JP2003013394A - Wet paper strength enhancing composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the wet paper strength by increasing the adsorptivity of a bisulfite-blocked urethane prepolymer, which is not effective alone as a wet paper strength enhancer added to paper at the papermaking stage, to cellulose fibers. Serve as an enhancer. A water-soluble blocked urethane prepolymer containing a terminal isocyanate group blocked with an alkali metal bisulfite, and a cationic organic substance in an amount sufficient to reverse the polarity of the blocked urethane prepolymer in a solution A wet paper strength enhancing composition comprising a mixture of

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to wet strength compositions, particularly wet strength compositions of the type added to stock made into paper in papermaking machines.

[0002]

BACKGROUND OF THE INVENTION Paper contains various additives such as fillers and paper strengthening agents in addition to cellulose fibers. The wet paper strength enhancer is an additive for increasing 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 regarding the use of urethane resins for this purpose. JP-A-6-
In 173196, it is proposed to use a urethane prepolymer containing an unblocked isocyanate group and a tertiary amino group or a quaternary ammonium salt group as a wet strength agent. This is added to a papermaking stock as an aqueous dispersion (emulsion), or is applied to a web after papermaking as a sizing agent. In GB2068034A, the isocyanate group of a urethane prepolymer is blocked with a ketoxime, and then this is reacted with a polyfunctional amine to form a urea-bonded blocked urethane prepolymer, which is dissolved in water in the form of an acid salt to prepare a papermaking paper. It is added to the stock or applied to the web after paper making. Applicant's Japanese Patent Application Laid-Open No. 5
No. 51896 discloses the use of acidic sodium sulfite as a blocking agent to render a blocked urethane prepolymer water-soluble, or when it is blocked with another blocking agent such as an oxime, for example a reaction with dimethylolpropionic acid. It is disclosed that the urethane prepolymer having a hydrophilic group introduced therein is blocked. This product is added to a web or paper after paper making by coating, impregnation or the like.

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

Japanese Patent Application Laid-Open No. 5-51896 filed by the applicant of the present invention
The sodium bisulfite block urethane prepolymer described in the publication is water soluble and is completely deblocked under the conditions encountered in the dryer part. However, in solution the blocked urethane prepolymer is negatively charged. In general, when a negatively charged or anionic paper additive is added to a papermaking stock, the adhesion rate to the cellulose fiber, that is, the yield is low, the performance is not fully exhibited, and it is economically disadvantageous. The load on the equipment increases. This is the reason why the bisulfite-blocked urethane prepolymer could not be added to paper stock to make paper.

Therefore, the object of the present invention is to make it possible to add a bisulfite-blocked urethane prepolymer to a papermaking stock and to eliminate the above-mentioned drawbacks.

[0007]

The present invention provides a water-soluble blocked urethane prepolymer containing a terminal isocyanate group blocked with an alkali metal bisulfite, and sufficient to reverse the polarity of the blocked urethane prepolymer in solution. Provided is a wet strength composition comprising a mixture with a cationic organic substance.

The present invention also provides a papermaking method comprising adding the wet strength composition to a papermaking stock, forming a web by a conventional method, and then drying.

The present invention allows the addition of bisulfite-blocked urethane prepolymers, which heretofore could not be added to papermaking stocks, to papermaking stocks with low deblocking of the blocked urethane prepolymers. Wet temperature benefits can be used to produce wet strength papers using existing papermaking machines. In addition, since the yield of the added composition is improved, the load on the wastewater treatment facility does not increase.

[0010]

Detailed Description As is well known, a urethane prepolymer is produced by reacting a polyether polyol or a polyester polyol with a polyisocyanate compound in excess of an NCO / OH equivalent ratio. Examples of the raw material polyether polyol, polyester polyol and polyisocyanate compound are well known in the field of urethane industry, and any of them can be used. As the polyol component, a trivalent or higher polyether polyol or polyester polyol having a molecular weight of 1,000 to 20,000 is preferable. Examples of the trifunctional alcohol include triols such as glycerin, hexanetriol, trimethylolethane, and trimethylolpropane, and alkanolamines such as triethanolamine, triisopropanolamine, and tributanolamine. Moreover, pentaerythritol is mentioned as a tetrafunctional alcohol component. Using these polyhydric alcohols as starting materials, alkylene oxide is polyadded in the presence of a basic catalyst to synthesize a polyether polyol. Examples of the alkylene oxide include ethylene oxide, propylene oxide, butylene oxide and the like. As the dibasic acid component constituting the polyester polyol component, saturated or unsaturated such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, phthalic acid, isophthalic acid, and terephthalic acid. The aliphatic dibasic acid and the aromatic dibasic acid of are mentioned. Also included are carbonic acids that form carbonates. As the dihydric alcohol component constituting the polyester polyol, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl- Aliphatic glycols such as 1,5-pentadiol and the like, alicyclic glycols such as cyclohexanediol, and aromatic glycols such as alkylene oxide adducts of bisphenol A and the like can be mentioned. A polyester polyol is obtained by subjecting these dibasic acid component and dihydric alcohol component to a condensation reaction.

