JP2003342894A - Loading material for low density paper, low density paper and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a loading material for low density paper, and to produce low density paper and to provide a method for producing the same. <P>SOLUTION: The method produces the low density paper with high rigidity by paper making a slurry for paper making obtained by adding the loading material for low density paper which contains pillar-shaped or tubular aggregated particles comprising flaky fine crystals of basic magnesium carbonate together with various kinds of chemicals for paper making to the pulp slurry. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a filler for low density paper,
The present invention relates to low density paper and a method for manufacturing the same. More specifically, it relates to a filler for low-density paper characterized by containing agglomerated particles of basic magnesium carbonate having a special shape, a low-density paper characterized by containing the agglomerated particles as a filler, and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, the weight of paper has been reduced for the purpose of saving paper pulp resources, reducing transportation costs and labor, and reducing the amount of dust generated. To reduce the weight of paper, that is, to reduce the weight of paper per unit area,
It is enough to reduce the amount of pulp used and the amount of filler mixed,
When the amount of pulp used is reduced, the paper becomes thin, and problems such as deterioration of optical properties such as opacity and deterioration of rigidity (resistance to bending) occur.

In order to supplement the optical properties such as opacity, a method of increasing the blending amount of filler such as calcium carbonate, kaolin, titanium oxide, etc. is generally adopted, but a filler having a density higher than that of pulp is often used. If this happens, the density of the paper will increase, and as a result, the rigidity will decrease. The stiffness and density of paper are related, and when the basis weight (weight of paper per unit area) is constant, the thicker the paper, that is, the lower the density, the higher the rigidity tends to be.

Therefore, in reducing the weight of paper, how to manufacture paper with low density and high rigidity is a major issue. Under such circumstances, many studies have been made on paper having low density and high rigidity, and various techniques have been proposed. For this purpose, for example, it is attempted to lower the density by optimizing the filler to be blended, and the bulky paper in which the shirasu balloon of Japanese Patent Publication No. 52-39924 is internally added, and the particle size of Japanese Patent Publication No. 4-50435 is 0. There is a proposal for bulky neutral paper produced by using hollow spherical vaterite of 0.5 to 30 μm as a filler.

Further, as those, Japanese Patent Laid-Open No. 2000-2000
Low density paper containing a specific amount of amorphous silica or amorphous silicate having a bulk specific gravity of 0.3 g / mL or less and a low density chemical of JP-A-282392, JP 2001-336088 A.
There has also been proposed a low density printing paper in which 30 to 80% by weight of all the pulp components in the publication are mechanical pulps and a zeolite having an oil absorption of 100 mL / 100 g or more is contained as a filler in an amount of 2 to 15% by weight based on the total pulp.

Then, as a study of the pulp to be used, a low-density high-smoothness paper composed of bacterial cellulose and hardwood pulp having a water retention of 1.1 to 1.5 in JP-A-6-248594 was used. JP-A-10
-204790, 90% by weight or more of LBKP having a freeness of 500 mLcsf or more containing 50 to 100% by weight of dipterocarp pulp among all pulps,
Addition rate of filler containing calcium carbonate is 20 to 30
Low-density book paper and the like, which are weight percent, have been proposed.

[0007] Further, the one proposed as using a foaming agent is a mixed paper sheet in which 3 to 20 parts by weight of expandable particles having a particle diameter of 5 to 30 µm, which are disclosed in Japanese Patent No. 3024591, are uniformly dispersed. Heat-foamed foam particle mixed paper, low density paper in which foam particles are uniformly dispersed in a pulp fiber layer containing a curled fiber as disclosed in JP-A-11-302991, and bacterial cellulose as disclosed in JP-A-11-200282. There are low density papers that contain expandable particles.

Further, a polymer obtained by polymerizing a radical polymerizable monomer having a carboxyl group as a main component and an acrylate-based monomer and a methacrylate-based monomer as disclosed in JP-A-2002-20996 is used as an outer shell,
There is also low-density paper characterized by containing heat-expandable microcapsules containing a volatile foaming agent which gasifies at a temperature below the softening point of the polymer.

