JPS618131A - Production of composite powder - Google Patents

Abstract

PURPOSE:To obtain a composite powder extremely excellent in the strike- through inhibiting effect of ink when used as a filler of paper, by pulverizing a mixture consisting of hydrated silicic acid and a powder with an isoelectric point of 7 or more so as to adjust the bulk specific density thereof to 0.18g/cc or less. CONSTITUTION:A mixture, which consists of a powder with an isoelectric point of 7 or more such as calcium carbonate, magnesium carbonate, alumina, aluminum hydroxide, zinc oxide or magnesium oxide and hydrated silicic acid, is pulverized so as to adjust the bulk specific density to 0.18g/cc or less to obtain a composite powder. The mixing ratio of hydrated silicic acid and the powder with an isoelectric point of 7 or more is desirably set to 4-47, pref., 5-20 by weight in the ratio of hydrated silicic acid/powder with an isoelectric point of 7 or more in order to keep high oil absorption by hydrated silicic acid and to obtain the composite powder especially excellent in the strike-through inhibiting effect of ink. As hydrated silicic acid, one obtained by the neutralization reaction of alkali silicate and an acid can be used.

Description

[Detailed description of the invention] The present invention relates to a method for producing a novel composite powder.

Specifically, when used as a paper filler, ink bleed-out is a method for producing a composite powder that is extremely effective in preventing it.

Conventionally, in order to reduce the weight of paper, the use of fillers with high oil absorption (secondly, ink bleed-through has been studied to prevent crystallization, and methods of reducing paper thickness. For example, There is a method in which an alkali silicate and an acid are reacted under certain conditions to produce hydrated silicic acid with a large oil absorption capacity, and this is added as a filler to paper.

However, when the above-mentioned hydrated silicic acid is added to the valve slurry to make paper, there is a problem in that the effect of preventing ink from bleeding out of the resulting paper is not sufficiently exhibited compared to the oil absorption amount of the powder.

That is, when paper is made by adding hydrated silicic acids with different oil absorption amounts to the pulp slurry, a phenomenon occurs in which the effect of preventing ink from bleeding out of the paper obtained increases little as the oil absorption increases. Reducing the weight of paper was a big problem.

The present inventors have conducted repeated research in order to solve the above problems. As a result, we obtained the knowledge that the above problem was caused by a change in the aggregation structure of hydrated silicic acid in the valve slurry (2) during paper making, resulting in a decrease in oil absorption after drying. Based on the above finding C = As a result of extensive research, we have found that a composite powder obtained by crushing a powder mixture of hydrated silicic acid and a specific powder under specific conditions (secondary grinding and re-agglomeration) has an oil absorption amount after immersion in water. The inventors have now completed the present invention by discovering that the decrease in ink is extremely small and that even when paper is made by adding it to pulp slurry as a filler, it can exhibit an excellent effect in preventing ink from bleeding out of paper.

The present invention is a method for producing a composite powder, which comprises pulverizing a mixture of hydrated silicic acid and a powder having an isocenter of 7 or more so that the bulk specific gravity is 0.18 f/cc or less. .

In the present invention, bulk specific gravity refers to a value measured according to JIS K6220.

In the present invention, the hydrated silicic acid obtained by a so-called wet method, which is a neutralization reaction between an alkali silicate and an acid, can be used without particular limitation. In particular, the oil absorption amount is 2 cc/ or more,
Preferably, it is 2.5 to 4 cc/f, since when used as a paper filler, a composite powder having an excellent effect of preventing ink bleed-through can be obtained.

Typical methods for producing the above-mentioned hydrated silicic acid include the following methods. That is, a method is preferred in which, when a raw material such as an alkali silicate is decomposed with a mineral acid such as sulfuric acid, the mineral acid is added in two parts to an aqueous aqueous silicate solution to produce hydrated silicic acid. General C2 is added in an amount of 37 to 45% of the total amount of mineral acid to be added at the first time, preferably as soon as possible (for example, within 10 minutes).
The temperature when adding JR to decompose the alkali silicate is preferably higher, and generally a temperature of 85°C to 95°C is suitable. Of course, these conditions differ depending on the type of raw materials, reaction equipment, etc., and therefore need to be determined in advance.

Further, in the present invention, it is extremely important to use a powder having an isoelectric point of 7 or more, preferably 8 or more as the powder to be mixed with the hydrated silicic acid. In other words, even if a powder with an equal N point lower than 7 is used and the specific pulverization described below is carried out together with hydrated silicic acid, the resulting composite powder will have a marked decrease in oil absorption when dried after immersion in water seawater. The effect of preventing paper ink from bleeding out does not exceed the effect when each powder is used alone, but rather tends to decrease. On the other hand, the agglomerated powder obtained by grinding together with the powdered hydrated silicic acid having the specific isocenter point 011 shows extremely little decrease in oil absorption even when dried after being immersed in water. The effect of preventing ink bleed-through is significantly improved compared to when the body is used alone. As the powder having an isoelectric point of 7 or more used in the present invention, one that is poorly soluble in water C is preferably used. For example, one powder or a combination of two or more of powders such as calcium carbonate, magnesium carbonate, alumina, aluminum hydroxide, zinc oxide, and magnesium oxide are suitable. Among these, calcium carbonate is particularly preferably used.

