JPH0359194A - Coated paper - Google Patents

Abstract

PURPOSE:To produce the title coated paper containing high yield pulp which is useful for newspaper or the like, because of its high light resistance such as ultraviolet ray fading, by coating base paper with a pigment of rutile titanium dioxide fulfilling specific conditions. CONSTITUTION:In the paper which is produced by coating a base paper comprising 10 to 100wt.% of high yield pulp with a coating composition mainly containing pigment and adhesive, the pigment is a rutile type of titanium dioxide fulfilling the conditions that the average particle size is d/D <=2 wherein d is an average particle size measured by the sedigraph X-ray permeation method for particle size distribution [d<=1.5mum; D is an average particle size measured by the electron microscopy in (mum)]. The content of the titanium is preferably 15 to 100%, based on the total pigment.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to coated paper containing high-yield pulp, and particularly to coated paper with excellent light resistance.

(Prior Art) In general, paper containing high-yield pulp containing lignin undergoes a yellowing-brown phenomenon due to absorption of light energy, resulting in a decrease in whiteness, which is a serious drawback in terms of storage stability.

Therefore, various methods have been proposed to improve the light resistance at the time of base paper manufacturing. For example, in the production of base paper containing high-yield pulp, aromatic amines and phenol derivatives are added as substances that inhibit the formation of phenoxy radicals in lignin to stop radical chain reactions, β- Although methods such as adding carotene to eliminate singlet oxygen and adding benzophenone derivatives as ultraviolet absorbers have been proposed, it is difficult to use high-yield bulb-containing base paper obtained by the above methods. With coated paper, the current situation is that no effect or only slight improvement in light resistance has been achieved, and the desired effect has not yet been achieved.

(Problems to be Solved by the Invention) In view of the above-mentioned current situation, the present inventors have solved the problem of low light fastness, which is a serious defect of coated paper containing high-yield pulp.
As a result of extensive research, we have found that when coated paper is coated with a coating composition that selectively uses rutile titanium dioxide with a specific particle size distribution as a pigment, The present invention was completed based on the discovery that the light resistance of coated paper was significantly improved.

(Means for Solving the Problems) The present invention is made by applying a coating composition containing a pigment and an adhesive as main components onto a base paper in which 10 to 100% by weight of the bulb composition is high-yield pulp. The coated paper is characterized in that it contains rutile titanium dioxide that satisfies the following conditions as the pigment.

≦ 2 d: Average particle diameter (μm) measured by Sedigraph XvA transmission particle size distribution measuring method, d≦1.5 μm・D: Average particle diameter (μm) measured by electron microscopy
.

(Function) The high yield pulp as used in the present invention includes, for example, stone ground pulp, pressurized stone ground pulp, refiner ground pulp, thermomechanical pulp, chemi-thermomechanical pulp, chemi-mechanical valve, bleached chemi-thermomechanical valve ( BCTMP), semi-chemical valves, etc., valves mainly produced by mechanical processing containing lignin produced by modified methods thereof, or deinking valves and regeneration valves containing these.

In general, high-yield pulps are widely used for newsprint, paperboard, medium-quality paper, medium-quality coated paper, tissues, paper towels, corrugated paper, and the like. In addition, recently there has been an increasing demand for thinner coated paper, and for this reason, coated paper based on base paper containing high-yield pulp has been increasingly commercialized as a way to improve opacity. There is. However, since high-yield pulp contains lignin, it has a drawback in that its light resistance (particularly, its resistance to fading under ultraviolet light) is very poor. For this purpose, using a conventionally known coating device on base paper containing high-yield pulp,
Coated paper obtained by coating with a coating composition has particularly poor storage stability and light resistance.

As mentioned above, in order to improve the low light resistance, which is a drawback of high-yield pulp, the present inventors have conducted extensive research and examination on the combination of the base paper and coating composition, and have found that the coating composition It has been discovered that when rutile titanium dioxide having a specific particle size distribution is selectively used as the pigment constituting the product, extremely excellent storage stability and light resistance (prevention of fading due to ultraviolet rays) can be obtained.

In general, coating pigments used for coated paper include inorganic pigments such as kaolin, calcium carbonate, aluminum hydroxide, zinc oxide, barium sulfate, talc, satin white, and titanium dioxide, and organic pigments such as plastic pigments. However, even when used alone or in combination, the light resistance when coated on high-yield pulp base paper was completely insufficient.

The present invention has an important feature in coating with rutile titanium dioxide having a specific particle size distribution,
Titanium dioxide has a higher hiding power than other pigments, so it is usually used as part of the pigment component of coating compositions with the main purpose of increasing opacity. It is used in an amount of about 0 to 20% by weight, although there is some variation depending on the type. Three types of crystal forms of titanium dioxide are known: anatase type, rutile type, and brutzite type, and the anatase type and rutile type are preferably used practically.

However, even if a coating layer containing anatase titanium dioxide is provided on a base paper containing high-yield pulp, almost no effect on light resistance is observed. However, it has become clear that when rutile titanium dioxide having a specific particle size distribution is used as a coating composition as in the present invention, the light resistance of paper containing high-yield pulp can be improved very effectively.