[0009]

Thus, although many studies have been made so far on low-density paper, a special treatment process is required and expensive chemicals must be used. It leaves things that must be done. Specifically, in the case of using a foaming agent, expanded particles are expensive, workability in papermaking is deteriorated, and a heat treatment for foaming the foaming agent is required, and thus ordinary papermaking Not only must another process be provided during the process, but there is also the problem that it is not easy to control the conditions of the heat treatment.

Regarding those using a specific filler, although some effect is recognized in reducing the density, when other quality is used in addition to reducing the quality other than the density or supplementing it, It has been pointed out that the effect on low density is drastically reduced. In addition, with regard to those that use specific pulp such as curled fiber, it is necessary to perform a special treatment during pulp production, which is a disadvantage for both economic efficiency and operability, and it is a technology with a high degree of industrial perfection. It is difficult to say that there is.

Under these circumstances, there has been a strong demand for the development of a low-density paper which can be manufactured more simply and is excellent in quality such as rigidity and a manufacturing method thereof. In the above,
The present inventors have succeeded in developing basic magnesium carbonate which is a columnar or tubular aggregated particle having a novel shape, that is, flaky fine crystals, and have already applied for a patent (Japanese Patent Application No. 2002-2002).
35110).

The inventors of the present invention attempted to solve the above problems by using this as a filler, and as a result, they found that a paper having a low density and a high rigidity could be produced and succeeded in the development. This is the present invention. That is, an object of the present invention is to make use of characteristics such as a unique shape of columnar or tubular agglomerated particles of basic magnesium carbonate and a low bulk density derived therefrom, which can reduce the density of paper and reduce the weight of paper. It is an object of the present invention to provide a filler for low-density paper, a low-density paper and a method for producing the same, which can suppress the decrease in rigidity, which is a problem.

[0013]

The present invention is intended to solve the above-mentioned problems, and has a columnar shape composed of flaky microcrystals developed by the present inventors and applied for a patent (Japanese Patent Application No. 2002-35110). The present invention relates to a filler for low-density paper, low-density paper, and a method for producing low-density paper, which uses basic magnesium carbonate which is a tubular aggregate particle.

The filler for low-density paper of the present invention is characterized by containing columnar or tubular agglomerated particles composed of flaky fine crystals of basic magnesium carbonate, and the low-density paper of the present invention is It is characterized by containing agglomerated particles as a filler. Further, the method for producing a low-density paper of the present invention is characterized by compounding the agglomerated particles as a filler to make a paper.

In the present invention, columnar or tubular aggregated particles of basic magnesium carbonate in which flaky fine crystals are aggregated, that is, aggregated particles aggregated in a card house structure are contained in the paper as a filler to reduce It is possible to reduce the rigidity, which is a problem in reducing the weight of the paper, while making the paper of high density. The flaky fine crystals forming the card house structure have a thickness of 0.005 to
0.5 μm and a diameter of 0.1 to 10 μm are preferable.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The embodiments of the present invention will be described in detail below, but the present invention is not limited thereto and is specified by the description of the claims. Needless to say.

The filler for low-density paper of the present invention is characterized by containing columnar or tubular agglomerated particles composed of flaky fine crystals of basic magnesium carbonate, which the present inventors have developed. And proposed (Japanese Patent Application No. 2002-3511)
0), with a thickness of 0.005-0.5 μm and a diameter of 0.1
It is a novel basic magnesium carbonate having a unique shape of columnar or tubular aggregated particles in which flaky fine crystals of 10 μm are gathered in a card house structure. The tubular aggregated particles are as shown in the electron micrographs of FIGS. 1 and 2.

