JPH11303000A - Multilayered paper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide paper that can be used as wood-free paper, printing paper, recording paper, electro-photographic printing and packaging paper or the like of a multilayered structure excellent smoothness, strength, particularly excellent rigidity. SOLUTION: This multilayered paper comprises usual paper layers that are mainly composed of cellulosic fibers on at least one side of the surface layer, the curled fibers having the humid curl factor of 0.4-1.0 and the low density layer containing micro fibers having >=0.15 bond-enhancing factor. In addition, this paper has a multilayer structure of 3 or more layers and at least one layer among their inner layers is a low-density layer and the both outermost layers of the front and back sides are composed of usual paper layers mainly containing cellulosic fibers.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a multilayer paper. More specifically, the present invention relates to a multi-layer sheet which is used for various high-quality papers, printing papers, information papers, electrophotographic papers, wrapping papers, etc., is lightweight, strong, and has excellent surface properties.

[0002]

2. Description of the Related Art In recent years, paper has been required to be lighter in terms of resource saving and distribution. However, simply reducing the basis weight of paper to reduce its weight involves a problem that the paper thickness is reduced and strength, particularly rigidity, is reduced. Therefore, there is a demand for a paper which is bulky and has high strength.

In order to produce bulky paper, various types of pulp to be used, beating preparation conditions, papermaking conditions, finishing conditions, and the like have been devised. However, many of the qualities required for a bulky sheet have mutually opposite properties, and there has been a limit in achieving both. Conventionally,
Examples of the bulky sheet include a mixture of partially mercerized cellulose fibers (Japanese Patent Application Laid-Open No. 7-189168) and a bulky sheet of cellulose fiber mixed with hollow spherical vaterite-type calcium carbonate (Japanese Patent Application Laid-Open No. Hei 3-12489).
No. 5) and a bulky sheet obtained by molding a mixture of a heat-fusible fiber and a crosslinked pulp obtained by reacting a fiber with a crosslinking agent in the presence of a softening agent (JP-A-4-20289).
No. 5), bulky paper comprising an eccentric core-sheath type or side-by-side type conjugate fiber whose crimp form is a spiral crimp
(JP-A-2-300398) and the like are disclosed.

[0004]

However, the low-density sheet obtained by these methods has a small number of points of contact between fibers and cannot be strongly bonded to cellulose fibers. There are problems such as low strength and poor smoothness. An object of the present invention is to provide a paper that can be used for high-quality paper, printing paper, information paper, electrophotographic paper, packaging paper, and the like having a multilayer structure with excellent smoothness and strength, particularly excellent rigidity.

[0005]

The present inventors have studied the relationship between the paper layer structure and the smoothness and strength, especially the stiffness in view of the current situation. As a result, the paper has a multi-layered structure and the pulp used for the middle layer is formed. It has been found that a paper having both excellent smoothness and strength can be obtained by specifying, and the present invention has been completed. That is, a first aspect of the present invention is that a curled paper having a wet curl factor in the range of 0.4 to 1.0 is formed on at least one surface layer of which is a plain paper layer mainly composed of cellulose fibers and at least one other layer has a wet curl factor of 0.4 to 1.0. A multilayer paper characterized by being a low-density layer containing fibers and fine fibers having a bond reinforcing factor of 0.15 or more.

A second aspect of the present invention is a curled fiber having a multilayer structure of three or more layers, wherein at least one of the middle layers has a wet curl factor in the range of 0.4 to 1.0, and A low-density layer containing fine fibers having a bond reinforcing factor of 0.15 or more, and both outermost layers on the front and back sides are plain paper layers mainly composed of cellulose fibers. " .

In the first or second invention, the low-density layer has a wet curl factor of 0.4 to 1.0.
And 35 to 98% of the weight of the low-density layer based on the total weight of the absolutely dried fibers of the low-density layer. %.

In the first or second aspect of the present invention, it is preferable that the low density layer has a density of 0.05 to 0.45.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The primary cause of the success of the present invention is that curled fibers having a wet curl factor in the range of 0.4 to 1.0 have a low bond strength between fibers, but have a bent fiber. Focusing on the fact that fine fibers having a bond strengthening factor of 0.15 or more have a strong property of strengthening the bond between fibers, the combination of these two materials That is, a low density layer is formed. A second cause of the success of the present invention is that the paper having a multilayer structure of two or more layers including the low-density layer is used for high quality paper, printing paper, information paper, electrophotographic paper or packaging paper. That is, a sheet which is light, strong, and has excellent surface properties.

That is, the multilayer paper of the present invention is characterized by being formed of two or more layers, and having a low density layer as one of the layers. In the case of two layers, one layer is a low density layer and one layer is a plain paper layer. In the case of three or more layers, at least one surface layer is a plain paper layer, and preferably, both outermost layers on both sides are plain paper layers. The low density layer may have two or more layers, and the plain paper layer may have two or more layers.

