JPH05117993A - Fluorescent whitening agent for paper - Google Patents

Abstract

PURPOSE:To provide the title agent excellent in whitening effect, resistance to heat, water and light, offset printability etc., suitable for coated paper etc., comprising an emulsion produced by polymerization of a monomer mixture prepared by dissolving or dispersing a specific compound in a vinyl monomer. CONSTITUTION:The objective whitening agent comprising an emulsion produced by polymerization of a monomer mixture prepared by dissolving or dispersing (A) pref. 1-10wt.% of a compound of the formula (R is H or 1-4C alkyl) in (B) a vinyl monomer such as styrene. It is preferable that the amount of the present emulsion to be added be 0.1-30 pts.wt. based on 100 pts.wt. of the pigment (e.g. talc) in a coating composition for paper.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluorescent whitening agent for paper which has a high whitening effect and is excellent in heat resistance, water resistance and light resistance.

[0002]

2. Description of the Related Art Generally, as a method for brightening organic materials such as fibers, cloths, papers and silver halide photographic light-sensitive materials, various fluorescent whitening agents are added with water or organic solvents. A method of dissolving or dispersing in certain methanol, acetone, ethyl acetate, dimethylformamide, dimethylsulfoxide, etc., impregnating the above organic material into the solution or dispersion and fixing it, water in which an optical brightener is dissolved or dispersed, or A method of applying an organic solvent to an organic material and then drying it, or a method of incorporating the organic solvent in a manufacturing step for molding the organic material, for example, a fiber spinning step, a film molding step, or the like is known.

Various types of fluorescent whitening agents are used as whitening agents for whitening organic materials. For example, in order to increase the commercial value of high-quality printing paper, the whiteness of coated paper is used. Various coating compositions for papers containing a fluorescent brightening agent together with a pigment and an aqueous binder have been studied and used in order to improve the above properties. As the fluorescent whitening agent used at that time, a water-soluble fluorescent whitening agent such as a diaminostilbenesulfonic acid type is mainly used.

However, in a paper coating composition using such a conventional water-soluble fluorescent whitening agent such as a diaminostilbenesulfonic acid type, the whitening effect is insufficient, and the heat resistance and water resistance are insufficient. However, it has been pointed out that there are drawbacks such as deterioration in water resistance, ink acceptability, and so-called offset printing suitability. Furthermore, since conventional diaminostilbene sulfonic acid-based optical brighteners are water-soluble, they easily elute when they come into contact with water and may be absorbed into the body due to skin contact, etc. It has been pointed out. In view of such a situation, as a result of intensive investigations by the present inventors, a water-insoluble optical brightener bis (benzoxazolyl) thiophene or its alkyl derivative having a specific average particle diameter was dispersed in water. When used together, it gives an excellent fluorescent whitening effect as compared with the water-soluble and water-insoluble fluorescent whitening agents which have been used conventionally, and the fluorescent whitening effect is excellent in heat resistance and water resistance. And applied for a patent to the destination (Japanese Patent Application No. 2-
No. 303687).

However, even in the method of using the paper coating composition using the water-insoluble fluorescent whitening agent, the light resistance is still insufficient, and the coated paper turns yellow by long-time light irradiation. It has the drawback of being easy. The object of the present invention is to improve the drawbacks of the above-mentioned conventional fluorescent whitening agents for paper, excellent fluorescent whitening effect used in paper coating compositions, heat resistance, excellent water resistance, etc. Another object is to provide an excellent optical brightener for paper.

[0006]

In view of the above situation, as a result of intensive studies, the present inventors have found that bis (benzoxazolyl) thiophene which is a water-insoluble brightening agent or its alkyl derivative is a vinyl monomer. The optical brightener for paper, which is composed of an emulsion obtained by dissolving or dispersing in water and then polymerizing in water, is superior to the water-soluble and water-insoluble optical brighteners that have been used conventionally. Gives a fluorescent whitening effect, and the fluorescent whitening effect is heat resistant,
It has been found that it is excellent in water resistance and also sufficiently satisfactory in light resistance. Further, it has been found that the fluorescent whitening agent for paper made of the emulsion has excellent properties such that it is dispersed in water in a stable state and impregnated and fixed to an organic material, and coating and drying are very easy. Invented. That is, the gist of the present invention relates to a fluorescent whitening agent for paper, which comprises an emulsion obtained by polymerizing a monomer mixture solution in which a compound represented by the general formula (I) is dissolved or dispersed in a vinyl monomer. ..

