JPH0615756B2 - Opacity improver for paper - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an opacity improver for paper, which can improve opacity without reducing paper strength, and more specifically to a specific cationic polymer. The present invention relates to an opacity improving agent for paper which has an emulsion as a main component.

2. Description of the Related Art In recent years, weight reduction of printing paper has been promoted in order to reduce wood resources and transportation costs. In particular, lightweight newspapers having a basis weight of 46 g / m ² have become the mainstream, and the development of further lightweight paper has been studied, and it has already started to be partially supplied. However, as the weight of paper becomes lighter, it is inevitable that the amount of paper stock and the thickness of paper will decrease, which may cause a decrease in paper strength and strike-through during printing (a phenomenon in which one side of the printed surface is visible through the other side). It's a problem.

Under such circumstances, various paper manufacturing companies have adopted various measures to solve the problem of strike-through at the time of printing, which is one of the technical problems of lightweight paper.

At present, as one of the countermeasures, inorganic fillers such as calcium carbonate, clay, talc, colloidal hydrous silica (commonly called white carbon), titanium oxide, and urea resin-based organic fillers are internally added. The use of these fillers improves whiteness, opacity, smoothness, printability, etc., and also has an effect of improving opacity after printing.

However, when these fillers are used as a filler during the papermaking of paper, there is a tendency that the binding of the cellulose fibers is inhibited and the strength of the paper is reduced. In the future, in order to further reduce the weight, it is necessary to increase the blending ratio of the filler, but the altitude of the paper is greatly reduced due to the double effect of the reduction of the basis weight and the increase of the blending amount of the filler. This is a major obstacle in promoting weight reduction.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention Under the above-mentioned problems, the present inventors have aimed to improve the opacity as well as the weight of paper, and to improve the opacity of the filler and the modifier which does not reduce the strength of paper. As a result of diligent study to obtain a cationic polyvinyl alcohol (hereinafter, "C-
It is abbreviated as "PVA". ), The cationic polymer emulsion obtained by emulsion polymerization of vinyl acetate and the inorganic-organic composite emulsion obtained by allowing white inorganic fine particles to coexist during the emulsion polymerization reduce paper strength. The inventors have found that the opacity is improved without being squeezed, and based on this finding, they have completed the present invention.

Means for Solving the Problems That is, the gist of the present invention is: (1) Cationic property obtained by emulsion-polymerizing vinyl acetate in the presence of C-PVA having an electric charge of 6 × 10 ⁻⁴ eq / g or more. Opacity improver for papers, which is mainly composed of polymer emulsion, (2) Charge is 6 × 10 ⁻⁴ eq / g or more, and white inorganic fine particles coexist in emulsion polymerization of vinyl acetate in the presence of C-PVA. An opacity improving agent for paper, which comprises a cationic polymer emulsion obtained by polymerization as a main component.

Hereinafter, the components of the present invention will be described in detail.

(Cationic Polyvinyl Alcohol) The C-PVA used in the present invention has an electric charge of 6 × 10 ^−4.
PV with eq / g or more and modified with cationic groups
It is A and can be produced by various methods such as a method of post-modifying the polymer and a method of copolymerization with a monomer having a cationic group. For example, JP-A-59-135202 discloses C-PVA having a structure represented by the following formula (I). Any such C-PVA can be used in the present invention.

C-PVA used in the present invention has a cationic charge of 6
× 10 ⁻⁴ eq / g or more. C-PVA having a cation charge in this range was not known to be used as an opacity improving agent in paper making, and even to be used as an additive.

The degree of polymerization of C-PVA is not particularly limited, but 20
A range of 0-3500 is suitable.

The degree of saponification is also not particularly limited, but a higher degree of saponification is preferred from the viewpoint of increasing hydrogen bonds in the paper.

The amount of C-PVA used during emulsion polymerization is 5 to 5 in the total solid content.
A range of 0% by weight, preferably 10-40% by weight is suitable. If it is less than 5% by weight, the effect of fixing the produced emulsion particles to the pulp is poor, and if it exceeds 50% by weight, the amount of emulsion particles produced is relatively reduced and the resin particles are unlikely to remain as resin particles in the pulp.

(Emulsion Polymerization) The initiation of emulsion polymerization is carried out by using an oxidation catalyst such as hydrogen peroxide or potassium persulfate, a cationic catalyst such as 2,2′-azobis- (2-amidinopropane) dihydrochloride alone or in combination,
Further, it is carried out by a conventional method using a redox reaction system in which it is used in combination with various reducing agents.

(White inorganic fine particles) As the white inorganic fine particles, colloidal silica, talc, clay, titanium oxide, barium sulfate and the like can be mentioned, and colloidal silica, that is, white carbon is particularly preferable. The blending ratio of the white inorganic fine particles is preferably 1 to 50% by weight in the emulsion solid content. 1
If it is less than 50% by weight, the effect of blending the white inorganic fine particles is poor, and if it exceeds 50% by weight, the stability of the emulsion produced is difficult and the paper strength is lowered.