In the present invention, the low-density layer refers to a layer having a density of 0.3.
And a layer having a density of 0.1 to 0.45.
0.35. The plain paper layer is a layer having properties similar to those of the paper that is generally used for the above-described various types of paper, and has a density greater than 0.45. The density of the plain paper layer is preferably in the range of 0.7 to 1.2.

The curled fiber used in the low-density layer of the multilayer paper of the present invention has an apparent length as compared with the original fiber length in which deformation such as curl or twist is fixed by chemical bonding by a crosslinking reaction. Pulp fiber having a reduced wet curl factor of 0.4 to 1.0 in the present invention.
Is used. By the way, the wet curl factor is an index indicating the degree of deformation of the fiber in a wet state.
Actual length of fiber after immersion in pure water for 24 hours (LA)
And the maximum projected length of the fiber (the length of the longest side of the rectangle surrounding the fiber, LB) is measured using a microscope, and [(LA / LB)
-1], which is a numerical value of how much the fiber is curved from the original linear length of the fiber.

The importance of the wet curl factor, which indicates the state of curl in a wet state, is that no matter how high the curl factor in a dry state, if the wet curl factor is small, the curl will return due to wetting when the curl factor is low, This is because it is difficult to achieve the density. Wet curl factor 0.4 ~
In the range of 1.0, the curled fiber is bent by imparting a considerable amount of deformation to the pulp fiber, and is cross-linked, so that the fiber is rigid.・ The product obtained by drying becomes a low density body. However, in this material, the entanglement between fibers is weak, and the hydroxyl groups (-O
Since H) is reduced, hydrogen bonds due to hydroxyl groups are hardly generated, and the obtained sheet has low sheet strength and cannot be put to practical use.

Known curled fibers can be used in the present invention. For example, a crosslinked fiber having an average water retention of 28% to 50% obtained by crosslinking the inside of a cellulosic fiber using a C2 to C8 dialdehyde and a C2 to C8 monoaldehyde having an acid functional group (Japanese Patent Publication No. 5-717)
No. 02) and a water retention of 25% to 60% obtained by internally crosslinking cellulosic fibers using C2 to C9 polycarboxylic acids.
Cross-linked fibers (JP-A-3-206174, JP-A-3-206174)
JP-A-206175, JP-A-3-206176), which are appropriately selected and used.

In the production of crosslinked fibers, after adding a crosslinking agent to the pulp fibers, mechanical stirring is performed, followed by fluffing and heat treatment. Large curled fibers are obtained. In the present invention, the water retention is 25 to 6 in terms of the balance between the degree of densification and the interlayer strength.
The use of 5% curled fiber is preferred, but not limiting. Incidentally, the water retention is a value obtained by dehydrating a fiber in a wet state by centrifugal force of 3000 G for 15 minutes and expressing the amount of water retained by the fiber in terms of the amount per unit weight of the fiber on a dry basis ( %), And the measurement method is JAPAN TAPPI No. 26
−78.

The cellulosic fiber used as a raw material of the curled fiber includes, for example, unbleached or bleached chemical pulp obtained by kraft pulping, sulfite pulping, alkali pulping of softwood or hardwood, or GP, Examples thereof include mechanical pulp such as RMP, TMP, and CTMP, cotton pulp, linter pulp, and waste paper pulp.

It is important that the fine fibers used in the low density layer of the multilayer paper of the present invention have a bond reinforcing factor of 0.15 or more. The size of the fiber is not particularly limited, but usually the number average fiber length is 0.0
Those having a range of 1 to 0.80 mm are preferably used.
Above all, 0.05-0.60 mm in terms of yield and dispersibility
Is more preferable.

As a material of the fine fiber, a natural polymer fiber, a synthetic polymer fiber, a semi-synthetic polymer fiber, or a material obtained by treating them is usually used. The natural polymer fibers include, for example, unbleached or bleached chemical pulp obtained by subjecting softwood or hardwood to kraft pulping, sulfite pulping, alkali pulping, or the like, or GP, RMP, TMP, CTMP, or the like. Mechanical pulp, or cotton pulp, linter pulp, waste paper pulp, cellulosic fibers such as bacterial cellulose, protein fibers such as wool, silk and collagen fibers, and complex sugar chain fibers such as chitin / chitosan fibers and alginate fibers. No. Examples of the synthetic polymer fiber include polyethylene fiber, polypropylene fiber, polyethylene-polypropylene sheath core fiber, polyacrylonitrile fiber, acrylic fiber, rayon fiber, polyester fiber, polyamide fiber, and the like. Examples thereof include fibers obtained by chemically modifying (modifying) natural products, such as acetylcellulose fibers.

Among them, those having biodegradability such as cellulosic fiber, aliphatic polyester fiber, acetylcellulose fiber and the like are preferable. Further, from the viewpoints of stability of raw material supply and cost, cellulosic fiber is preferable. Or what is obtained by processing it is more preferable.

