JPS63235597A - Opacity enhancer for paper - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an opacity improver for paper that can improve opacity without reducing paper strength, and more particularly relates to a paper opacity improver that can improve opacity without reducing paper strength, and more particularly, This invention relates to an opacity improver for paper whose main component is an emulsion.

BACKGROUND OF THE INVENTION In recent years, efforts have been made to reduce the weight of printing paper due to the shortage of wood resources and to reduce transportation costs. In particular, for newsprint, Tsubo J.
Lightweight paper such as i4 Bg/G has become mainstream, and the development of even lighter paper is being considered and has already begun to be supplied in some areas. However, as paper becomes lighter, it is inevitable that the paper stock and thickness will decrease, resulting in a decrease in paper strength and print-through (a phenomenon in which one printed surface shows through the other). This has become a problem.

Under these circumstances, paper manufacturers have adopted various measures to solve one of the technical problems faced by lightweight paper, which is cross-cutting during printing.

Currently, as one of the countermeasures against this problem, inorganic fillers such as calcium carbonate, clay, talc, colloidal hydrated silica (commonly known as white carbon), titanium oxide, and organic fillers such as urea resin are used as internal additives.

The use of these fillers improves whiteness, opacity, smoothness, printability, etc., and the effect of improving opacity after printing is also observed.

However, when these fillers are used as fillers during paper making, they tend to inhibit the bonding between cellulose fibers and reduce the strength of the paper. In order to aim for further weight reduction in the future, it is necessary to increase the blending ratio of filler, but the strength of one paper will be greatly reduced due to the dual effects of decreasing basis weight and increasing the blending of filler. This is a major hindrance to promoting weight reduction.

Problems to be Solved by the Invention Under the above-mentioned problematic situation, the present inventors have developed a filler or modifier that reduces the weight of paper and improves its opacity, while also not reducing paper strength. As a result of intensive studies to obtain cationic polyvinyl alcohol (rC-
It is abbreviated as PVAJ. ), and an inorganic-organic composite emulsion obtained by coexisting white inorganic fine particles during the emulsion polymerization. It was discovered that opacity can be improved without reducing paper strength, and the present invention was completed based on this knowledge.

Means for solving the problems, that is, the gist of the present invention is as follows: (1) The main component is a cationic polymer emulsion obtained by emulsion polymerization of ethylenically unsaturated monomers in the presence of C-PVA. An opacity improver for paper.

(2) A paper product whose main component is a cationic polymer emulsion obtained by coexisting white inorganic fine particles during emulsion polymerization of an ethylenically unsaturated monomer in the presence of C-PVA. Transparency improver.

Hereinafter, the constituent elements of the present invention will be explained in detail.

(Cationic polyvinyl alcohol) The C-PVA used in the present invention is PVA modified with cationic groups, and various methods such as post-modification of the polymer and copolymerization with a monomer that accommodates cationic groups can be used. For example, JP-A-56-47402
The publication discloses c-PVA having the structure of the following formula (1), and JP-A-59-135202 discloses C-PVA having the structure of the following formula (n). Some are commercially available. These C-PVA
Any of these can be used in the present invention.

υi The C-PVA used in the present invention has a cationic charge of 5
X 10-'eq/g or more is preferable; if it is less than this, the effect of fixing the produced emulsion to the pulp will be poor.

There is no particular restriction on the degree of polymerization of C-PVA, but 20
A range of 0 to 3500 is suitable.

There is no particular restriction on the degree of saponification, but a higher degree of saponification is preferable in terms of increasing the number of hydrogen bonds in a single 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 from 10 to 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 it is difficult to remain as resin particles in the pulp.

(Emulsion polymerization) Emulsion polymerization is initiated by using an oxidation catalyst such as hydrogen peroxide or potassium persulfate, or a cationic catalyst such as 2,2'-7zobis-(2-amidinopropane) di#1# salt, either alone or in combination.
Furthermore, it is carried out in a conventional manner using a redox reaction system in combination with various reducing agents.

(Ethylenically unsaturated monomer) Ethylenically unsaturated monomers used in emulsion polymerization include vinyl esters such as vinyl acetate and vinyl propionate,
Examples include acrylic esters such as methyl acrylate and ethyl acrylate, methacrylic esters such as methyl methacrylate and ethyl methacrylate, acrylic acid, vinyl chloride, acrylonitrile, and various ethylenically unsaturated monomers such as styrene. They can be used alone or in combination. Among these ethylenically unsaturated monomers, vinyl acetate and acrylic ester are particularly preferred.

(White inorganic fine particles) Examples of white inorganic fine particles include colloidal silica, talc, clay, titanium oxide, barium sulfate, etc.
Colloidal silica, i.e. white carbon, is particularly preferred.The blending ratio of white inorganic fine particles is preferably 1 to 50% by weight based on the solid content of the emulsion.If it is less than 1% by weight, the effect of blending white inorganic fine particles will be poor.
If it exceeds 50% by weight, the stability of the produced emulsion will be compromised and the strength of the paper will decrease, which is not preferable.