A urethane prepolymer is obtained by reacting the obtained polyol component with a polyisocyanate component. Isocyanate compound is not particularly limited,
Organic polyisocyanate compounds such as tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI) polymeric MDI, hexamethylene diisocyanate (HMDI), xylylene diisocyanate (XDI), tetramethyl xylylene diisocyanate (TMXDI), isophorone diisocyanate (IPDI) However, when non-yellowing is required, aliphatic isocyanates such as HMDI, alicyclic isocyanates such as IPDI, and araliphatic isocyanates such as XDI and TMXDI are preferable.

The above polyether polyol and organic polyisocyanate are mixed, and NCO group /
Active hydrogen group equivalent ratio> 1 at 30 to 130 ° C., 30 minutes to 50
By carrying out the reaction for a time, a urethane prepolymer having at least 0.5% by weight or more, preferably 1 to 8% by weight, of a urethane prepolymer is obtained.

Sodium bisulfite or potassium bisulfite is preferred because it is required to dissociate at low temperature as a blocking agent for blocking isocyanate groups used in the present invention. For the block with bisulfite, a known method is used in which bisulfite is dissolved in water at an appropriate concentration.

The synthesis of the urethane prepolymer is a non-solvent system, but depending on the viscosity of the urethane prepolymer,
A solvent which is inactive with isocyanate and can dissolve the urethane prepolymer may be used. Examples of these solvents include dioxane, methyl ethyl ketone, dimethylformamide, tetrahydrofuran, N-methyl-2-pyrrolidone, toluene, and propylene glycol monomethyl ether acetate. Further, a solution or emulsion of an antioxidant or a light stabilizer may be used in combination with the urethane prepolymer aqueous solution. Examples of the antioxidant include solutions or emulsions of hindered phenol-based or semicarbazide-based antioxidants. Examples of the light stabilizer include solutions or emulsions of light stabilizers such as hindered amine (HALS) type, benzophenone type, and benzotriazole type.

Blocking with bisulfite is advantageous over other blocking agents in that it serves to reversibly block free cyanate groups while at the same time solubilizing the prepolymer in water. However, due to the introduced sulfonic acid groups, the resulting aqueous solution of blocked urethane prepolymer is negatively charged or anionic. Therefore, the polarity of the prepolymer must be reversed, that is, cationically charged, in order to efficiently adsorb it to the anionically charged pulp slurry.

The composition of the present invention simultaneously adds a cationic additive to the papermaking stock to reverse the polarity of the aqueous solution of the anionic blocked urethane prepolymer, ie to make it cationic. This cationic additive substance forms a complex with the anionic blocked urethane prepolymer and plays a role of assisting its adsorption to the cellulose fiber.

The first class of cationic organic substances which can be used for this purpose are cationic surfactants represented by alkyl trimethyl ammonium salts, alkyl dimethyl benzyl ammonium salts, alkyl pyridinium salts. The second class are cationic polymers containing amino or quaternary ammonium groups. Examples thereof include dicyandiamide / diethylenetriamine condensate, dicyandiamide / diethylenetriamine / formaldehyde condensate, dicyandiamide / ammonium chloride / formaldehyde condensate, a dicyandiamide-based amino resin, a polymer and a copolymer of diallyldimethylammonium salt, and a salt form. It is a cationic urethane oligomer having a tertiary amino group or a quaternary ammonium group. In this product, a part of the free cyanate group of the urethane oligomer is reacted with a tertiary amino alcohol such as N-methyldiethanolamine to introduce a tertiary amino group, and after neutralization or quaternization with an acid, the remaining free isocyanate group is treated with water. It can be produced by chain extension with.