In the low-density paper of the present invention, it is important to contain columnar or tubular agglomerated particles consisting of flaky fine crystals in a unique shape of basic magnesium carbonate, and as atypical or spherical agglomerated particles. The usual basic magnesium carbonate obtained cannot fulfill the task of the invention, namely the task of providing a paper with lower density and higher stiffness.

The columnar or tubular agglomerated particles of basic magnesium carbonate are not particularly limited as long as they are in the range disclosed in the above proposal, but if the outer diameter is too large or the length is too long. Although there is no problem in lowering the density, the tensile strength and the tear strength are lowered, and on the contrary, if it is too small, the effect of lowering the density may be difficult to be exhibited.

Taking these points into consideration, the columnar or tubular aggregated particles of basic magnesium carbonate have an outer diameter of 1 to 20 μm, a length of 5 to 200 μm, and an aspect ratio of 2 to 20. Is preferred. further,
Regarding the form of the basic magnesium carbonate in the present invention, by using tubular agglomerated particles, it is possible to further enhance the effect of reducing the density and increasing the rigidity of the paper.

Regarding the shape of the tubular agglomerated particles, the closer the inner diameter is to the value of the outer diameter, the more voids there are and the greater the effect of lowering the density is, but the wall portion of the tubular agglomerated particles becomes too thin. Then, when stress is applied in the paper making process, some particles are destroyed, and the desired effect may not be obtained. Considering these points, when selecting a tubular form of basic magnesium carbonate, an outer diameter of 1
~ 20μm, inner diameter 0.5 ~ 5μm, inner diameter / outer diameter ratio 0.2
It is more preferable to use tubular agglomerated particles having a particle size of ˜0.9 and a length of 5 to 200 μm.

The columnar or tubular agglomerated particles of the basic magnesium carbonate have been newly developed by the present inventors in Japanese Patent Application No. 20.
No. 02-35110, but the production is not limited to the above-mentioned method.
Any material can be used as long as it can manufacture the material having the above-mentioned shape. In the newly developed manufacturing method, a water-soluble magnesium salt such as magnesium sulfate or magnesium chloride and a water-soluble carbonate such as sodium carbonate or ammonium carbonate are mixed in an aqueous solution, and both are reacted in two steps. It is a thing.

The reaction is carried out at a temperature of 20 to 60 ° C. for the first step of producing magnesium carbonate columnar particles having a diameter of 0.5 to 10 μm and a length of 5 to 500 μm, and the magnesium carbonate columnar particles. And a second step of heat treating the suspension of 1. at a temperature higher than the temperature at which magnesium carbonate was produced in the first step and at a temperature of 35 to 80 ° C., preferably in the second step. The magnesium carbonate suspension is heat-treated at a pH of 7.5 to 11.5. The basic magnesium carbonate has a chemical formula of mMgCO ₃ · Mg (OH) ₂ ·.
nH ₂ O (m: 3 to 5, n: 3 to 8), and magnesium orthocarbonate produced during the reaction in the above-mentioned production method is represented by MgCO ₃ .3H ₂ O. It is what is done.

The columnar or tubular aggregated particles of the basic magnesium carbonate are the filler for low density paper of the present invention, and the low density paper of the present invention contains the filler. The content thereof is not particularly limited and may be appropriately adjusted according to the intended quality of paper. In addition,
Increasing the content of columnar or tubular agglomerated particles of basic magnesium carbonate has a greater effect on reducing the density of the paper, and a paper having higher rigidity can be obtained.

However, if the content is too small, the effect of lowering the density becomes small, and conversely, if the content is too large, the paper will be excellent in terms of density and rigidity, but the tensile strength and tear strength will be great. It may also lead to deterioration of strength characteristics such as the above and operability in the paper making process. Therefore, the density and stiffness of the paper,
Considering other balance such as quality and operability,
Under suitable conditions, the content of columnar or tubular agglomerated particles of basic magnesium carbonate is 2 to 25% by weight, more preferably 4 to 20% by weight, based on the absolute dry weight of the paper to be produced. is there.