As the mechanical treatment, in addition to the treatment with a beater such as a disc refiner, a conical refiner, and a beater which are usually used for paper paper, for example, a medium stirring mill treatment (Japanese Patent Application Laid-Open No. 4-18186), a vibration mill Treatment (JP-A-6-10286), treatment with a high-pressure homogenizer, colloid mill treatment, and the like may be used, but the present invention does not particularly limit the treatment apparatus. Among the processing apparatuses, the fine fiber pulp obtained by the medium stirring mill or the vibration mill is more easily obtained than the pulp fibers obtained by other processing apparatuses. It is particularly preferable that curled fibers used in the present invention can be efficiently and firmly bonded to each other because the fibers are finely dimensionally formed.

Incidentally, the medium stirring mill is a device for inserting a stirrer into a grinding container filled with glass beads or alumina beads and rotating at a high speed to grind the dispersion in the slurry by shearing stress. Type, distribution tube type, annular type, etc. A vibration mill is a device that vibrates a crushing container at high speed and applies a force such as an impact force or a shearing force to a dispersion in a slurry by beads, balls, rods, or the like filled in the container. In addition, the high-pressure homogenizer applies high pressure to pass between small-diameter orifices,
This is a device for crushing a dispersion in a slurry.

The binding enhancement factor (BF) referred to in the present invention.
Is calculated by (E2−E1) / E1. However, E1
Is mixed with 50% by weight of bleached hardwood kraft pulp and 50% by weight of softwood bleached kraft pulp to form an aqueous slurry,
It is beaten to a Canadian standard freeness of 500 ml, dewatered and air-dried with a hand making machine, and then heat-treated at 130 ° C. for 1 minute to prepare a sheet having a basis weight of 60 g / m ² , at 20 ° C. and 65%
The ultrasonic elasticity modulus measured after adjusting the humidity to RH is shown. E2
Indicates the ultrasonic elastic modulus when an aqueous slurry was prepared by replacing 50% of the mixed beaten pulp fibers with fine fibers, and a sheet was prepared and measured in the same manner as in the measurement of E1.
In the present invention, the fine fibers can be used alone or in combination of two or more.

In the present invention, the binding enhancement factor is 0.1
It is characterized in that 5 or more fine fibers are used, and preferably those having a bond reinforcing factor in the range of 0.15 to 1.50 are used. When using fine fibers of less than 0.15, the bond between the curled fibers becomes insufficient,
The resulting low-density middle-layer sheet has low strength and is not practical. Among the fine fibers used in the present invention,
When a bond strengthening factor of 0.2 or more is used, the sheet strength is high, which is more preferable.

The mixing ratio of the curled fiber and the fine fiber in the low-density layer of the multilayer paper of the present invention can be appropriately selected according to the purpose because the balance between the density and the interlayer strength can be controlled by changing the mixing ratio. can do. That is, when importance is placed on the interlayer strength over the density,
If the density of the fine fibers is increased and the density is more important than the interlayer strength, the density of the curled fibers may be increased. For example, when fine fibers are used in a ratio of 2 to 65% by weight based on the total fiber dry weight, and curled fibers are used in a ratio of 35 to 98% by weight based on the total fiber dry weight, the balance between density and sheet strength is particularly high. Excellent and preferred.
Among them, the range of 5 to 40% by weight of fine fiber and the range of 60 to 95% by weight of curled fiber is preferable.

The pulp constituting the plain paper layer in the multilayer paper of the present invention must have a freeness of 400 ml or less, more preferably 350 ml or less in Canadian standard freeness (hereinafter abbreviated as CSF). Advance the beating CSF
The lower the value, the higher the rigidity of the multilayer paper. For this reason, when the sheet density of the low density layer is low,
It is necessary to reinforce the decrease in the strength of the layer with a plain paper layer. By using pulp having a further improved degree of beating in the plain paper layer, the rigidity of the multilayer paper can be maintained or increased. Conversely, if the CSF exceeds 400 ml, the strength of the multi-layer paper is greatly reduced, which is not suitable for practical use.

The pulp used for the plain paper layer is a non-wood pulp such as softwood, hardwood bleached chemical pulp, mechanical pulp, waste paper pulp, linter, hemp, etc. obtained by kraft pulping, sulfite pulping, alkali pulping or the like. And the like, but are not particularly limited in the present invention.
The pulp is used alone after being beaten to a predetermined CSF level, but some pulp may be blended to a predetermined CSF level, and further, fine fibers used in the middle layer and various pulp may be blended to form a CSF. May be used to be 400 ml or less. The beating machine is not particularly limited as long as it can beat to a predetermined CSF level, and a known beating machine such as a double disc refiner, a single disc refiner, and a beater may be used.

