JP5817651B2 - High opacity paper - Google Patents

Description

The present invention relates to a high opacity paper that achieves high opacity without providing a difference in whiteness between the front and back surfaces while providing a low basis weight without providing a pigment coating layer.

In recent years, paper weight reduction has been desired due to social demands such as resource saving, logistics cost reduction, and paper waste reduction. However, the light weight of paper has a great negative effect on the paper quality. In particular, the printed paper has a problem of seeing through printed characters. In addition, due to increased consideration for privacy and prevention of information leakage, improvements in opacity on envelopes and secret labels that are difficult to see the contents are required.

As a means for achieving high opacity at a low basis weight, use of mechanical pulp is conceivable, but there is a limit in whiteness and there is a problem of fading, which is not suitable for printing paper.
In addition, white carbon, light calcium carbonate, and inorganic pigments called talc may be added more than usual, but not only the strength of the paper is reduced, but it cannot be sufficiently fixed in the paper layer and is released. This can easily cause problems in the printing and processing stages.
In addition, as a method of increasing the opacity and whiteness, a method of applying a pigment having a high whiteness or opacity together with an adhesive to the surface of the base paper can be considered, but a certain amount of coating is required, and the basis weight is reduced. In order to suppress this, the basis weight of the base paper has to be lowered, the paper strength is insufficient, and there is a possibility of running out of paper during printing.

A printing paper containing a purple pigment and / or a blue pigment and having an opacity of 85% or more and having a basis weight of 70 g / m ² or more is disclosed, but this cannot be achieved without providing two coating layers, The opacity is not so high. (Patent Document 1)
In addition, offset printing paper that has achieved transparency and whiteness by blending black dye and titanium dioxide in the coating layer and using specific mechanical pulp in the base paper has been disclosed. The amount of use increases, and it is necessary to process mechanical pulp, which increases costs. (See Patent Document 2)
Although a method of applying a fluorescent whitening agent together with a water-soluble adhesive to the surface of the base paper and keeping it on the surface is disclosed, the paper thickness that can be handled is limited, and there are limits to improving opacity and whiteness Yes (Patent Document 3)
At present, no pigment coating layer has been achieved that achieves high opacity and whiteness at a relatively low basis weight while maintaining printability and processability.

JP 2011-26756 A WO2009 / 123237 JP 2002-69896 A

In order to solve the above problems, the present invention is to provide a paper that achieves high opacity and whiteness without providing a pigment coating layer, and has printability and processability.

As a result of intensive research on whiteness, opacity, printability, and processability, the present inventors have suppressed the blending amount of titanium dioxide, maintained paper strength, and made the black colorant have no difference between the front and back. The present invention is completed by making it exist uniformly.
The present invention includes the following inventions.

(1) Without having a pigment coating layer, the base paper contains titanium dioxide in the range of 5% by mass to 20% by mass, the black and white colorant is uniformly contained on the front and back, and the whiteness measured according to JISP8148 is High opacity paper having 75% or more and an opacity measured according to JISP8149 of 98% or more and a basis weight of 70 to 120 g / m ² .

(2) The high opacity paper according to (1), wherein the base paper contains a fluorescent brightening agent in a range of 500 to 8000 ppm.

(3) The titanium dioxide, the black colorant, and the fluorescent brightening agent are contained in a range of 500 to 250 ppm black coloring agent and 8000 to 500 ppm fluorescent whitening agent with respect to 5% to 20% by mass of titanium dioxide. The high opacity paper according to (1) or (2).

(4) High opacity paper in which the high opacity paper according to (1) to (3) is an envelope paper having a difference in whiteness between the front and back sides of less than 1%.

(5) High opacity paper in which the use of the high opacity paper described in (4) is envelope paper.

The present invention can be used not only for printing paper but also for products that require opacity, whiteness, printability, and processing suitability such as envelope paper and secret label, and the manufacturing method does not require complicated steps. Therefore, both workability and economy are excellent.

In the present invention, it is important that titanium dioxide is contained in the base paper in the range of 5% by mass to 20% by mass, and the black colorant is uniformly contained on the front and back sides. There are other pigments that are said to be effective in improving opacity, but other pigments are not preferable because the amount of black colorant added increases, resulting in a decrease in whiteness.

