepolymer water-soluble after introduction, but such that free isocyanate remains. This ratio naturally varies depending on the types of the prepolymer raw material polyol and polyisocyanate, the type of hydrophilic group, and the like, but is generally 10 to 50% equivalent of the prepolymer isocyanate content.

Blocking agents for blocking the remaining isocyanate groups are phenols having an electron withdrawing group at the ortho or para position. Ortho or para-aminophenol is also a phenol having an electron withdrawing group at the ortho or para position, but is not included in the blocking agent because the amino group reacts irreversibly with the isocyanate group to form a urea bond. Phenols having an electron withdrawing group such as trifluoromethyl, nitro, cyano, acetyl, alkoxycarbonyl, carboxyl, alkylsulfonyl and the like can be used. Particularly preferred electron withdrawing groups are free and esterified carboxyl groups. Specific examples include p-hydroxybenzoic acid and its esters, salicylic acid and its esters. These compounds are highly safe for the human body and the environment, and are used as preservatives for foods, cosmetics, pharmaceuticals, or as analgesics. Therefore, there is little concern about safety even if it remains on paper after deblocking or is contained in wastewater from factories.

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. This method is particularly suitable when using a polyester polyol as the polyol component of the urethane prepolymer.
If a bifunctional tertiary amino alcohol is used to introduce a hydrophilic group and a bifunctional polyester polyol is used as the polymer polyol component, trimethylolpropane, glycerin, etc. Functional or higher molecular weight polyols can be added to the reaction system. In this case, the polyisocyanate compound must have an NCO / OH equivalent ratio excess with respect to the total of all polyol components, that is, polyether polyol, polyester polyol, polyfunctional tertiary amino alcohol and OH group of trifunctional or higher functional low molecular weight polyol. No.

All of the terminal isocyanate groups of the urethane prepolymer having a hydrophilic group or a precursor thereof in the chain thus obtained are blocked by the above-mentioned blocking agent. The precursor (tertiary amino group) of the hydrophilic group is also quaternized with a quaternizing agent such as dimethyl sulfate.
Or a water-soluble blocked urethane prepolymer having a hydrophilic group and a blocked isocyanate group.

The wet paper strength enhancer of the present invention can be applied to a web after papermaking by a method such as coating, such as 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 in terms of 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.

[0020]

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 Polyether polyol having an average molecular weight of 3000 (ethylene oxide and propylene oxide were added to glycerin at a concentration of 70 /
(Additionally polymerized at a weight ratio of 30) 300
And 50.4 parts of hexamethylene diisocyanate in 1 part
The reaction was carried out at 00 ° C. for 150 minutes to obtain a urethane prepolymer having a free isocyanate group content of 6.4% (calculated from the charged amount). The temperature of the system was once lowered to 70 ° C, and 8.9 parts of N, N-dimethylethanolamine was added.
Minutes. At this time, the free isocyanate group content was 2.3%. Next, the temperature of the system was set to 50 ° C., 27.6 parts of p-hydroxybenzoic acid was added, the internal temperature was raised to 70 ° C., and the reaction was performed for 120 minutes. After confirming that the reaction of the free isocyanate group has disappeared, dimethyl sulfate 12.
6 parts were added and a quaternization reaction was performed at 70 ° C. for 180 minutes.
It was diluted with 600 parts of water to obtain a transparent and viscous heat-reactive blocked urethane prepolymer solution having a solid content of 40%.

Example 2 A transparent, viscous, heat-reactive blocked urethane having a solid content of 40% was prepared in the same manner as in Example 1 except that 38.8 parts of butyl p-hydroxybenzoate was used instead of p-hydroxybenzoic acid. A prepolymer solution was obtained.

Example 3 Instead of p-hydroxybenzoic acid, 27.6 salicylic acid
In the same manner as in Example 1, a transparent viscous heat-reactive blocked urethane prepolymer solution having a solid content of 40% was obtained by using the same method.