As mentioned above, the rutile-type titanium dioxide used in the present invention has an average particle diameter (d) measured by Sedigraph X-ray transmission particle size distribution measurement method and an average particle diameter measured by an electron microscope. It is a specific titanium dioxide in which the ratio of (D) is 2 or less.

The reason why the specific rutile-type titanium dioxide shown above exhibits an excellent effect on light resistance is not necessarily clear, but it shows a stronger and tighter crystal unit than other titanium dioxides, and the secondary particle size ( d) and -order particle diameter (D)
The ratio is 2 or less, more preferably 1. It is thought that this is because by using rutile titanium dioxide having a specific particle size distribution of 8 or less, ultraviolet rays are completely cut off by the coating layer and do not reach the base paper layer. However, with titanium dioxide outside the particle size distribution of the present invention, the desired light resistance effect could not be found even if the crystal form was rutile.

Note that when rutile titanium dioxide is blended in an amount of 15% by weight or more, especially 25ft1% or more based on the total pigment, the desired effect of improving light resistance is more markedly observed. Therefore, such an aspect is one of the preferred embodiments of the present invention. It is one. Coating pigments are usually slurried using various types of stirrers and prepared into a coating liquid. It is used in the form of aggregates. Therefore, the present inventors measured a titanium dioxide slurry obtained by processing with a general stirrer using a Sedigraph X-ray transmission particle size distribution measurement method, and found that - so-called secondary particles, in which many charcoal particles aggregated, The resulting aggregate is measured as if it were a primary particle and its average particle diameter is defined as (d), while the average particle diameter (D) measured by electron microscopy is regarded as a clear primary particle.
As a result of intensive research on the particle size distribution of titanium dioxide, we found that the average particle size measured by Sedigraph (hereinafter referred to as secondary particle size) is 1.5 μm or less, and the ratio to the primary particle size is 2 or less. Preferably 1. Selective use of rutile-type titanium dioxide of 8 or less reduces light fastness (particularly BCTMP), which is a serious defect in coated papers containing high-yield bulbs.
The present inventors have found that the problem of light resistance of coated paper can be solved extremely efficiently, and have completed the present invention. In addition,
If the secondary particle diameter, expressed as the average particle diameter, measured in an aqueous dispersion system is 1.5 μm or more, the desired effect on light resistance cannot be obtained, which is not preferable.

Furthermore, it has been found that it is even more effective to obtain the desired effects of the present invention when the above-mentioned specific titane dioxide satisfies the following formula.

The above formula is based on the particle size around 50% by weight (in the range of 30 to 70!1 fft% in the present invention), which indicates the average particle size measured by Zedigraph X-ray transmission particle size distribution measuring method. This is a formula to find the width of the distribution. Therefore, the calculation result of the above formula can be said to be an index indicating the uniformity of particles.

Incidentally, when the uniformity of the particles is O, it means that only a single particle with the same particle diameter is used, and the uniformity is excellent. On the other hand, when the uniformity of the particles is 1 or more, the particles become a collection of irregular particles. Therefore, if such titanium dioxide is used, there will be local differences in the hiding properties of the coating layer, and as a result, there is a possibility that the desired fading resistance improvement effect may not be obtained.

The adhesive that is the other main component of the coating composition of the present invention is not particularly limited, and includes, for example, styrene-butadiene,
Styrene/acrylic, vinyl acetate/acrylic, ethylene/
Various copolymers such as vinyl acetate, butadiene/methyl methacrylate, and vinyl acetate/butyl acrylate, and alkali-sensitive adhesives such as polyvinyl acetate, as well as polyvinyl alcohol, maleic anhydride/styrene copolymers, and isobutyne.・Synthetic adhesives such as maleic anhydride copolymers and acrylic acid/methacrylate copolymers, as well as oxidized starches, etherified starches, esterified starches, enzyme-modified starches, and cold water-soluble products obtained by flash-drying them. starch,
The adhesive is appropriately selected from natural adhesives such as casein and soybean protein.

Note that the blending ratio of the adhesive is generally adjusted within a range of about 5 to 25% by weight of the solid content based on 1 part of the pigment. In addition, various auxiliary agents such as a dispersant, thickener, water retention agent, antifoaming agent, waterproofing agent, lubricant, dye, and pH adjuster may also be blended as necessary.

In addition, when adjusting the coating composition, various mixers,
A mixing agitator such as a Ni-Goo or a ball mill is appropriately selected and used depending on the type of coating composition.

The coating composition of the present invention is coated in a single layer or in multiple layers on one or both sides of a base paper for coating.

In this case, the formulation of the coating composition applied to both sides and the coating composition constituting each layer in multilayer coating can be changed as appropriate according to conventional methods.

The coating method is not particularly limited, and examples include an air knife coater, a roll coater 1, a paddle and inverter type blade coater with beveled and bent blades, bill blades, twin coaters, etc. Various blade coaters such as blade and chambrax, short dwell coaters, etc.
Various known coating devices can be used as appropriate.