When the content of titanium dioxide is less than 5% by mass, the effect of improving opacity is small, the amount of black colorant increases, and the whiteness decreases. If added in excess of 20% by mass, both the opacity and the whiteness are improved, but the paper strength is reduced, the printability is affected, and this is disadvantageous economically, which is not preferable. It becomes possible to enhance the opacity effect by containing the black colorant uniformly on both sides.

Titanium dioxide is excellent in improving opacity and whiteness, and the titanium dioxide used in the present invention is not particularly limited, and the crystal system may be anatase type or rutile type. As the surface treatment of titanium dioxide, various treatments such as inorganic treatment and organic treatment such as silicic acid treatment, alumina treatment, and aluminum phosphate treatment are performed, but there is no particular limitation. In addition, there is no problem even with a type having excellent weather resistance doped with antimony or the like. The production method of titanium dioxide includes a sulfuric acid method and a chlorine method, but is not particularly limited, and the particle size is not particularly limited, but it is preferable to use a particle size of 0.1 μm to 5.0 μm. The structure of titanium oxide includes anatase and rutile types, but the anatase type has a lighter specific gravity of 3.9 (rutile 4.2) than the rutile type, so it tends not to fall off on the wire and tends to improve yield. .

The black colorant is not particularly limited to dyes and pigments. The dyes are direct dyes, acid dyes, basic dyes, azo direct dyes, and the pigments are organic pigments and inorganic pigments. There is no limitation, and there is no problem even if one or more kinds are used. For example, carbon black, aniline black, graphite, iron black and the like can be used, but carbon black is preferable because it is excellent in water resistance and light resistance.

The black colorant is effective for increasing the opacity, but reduces the whiteness, so when the black colorant is contained in the range of 250 to 500 ppm with respect to 5 to 20% by mass of titanium dioxide, It is preferable because the balance between opacity and whiteness can be easily obtained. If the black colorant is less than 250 ppm, a large amount of titanium dioxide must be blended. If the black colorant exceeds 500 ppm, a large amount of fluorescent whitening agent must be added, resulting in reduced paper strength and high cost. May be incurred.

In the present invention, it is preferable to contain a fluorescent brightening agent.
There is no limitation on the fluorescent whitening agent to be used, but fluorescent whitening agents such as stilbene, coumarin, pyrazoline, naphthalimide, bisbenzoxazolyl, bisstilbiphenyl can be used. A stilbene fluorescent whitening agent is preferred because of its high affinity with a surface treatment agent such as starch. When using a fluorescent brightening agent together with modified starch, it is preferable to add it to gelatinized starch, and when added to starch that has not been gelatinized, starch staining is poor and it is not preferable because a crosslinking agent or the like is required. .

Addition of a fluorescent brightening agent improves whiteness. When obtaining a whiteness of 75% or more, it is preferable to contain a fluorescent whitening agent in the base paper in the range of 500 to 8000 ppm. When a small amount of titanium dioxide is used, in order to obtain a desired opacity, a large amount of a black colorant must be blended. Therefore, a large amount of a fluorescent whitening agent must be blended. However, if the optical brightener exceeds 8000 ppm, the whitening effect may be reduced and the cost may increase. When the optical brightener is less than 500 ppm, it is necessary to make the black colorant a small amount. In that case, a large amount of titanium dioxide must be blended, which may reduce paper strength and cost. .

The fluorescent brightening agent may be added in the above range, either internally or externally. However, it is preferable that the fluorescent brightener is both externally added and internally added. With only external additions, the color of the end face when paper is stacked after cutting may be uneven, and from the viewpoint of yield, internal additions are more lossy than external additions and have a heavy load on drainage. Therefore, it is preferable to add externally or internally to add a fluorescent brightening agent to the paper.
In the case of external addition, it is preferably applied together with a surface sizing agent that improves printability.

Chemical pulp can be used as a pulp raw material used for the base paper used in the present invention. In addition to chemical pulp, various pulps can be used depending on the application, for example, deinked pulp (DIP), groundwood pulp (GP), refiner groundwood pulp (RGP), thermomechanical pulp (TMP), chemithermo Examples include mechanical pulp (CTMP), chemi-ground pulp (CGP), and semi-chemical pulp (SCP). As the deinked pulp, it is possible to use deinked pulp made from selected waste paper such as high quality paper, medium quality paper, lower grade paper, newspaper, flyers, magazines, etc., or unselected waste paper mixed with these. Moreover, when using deinked pulp in this invention, it is preferable to mix | blend the high whiteness pulp selected centering on quality paper.