Example 4 A polyester polyol having an average molecular weight of 1,000 (1,4
-Polycondensation of butanediol and adipic acid) 2
00 parts, 5 parts of trimethylolpropane, 20 parts of N-methyldiethanolamine and 96 parts of hexamethylene diisocyanate were reacted at 50 ° C. for 120 minutes to obtain a urethane prepolymer having a free isocyanate group content of 3.6% (calculated from the charged amount). Obtained. The temperature of the system was lowered to 30 ° C and p-
Add 55 parts of butyl hydroxybenzoate, and add
The reaction was performed for 0 minutes. After confirming the disappearance of the free isocyanate group, 46.2 parts of dimethyl sulfate was added, and the mixture was added at 55 ° C for 30 minutes.
A quaternization reaction was carried out for 1 minute, and the mixture was diluted with 1200 parts of water to obtain a transparent, cloudy and viscous heat-reactive blocked urethane prepolymer aqueous solution having a solid content of 20%.

Example 5 A polyester polyol having an average molecular weight of 1,000 (1,4
-Polycondensation of butanediol and adipic acid) 1
50 parts of polyethylene glycol having an average molecular weight of 1000, 50 parts of trimethylolpropane, 20 parts of N-methyldiethanolamine and 96 parts of hexamethylene diisocyanate were reacted at 50 ° C. for 120 minutes to obtain a free isocyanate group content of 3.5% (prepared). (Calculated from the amount). The temperature of the system was lowered to 30 ° C and p-
Add 55 parts of butyl hydroxybenzoate, and add
The reaction was performed for 0 minutes. After confirming the disappearance of the free isocyanate group, 46.2 parts of dimethyl sulfate was added, and the mixture was added at 55 ° C for 30 minutes.
A quaternization reaction was performed for 1 minute, and the mixture was diluted with 1200 parts of water to obtain a light brown transparent heat-reactive blocked urethane prepolymer aqueous solution having a solid content of 20%.

Comparative Example 1 Instead of p-hydroxybenzoic acid, phenol 18.8 was used.
In the same manner as in Example 1, a transparent viscous heat-reactive blocked urethane prepolymer solution having a solid content of 40% was obtained by using the same method.

Comparative Example 2 A heat-reactive blocked urethane prepolymer solution having a solid content of 40% was prepared in the same manner as in Example 1 by using 17.4 parts of butanone oxime (methyl ethyl ketoxime) instead of p-hydroxybenzoic acid. 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.

400 g of this 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 adjusted to a solid content of 5% in advance were added to 594 g of water. Concentration 3
% And adjusted to pH 8.0 with sodium bicarbonate to obtain a 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 epochlorohydrin 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 ────────────────────────────────── Wet paper strength enhancer addition amount (%) Wet Tensile (pulp strength in stock (Kg / cm) as pure content based on dry weight) ─────────────────────────────── {Example 1 1 0.69 Example 2 1 0.72 Example 3 1 0.71 Example 4 1 1.28 Example 5 1 1.20} {Blank control 0 0.21 Comparative example 1 1 0.20 Comparative example 2 1 0.21 Comparative example 3 1 0.67} ─────────────────────────────────

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 enhancers of Comparative Examples 1 and 2 do 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. Therefore, it is not suitable for a wet paper strength enhancer of the type added in the stock preparation step.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4J034 CD01 DF01 DG01 HD03 HD15 JA41 JA42 RA09 4L055 AC06 AG85 AH17 BD10 EA20 EA32 FA13 GA50

Claims (8)

[Claims] 1. A wet paper strength enhancer comprising a water-soluble blocked urethane prepolymer having a hydrophilic group and a blocked isocyanate group, wherein the blocking agent is a phenol having an electron withdrawing group at the ortho or para position. Agent. 2. The wet paper strength enhancer according to claim 1, wherein said electron withdrawing group is a carboxyl group or an esterified carboxyl group. 3. The wet paper strength enhancer according to claim 1, wherein said blocking agent is selected from parahydroxybenzoic acid, parahydroxybenzoic acid ester, salicylic acid, and salicylic acid ester. 4. The wet paper strength enhancer according to claim 1, wherein said hydrophilic group is a quaternary ammonium group. 5. The wet strength agent according to claim 1, wherein the urethane prepolymer is a reaction product of a polyether polyol and / or a polyester polyol with an aliphatic or alicyclic 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 amount of the wet paper strength enhancer added is 0.1 to 5.0% based on the weight of the fiber in the stock.
Papermaking method. 8. A paper with enhanced wet strength obtained by the papermaking method according to claim 6.