[0007]

[Chemical 2]

(In the formula, R represents a hydrogen atom or a carbon number of 1 to 4)
Represents an alkyl group of. ). In the general formula (I), R is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and the alkyl group may be linear or branched. Specifically, a methyl group, an ethyl group, an n-propyl group,
Isopropyl group, n-butyl group, isobutyl group, sec
Examples include -butyl group and t-butyl group. Among them, bis (benzoxazolyl) thiophene having a hydrogen atom, a methyl group or a t-butyl group or its alkyl derivative is preferably used. All of these compounds are known compounds and can be easily produced by, for example, the method described in JP-A-2-240083 or a method analogous thereto.

That is, as shown by the following reaction formula, it can be produced by reacting a thiophene dicarboxylic acid diester with an aminophenol in the presence of an acid catalyst.

[0010]

[Chemical 3]

The general formula (I) produced by such a method
The compound represented by is usually purified and obtained in the form of coarse particles, but in the present invention, it is dissolved or dispersed in the vinyl monomer as it is, and emulsified or dispersed in water with an emulsifier or the like to be polymerized. To obtain an optical brightener for paper as an emulsion.

The vinyl monomer used in the present invention is one or more selected from styrene, acrylic acid, methacrylic acid, methyl methacrylate, ethyl methacrylate, vinyl chloride, acrylonitrile, vinyl acetate and the like. The amount of the compound represented by the general formula (I) used to be used is usually 0.1 to 1
It is 5.0 wt% and preferably 1.0 to 10 wt%. When the amount is less than 0.1 wt%, the fluorescent whitening effect is not sufficiently obtained, and when the amount is more than 15.0 wt%, the stability of the obtained emulsion is lowered and the fluorescent whitening effect is not sufficiently obtained.

In the polymerization according to the present invention, the amount of the vinyl-based monomer with respect to water is usually 5 to 70% by weight, preferably 20 to 50% by weight. If the amount is less than 5% by weight, the formation of emulsion is not sufficient. 70 wt%
If the amount exceeds the above range, the emulsion polymerization liquid is solidified and does not become an emulsion. As the emulsifier used for emulsification, known anionic or nonionic emulsifiers can be used alone or in combination. Examples thereof include anionic emulsifiers such as alkylbenzene sulfonates, alkyl sulfonates, and alkyl sulfates, nonionic emulsifiers such as polyoxyethylene polyoxypropylene block polymers, polyoxyethylene alkyl ethers, and polyoxyethylene alkyl allyl ethers. And the like. Preferably, anionic alkyl sulfonate and a nonionic polyoxyethylene polyoxypropylene block polymer are used in combination to obtain good results.

The amount of the emulsifier added is usually 3 to 30% by weight, preferably 3 to 20% by weight, based on the vinyl monomer. As the polymerization initiator, known polymerization initiators used in radical polymerization can be used alone or in combination. Examples thereof include benzoyl peroxide, azobisisobutyrylonitrile, and persulfates such as potassium persulfate and ammonium persulfate. The amount of the polymerization initiator added is usually 0.1 to 20 wt% with respect to the vinyl monomer.
%, And preferably 0.2 to 2.0 wt%.

When the optical brightener for paper of the present invention is used as a coating composition for paper, the emulsion is added as it is during the preparation thereof. The addition amount of the emulsion as the fluorescent whitening agent for paper of the present invention in the paper coating composition can be selected at an arbitrary ratio, but is usually 0 per 100 parts by weight of the pigment in the paper coating composition. 0.01 to 50 parts by weight, preferably 0.1 to 30 parts by weight. 0.01
If the amount is less than the weight part, the fluorescent whitening effect cannot be sufficiently obtained,
This is because if it is used in an amount of more than 50 parts by weight, the viscosity of the obtained coating composition may increase and it may become unsuitable for coating.