The raw material slurry used for the low-density layer in the multilayer paper of the present invention may contain, depending on the purpose, natural pulp fibers, organic synthetic fibers, foamable microcapsules, paper strength enhancers, in addition to the above-mentioned curled fibers and fine fibers. A sizing agent, a retention aid, a filler, a slime control agent, a dye, a fluorescent brightener, a pH adjuster, an antifoaming agent, and the like can be selected and blended. Similarly, to the raw material slurry used in the outer layer,
Other than pulp raw materials, select and mix organic synthetic fibers, paper strength enhancers, sizing agents, retention enhancers, fillers, slime control agents, dyes, fluorescent brighteners, pH adjusters, defoamers, etc. Can be. These may be used in combination of two or more.

Examples of the natural pulp fibers that can be blended in the low-density layer of the multilayer paper of the present invention as needed include, for example, softwood chemical pulp, hardwood chemical pulp, or GP, RMP, TMP.
Examples thereof include bleached or unbleached, unbeaten or beaten, mechanical pulp such as MP, CTMP, etc., waste paper pulp, cotton pulp, linter pulp, and the like, and those in which the rigidity of fibers is enhanced by chemical treatment. By the way, as the one that strengthens the rigidity of the fiber by chemical treatment,
Specific examples include swollen pulps such as mercerized pulps and liquid ammonia-treated pulps. The fibers are more effective in lowering the density than fibers not subjected to a chemical treatment. These may be used alone or in combination of two or more. The amount of the pulp fiber varies depending on the use of the multilayer paper of the present invention, but can be in the range of 0 to 63% by weight, preferably 0 to 40% by weight, based on the total fiber solids in the layer. You.

The foamable microcapsules usable in the low-density layer of the present invention are obtained by encapsulating a low-boiling solvent in fine resin particles, and have a diameter of 3 to 5 times at a temperature of 70 to 150 ° C. and a volume of 30 to 5 times. These particles have an average particle diameter of 5 to 30 μm that expands 120 times. As the resin, a thermoplastic resin composed of a copolymer such as vinylidene chloride, acrylonitrile, acrylate, and methacrylate is usually used.As the low-boiling solvent, isobutane, pentane, petroleum ether, hexane, and a low-boiling halogenated solvent are usually used. Those manufactured using a low boiling point solvent such as a hydrocarbon are used. They are,
Two or more of them may be used alone or in combination. The amount of the foamable microcapsules varies depending on the use of the low-density body, but is usually added in the range of 0 to 30% by weight of the total solids. The foamable microcapsules are foamed by heat in the drying step, and have an effect of further lowering the density.

Examples of the organic synthetic fibers usable for the low density layer and the plain paper layer of the multilayer paper of the present invention include polyethylene fibers, polypropylene fibers, polyacrylonitrile fibers, acrylic fibers, rayon fibers, polyester fibers, and the like.
Examples thereof include polyamide fibers, and among them, biodegradable fibers such as aliphatic polyester and acetyl cellulose are particularly preferable. Further, as the shape of the fiber, a fiber having a bend such as a curl is more preferable than a straight fiber because an effect on lowering the density can be expected. These may be used alone or in combination of two or more. The amount of the organic synthetic fiber varies depending on the use of the low-density body, but can be added in the range of 0 to 40% by weight of the total solids. The addition of organic synthetic fibers is generally effective in improving the strength in a wet state of water.

Examples of paper strength enhancers usable in each layer of the present invention include urea formaldehyde resin, melamine formaldehyde resin, polyamide urea formaldehyde resin, ketone resin, polyamide epichlorohydrin resin, polyamide polyamine epichlorohydrin resin, glycerol polyglycidyl ether resin And polyethyleneimine resins. These may be used alone or in combination of two or more. The amount of the paper strength enhancer varies depending on the application, but is usually added in the range of 0 to 2% by weight of the total solids. The addition of a paper strength enhancer is generally effective in improving strength and the like. In particular, when a wet paper strength enhancer is used, there is a great effect on improving the strength in a wet state with water.

The internal sizing agent that can be used in each layer of the present invention includes a rosin-based sizing agent, an alkyl ketene dimer, an alkenyl succinic anhydride, a stearic anhydride, etc., depending on the sheet production method. is not.

The fillers usable in each layer of the present invention include:
For example, there are heavy calcium carbonate, light calcium carbonate, talc, kaolin, titanium dioxide, aluminum hydroxide, and the like. If necessary, pigments can be appropriately used in combination. The method for producing the multilayer paper of the present invention can be applied by a conventional assembling technique as appropriate, and a single head box for multilayer papermaking, such as Strata-flow by Beloit, Contro-flow by Tampera, HTB by KMW. -3L, Voith-
It may be manufactured by using a multi-layering technique using a paper machine using Step DiffusorHeadbox or the like of Sluzer.