There are chemical pulps manufactured by the kraft pulp method and those manufactured by the sulfite pulp method, and both of them can be used in the present invention. In the specification, it may be simply referred to as kraft pulp) from the viewpoint of production cost. In general, chemical pulp removes lignin, which is a wood-derived component, in the production process, so the whiteness of the pulp is high, but on the other hand, the opacity of the produced paper tends to be low. However, according to the present invention, opacity can be improved even when chemical pulp is used.

In a preferred embodiment of the present invention, the content of chemical pulp in the raw material pulp is 60% by weight or more in the total pulp, more preferably 80% by weight or more, further preferably 90% by weight or more, and most preferably 100% by weight. . When the content of the chemical pulp is 100% by weight, lignin is not contained and the component for coloring the printing paper is the smallest. In addition, since it does not contain lignin, the absorption of ultraviolet rays can be suppressed so that the efficacy of the fluorescent dye is not inhibited, and the whiteness of the printing paper can be increased. The lower the chemical pulp content, the more disadvantageous in terms of whiteness. The freeness of the pulp to be used is not particularly limited, but considering the balance between opacity and paper strength, it is preferable to use one having a range of 200 to 550 ml CSF.

In the present invention, known papermaking additives can be used. For example, sulfuric acid bands and various anionic, cationic, nonionic or amphoteric yield improvers, drainage improvers, various paper strength enhancers and internal additive sizing agents, etc. Can be used. Examples of the dry paper strength improver include polyacrylamide and cationized starch, and examples of the wet paper strength improver include polyamidoamine epichlorohydrin. These chemicals are added within a range that does not affect the formation and operability. Examples of neutral sizing agents include alkyl ketene dimers, alkenyl succinic anhydrides, and neutral rosin sizing agents. Furthermore, dyes, fluorescent brighteners, pH adjusters, antifoaming agents, pitch control agents, slime control agents and the like can be added as necessary.

The paper making method of the base paper in the present invention is not particularly limited, and a long paper machine including a top wire, an on-top former, a gap former, a round paper machine, a paperboard paper using a long paper machine and a round paper machine in combination. Machine, Yankee dryer machine, etc. The pH during papermaking may be acidic, neutral, or alkaline. The paper making speed is not particularly limited.

In this invention, you may have a coating layer which does not contain a pigment in the one side or both surfaces of the base paper mentioned above. By applying the coating on the base paper, the surface strength and smoothness of the base paper can be improved. In the present invention, in addition to the optical brightener, conventionally used starches such as micronized starch and oxidized starch, styrene butadiene copolymer resin, acrylic resin, in the coating layer containing no pigment, Binders such as vinyl acetate resin, urethane resin, polyvinyl alcohol, surface sizing agent, cationic resin, anionic resin, nonionic resin, surfactant, pH regulator, viscosity modifier, softener, gloss imparting agent, waxes , Dispersants, flow modifiers, stabilizers, antistatic agents, crosslinking agents, sizing agents, fluorescent brighteners, colorants, UV absorbers, antifoaming agents, water resistance agents, water-soluble metal salts, plasticizers, Various auxiliary agents such as lubricants, preservatives and fragrances can be suitably contained in one kind or two or more kinds.

In the present invention, the coating layer containing no pigment is, for example, an air knife coater, a blade coater, a rod coater, a gate roll coater, a rod metalizing size press, a blade metalling size press, a pre-metalling size press, a curtain coater, or a spray coater. Using a coater (coating machine) such as a two-roll pound type (two-roll type) size press coater, various starches such as modified starch, micronized starch, oxidized starch, styrene-butadiene copolymer resin, A coating solution (surface treatment solution) mainly composed of a water-soluble polymer such as an acrylic resin, a vinyl acetate resin or a urethane resin, or a water-soluble polymer such as polyacrylamide or polyvinyl alcohol. .