It is essential for the filler for low density paper of the present invention to contain columnar or tubular agglomerated particles of basic magnesium carbonate, but other than that, calcium carbonate, kaolin, titanium oxide, silica may be added if necessary. , Components such as talc that are usually added to the filler may be mixed. In particular, as the quality required for the target paper, when optical properties such as high whiteness and opacity are required, by mixing an appropriate amount of titanium oxide or calcium carbonate, the basic magnesium carbonate columnar or It is possible to obtain a paper that has both the characteristics of low density and high rigidity, which are the effects of tubular aggregated particles, and the high optical characteristics of titanium oxide and calcium carbonate.

The pulp used in the low-density paper of the present invention can be used without any particular limitation. Kraft pulp, sulfite pulp, which is made of commonly used hardwood or coniferous wood as a raw material, Chemical pulp such as soda pulp, semi-chemical pulp such as semi-chemical pulp and chemi-mechanical pulp, mechanical pulp such as groundwood pulp and thermo-mechanical pulp, and non-wood fiber pulp made from mulberry, sanpei, flax, hemp, kenaf, etc. It is possible to use one kind or a mixture of two or more kinds selected from deinking pulp made from waste paper.

There are no particular restrictions on the grade or application of the low-density paper suitable for production using the filler for low-density paper of the present invention, and various types can be produced, and high-grade to low-grade printing paper and thin sheets can be produced. Uncoated printing paper such as printing paper, coated printing paper base such as art paper and coated paper, slightly coated printing paper base, information paper such as PPC paper and information recording paper, newsprint paper, wallpaper base paper, etc. Can be illustrated.

Regarding the basis weight of the paper produced and the content of the filler
Also, the range where the specified density and rigidity can be developed.
There is no particular limitation as long as it is a paper like the one described above.
It may be selected according to the grade and application of
Has a basis weight of 25 to 75 g / m ², The filler is the dry weight of paper
5 to 25% by weight of which 20 to 10%
0 wt%, more preferably 50-100 wt% basic
Columnar or tubular aggregates of magnesium carbonate
And is desirable. Needless to say, the book
In the invention, it is essential to include the agglomerated particles.
Is.

The content of the filler as used herein includes calcium carbonate, kaolin, talc, which is used in addition to columnar or tubular agglomerated particles of basic magnesium carbonate.
Indicates the total content of fillers such as silica and talc.
By setting the basis weight and the filler content like this,
The low-density paper of the present invention more efficiently develops the effect of lowering the density and improving the rigidity, and also has other properties such as strength characteristics such as tensile strength and tear strength, and optical characteristics such as whiteness and opacity. It is possible to make paper excellent in balance with.

Next, a method for producing the low density paper of the present invention will be described. The low-density paper of the present invention is produced by an ordinary papermaking method, for example, by papermaking a stock slurry in which the low-density paper filler of the present invention and various paper-making agents are added to the pulp slurry as described above. The filler contains at least columnar or tubular agglomerated particles made of flaky fine crystals of basic magnesium carbonate.

Regarding the paper-making chemicals to be added to the pulp slurry together with the above-mentioned filler, sizing agents, size-fixing agents, retention-improving agents, drainage-improving agents, paper-strengthening agents, and water-proofing agents used in ordinary papermaking. There is no problem in properly using agents such as agents, water repellents, defoamers, slime control agents and dyes. Furthermore, after papermaking, a water-soluble polymer such as starch or water-soluble cellulose can be applied to the surface, if necessary. The surface of the base paper obtained by the above method may be coated with a coating agent containing an inorganic or organic coating pigment and a binder as main components.

Papers containing columnar or tubular agglomerated particles composed of flaky fine crystals of basic magnesium carbonate thus produced as a filler are generally calcium carbonate, kaolin, titanium oxide, silica, talc and the like. The density can be lowered as compared with the paper in which only the used filler is internally filled. Moreover, it is possible to improve the rigidity of the paper, and it is possible to solve the problem of the decrease in the rigidity when reducing the weight of the paper.