Further, the optical brightening agent for paper of the present invention can be used as a pigment substitute in the paper coating composition together with the pigment. In this case, the weight ratio of the pigment / optical brightening agent for paper is usually 99/1 to 50/50, preferably 70/30 to 90/10. When the amount of the fluorescent whitening agent for paper is less than 1 part by weight, the fluorescent whitening effect is not sufficiently obtained, and when it is used over 50 parts by weight, the viscosity of the coating composition for paper becomes high and it becomes unsuitable for coating. Because there is.

As the pigment in the paper coating composition,
Examples include white inorganic pigments such as kaolin clay, talc, titanium dioxide, aluminum hydroxide, calcium carbonate, and satin white, and white organic pigments containing polystyrene, urea resin, etc. as the main components, and these are mixed alone or in any ratio. Then used. As the aqueous binder, water-soluble binders such as oxidized starch, esterified starch, polyvinyl alcohol, casein, and gelatin, and emulsion dispersion systems of styrene, butadiene-based resin, vinyl acetate-based synthetic resin, ethylene / vinyl acetate-based synthetic resin, etc. And the like, and these may be used alone or in combination at any ratio. In the coating composition for paper, in addition to the fluorescent whitening agent for paper of the present invention, a pigment, and an aqueous binder, a dispersant, a viscosity modifier, a defoaming agent, if necessary, in a range that does not impair the effects of the present invention, A preservative, a lubricant, a water resistance agent, an auxiliary agent such as a printability improver, and a small amount of a dye which is a bluing agent may be contained.

The viscosity and pH value of the paper coating composition using the optical brightening agent for paper of the present invention are as shown in the following examples, and the paper coating composition conventionally used. It can be used without any problem in coatability in the same manner as. The paper coating composition using the optical brightener for paper of the present invention is a commonly used method, for example, a blade coater, a bar coater, an air knife coater, a size press coater, a gate roll coater, and a cast coater. A coated paper can be obtained by applying it on a paper substrate, subjecting it to ordinary drying, and then subjecting it to a gloss finishing treatment, if necessary. As described above, when the paper optical brightening agent of the present invention is used in a paper coating composition, a particularly preferable fluorescent whitening effect is obtained, but in addition, the following items are mixed and used. A fluorescent whitening effect can be obtained. For example, cellulose fibers such as cotton, hemp and ramie, regenerated fibers such as rayon and viscose, cellulose films such as acetyl cellulose, polymer molded products such as polyethylene and polystyrene, polyamides such as 6,6-nylon and polyethylene terephthalate, Examples include molded products containing polyester fibers, silver halide photographic light-sensitive materials, and the like.

[0019]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. In the examples, parts and% are all weight units. Example 1 0.75 parts of sodium lauryl sulfate (Kanto Kagaku Co. (reagent) (reagent)) as an anionic dispersant, 70 parts of water in which dissolved oxygen was removed beforehand, and an ethylene oxide-propylene oxide copolymer as a nonionic dispersant. 4.5 parts (manufactured by Sanyo Kasei Co., Ltd., New Pole PE64) were completely dissolved. To this was added 30 parts of styrene in which 1.5 parts of bis (t-butylbenzoxazolyl) thiophene coarse particles (particle size about 15 μm) were dissolved. Then, after adding 0.1 part of potassium persulfate, 60 to 70 while stirring vigorously.
After the temperature was raised to ° C, polymerization was carried out for 6 hours to obtain an emulsion of a fluorescent whitening agent for paper.

Example 2 An emulsion of a fluorescent whitening agent for paper was obtained in the same manner as in Example 1, except that bis (t-butylbenzoxazolyl) thiophene was changed to bis (methylbenzoxazolyl) thiophene. It was

Example 3 An emulsion of a fluorescent whitening agent for paper was obtained in the same manner as in Example 1 except that bis (t-butylbenzoxazolyl) thiophene was changed to bis (benzoxazolyl) thiophene. ..