In the present invention, the paper produced as described above is surface-treated as necessary. In a preferred embodiment, the printing paper of the present invention can be surface-treated with a calendar such as a machine calendar, a super calendar, or a high temperature soft nip calendar.

The opacity of the high opacity paper of the present invention is 98% or more, and the whiteness is 75% or more. The whiteness can be adjusted by improving the whiteness of the pulp or adding the fluorescent dye.
The basis weight is 70 to 120 g / m ² , and the whiteness difference between the front and back is preferably 1% or less. High opacity paper by coloring the back side is on the market, but when printing on one side, it may be printed on the colored side by mistake, resulting in a great deal of damage. However, it is preferable that the difference in whiteness between the front and back sides is as small as less than 1% because the same finish can be obtained regardless of whether the front or back side is printed.

The type of paper applicable to the present invention is not particularly limited as long as opacity is required. It can also be used for recording paper such as printing paper, ink jet paper, electrophotographic paper, etc., especially envelope paper where the concealment of the contents is important, in particular, conventionally the back side was printed to provide concealment Suitable for confidential envelopes. It can also be used as a paper for a secret label.

  The present invention will be specifically described by the following examples, but of course, they are not intended to limit the scope of the present invention. In the examples, “parts” and “%” represent “parts by mass (solid component)” and “mass%” unless otherwise specified.

Example 1
[Preparation of paper]
100 parts of hardwood bleached kraft pulp (420 ml CSF), 0.05 part of sizing agent (trade name: Fibran 81, manufactured by Arakawa Chemical Industries), 0.8 part of cationic starch (trade name: Kate F, manufactured by Oji National Corporation) , 1.0 part of aluminum sulfate, 0.02 part of yield agent (trade name: Keith Rock RP401L, manufactured by Kyowa Sangyo Co., Ltd.), 350 ppm of black colorant (trade name: Kayafect Black S, manufactured by Nippon Kayaku Co., Ltd.), fluorescence enhancement Whitening agent (trade name: Kaya Hall TAC, manufactured by Nippon Kayaku Co., Ltd.) 4000 ppm is added, and titanium dioxide (trade name: R-780, particle size 0.24 μm, manufactured by Ishihara Sangyo Co., Ltd.) is blended so that the ash content is 15%. Water was added to the product and mixed well to prepare a stock with a slurry concentration of 0.05%, and this was used to make a two-roll type size press using a multi-roll paper machine. In addition, starch (trade name: Ace A, manufactured by Oji Cornstarch Co., Ltd.) having a solid content concentration of 6% and fluorescent whitening agent (trade name: Kayahol EX-N, manufactured by Nippon Kayaku Co., Ltd.) 2000 ppm on both sides of the base paper 2.8 g / m ^{2 was} applied and dried to prepare a paper having a basis weight of 80 g / m ² .

Example 2
A paper was prepared in the same manner except that the titanium dioxide of Example 1 was 5%, the black colorant was 450 ppm, and the fluorescent brightener in the paper was 6000 ppm.

Example 3
A paper was prepared in the same manner except that the titanium dioxide in Example 1 was 20% and the black colorant was 300 ppm.

Example 4
A paper was prepared in the same manner except that 20% of the titanium dioxide in Example 1, 300 ppm of the black colorant, 500 ppm of the fluorescent whitening agent in the paper, and 0 ppm of the fluorescent whitening agent applied by the size press apparatus. did.

Example 5
Except for 20% of titanium dioxide of Example 1, 250 ppm of black colorant, 500 ppm of fluorescent whitening agent in the paper, 0 ppm of fluorescent whitening agent applied with a size press device, and basis weight of 120 g / m ^2. Made a paper in the same manner.

Example 6
A paper was prepared in the same manner except that the titanium dioxide of Example 1 was 5%, the black colorant was 400 ppm, the fluorescent whitening agent in the stock was 6000 ppm, and the basis weight was 120 g / m ² .

Example 7
A paper was prepared in the same manner except that the titanium dioxide of Example 1 was 5%, the black colorant was 500 ppm, the fluorescent whitening agent in the paper was 6000 ppm, and the basis weight was 72 g / m ² .

Example 8
A paper was prepared in the same manner except that the black colorant of Example 1 was 600 ppm and the fluorescent whitening agent in the paper was 6000 ppm.