The ratio of cationic organic material to bisulfite-blocked urethane prepolymer should be greater than 1 in the molar ratio of cation groups / anion groups. However, the material itself should not be over-blended as it does not enhance paper strength.

The wet paper strength enhancer of the present invention is added to a papermaking stock together with other additives such as a filler, and is added to paper made through a wire section, a press section, a dryer section, etc. by a conventional method. Are suitable. In the dryer section of a papermaking machine, the paper is heat dried through a row of cylinders that are typically heated to a maximum of 130 ° C. The paper strengthening agent of the present invention is sufficiently deblocked under these heating conditions, and the regenerated urethane prepolymer serves as a binder to strengthen the bond between the paper fibers.

The amount of the paper strengthening agent of the present invention to be added largely depends on the desired paper quality with respect to paper strength, and is 0.1 to 0.1% of the dry weight of the fiber (pulp) as the blocked urethane prepolymer.
A range of 5% can be varied. In special cases it is also possible to add more than 5% by weight.

[0021]

EXAMPLES The present invention will be described below by way of examples by simulating an actual papermaking process. In these, "parts" and "%" are based on weight unless otherwise specified.

Synthesis Example 1 300 parts of hexylene carbonate (molecular weight 1000),
Hexamethylene diisocyanate (101 parts) was added to trimethylolpropane (13.4 parts) and the mixture was reacted at 100 ° C. for 2 hours to obtain a urethane prepolymer having 3.3% by weight of free isocyanate groups. Then, once the system temperature is 5
Decrease to 0 ℃, 30% sodium bisulfite aqueous solution 110
Parts were added, and the mixture was stirred at 45 ° C. for 60 minutes, and then water 12
The mixture was diluted with 65 parts to prepare a transparent viscous anionic blocked urethane prepolymer aqueous solution having a resin content of 25%.

Synthesis Example 2 Polyester of ethylene oxide 2 mol adduct of bisphenol A and maleic acid (molecular weight 2000) 200
To the parts, 33.6 parts of hexamethylene diisocyanate was added and reacted at 100 ° C. for 2 hours to obtain a urethane prepolymer having 4% by weight of free isocyanate groups. Next, the temperature of the system was once lowered to 50 ° C., 84 parts of 30% potassium bisulfite aqueous solution was added, and the mixture was stirred at 45 ° C. for 60 minutes and then diluted with 718 parts of water to give a transparent viscous resin content of 25%. An aqueous solution of anionic blocked urethane prepolymer was prepared.

Synthesis Example 3 Polytetramethylene glycol (molecular weight 1000) 30
0 parts, 13.4 parts of trimethylolpropane and 101 parts of hexamethylene diisocyanate were added, and 100 ° C x 2
The reaction was carried out for a time to obtain a urethane prepolymer having 3.3% by weight of free isocyanate groups. Next, the temperature of the system was once lowered to 50 ° C., 110 parts of a 30% sodium bisulfite aqueous solution was added, and the mixture was stirred at 45 ° C. for 60 minutes,
It was diluted with 1265 parts of water to prepare a transparent viscous anionic blocked urethane prepolymer aqueous solution having a resin content of 25%.

Synthesis Example 4 100.8 parts of hexamethylene diisocyanate was added to 300 parts of a polyester polyol (molecular weight 1500) of terephthalic acid and 3-methyl-1,5-pentadiol to obtain 10 parts.
Reaction was carried out at 0 ° C for 2 hours to give 8.4 free isocyanate groups.
A urethane prepolymer having a weight% was obtained. Next, the temperature of the system was once lowered to 50 ° C., 35.7 parts of N-methyldiethanolamine was added, and the mixture was stirred at 65 ° C. for 60 minutes to obtain a urethane prepolymer having 2.0% by weight of free isocyanate groups. Then, once the system temperature is 50 ℃
Down to 37.8 parts dimethylsulfate and add 50 ℃ x 2
The quaternization reaction was performed for 0 minutes. Then, the mixture was diluted with 1897 parts of water to prepare a viscous cationic urethane polymer aqueous solution having a resin content of 25%.