The ratio of the low density layer in the multilayer paper of the present invention to the whole paper is preferably 20 to 80% by weight, more preferably 25 to 70% by weight in absolute weight ratio. If it is less than 20% by weight, the effect of lowering the density is small, and if it exceeds 80% by weight, the strength is greatly reduced. Also, the total basis weight of the plain paper layer is at least 5 g / m ² or more, preferably 7 g / m ² or more.
g / m ² or more. If it is less than 5 g / m ² , it is difficult to cover the layer in contact with the middle layer, and the effect of improving smoothness is small.

The obtained multilayer paper is subjected to starch, modified starch, casein, polyvinyl alcohol, carboxymethylcellulose, latex, alkyl ketene dimer, maleic anhydride, styrene-acrylic acid on the surface of the paper by various size presses or coaters. Various surface sizing agents,
A pigment, a dye or the like may be applied.

The basis weight of the paper of the present invention is appropriately determined according to the use and purpose, but is selected from the range of 30 to 300 g / m ² . The multilayer paper of the present invention thus obtained is excellent in smoothness and rigidity and may be used as it is as high quality paper, as printing paper or electrophotographic paper, and further coated on the surface with a paint containing a pigment or a binder as a main component. It can also be used as a base paper for coated paper, and even when finished in each product, the paper has excellent rigidity, so that the effect on weight reduction can be sufficiently maintained and contribute to the quality of the final product. Moreover, it can also be laminated with a film or a metal foil to form a packaging material.

[0037]

EXAMPLES The present invention will be described more specifically with reference to the following examples, but it should be understood that the present invention is not limited to these examples.
In Examples and Comparative Examples, “parts” and “%” indicate “parts by weight” and “% by weight” unless otherwise specified.

Example 1 A multilayer paper having a three-layer structure was prepared according to the following formulation. (1) Preparation of Raw Material for Outer Layer (Plain Paper Layer) 300 g of absolutely bleached hardwood bleached kraft pulp having 630 ml of Canadian Standard Freeness (CSF) was prepared.
Water was added to this pulp, disintegrated with a disintegrator to adjust the concentration to 2%, and the CSF50 was adjusted using a laboratory Niagara beater (capacity: 23 liters, manufactured by Tozai Seiki Co., Ltd.).
Beated to 0 ml. A 1.5-liter Dynomill (model: KDL-PILOT, manufactured by Shinmaru Enterprises Co., Ltd.) filled with 80% of glass beads having an average particle size of 2 mmφ is filled with an aqueous slurry of bleached kraft pulp having a solid content of 1%. ) Fine fibers having a number average fiber length of 0.28 mm and a bond reinforcing factor of 0.53 were obtained by introducing and passing through the apparatus at 350 ml / min. The water retention of the fine fibers was measured and found to be 285%. 70 parts of the beaten LBKP and 30 parts of fine fibers are blended, and light calcium carbonate (trade name: ALBAGROS S) is used as a filler.
F, manufactured by Pfizer MSP) to pulp 10%, and Ace K100 (manufactured by Oji Cornstarch) as a paper strength agent
1% to pulp, sulfuric acid band as fixing agent to pulp 0.5%, AKD as sizing agent (trade name: SPK-9)
03, Arakawa Chemical Industry Co., Ltd.) was added to the pulp at 0.5%. When the CSF of this slurry was measured, it was 320 m
l. A 0.65 g portion of the slurry was dried to obtain a square (25 mm) having an 80 mesh bronze wire.
cm × 25cm) 10g /
After forming a wet sheet of m ² on the wire, the thickness 2
Place 80 μm filter paper on the wet sheet and place it on top of thickness 1
Coating was performed by placing two filter papers each having a thickness of 2 mm and a stainless steel plate and rolling a metal roll from above.
The wet sheet thus obtained was peeled off from the wire while adhering to the thin filter paper, and stored on a flat surface without drying. In addition, a basis weight of 10 obtained by the same formulation.
Another wet sheet of g / m ² was prepared.

(2) Preparation of raw material for middle layer (low density layer) Softwood bleached kraft pulp without beating treatment 2
To 100 g, a non-formalin-based crosslinking agent (trade name: Sumitex ULW, manufactured by Sumitomo Chemical Co., Ltd.) and its crosslinking aid (trade name: Sumitex ACCELERATER ACX, manufactured by Sumitomo Chemical Co., Ltd.) were each 10 g in terms of active ingredients, 5
g of an aqueous solution containing 200 g was added and mixed well. This pulp impregnated with the cross-linking agent is kept in a wet state while the wet pulp is a 1-liter double-arm kneader (model: S1-1, manufactured by Moriyama Seisakusho)
At room temperature, double arms at 60rpm and 100rpm respectively
After rotating at pm, a kneading treatment was performed for 50 minutes.
Next, the kneaded pulp was placed in a Warburg blender in a wet state and fibrillated. Further, the fiber was taken out of the bag, placed in a stainless steel vat, and heated in a blow dryer at 150 ° C. for 30 minutes to complete the crosslinking reaction, thereby obtaining a curled fiber. When the wet curl factor of this curled fiber was measured, it was 0.65 and the water retention was 48%. When the freeness of this fiber was measured, it was 705 ml. 80 of this curled fiber
Parts of fine fiber used as a raw material of the outer layer, and 20 parts of fine fibers used as filler, and light calcium carbonate (trade name: A
LBAGLOSSF, manufactured by Pfizer MSP) to 10% of pulp, ACE K100 (manufactured by Oji Cornstarch) as a paper strength enhancer, 1% of pulp, sulfuric acid band as fixing agent, 0.5% of pulp, and AKD as sizing agent (Trade name: SPK-903, manufactured by Arakawa Chemical Industries) was added in an amount of 0.5% based on pulp.