The mixing ratio of the above-mentioned hydrated silicic acid and the powder having an isoelectric point of 7 or more is 4 to 4 by weight.
47, preferably 5 to 20, in order to maintain high oil absorption due to hydrated silicic acid and to obtain a composite powder that is particularly effective in preventing ink from striking paper.

In the present invention, it is possible to crush a mixture of hydrated silicic acid and a powder having an isoelectric point of 7 or more until the bulk specific gravity becomes 0.18 f/cc or less. This is necessary in order to effectively prevent the decrease in oil absorption of the resulting composite powder after immersion in water (C2). It refers to the bulk specific gravity immediately after. Therefore, while the obtained composite powder is stored or transported, its bulk specific gravity increases, and
Those exceeding r/cc can also fully exhibit the effects of the present invention, and are included in one embodiment of the present invention. If the bulk specific gravity of the composite powder obtained by pulverization is larger than the above range, each powder will not be sufficiently pulverized, and strong agglomerations will not be formed between each powder (1), and the desired composite powder will not be formed. I can't get it.

There are no particular limitations on the method of pulverizing the pre-milled powder mixture until it has a bulk specific gravity of 0.185'/cc or less. A typical method is to use a fluid energy mill to crush the material so that the fluid pressure at its inlet nozzle (c or less, referred to as the crushing pressure) is 5υ or more, preferably 6 to 20\i. As the fluid energy mill, known ones may be used without limitation. Generally, Jet-O-Mizer (trade name) is used.

Jet mill (trade name) etc. are suitable.

As can be understood from the above explanation, the composite powder obtained by the method of the present invention has the ability to exhibit extremely little decrease in oil absorption after being immersed in water and dried. Therefore,
Even when paper is made by adding C2 to the valve slurry as a filler, it exhibits excellent oil absorption in the paper and exhibits an excellent effect in preventing ink bleed.

The composite powder desired by the present invention is I]i! Although the mechanism by which the described performance is achieved is not clear, the present inventors have discovered that by pulverizing powders with different surface charge states to a particle size below a specific particle size, a unique agglomeration that differs from a simple mixture of powders can be achieved. Forming a structure C: It is estimated that this is due to the formation of a structure.

Examples will be shown below to specifically explain the present invention, but
The present invention is not limited to these examples.

In the Examples, the oil absorption amount of the powder, the oil absorption amount after the powder was immersed in water, the degree of leaching of the ink after printing, and the average particle diameter were measured by the following methods.

1) Oil absorption amount It was conducted according to JISK-5101.

11) Oil absorption amount after immersion in water Sample powder was immersed in water, filtered, and left to dry at 80°C. Next, the dried cake was loosened on a 100-mesh sieve, and the oil absorption amount was measured by the method described in [1].

111) When removing printing ink, stack 10 sample papers and check the reflectance of the surface (Rvl).
was measured. On the other hand, the surface reflectance (Ro3) was measured by applying a black sheet from the back to one of the above sample papers.Also, black ink for an offset rotary press was applied to the entire surface of one side of the above sample paper, and the other side after drying. (Blank paper side) reflectance (Ri 1) was measured, and from these measured values, the opacity r11 of the printed MiT and the opacity r2 after printing were determined using Shimohi's formula.

O Opacity of printing I r1 (%1-, ;X100O Opacity after printing r2 (%) = curtain
r2r1. Using r2, the degree of cross-removal of printing ink was determined by the following formula.

1 r2 Degree of strike-through of printing ink = -X 100'' It can be concluded that the lower the degree of strike-through of printing ink, the better the ability to prevent the strike-through of printing ink.

(1v) Average particle size.

The particle size distribution was measured using Coulter Counter TA-II (trade name: manufactured by @1biyori-sama), and 50%
The particle size is shown below.

Example After mixing the hydrated silicic acid having the columnar shape shown in Table 1 and the powder in the ratio shown in Table 1, the mixture was pulverized using Jet-O-Mizer C (trade name) at the crushing pressure shown in Table 1. did. The average particle diameter, oil absorption, and water (= oil absorption after immersion) of the obtained composite powder are shown in Table 1.The obtained composite powder was also used as a filler, mixed at the following blending ratio, and A pulp slurry having a concentration of 1% was prepared and paper was made according to JIS P-8209.The ink removal rate after printing was measured for the obtained paper.The results are also shown in Table 1.

In Table 1, the particle size indicates the average particle size.

Claims (1)

[Claims] 1. A composite powder characterized by pulverizing a mixture of hydrated silicic acid and a powder having an isoelectric point of 7 or more so that the bulk specific gravity is 0.18 g/cc or less. Production method. 2. Claim 1, wherein the powder having an isoelectric point of 7 or more is at least one kind of powder selected from the group consisting of calcium carbonate, magnesium carbonate, alumina, aluminum hydroxide, zinc oxide, and magnesium oxide. The method described in section. 3. Weight ratio of hydrated silicic acid/powder with an isoelectric point of 7 or more is 4 to 4
7. The method according to claim 1, wherein the method is: 4. Grind to 5mg/cm^ by fluid energy mill.
The method according to claim 1, characterized in that the process is carried out at two or more crushing pressures.