Further, the columnar or tubular agglomerated particles composed of flaky fine crystals of basic magnesium carbonate are materials excellent in oil absorbency and water absorbability, so that the low content of the present invention containing the basic magnesium carbonate. Density paper is also excellent in quality such as ink acceptability, opacity after printing, and printability. Further, the basic magnesium carbonate is
It can also be used as a coating pigment for papermaking, and the coated paper coated with the basic magnesium carbonate exhibits not only weight saving but also excellent ink acceptability, opacity after printing, printability, etc. .

[0035]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples and is specified by the scope of claims. It goes without saying that it is a thing.

Production Example 1 Production of Tubular Aggregate Particles of Basic Magnesium Carbonate Magnesium sulfate heptahydrate aqueous solution (12
5 g / L) 2.0 L, while maintaining the temperature at 40 ° C., 0.50 L of anhydrous sodium carbonate aqueous solution (220 g / L) was gradually added and stirred for 50 minutes to have a diameter of 1 to 3 μm and a length of 10 Columnar particles of magnesium normal carbonate of ˜50 μm were generated.

Subsequently, the suspension of columnar particles of magnesium bicarbonate was heated to 120 ° C. while maintaining the temperature at 55 ° C.
After stirring for a minute, the thickness is 0.01 to 0.04 μm and the diameter is 0.
The outer diameter is 1-5μ, which consists of flake-like fine crystals of 5-2μm.
m, inner diameter 0.5 to 3 μm, inner diameter / outer diameter ratio 0.4 to
0.6, length 5 to 20 μm, aspect ratio 3 to 10
To obtain tubular magnesium agglomerated particles of basic magnesium carbonate.

Production Example 2 Production of Columnar Aggregate Particles of Basic Magnesium Carbonate Magnesium sulfate heptahydrate aqueous solution adjusted to 50 ° C. (12
5 g / L) 2.0 L, while maintaining the temperature at 50 ° C., 0.50 L of ammonium carbonate aqueous solution (250 g / L) was gradually added and stirred for 40 minutes to give a diameter of 0.5 to 2 μm and a length of Columnar particles of magnesium normal carbonate of 10 to 50 μm were generated.

Then, an appropriate amount of aqueous ammonia was added to the suspension of columnar particles of magnesium carbonate to adjust the pH to 9.5, and then heated to maintain the temperature at 65 ° C. 180
After stirring for a minute, the thickness is 0.02 to 0.1 μm and the diameter is 2 to
The outer diameter is 5-10μ, which consists of flaky fine crystals of 5μm.
m columnar aggregated particles of basic magnesium carbonate having a length of 20 to 40 μm and an aspect ratio of 4 to 8 were obtained.

Production Example 3 Production of Synthetic Calcium Carbonate Calcium hydroxide slurry adjusted to 28 ° C. (75 g /
L) Carbon dioxide gas was introduced into 2.0 L at a rate of 0.30 L / min to obtain a major axis of 1.0 to 1.2 μm and a minor axis of 0.2 to
0.3 μm spindle-shaped calcium carbonate was obtained.

[Example 1] 100 parts by weight of a hardwood kraft pulp (beating degree of 211 mLcsf) was added to 40 parts by weight of the basic magnesium carbonate tubular agglomerated particles obtained in Production Example 1 as a filler for low density paper. In addition, after stirring and mixing uniformly, an appropriate amount of an aqueous solution of polyacrylamide was added as a coagulant, and then a wet paper was obtained by hand making using a square hand making sheet machine. The obtained wet paper is squeezed with a press machine at a pressure of 5.0 kgf / cm ² , and then dried with a drum dryer having a surface temperature of 130 ° C. to obtain a basis weight of 33 g.
/ M ² and a filler content of 18% by weight were obtained.