(3) Preparation of Three-Layer Sheet An absolutely dry 1.4 g portion of this slurry was taken, and a square (25 cm × 25 c) equipped with an 80 mesh bronze wire was prepared.
m) A wet sheet having a basis weight of 20 g / m ² was formed on the wire by a hand sheet machine. Then, thickness 280μ
The outer layer sheet attached to the filter paper is placed on top of the filter paper so that the filter paper is on top, two filter papers each having a thickness of 1 mm and a stainless steel plate are placed on the outer sheet, and a metal roll is rolled from above to perform a coating process. Was given. The wet sheet having the two-layer structure was peeled off from the wire, layered on another outer layer sheet previously prepared and placed, and 3.5 kg / cm according to a conventional method with thin filter paper adhered to the upper and lower sides. ^At a pressure of ² ,
A first wet press for 5 minutes and a second wet press for 2 minutes were applied. Then, this sheet is 25cm x 25c
m and placed in a hot air drier at 105 ° C. and dried to a constant weight. After humidifying this sheet at 20 ° C. and 65% RH, the three-layer sheet had a basis weight of 40.3 g / m ² and a thickness of 84 μm.
In addition, using only the raw material of the middle layer, a basis weight of 60 g was obtained by an ordinary method.
/ M ² was prepared and its density was measured.
The density was 0.23 g / cm ³ . The obtained sheet is actually transferred to an electrophotographic copying machine (model: Vivance 67).
5, manufactured by Fuji Xerox Co., Ltd.), and the suitability for PPC was determined. Table 1 shows the measurement results of the basis weight, density, and Clark stiffness of the obtained sheet. The methods for measuring the bond reinforcing factor, number average fiber length, water retention, wet curl factor, and Clarke stiffness are described below.

Evaluation method [Measurement method of bond strengthening factor] 50% of hardwood bleached kraft pulp and 50% of softwood bleached kraft pulp were mixed to prepare a 2% concentration, and a Niagara beater for experiment (capacity: 23L, Tozai Seiki Co., Ltd.) The material was beaten to a Canadian Standard Freeness (CSF) of 500 ml, and 3.7 g of this stock was dried without any chemicals. Using a 150-mesh wire, a square shape (25 cm × 25 cm) was used.
m) A sheet is formed by a hand making machine, and after a coaching process, a wet press is performed for 5 minutes (first press) and 2 minutes (second press) at a pressure of 3.5 kg / cm ² according to a conventional method. After that, drying was carried out at room temperature by a blast dryer between the frames. Thereafter, the sheet 1 was heat-treated at 130 ° C. for 2 minutes to prepare a sheet 1 having a basis weight of 60 g / m ² , and was heated at 20 ° C. and 65% RH.
It was conditioned. On the other hand, the NL mixed beaten pulp 50% by weight
And 3.7 g of bone dry from a raw material in which 50% by weight of fine fibers are well mixed, and a sheet 2 is prepared in the same manner,
The humidity was adjusted at 20 ° C. and 65% RH. After measuring the density of sheets 1 and 2, a dynamic Young's modulus measuring device (Nomura Shoji Co., Ltd.)
And model: SST-210A) to determine the elastic modulus (GP) of the sheets 1 and 2 by measuring the ultrasonic wave propagation velocity.
a) was measured. The elastic modulus (E) was calculated by the following equation. E (GPa) = ρ (g / cm ³ ) × {S (km / s)} ² where ρ is the density (g / cm ³ ) of the sheet after humidity control, and S is the ultrasonic wave propagation velocity (km / s). ). When the elastic modulus of the sheet 1 is E1 (GPa) and the elastic modulus of the sheet 2 is E2 (GPa), the bond strengthening factor is ｛(E2 / E1) −
It is represented by 1｝.

[Measurement method of number average fiber length] Measured by a Kayani fiber length measuring instrument (model: FS-200).