Examples and Comparative Examples The papermaking test was conducted according to JIS P 8209-1961. NBKP (softwood sulphate pulp) 360 (g) is torn into pieces of about 3 cm and immersed in 5 (L) of water overnight.
8 (L) was added and beaten in a Niagara beaker for 30 minutes to obtain a pulp concentration of 1.57 (%) and a freeness of 600 (m
l) (Canadian standard freeness, 20 ° C., 0.3%). This pulp slurry 382.2
(G) and 1.5 (g) of the aqueous solutions of Examples and Comparative Examples adjusted in advance to a solid content of 1.6% (corresponding to 0.4% of the dry weight of pulp) were added to 816.3 (g) of water. Pulp density 0.
The stock was 5%. The thus-prepared stock 200 (g) was sampled, paper-made by a sheet machine, and put on a press machine (3.5 kg / m ² × 5 minutes) to obtain 110
The sheet was dried at 30 ° C. for 30 seconds and made into a test sheet having a basis weight of 50 (g / m 2). Length 11 (cm) × width 1.5 (c
The paper piece of m) was cut and mounted on an autograph standard tensile tester at a chuck distance of 5 (cm), and the tensile strength was measured by moistening the central part with a brush. No paper strengthening agent was added to the blank control. In addition, as a reference example, a commercially available polyamide epichlorohydrin-based resin wet paper strength enhancer was added to a stock having a pulp concentration of 3% in an amount of 5 (%) as an aqueous dispersion to give 6 (g).
Was added (corresponding to 1.0% of pulp dry weight). The results are shown in the table.

Table 1 ─────────────────────────────────── Blocked urethane Cationic organic substance Wet tension pre Polymer addition amount Addition amount Strength (to pulp dry weight (kg / cm of pulp dry weight to solid content%) to solid content%) ────────────────────── ─────────────── Example 1 Synthetic Example 1 Cationic surfactant ¹ 0.75 0.20 0.20 Example 2 Synthetic Example 1 Dicyandiamide resin ² 0.72 0.36 0 .04 Example 3 Synthetic Example 1 Quaternized diallylamine 0.73 Copolymer ³ 0.30 0.10 Example 4 Synthetic Example 1 Synthetic Example 4 Urethane oli 0.67 Gomer 0.18 0.22 Example 5 Synthetic Example 2 Quaternized diallylamine 0.71 Copolymer ³ 0.30 0.10 Implementation Example 6 Synthesis Example 3 Same as above 0.65 0.30 0.10 ──────────────────────────────────── Blank None None 0.22 Control Comparative Example 1 Synthesis Example 1 None 0.24 0.40 Comparative Example 2 Synthesis Example 2 None 0.25 0.40 Comparative Example 3 Synthesis Example 3 None 0.22 0.40 Reference Example Commercially available Polyamide epichlorohydrin resin 0.67 1.0 ─────────────────────────────────── Note 1: Lauryltrimethylammonium Ethoxysulfate Note 2: Dicyandiamide / diethylenetriamine / formaldebi condensate (molecular weight 5000) Note 3: Polydiallyldimethylammonium chloride copolymer (molecular weight 10000)

From the above results, the bisulfite-blocked urethane prepolymer alone does not enhance the paper strength because it is not adsorbed by the cellulose fibers in the papermaking stock, but when used in combination with a cationic organic substance, it becomes commercially available polyamide epichlorohydrone. It can be seen that it shows a comparable paper strength increasing effect.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takeshi Miyamura             1-6-15 Sakuradai, Minami Azajigaoka, Kameoka, Kyoto Prefecture F-term (reference) 4L055 AA02 AC06 AG80 AG85 AH17                       FA13

Claims (7)

[Claims] 1. A water-soluble blocked urethane prepolymer containing a terminal isocyanate group blocked with an alkali metal bisulfite, and a cationic organic compound in an amount sufficient to reverse the polarity of the blocked urethane prepolymer in solution. Wet strength composition comprising a mixture with substances. 2. The wet strength composition of claim 1 wherein the cationic additive is a cationic surfactant. 3. The wet strength composition of claim 1, wherein the cationic organic substance is a dicyandiamide-based amino resin. 4. The wet strength composition of claim 1, wherein the cationic organic substance is a polymer or copolymer of quaternized diallylamine. 5. The wet strength composition according to claim 1, wherein the cationic organic substance is a urethane oligomer having a tertiary amino group in the form of a quaternary ammonium salt or an acid salt. 6. A papermaking method comprising adding the wet strength composition of any one of claims 1 to 5 to a papermaking stock, forming a web by a conventional method and then drying. 7. A wet strength paper produced by the paper manufacturing method of claim 6.