Example 4 In 70 parts of water in which dissolved oxygen was removed beforehand, 0.75 part of sodium lauryl sulfate (Kanto Chemical Co., Inc. (reagent)) as an anionic dispersant, and ethylene oxide-propylene oxide as a nonionic dispersant. 4.5 parts of a copolymer (Newyole PE64, manufactured by Sanyo Kasei Co., Ltd.) was completely dissolved. A mixed solution of styrene (27 parts) and acrylic acid (3 parts) in which 1.5 parts of bis (t-butylbenzoxazolyl) thiophene coarse particles (particle size: about 15 μm) were dissolved was neutralized with a 10% aqueous sodium hydroxide solution. And then added. Next, after adding 0.1 part of potassium persulfate, the temperature was raised to 60 to 70 ° C. with vigorous stirring, and polymerization was carried out for 6 hours to obtain an emulsion of a fluorescent whitening agent for paper.

Test Example 1 Using the emulsion of the fluorescent whitening agent for paper obtained in Example 1,
A paper coating composition having the formulation shown in Table 1 was prepared, and the viscosity and pH were measured.

[0024]

[Table 1]

Further, with respect to the coated paper obtained by applying the coating composition for paper onto commercially available high-quality paper, the whiteness, coating suitability, etc. were measured and observed, and the results in Table 2 were obtained.

[0026]

[Table 2]

The coating composition was applied onto a paper substrate by hand coating one side using a wire rod to a weight of about 20 g / m ² , drying and calendering. The measuring method and the evaluating method are as follows. (1) Coating composition a) Viscosity The viscosity at 60 rpm was measured with a B-type viscometer. The measurement temperature was 25 ° C. b) pH The pH was measured using a glass electrode pH meter at a measurement temperature of 25 ° C.

(2) Whiteness of coated paper The whiteness was measured using a colorimeter (Macbeth MS2000: manufactured by Macbeth). The larger the value, the better the whiteness. (3) Coating suitability Wire rod No. In 3 the paper was applied and judged by the presence or absence of streaking. The evaluation was made into the following three stages. ○: There is no streak. Δ: There are streaks to the extent that it is not noticeable. ×: There is a streak that was an eye.

(4) Heat resistance test of fluorescent whitening effect The coated paper was left to stand in an oven at 150 ° C. for 30 minutes for heat treatment. The whiteness before and after the heat treatment was measured, and the heat resistance of the fluorescent whitening effect was evaluated by calculating the whiteness residual ratio by the following formula. Whiteness residual rate (%) = (whiteness after heat treatment / whiteness before heat treatment) × 100 In the case of 80% or more: ○ In the case of 75 to 80%: Δ In the case of 75% or less: ×

(5) Water resistance test of fluorescent whitening effect One drop of water was dropped on the coated paper, and after drying, the whiteness was visually observed with respect to the change of the fluorescent whitening effect at the drop of water drop. The water resistance of the fluorescent whitening effect was evaluated. The evaluation was performed on a scale of 5: when the whiteness of the peripheral dry part was not changed at all, excellent: 5, and when the whiteness before the coating composition was applied was reduced to poor: 1.

(6) Printability test of coated paper (a) Ink acceptability A printing test was carried out after preliminarily moistening the coated surface with water using an RI tester (JIS-K-5701) to accept the ink. The sex was visually observed and evaluated. The evaluation was performed in five grades of excellent 5 to inferior 1, with the ink acceptability of the coated paper coated with the coating composition containing no optical brightener being set to 3. (B) Water resistance (wet pick method) The coated surface was wetted with a water supply roll using an RI tester and then printed, and the state of falling and damage of the coating layer was visually observed and evaluated. The evaluation was carried out in 5 grades of excellent 5 to inferior 1, with the ink acceptability of the coated paper coated with the coating composition containing no optical brightener being set to 3.