[Method of measuring water retention] Water retention was measured by JAPAN
TAPPI No. It measured according to 26-78. When the carded fiber was in a dry state, the following was performed. Collect 0.5 g of absolutely dry paper stock and 100 ml of distilled water
And then allowed to stand at room temperature for 24 hours to allow sufficient water impregnation, then the stock is collected on a filter and then centrifuged with a G2 glass filter (model:
(H-103N, manufactured by Domestic Centrifuge Co., Ltd.) and centrifuged at 3,000 G for 15 minutes. The sample subjected to the centrifugal dehydration treatment is taken out from the centrifuge tube, the weight in a wet state is measured, and then dried in a dryer at 105 ° C. until a constant weight is obtained.
The dry weight was measured, and the water retention was calculated by the following equation. Water retention (%) = {(WD) / D} × 100 where W is the wet weight (g) of the sample after centrifugal dehydration, and D is the dry weight (g) of the sample. In the case of fine fibers,
The solid content was adjusted to a range of 6 to 9%, and a sample was collected so as to have an absolute dry weight of 0.7 g, placed in a centrifuge tube having a G3 glass filter, and subjected to centrifugal dehydration treatment in the same manner as described above. The water retention was calculated from the wet weight and the dry weight by the above equation.

[Measurement Method of Wet Curl Factor] 100 pieces of curled fibers after being immersed in distilled water at room temperature for 24 hours are placed on a microscope slide glass, and each fiber is used for each fiber using an image analyzer. The actual (linear) length LA (μm) and the maximum projected length (equal to the length of the longest side of the rectangle surrounding the fiber) LB (μm) were measured, and the wet curl factor was obtained from the following equation. The average value was used. Wet curl factor = (LA / LB) -1

[Measurement Method of Clark Stiffness] Clark stiffness was measured according to JIS P8143.

Example 2 A multilayer paper having a three-layer structure was prepared according to the following formulation. (1) Preparation of outer layer (plain paper layer) Water was added to 630 ml of hardwood bleached kraft pulp to adjust the concentration to 2%, and beaten to 380 ml of CSF using a laboratory Niagara beater (capacity: 23 liters). To this pulp, the additive chemicals used for producing the outer layer of Example 1 were added in the same manner in terms of the type and the addition ratio, to prepare a raw material slurry. An absolutely dry 1.2 g portion of this slurry was taken, and a square (25 mm) equipped with an 80 mesh bronze wire was used.
cm × 25cm) 18g /
After forming an m ² wet sheet on the wire, two wet outer layer sheets were prepared on thin filter paper in exactly the same manner as in the outer layer preparation procedure of Example 1.

(2) Preparation of Middle Layer (Low Density Layer) To 70 parts of the curled fiber and 15 parts of the fine fibers used in Example 1, 15 parts of bleached kraft pulp of 630 ml of unbeaten hardwood was mixed with 630 ml of CSF. The additive chemicals used in 1 were added in the same manner with respect to the type and the addition ratio, and a raw material slurry was prepared. Take 1.2 g of absolutely dry from this slurry and add 8 g
Square with 0 mesh bronze wire (25cm ×
25 cm) A wet sheet having a basis weight of 18 g / m ² was formed on the wire by a hand-made sheet machine.

(3) Preparation of three-layer sheet
The layers were overlaid, wet pressed and dried. The basis weight of the obtained sheet after humidity control is 53.9 g / m ² , and the thickness is 8
It was 5.6 μm. Also, using only the middle layer raw material,
A sheet having a basis weight of 60 g / m ² was prepared by a conventional method, and its density was measured. The density was 0.25 g / cm ³ . The obtained sheet is actually transferred to an electrophotographic copying machine (model:
(Vision 675, manufactured by Fuji Xerox Co., Ltd.), and the suitability for PPC was evaluated. Table 1 shows the measurement results of the basis weight, density, and Clark stiffness of the obtained sheet.

Example 3 A multilayer paper having a three-layer structure was prepared according to the following formulation. (1) Preparation of outer layer (plain paper layer) As the raw material pulp, 500 ml of hardwood bleached kraft pulp of 500 ml of CSF used for preparing the outer layer of Example 1 was used.
Parts and 20 parts of fine fibers, and the same procedure as in Example 1 was carried out, except that the additives were added and the basis weight was 14.5 g / m ^2.
Was prepared.

(2) Preparation of Middle Layer (Low Density Layer) Using a thermomechanical pulp refined to 370 ml of CSF, pre-dried to a solid concentration of 50%, Similarly, a thermomechanical pulp curled fiber was obtained. The obtained pulp CSF had 465 ml, a number average fiber length of 0.73 mm, a water retention of 51%, and a wet curl factor of 0.52. 96 parts of the obtained pulp and 4 parts of the fine fibers used in Example 1 were blended, and the chemicals used in Example 1 were added in the same manner in terms of type and addition rate to prepare a raw material slurry. An absolutely dry 0.92 g portion of this slurry was taken, and the basis weight was 2 using a square (25 cm × 25 cm) hand-made sheet machine equipped with an 80 mesh bronze wire.
A 9 g / m ² wet sheet was formed on the wire.