Example 2 Production Example 2 as a filler for low density paper
Columnar agglomerated particles of basic magnesium carbonate 3 obtained in
A handmade paper was obtained in the same manner as in Example 1 except that 5 parts by weight was used.

[Example 3] Production Example 1 as a filler for low-density paper
Aggregate of basic magnesium carbonate tubular particles 3 obtained in
A handmade paper was obtained in the same manner as in Example 1 except that 5 parts by weight and 8 parts by weight of commercially available titanium oxide (anatase type, average primary particle diameter 0.15 μm) were mixed and used.

[Example 4] 100 parts by weight of a hardwood kraft pulp (beating degree of 447 mLcsf) was added to 15 parts by weight of the basic magnesium carbonate tubular agglomerated particles obtained in Production Example 1 as a filler for low density paper. In addition, after stirring and mixing uniformly, an appropriate amount of an aqueous solution of polyacrylamide was added as a coagulant, and then a wet paper was obtained by hand making using a square hand making sheet machine. The obtained wet paper is squeezed with a press at a pressure of 5.0 kgf / cm ² , and then dried with a drum dryer having a surface temperature of 130 ° C. to obtain a basis weight of 63 g.
/ M ² and a filler content of 8% by weight were obtained.

Comparative Example 1 To an aqueous slurry of 100 parts by weight of hardwood kraft pulp (beating degree of 211 mLcsf), 40 parts by weight of the synthetic calcium carbonate obtained in Production Example 3 was added as a filler, and the mixture was stirred and uniformly mixed. After adding an appropriate amount of an aqueous solution of polyacrylamide as a coagulant, a wet paper was obtained by hand making using a square hand making sheet machine. The obtained wet paper is squeezed with a press at a pressure of 5.0 kgf / cm ² , and then dried with a drum dryer having a surface temperature of 130 ° C. to obtain a basis weight of 33 g / cm ² and a filler content of 18% by weight.
A handmade paper was obtained.

Comparative Example 2 35 parts by weight of the synthetic calcium carbonate obtained in Production Example 3 and 8 parts by weight of titanium oxide (anatase type, average primary particle diameter 0.15 μm) were mixed and used as a filler. In the same manner as in Comparative Example 1, a handmade paper was obtained.

Comparative Example 3 As a filler, commercially available basic magnesium carbonate (amorphous agglomerated particles of 2 to 20 μm) 40
A handmade paper was obtained in the same manner as in Comparative Example 1 except that parts by weight were used.

Comparative Example 4 15 parts by weight of the synthetic calcium carbonate obtained in Production Example 3 as a filler was added to an aqueous slurry of 100 parts by weight of hardwood kraft pulp (beating degree of 447 mLcsf), and the mixture was stirred and uniformly mixed. After adding an appropriate amount of an aqueous solution of polyacrylamide as a coagulant, a wet paper was obtained by hand making using a square hand making sheet machine. The obtained wet paper was squeezed with a press machine at a pressure of 5.0 kgf / cm ² , and then dried with a drum dryer having a surface temperature of 130 ° C. to obtain a basis weight of 63 g / m ² and a filler content of 8% by weight. A handmade paper was obtained.

[Evaluation of Handmade Paper] The handmade papers obtained in Examples and Comparative Examples were evaluated for density and rigidity.
Density is measured in accordance with JIS P 8118 (testing method for thickness and density of paper and paperboard), and rigidity is determined according to JIS P 8143 (stiffness test method by Clark stiffness tester for paper). Was measured. The evaluation results are shown in Table 1. It should be noted that the larger the Clark stiffness, the better.

[0050]

[Table 1]

As is clear from Table 1, the handmade papers obtained in the examples have the same basis weight and the same filler content as those of the handmade papers of the comparative examples. I understand. That is, the grammage is about 33 g / m ² , and the filler content is about 18% by weight in both the examples and the comparative examples.
Comparing Examples 1 to 3 with Comparative Examples 1 to 3, the density of the handmade paper of Comparative Example is 0.54 to 0.57 g / cm ³ , while 0.48 to 0 in Example. 0.52 g / cm ³
Thus, a low density of about 0.1 g / cm ³ is achieved at the maximum.