(Cationic Polymer Emulsion) Emulsion particles produced by emulsion polymerization have an average particle size of 0.1 to 1 μm, preferably in the range of 0.2 to 0.6 μm, which has a high light scattering effect and is effective in improving paper strength. Is good.

The additive of the cationic polymer emulsion to the paper varies depending on the properties of the emulsion such as the kind of pulp and the content of the cationic group, but the emulsion solid content is 0.1 to 10 relative to the absolutely dried raw material pulp solid content. The weight range is preferably 0.1 to 5% by weight. If it is less than 0.1% by weight, the above-mentioned effect is poor, and if it exceeds 10% by weight, the emulsions added to the paper are likely to form a melted film, which may rather impair the opacity. When the white inorganic fine particles are blended to form an organic-inorganic composite emulsion, the amount of addition is 0.1 to 50% by weight, preferably 0.1 to 3% by weight of emulsion solids relative to the raw pulp solids.
The range of 0% by weight is preferable. If it is less than 0.1% by weight, the above-mentioned effects are poor, and if it exceeds 50% by weight, the papermaking property is deteriorated.

(Pulp) The pulp used in the present invention includes KP, GP,
It is mainly composed of wood pulp such as DIP or vegetable fiber, and can be used alone or in combination.

Action Among the effects exerted by the emulsion of the present invention, with respect to paper strength, a film obtained from a resin emulsion, particularly an emulsion containing a vinyl acetate resin as a main component, is generally highly flexible and is fused to fibers in pulp. It is expected that the strength will be improved by strengthening the bond between the fibers.

However, it is a well-known fact that, when a vinyl acetate resin emulsion or an acrylic ester emulsion is dried, the emulsion particles are fused to each other to form a transparent film. The above-mentioned cathin-on polymer emulsion, which is an emulsion, has a poor function of improving the opacity of paper, and is rather thought to increase the transparency. However, as a result of research, it was confirmed that the above-mentioned emulsion has an effect of improving transparency (particularly, white paper opacity) far beyond what was originally expected.

The theoretical basis for the effect of the cationic polymer emulsion of the present invention to improve the opacity of paper is not clear, but comparing the electron micrographs shown in FIGS. 1 to 4, white carbon alone (see FIG. ) Or a urea resin-based filler (FIG. 2) is used, the cationic emulsion of the present invention is used (FIGS. 3 and 4), and when the addition amount is within a certain range, the emulsion particles are about 10 μm. It is presumed that they are settled in the fiber as individual aggregates, and contribute to the scattering of light.

Further, from these figures, it is recognized that the emulsion used in the present invention is different from other inorganic / organic fillers and a part of the aggregated particle surface is melted and fused with the cellulose fiber,
This is considered to be one of the reasons for improving the strength of paper.

Examples Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples. The percentages and parts are by weight.

Examples 1 to 6 and Comparative Examples 1 to 3 (b) Preparation of Emulsion As a polyvinyl alcohol having a cationic group (saponification degree: 98.5%, cationic charge: 8 × 10 ⁻⁴ eq / g),
Structure of the following formula With C-PVA (manufactured by Denki Kagaku Kogyo Co., Ltd.,
It is abbreviated as "C-PVA". ) To 70 parts of 530 parts of ion-exchanged water was added and dissolved by heating at 80 ° C., then cooled to room temperature, and the pH was adjusted to 4.0 with a 4% tartaric acid aqueous solution. The temperature of this solution is raised to 70 ° C., and 10 parts of ion-exchanged water is added to 2,
2'-azobis (2-amidinopropane) dihydrochloride 0.
35 parts in 80 parts of an aqueous solution and 2 parts of ion-exchanged water
At the same time, the respective polymerization initiators of the aqueous solution in which 6 parts of% H ₂ O ₂ are dissolved are added at the same time, and immediately after that, 400 parts of vinyl acetate monomer (VAc) is added dropwise.

The addition amount was adjusted so that the monomer dropping was completed in 3 hours, the liquid temperature was raised to 80 ° C., and emulsion polymerization was carried out for 3 hours. Thereafter, the temperature was raised to 90 ° C., an aging reaction was performed for 30 minutes, and then the mixture was cooled to room temperature to obtain a cationic vinyl acetate resin emulsion.

Solids content 46.7%, viscosity at 20 ° C is 7900 cps
Met. This emulsion is referred to as emulsion A.

Hereinafter, emulsions B and C were prepared in the same manner except that the compounding ratio of C-PVA and VAc was changed.