Further, the coating amount is in the range of about 10 to 30 g/bo after drying, and it is coated on one or both sides, and is generally finished using a finishing device such as a super calender or a gloss calender.

The present invention will be described in more detail with reference to Examples below, but it is of course not limited thereto.

Example 1 100 parts of rutile titanium dioxide having the particle size characteristics shown in Table 1 was dispersed in water using a Coles disperser with 0.3 parts of sodium polyacrylate to prepare a pigment slurry. As an adhesive to the pigment slurry, heat at 95°C in advance.
5 parts of oxidized starch (manufactured by Tamago Cornstarch Co., Ltd./Ace A) obtained by steaming for 30 minutes at a concentration of 128%, and 5 parts of styrene-butadiene copolymer latex (manufactured by Sumitomo Naugatac Co., Ltd./5 parts)
10 parts of N-307) were added, and furthermore, 0.1 part of a silicone antifoaming agent and 0.5 part of calcium stearate were added, and the mixture was stirred and mixed to obtain a coating liquid. The coating liquid obtained as described above was coated with a blade coater on a base paper of 74 g/m2 containing 80% by weight of high yield pulp (BCTMP) so that the dry weight was 20 g/nf per side. A coated paper containing high yield pulp (BCTMP) was obtained by coating both sides using a supercalender. The quality (light resistance test) results are listed in Table 1.

Examples 2 to 7 Rutile titanium dioxide and light calcium carbonate (trade name: Tama Pearl TPK) having particle size characteristics as shown in Table 1
/manufactured by Okutama Kogyo Co., Ltd.) and kaolin (product name: HT clay/
Coated paper containing high-yield pulp (BCTMP) was obtained in the same manner as in Example 1, except that BCTMP (manufactured by EMC Corporation) was blended in the proportions shown in Table-1, and the quality results are shown in Table-1.

Example 8 Rutile-type titanium dioxide, kaolin, and calcium carbonate were mixed in the proportions shown in Table 1, and high-yield pulp (BCT
A high yield pulp (BCTMP) was prepared in the same manner as in Example 1, except that a base paper containing 50% by weight of MP) was used.
The quality results are listed in Table 1 for the coated paper containing the above.

Example 9 Rutile-type titanium dioxide, kaolin, and calcium carbonate were used in the proportions shown in Table 1, and high-yield pulp (MP) was produced.
A high-yield pulp-containing coated paper was prepared in the same manner as in Example 1, except that a base paper containing 10% by weight of .

Example 10 Rutile titanium dioxide, kaolin, and calcium carbonate were used in the proportions shown in Table 1, and high yield pulp (MP) was produced.
A high-yield pulp-containing coated paper was prepared in the same manner as in Example 1, except that a base paper containing 50% by weight of the following was used, and the quality results are shown in Table 1.

Comparative Example 1 Coated paper containing high-yield pulp (BCTMP) was prepared in the same manner as in Example 1, except that the pigment formulation was 100 parts by weight of anatase titanium dioxide having particle size characteristics as shown in Table 1. The quality results are listed in Table-■.

Comparative Examples 2 to 3 A coated paper containing high-yield pulp (BCTMP) was prepared in the same manner as in Example 1, except that 100 parts by weight of rutile titanium dioxide having a particle size distribution as shown in Table 1 was used. The quality results are listed in Table-1.

Comparative Examples 4 to 6 Coated papers containing high yield pulp (BCTMP) were prepared in the same manner as in Example 1 except that the pigment formulations shown in Table 1 were used, and the quality results are shown in Table 1.

After irradiating ultraviolet rays for 4 hours using a weather meter (manufactured by Tokyo Rika Kogyo Co., Ltd., 2 lights), the whiteness before and after irradiation was measured using a Hunter whiteness meter to numerically evaluate the degree of decrease in whiteness. The light resistance was evaluated by the whiteness reduction rate (%) shown in the following formula. The lower the numerical value, the better the light resistance (ultraviolet fading resistance).

◎ O△ Very good Good Normal All had extremely superior light resistance (ultraviolet fading resistance) compared to pulp-containing coated paper.

Claims (3)

[Claims] (1) In a coated paper obtained by applying a coating composition containing a pigment and an adhesive as main components onto a base paper in which 10 to 100% by weight of the pulp composition is high-yield pulp, the pigment is used under the following conditions. A coated paper characterized by containing rutile-type titanium dioxide that satisfies the following. d/D≦2 d: Average particle diameter (μm) measured by Sedigraph X-ray transmission particle size distribution measuring method, d≦1.5 μm D: Average particle diameter (μm) measured by electron microscopy (2) 15 to 1 rutile titanium dioxide to all pigments
The coated paper according to claim 1, wherein the coated paper contains 00% by weight. (3) The coated paper according to claim (1) or (2), wherein the rutile titanium dioxide satisfies the following conditions. 0≦[Log(d_1/d_2)]/0.4≦1d_1
: Particle diameter (μm) when the cumulative weight measured by Sedigraph X-ray transmission particle size distribution measurement method reaches 70% d_2: The cumulative weight measured by Sedigraph X-ray transmission particle size distribution measurement method reaches 30% particle size (μm
)