Further, comparing Example 4 with Comparative Example 4 in which the basis weight is about 63 g / m ² and the filler content is about 8% by weight, the density of the handmade paper of Comparative Example is 0.56 g / cm ^3. On the other hand, in the embodiment, it is 0.52 g / cm ³ , which is about 0.
A low density of 04 g / cm ³ has been achieved. further,
The handmade papers of the examples also have excellent rigidity.

That is, according to Table 1, when the handmade paper of the example and the handmade paper of the comparative example are compared at substantially the same basis weight and the same filler content, the rigidity is excellent. For example, when comparing the handsheet paper of Comparative Example 1 and handsheet paper of Example 1, but the basis weight of both and filler content is the same, in Example 1, Clark stiffness is 16.1cm ^3/10
To which the 0, Comparative Example 1, 13.4cm ^3/10
It is 0, which means that the present invention is excellent in Clark stiffness.

[0054]

The filler for low-density paper of the present invention is characterized by containing columnar or tubular agglomerated particles composed of flaky fine crystals of basic magnesium carbonate, and the low-density paper of the present invention is
It is characterized by containing the same agglomerated particles as a filler, which is a paper with a lower density than paper containing only calcium carbonate, kaolin, titanium oxide, etc. used as a normal filler. Become. Further, it is possible to suppress the decrease in rigidity, which was a problem in reducing the weight of paper.

[Brief description of drawings]

FIG. 1 is an SEM photograph showing the particle shape of the basic magnesium carbonate of Production Example 1 used in Example 1 (× 1,00).
0).

2 is a SEM photograph (× 25,000) showing the particle shape of the basic magnesium carbonate of Production Example 1 used in Example 1. FIG.
0).

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Claims (10)

[Claims] 1. A filler for low-density paper, comprising columnar or tubular agglomerated particles composed of flaky fine crystals of basic magnesium carbonate. 2. The outer diameter of columnar or tubular agglomerated particles composed of flaky fine crystals of basic magnesium carbonate is 1 to 20 μm.
The filler for low-density paper according to claim 1, wherein m, the length is 5 to 200 μm, and the aspect ratio is 2 to 20. 3. The filler for low-density paper according to claim 1, wherein the tubular agglomerated particles composed of flaky fine crystals of basic magnesium carbonate have an inner diameter of 0.5 to 5 μm. 4. A low-density paper characterized by containing columnar or tubular agglomerated particles composed of flaky fine crystals of basic magnesium carbonate as a filler. 5. The outer diameter of columnar or tubular agglomerated particles composed of flaky fine crystals of basic magnesium carbonate is 1 to 20 μm.
The low-density paper according to claim 4, wherein m, the length is 5 to 200 μm, and the aspect ratio is 2 to 20. 6. The low-density paper according to claim 4, wherein the tubular agglomerated particles composed of flaky fine crystals of basic magnesium carbonate have an inner diameter of 0.5 to 5 μm. 7. The content of columnar or tubular aggregated particles of basic magnesium carbonate is 2 to 25 relative to the absolute dry weight of paper.
The low-density paper according to any one of claims 4 to 6, which has a weight percentage. 8. A basis weight of 25 to 75 g / m ² and a filler of 5 to 25% by weight based on the absolute dry weight of paper, 20 to 100% by weight of which is columnar or tubular of basic magnesium carbonate. An aggregated particle according to any one of claims 4 to 7.
Low-density paper according to item. 9. The low-density paper according to claim 4, which has a density of 0.40 to 0.55 g / cm ³ . 10. A method for producing low-density paper, which comprises blending columnar or tubular agglomerated particles composed of flaky fine crystals of basic magnesium carbonate as a filler to prepare paper.