After adding 100 parts of white carbon powder to 530 parts of ion-exchanged water and stirring and dispersing at room temperature, 100 parts of C-PVA is added and heated and dissolved at 80 ° C. This aqueous solution was cooled to room temperature, adjusted to pH 4.0 with a 4% tartaric acid aqueous solution, and then heated to 70 ° C. to obtain 10 parts of ion-exchanged water with 2,2′-.
Azobis- (2-amidinopropane) dihydrochloride (0.2 parts) dissolved in an aqueous solution and ion-exchanged water (80 parts) contained 35% H.
Immediately after simultaneously adding each polymerization initiator of an aqueous solution in which 6 parts of ₂ O ₂ is dissolved, dropwise addition of 370 parts of VAc is started. The addition amount was adjusted so that the dropping of the monomer was completed in 3 hours, the liquid temperature was raised to 80 ° C., and emulsion polymerization was performed for 3 hours. After that, the temperature was raised to 90 ° C., a thermal reaction was performed for 30 minutes, and then the mixture was cooled to room temperature to obtain a white carbon-containing cationic vinyl acetate resin emulsion. The solid content was 42.8%, and the viscosity at 20 ° C. was 8200 cps. This emulsion is referred to as emulsion D.

Hereinafter, an emulsion E was prepared in the same manner except that talc was used instead of white carbon.

Details of the produced emulsion are shown in Table 1.

(B) Papermaking test While the 0.8% slurry dispersion of pulp (blended pulp: 130 ml CSF) was well stirred, the emulsions A to E were added to the pulp in a solid content ratio of 2%, and then 2
The mixture is stirred for 1 minute and the pH of the slurry dispersion is adjusted to 5.5 with a sulfuric acid band. Then, the mixture was stirred for 2 minutes, diluted with water to 0.4% of the solid content of the slurry dispersion, and stirred, and then a square paper machine (manufactured by Kumagai Riki) was used to weigh 46 ± 2 g / gram.
The paper was made to have a size of m ² .

Next, the wet paper was compressed and dehydrated at 3.5 Kg / cm ² for 5 minutes, and the absorbent paper was replaced, compressed and dehydrated at the same pressure for 2 minutes, and then contact-dried with a rotary dryer (surface temperature of about 110 ° C.) for 3 minutes. It was The obtained paper was conditioned under conditions of 20 ° C. and 65% RH for 24 hours or more, and subjected to various paper strength physical property tests.

The results are shown in Examples 1 to 5 in Table 2.

As a reference, the results of the same test using the emulsion-free additive, the cationic PVA alone, the white carbon, and the urea resin-based organic filler are shown in Comparative Examples 1 to 1 of Table 2.
2 and Reference Examples 1-2.

The paper using the emulsion of the present invention has a large breaking length (the length at which the suspended paper is cut by its own weight), has excellent paper strength, and has no opacity in addition to the non-added one or the cationic one. There are some that are higher than those using PVA and urea resin-based fillers and are comparable to or higher than those using white carbon alone. As described above, the vinyl acetate resin-based emulsion makes the paper opaque. Given that it was unexpected to increase the properties, it can be seen that the cationic polymer emulsions of the present invention are excellent paper opacifiers. Also, considering that the industry is struggling to increase the opacity by only 1 to 2%, for example, the opacity is increased by 3 to 4% as compared with the additive-free one. Moreover, it should be said that not reducing the strength of the paper is a great effect.

Effect of the Invention The cationic polymer emulsion of the present invention can be used as an opacity improving agent for paper, and has the effect of improving the strength of paper and improving the opacity.

In particular, even when the emulsion of the present invention belonging to the vinyl acetate resin-based emulsion was added alone, the improvement in the opacity of the white paper was more than the initially expected effect. In the future, there is a possibility to use this performance to manufacture lightweight paper.

[Brief description of drawings]

FIG. 1 is an electron micrograph showing the inside of the paper manufactured by Reference Example 1 (white carbon alone added to the paper), that is, the particle structure of white carbon attached to cellulose fibers. FIG. 2 is an electron micrograph showing an internal state of the paper manufactured by Reference Example 2 (a paper obtained by adding a urea resin-based organic filler to the paper), that is, a particle structure of the urea resin attached to the cellulose fibers. FIG. 3 is an electron micrograph showing the internal state of the paper produced by Example 1 (a product obtained by adding a cationic vinyl acetate resin emulsion to paper), that is, the structure of emulsion particles fixed or fused to cellulose fibers. Is. FIG. 4 is a further enlarged photograph of a part of FIG.

 ─────────────────────────────────────────────────── --Continued from the front page (56) Reference JP-A-56-99214 (JP, A) JP-A-56-88401 (JP, A) JP-A-56-79102 (JP, A) JP-A-56- 47402 (JP, A) JP 59-217702 (JP, A) JP 59-71316 (JP, A)

Claims (3)

[Claims] 1. An opacity improvement for paper comprising a cationic polymer emulsion obtained by emulsion polymerization of vinyl acetate as a main component, in the presence of a cationic polyvinyl alcohol having an electric charge of 6 × 10 ⁻⁴ eq / g or more. Agent. 2. A cationic polymer emulsion obtained by emulsion polymerization of vinyl acetate in the presence of a cationic polyvinyl alcohol having an electric charge of 6 × 10 ⁻⁴ eq / g or more in the presence of white inorganic fine particles. An opacity improving agent for paper, which contains as a main component. 3. The opacity improver for paper according to claim 2, wherein the white inorganic fine particles are at least one selected from colloidal hydrous silica, clay, talc and titanium oxide.