(Cationic polymer emulsion) The average particle size of the emulsion particles produced by emulsion polymerization is 0.11-11L, preferably 0.2-0.6JLm, which has a high light scattering effect and is advantageous for improving paper strength. Good range.

The amount of cationic polymer emulsion added to paper varies depending on the properties of the emulsion such as the type of pulp and cationic group content, but the emulsion solid content is 0.1 to 10% of the solid content of the bone-dry raw pulp. It is preferably in the range of 0.1 to 5% by weight. If it is less than 0.1% by weight, the above-mentioned effect will be poor, and if it exceeds 10% by weight, the emulsion added to the paper will melt into a film. opacity may be impaired. Organic s41 with white inorganic fine particles! When preparing a composite emulsion, the amount added is 0.1 to 50% by weight, preferably 0.1% by weight of the emulsion solid content based on the solid content of the raw material pulp.
A content in the range of ~30% by weight is preferable; if it is less than 0.1% by weight, the above-mentioned effects will be poor, and if it exceeds 50% by weight, paper-making properties will deteriorate.

(Pulp) Regarding the pulp used in the present invention, KP, GP,
It is mainly made of wood pulp such as DXP and vegetable fibers, and can be used alone or in combination.

action Among the effects exhibited by the emulsion of the present invention.

Regarding paper strength, films obtained from resin emulsions, especially emulsions whose main component is vinyl acetate resin, are generally highly flexible, and when fused to the fibers in the pulp, the bonds between the fibers are strengthened, resulting in improved strength. I can predict what will happen.

However, it is a well-known fact that when a vinyl acetate resin emulsion or an acrylic ester emulsion is dried, the emulsion particles fuse together to form a transparent film.

From this point of view, the cationic polymer emulsion, which is a vinyl acetate resin emulsion, was thought to lack am@ which improves the opacity of paper, but rather to increase transparency. However, as a result of research, it was found that the above emulsion has an effect of improving opacity (particularly white paper opacity) much more than originally expected.

The theoretical basis for the effect of the cationic polymer emulsion of the present invention on improving the opacity of paper is not fully clear, but when comparing the electron micrographs shown in Figures 1 to 4, it is clear that white carbon alone was used (Figure 1 ) or urea resin filler (Figure 2), when the cationic emulsion of the present invention is used (Figures 3 and 4), the amount added is about 10 parts m within a certain range. It is presumed that the emulsion particles are fixed in the fiber as individual lumps and contribute to light scattering.

Furthermore, from these figures, it is recognized that the emulsion used in the present invention is different from other inorganic/organic fillers in that part of the surface of the aggregated particles is fused to the cellulose fibers.
This is thought to be a factor in improving the paper strength.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples. Note that % and parts are based on weight.

Examples 1 to 6 and Comparative Examples 1 to 3 (a) Preparation of emulsion Polyvinyl alcohol having a cationic group (degree of saponification 98.5%, cationic charge 8X10-'sq/g) has the structure ltl of the following formula. C-PVA (manufactured by Denki Kagaku Kogyo Co., Ltd., hereinafter referred to as
It is abbreviated as rC-pvAJ. ), 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 wJ with a 4% tartaric acid aqueous solution. This solution was heated to 70°C, and an aqueous solution of 0.2 part of 2.2°-azobis-(2-amidinopropane) dihydrochloride dissolved in 10 parts of ion-exchanged water and 35% H2O26 in 80 parts of ion-exchanged water were added. Immediately after addition of the respective polymerization initiators in an aqueous solution of 1.5 parts dissolved therein, the dropwise addition of 400 parts of vinyl acetate monomer (VA c) is started.

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

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

Emulsions B and C were prepared in the same manner except for changing the blending ratio of C-PVA and VAc.

After adding 100 parts of white carbon powder to 530 parts of ion-exchanged water and stirring and dispersing at room temperature, C-PVA 100
1 part and heat and dissolve at 80°C.

This aqueous solution was cooled to room temperature and adjusted to pH with 4% tartaric acid aqueous solution.
After adjusting the temperature to 4.0, the temperature was raised to 70°C and an aqueous solution of 0.2 part of 2,2'-azobis-(2-amidinopropane) dihydrochloride dissolved in 10 parts of ion-exchanged water and 80% of ion-exchanged water were prepared. After simultaneously adding each polymerization initiator in an aqueous solution containing 26 parts of 35% H2O in
Begin dropwise addition of 370 parts. The amount added was adjusted so that the monomer dropwise addition was completed in 3 hours, and the liquid temperature was raised to 80° C. to carry out emulsion polymerization for 3 hours. Thereafter, the temperature was raised to 90° C. to perform an aging reaction for 30 minutes, and then 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.

Emulsion E was prepared in the same manner except that talc was used instead of white carbon.