Example 9
A paper was prepared in the same manner except that the black colorant of Example 1 was 200 ppm and the fluorescent whitening agent in the paper was 6000 ppm.

Example 10
The same procedure was followed except that the black colorant of Example 1 was 200 ppm, the fluorescent brightener in the stock was 6000 ppm, and calcium carbonate (trade name: TP-121, manufactured by Okutama Kogyo Co., Ltd.) was used as an ash content of 3%. A paper was prepared.

Example 11 (Reference Example)
A paper was prepared in the same manner except that the fluorescent whitening agent in the stock of Example 1 was 0 ppm and the fluorescent whitening agent applied with a size press was 0 ppm.

Example 12
A paper was prepared in the same manner except that the fluorescent whitening agent in the stock of Example 1 was changed to 8000 ppm.

Comparative Example 1
A paper was prepared in the same manner except that the titanium dioxide of Example 1 was 3%, the black colorant was 800 ppm, and the fluorescent whitening agent in the paper was 8000 ppm.

Comparative Example 2
A paper was prepared in the same manner except that the titanium dioxide of Example 1 was 3%, the black colorant was 500 ppm, the fluorescent brightener in the stock was 8000 ppm, and the basis weight was 120 g / m ² .

Comparative Example 3
A paper was prepared in the same manner except that the titanium dioxide of Example 1 was 25%, the black colorant was 250 ppm, and the fluorescent whitening agent in the paper was 3000 ppm. However, due to the high content of titanium dioxide, the cost was high.

Comparative Example 4
A paper was prepared in the same manner except that the titanium dioxide of Example 1 was 20%, the black colorant was 500 ppm, the fluorescent whitening agent in the stock was 6000 ppm, and the basis weight was 65 g / m ² .

Comparative Example 5
Commercially available confidential envelope paper was evaluated.

The obtained paper was evaluated by the following method. The obtained results are shown in Table 1.
(Evaluation)
[Whiteness and opacity]
The whiteness was measured according to JISP8148, and the opacity was measured according to JISP8149 using a spectral whiteness colorimeter (manufactured by Suga Test Instruments Co., Ltd., model SC-10WN type).

[High concealment envelope paper suitability]
Envelopes were produced using the obtained paper, paper with printed lines was enclosed, and visibility from the outside of the envelopes was evaluated. Visibility evaluation was evaluated by 5 people, “◯” when all were not visible, “Δ” when 3 were not visible, and “×” when all were visible.
For image printing, black printing was performed with an inkjet printer Epson EP-302.

表１から明らかなように、本発明で得られる用紙は、白色度が高く、かつ白色度の表裏差が極めて少ない、非常に不透明度の高い安価な用紙である。

As is apparent from Table 1, the paper obtained by the present invention is an inexpensive paper having a high whiteness and a very low whiteness and a very high opacity.

  Since the present invention is white, has almost no difference between the front and back, and has high opacity, the printed image line portion is difficult to see through the back, and when used for envelope paper, the contents are difficult to see through. It is extremely useful as a high-priced paper.

Claims (5)

Without having a pigment coating layer, the base paper contains titanium oxide in the range of 5% by mass to 20% by mass, the black and white colorant is uniformly contained on the front and back, and the base paper contains a fluorescent whitening agent of 500 to 8000 ppm. contained in a range of, in whiteness was measured in accordance with JIS P 8148 of 75% or more and opacity was measured according to JIS P 8149 is 98%, a basis weight of at ^70g / ^{m 2 ~120g} / m 2 High opacity paper characterized by being. 2. The high opacity paper according to claim 1, wherein the fluorescent whitening agent is internally added, and further the fluorescent whitening agent is externally added.   The titanium oxide, the black colorant, and the fluorescent brightening agent are contained in a range of 500 to 250 ppm black coloring agent and 8000 to 500 ppm fluorescent whitening agent with respect to 5% by mass to 20% by mass of titanium oxide. The high opacity paper according to claim 1 or 2. The high opacity paper according to any one of claims 1 to 3, wherein the difference in whiteness between the front and back is less than 1%.   The highly opaque paper according to claim 4, wherein the highly opaque paper is an envelope paper.