(7) Light resistance test of fluorescent whitening effect The coated paper was irradiated with carbon arc at 60 ° C. for 4 hours, the whiteness before and after irradiation was measured, and the degree of yellowing was examined. The evaluation was carried out by calculating the light resistance of the fluorescent whitening effect by calculating the whiteness residual ratio below. Whiteness residual rate (%) = (whiteness after irradiation / whiteness before irradiation) × 100 In the case of 90% or more: ○ In the case of 85 to 90%: Δ In the case of 85% or less: ×

Test Examples 2 to 3 Using the emulsion of the fluorescent whitening agent for paper obtained in Example 1,
A paper coating composition having the same composition as in Table 1 was prepared, except that the amount of the compound represented by the formula (I) in the emulsion added in terms of pure content was changed to Test Example 1 A coated paper was obtained in the same manner as in. The whiteness of the coated paper obtained was observed and measured, and the results shown in Table 2 were obtained. The measuring method and the evaluating method are the same as in Test Example 1.

Test Examples 4 to 6 Using the emulsion of the fluorescent whitening agent for paper obtained in Example 2,
A paper coating composition having the same composition as in Table 1 was prepared, except that the amount of the compound represented by the formula (I) in the emulsion added in terms of pure content was changed to Test Example 1 A coated paper was obtained in the same manner as in. The whiteness of the coated paper obtained was observed and measured, and the results shown in Table 2 were obtained. The measuring method and the evaluating method are the same as in Test Example 1.

Test Examples 7 to 8 The emulsion of the fluorescent whitening agent for paper obtained in Example 3 was used,
A paper coating composition having the same composition as in Table 1 was prepared, except that the amount of the compound represented by the formula (I) in the emulsion added in terms of pure content was changed to Test Example 1 A coated paper was obtained in the same manner as in. The whiteness of the coated paper obtained was observed and measured, and the results shown in Table 2 were obtained. The measuring method and the evaluating method are the same as in Test Example 1.

Test Examples 9 to 10 Using the emulsion of the fluorescent whitening agent for paper obtained in Example 4,
A paper coating composition having the same composition as in Table 1 was prepared, except that the amount of the compound represented by the formula (I) in the emulsion added in terms of pure content was changed to Test Example 1 A coated paper was obtained in the same manner as in. The whiteness of the coated paper obtained was observed and measured, and the results shown in Table 2 were obtained. The measuring method and the evaluating method are the same as in Test Example 1.

Comparative Example 1 A paper coating composition was prepared in the same manner as in Test Example 1 except that the emulsion shown in Table 1 was not used as an optical brightening agent for paper. I got coated paper. The whiteness of the coated paper obtained was observed and measured, and the results shown in Table 2 were obtained. The measuring method and the evaluating method are the same as in Test Example 1.

Comparative Example 2 In the formulation shown in Table 1, as a fluorescent whitening agent for paper, WHITEX B. B. Liqui
A coating composition for paper was prepared in the same manner as in Test Example 1 except that d (manufactured by Sumitomo Chemical Co., Ltd.) was added in an amount shown in Table 2 and used.
A coated paper was obtained in the same manner as in Test Example 1. The whiteness of the coated paper obtained was observed and measured, and the results shown in Table 2 were obtained. The measuring method and the evaluating method are the same as in Test Example 1.

[0039]

EFFECTS OF THE INVENTION By using the optical brightening agent for paper of the present invention, a high whitening effect which cannot be obtained by the conventional water-soluble optical brightening agent can be obtained with a small amount, and the whitening effect is It also has excellent heat resistance, water resistance and light resistance. Further, by using the paper coating composition using the optical brightener for paper of the present invention, it is possible to provide a coated paper having characteristics excellent in offset printing suitability.

Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display area D21H 21/30

Claims (1)

[Claims] 1. A fluorescent whitening agent for paper, which comprises an emulsion obtained by polymerizing a monomer mixture solution in which a compound represented by the general formula (I) is dissolved or dispersed in a vinyl monomer. [Chemical 1] (In the formula, R represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.)