Next, 524 parts of ion-exchanged water was added to 123 parts of C-PVA and dissolved by heating at 80°C, cooled to room temperature, mixed with 2 parts of acrylic #, and then adjusted to pH 4 with 4% tartaric acid aqueous solution.
Adjusted to 0. The temperature of this solution was raised to 70°C, and the total amount of an aqueous solution prepared by dissolving 0.2 part of 2°2°-azobis-(2-amidinopropane) dihydrochloride in 10 parts of ion-exchanged water was mixed with 100 parts of ion-exchanged water. After simultaneously adding half of the aqueous solution containing 3.4 parts of potassium persulfate, VAcJ
Initial emulsion polymerization is carried out by adding 6 parts at once.

The polymerization temperature was set at 70 to 80°C, and the reaction was continued until no reflux of V and Ac was observed.
Raise the temperature to ℃. Add the remaining half of the potassium persulfate aqueous solution and 182 parts of VAc dropwise to this. Adjust so that the addition of both solutions is completed in 2 hours, and carry out emulsion polymerization.
After raising the temperature to .degree. C. and carrying out an aging reaction for 30 minutes, the reaction apparatus was cooled to room temperature while being left open to obtain a cationic vinyl acetate resin emulsion. The solid content was 37.5%, and the viscosity at 20°C was 4300 CPS. This emulsion is referred to as emulsion F.

Details of the emulsion produced above are shown in Table 1.

(Left below) (B) Papermaking test pulp (compounded pulp: 130mfLC3F) (7) 0
．． While stirring the 8% slurry dispersion liquid well, the above A-
After adding the emulsion of F to the pulp at a solid content ratio of 2%, the mixture was stirred for 2 minutes and the pH of the slurry dispersion was adjusted to 5.5 using a sulfuric acid band.

After that, it was stirred for 2 minutes, and the solid content of the slurry dispersion was reduced to 0.4% with water. The paper was made to look like this.

Next, the wet paper was compressed and dehydrated for 5 minutes at 3.5Kg/crtf.
After replacing the absorbent paper and compressing and dehydrating for 2 minutes at the same pressure, the paper was dried in contact with a rotary dryer (surface temperature approximately 110°C) for 3 minutes.The obtained paper was dried under the conditions of 20°C and 65% RH. The humidity was controlled for 24 hours or more, and the paper was subjected to various paper strength and physical property tests.

The results are shown in Examples 1 to 6 in Table 2.

For reference, the results of similar tests using emulsion-free products, cationic PVA alone, white carbon, and urea resin organic fillers are shown in Table 2 for Comparative Examples 1 to 2.
2 and Reference Examples 1 and 2.

The paper using the emulsion of the present invention has a long tearing length (the length that the suspended paper breaks under its own weight), excellent paper strength, and opacity as well, such as additive-free and cationic. Some products show higher values than those using PVA and urea resin fillers, and are comparable to or even higher than those using white carbon alone.In the first place, as mentioned above, vinyl acetate resin emulsions reduce the opacity of paper. The cationic polymer emulsions of this invention are found to be excellent paper opacifying agents, given that their increased properties were unexpected.

In addition, considering that in this industry it takes a lot of effort to increase the opacity by only 1 to 2%, for example, it is possible to increase the opacity by 3 to 4% compared to a product without additives. It should be said that not reducing the strength of the paper is a major effect.

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

In particular, even when the emulsion of the present invention, which belongs to vinyl acetate resin emulsions, was added alone, the opacity of white paper was improved, which was more effective than initially expected. In the future, this opens the possibility of utilizing this performance to produce lightweight paper.

[Brief explanation of drawings]

FIG. 1 is an electron micrograph showing the inside of the paper produced in Reference Example 1 (in which white carbon was added alone to the paper). FIG. 2 is an electron micrograph showing the inside of the paper produced in Reference Example 2 (a paper in which a urea resin organic filler was added). FIG. 3 is an electron micrograph showing the inside of the paper produced in Example 1 (a paper in which a cationic vinyl acetate resin emulsion was added). FIG. 4 is a further enlarged photograph of a part of FIG. 3.

Claims (1)

[Scope of Claims] (1) An opacity improver for paper whose main component is a cationic polymer emulsion obtained by emulsion polymerization of an ethylenically unsaturated monomer in the presence of cationic polyvinyl alcohol. (2) Claim No. 1 in which the ethylenically unsaturated monomer is vinyl acetate and/or acrylic ester
Opacity improver for paper as described in . (3) Opacity for paper whose main component is a cationic polymer emulsion obtained by polymerizing an ethylenically unsaturated monomer in the presence of cationized polyvinyl alcohol in the coexistence of white inorganic fine particles. improver. (4) Claim No. 3 in which the ethylenically unsaturated monomer is vinyl acetate and/or acrylic ester
Opacity improver for paper as described in . (5) The opacity improver for paper according to claim (3), wherein the white inorganic fine particles are at least one selected from colloidal hydrated silica, clay, talc, and titanium oxide.