(3) Preparation of three-layer sheet
The layers were overlaid, wet pressed and dried. The basis weight of the obtained sheet after humidity control is 57.7 g / m ² , and the thickness is 8
It was 4.7 μm. Also, using only the middle layer raw material,
A sheet having a basis weight of 60 g / m ² was prepared by a conventional method, and the density was measured. The density was 0.30 g / cm ³ . The obtained sheet is actually transferred to an electrophotographic copying machine (model: V
(p. 675, manufactured by Fuji Xerox Co., Ltd.), and the suitability for PPC was determined. Table 1 shows the measurement results of the basis weight, density, and Clark stiffness of the obtained sheet.

Comparative Example 1 Example 2 was used as a raw material pulp.
380 ml of hardwood bleached kraft pulp used for preparing the outer layer of CSF was prepared. To the pulp, the additive chemicals used in Examples 1 to 3 were added in exactly the same manner in terms of type and addition rate to prepare a raw material slurry. Absolutely dry 4 from this raw material slurry
g of raw material, and a square sheet machine was used to obtain Example 1.
A wet sheet was produced in the same manner as in the procedure for producing the outer layer. From this wet sheet, a one-layer sheet was produced in exactly the same manner as the procedure for producing a three-layer sheet in Example 1. The basis weight of this sheet after humidity control was 64.3 g / m ² , and the thickness was 85.5 μm. The obtained sheet was actually fed to an electrophotographic copying machine (model: Vivance 675, manufactured by Fuji Xerox Co., Ltd.) and the suitability for PPC was determined.
Both runnability and printability were good. Table 1 shows the measurement results of basis weight, density, and Clark stiffness of the obtained sheet.
Shown in

<Comparative Example 2> A one-layer sheet was prepared by blending pulp such that the pulp blending ratio of the entire three-layered sheet prepared in Example 1 was the same. That is, 40 parts of curled fiber used in Example 1, 25 parts of fine fiber, C
A raw material slurry was prepared by blending 25 parts of SF bleached kraft pulp with 320 ml of SF, and adding the additive chemicals used in Example 1 in the same manner in terms of type and addition rate. From the raw slurry, a raw material equivalent to 4.3 g of absolutely dry was taken, and a wet sheet was prepared in the same manner as in the case of forming the outer layer in Example 1 using a square sheet machine. From this wet sheet, a one-layer sheet was produced in exactly the same manner as the procedure for producing a three-layer sheet in Example 1. The basis weight of this sheet after humidity control was 65.7 g / m ² , and the thickness was 84.8 μm. The obtained sheet was actually fed to an electrophotographic copying machine (model: Vivance 675, manufactured by Fuji Xerox Co., Ltd.) and the suitability for PPC was checked. As a result, the running property was good, but unevenness was noticeable in printing. It was not practical. Table 1 shows the measurement results of the basis weight, density, and Clark stiffness of the obtained sheet.

[0054]

[Table 1]

The thickness of each of the sheets of Examples 1 to 3 and Comparative Examples 1 and 2 is around 85 μm. As is clear from Table 1, the sheets of Examples 1 to 3 have strength, In particular, the stiffness is a sufficient level of the sheet as compared with Comparative Example 1. Example 1 has the same level of rigidity as Comparative Examples 1 and 2, even though the basis weight is only 40 g / m ² .
Further, in Example 2, although the basis weight is lower than Comparative Examples 1 and 2, it has stiffness far exceeding that of Comparative Example. On the other hand, as shown in Comparative Example 2, even if the raw materials used in Example 1 are mixed in one layer, a sheet having high rigidity as shown in Example 1 cannot be obtained.

[0056]

As described above, the present invention provides a lightweight paper which can be used for high quality paper, printing paper, information paper, electrophotographic paper, wrapping paper, etc. having a multilayer structure excellent in smoothness and strength, especially rigidity. Is provided.

Claims (4)

[Claims] 1. At least one surface layer is a plain paper layer mainly composed of cellulose fibers, and at least one other layer is
A curled fiber having a wet curl factor in the range of 0.4 to 1.0, and a bond reinforcing factor of 0.1
A multilayer paper comprising a low density layer containing 5 or more fine fibers. 2. It has a multilayer structure of three or more layers, and at least one of the middle layers has a wet curl factor of 0.4.
Plain paper containing curled fibers in the range of ~ 1.0 and fine fibers having a bond reinforcing factor of 0.15 or more, and both outermost layers on the front and back sides are mainly composed of cellulose fibers. Multilayer paper characterized by being a layer. 3. A low-density layer in which a curled fiber having a wet curl factor in the range of 0.4 to 1.0 is bound in an amount of 35 to 98% based on the total dry fiber weight of the low-density layer. 3. The multilayer paper according to claim 1, wherein the low-density layer contains 2-65% of fine fibers having a factor of 0.15 or more based on the total fiber weight of the low-density layer. 4. The low-density layer has a density of 0.05 to 0.4.
The multilayer paper according to any one of claims 1 to 3, which is 5.