JP7248438B2 - Decorative board base paper - Google Patents

Description

TECHNICAL FIELD The present invention relates to a base paper for decorative laminate used for manufacturing a melamine decorative laminate.

Melamine decorative boards are widely used as building materials and interior materials for furniture because they are excellent in wear resistance, heat resistance, chemical resistance, and the like. The base paper for decorative laminates used for these melamine decorative laminates is required to have concealability to hide the substrate. Therefore, the base paper for decorative laminate is internally added with titanium oxide, which has the highest refractive index among white pigments (Patent Document 1).

If the content of titanium oxide is increased, the hiding power is improved, but the cost is increased and the texture may be deteriorated. Therefore, it is required to reduce the titanium oxide content within a range that satisfies the required hiding property. However, in general decorative laminate base papers to which titanium oxide is internally added, a titanium oxide content of 30% by mass or more is required to satisfy the hiding rate required for decorative laminate base papers.

JP-A-2006-97198

An object of the present invention is to provide a base paper for decorative laminate which is excellent in concealability in spite of its low content of titanium oxide.

Means for solving the problems of the present invention are as follows.
1. A base paper for decorative laminate, characterized in that the content of titanium oxide is 28% by mass or less and the opacity (JIS P8149:2000) is 91% or more.
2. 1. The titanium oxide content is 24% by mass or less. The base paper for decorative laminate described in .
3. 1. The opacity is 94% or more. or 2. The base paper for decorative laminate described in .
4.1. ~3. Melamine decorative paper comprising the base paper for decorative laminate according to any one of
5.1. ~3. A melamine decorative board comprising the base paper for decorative board according to any one of .

The base paper for decorative laminate of the present invention has high hiding power in spite of its low content of titanium oxide. The base paper for decorative laminate of the present invention has a high yield of titanium oxide during the manufacturing process, and the content of titanium oxide in the fiber-containing slurry before papermaking can be reduced, so the raw material cost is low. In addition, since the amount of inorganic pigment contained in the waste liquid after papermaking is small, the cost for waste liquid treatment is low.

TECHNICAL FIELD The present invention relates to base paper for decorative lamination having a titanium oxide content of 28% by mass or less and an opacity (JIS P8149:2000) of 91% or more.
The base paper for decorative laminate of the present invention has a titanium oxide content of 28% by mass or less, preferably 26% by mass or less, more preferably 24% by mass or less, relative to the total mass of the decorative laminate base paper. More preferably, it is 22% by mass or less. The base paper for decorative laminate of the present invention has an opacity of 91% or more, preferably 94% or more, more preferably 95% or more, as measured in accordance with JIS P8149:2000. Preferably, it is more preferably 97% or more. In the base paper for decorative laminate of the present invention, the lower limit of the content of titanium oxide is not particularly limited as long as it satisfies the above opacity, but is about 15% by mass.
BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to this, and can be implemented in various modifications within the scope described.

[Titanium oxide composite fiber]
The base paper for decorative laminate of the present invention preferably contains titanium oxide conjugated fibers (hereinafter also simply referred to as conjugated fibers) as papermaking fibers.
A titanium oxide composite fiber is a fiber for papermaking in which an inorganic binder is fixed to the fiber, and titanium oxide is fixed to the inorganic binder, whereby the titanium oxide is fixed to the fiber through the inorganic binder.

- Fiber The fiber constituting the conjugate fiber is not particularly limited, and includes natural fiber, synthetic fiber, semi-synthetic fiber, inorganic fiber, and the like. Natural fibers include, for example, cellulose fibers, wool, silk thread, protein fibers such as collagen fibers, and composite sugar chain fibers such as chitin/chitosan fibers and alginic acid fibers. Synthetic fibers include, for example, fibers made of polyester, polyamide, polyolefin, acrylic, and the like. Semi-synthetic fibers include fibers made of rayon, lyocell, acetate, and the like. Examples of inorganic fibers include glass fibers, carbon fibers, and various metal fibers. Hybrid fibers can also be used, and more specifically, hybrid fibers of synthetic fibers, inorganic fibers, etc. and cellulose fibers can also be used. The fibers exemplified above can be used alone or in combination of two or more.

Examples of raw materials for cellulose fibers include pulp fibers (wood pulp and non-wood pulp), bacterial cellulose, animal-derived cellulose such as sea squirt, and the like.
Wood pulp may be produced by pulping wood raw materials. Wood raw materials include red pine, black pine, Sakhalin fir, spruce, red pine, larch, fir, hemlock, cedar, cypress, larch, white fir, spruce, hiba, Douglas fir, hemlock, white fir, spruce, balsam fir, cedar, pine, Coniferous trees such as Mercury pine and radiata pine, and mixtures of these, broadleaf trees such as beech, birch, alder, oak, tab, chinensis, white birch, cotton willow, poplar, ash, willow, eucalyptus, mangrove, lauan, and acacia, and mixtures thereof material is exemplified.

The method of pulping a material such as a wood raw material (woody raw material) is not particularly limited, and a pulping method commonly used in the paper industry is exemplified. Wood pulp can be classified by pulping method, for example, chemical pulp cooked by methods such as Kraft method, sulfite method, soda method, polysulfide method; mechanical pulp obtained by mechanical power such as refiner and grinder; semi-chemical pulp obtained by mechanical pulping after pretreatment with a cellulose; waste paper pulp; deinked pulp, and the like. The wood pulp may be unbleached (before bleaching) or bleached (after bleaching).

Raw materials for non-wood pulp include cotton, hemp, sisal hemp, Manila hemp, flax, straw, bamboo, bagasse, kenaf, sugar cane, corn, rice straw, mulberry, and mitsumata.

The pulp fibers may be either unbeaten or beaten, and may be selected depending on the physical properties of the composite fiber, but beating is preferred. Beating is expected to improve the strength of pulp fibers and promote the adhesion of titanium oxide and an inorganic binder. Also, an improvement in the strength of the resulting sheet can be expected. The degree of beating of pulp fibers can be represented by the Canadian Standard freeness (CSF) specified in JIS P 8121-2:2012. As the beating progresses, the drainage state of the pulp fibers decreases and the freeness decreases. The freeness of pulp fibers is usually 600 ml or less, but in the present invention, it can be 550 ml or less, 500 ml or less, 450 ml or less, 400 ml or less, or 350 ml or less from the viewpoint of improving the strength of the base paper for decorative laminate.

Among the examples shown above, the fibers constituting the composite fibers are preferably cellulose fibers, and more preferably contain wood pulp or a combination of wood pulp and non-wood pulp and/or synthetic fibers. , most preferably only wood pulp. As the wood pulp, it is preferable to use a mixture of softwood pulp and hardwood pulp from the viewpoint of achieving both strength and texture. The mass ratio (dry weight) of softwood pulp and hardwood pulp can be in the range of 5/95 to 95/5.

Although the fiber length of the composite fibers is not particularly limited, for example, the average fiber length is about 0.1 μm to 15 mm, 10 μm to 12 mm, 50 μm to 10 mm, 200 μm to 8 mm, and the like. It is preferable that the average fiber length is longer than 50 μm because dehydration and sheeting are easy. It is more preferable that the average fiber length is longer than 200 μm because dehydration and sheeting in a normal papermaking process are easy.

Although the fiber diameter of the fibers to be combined is not particularly limited, for example, the average fiber diameter is about 1 nm to 100 μm, 10 nm to 100 μm, 0.15 μm to 100 μm, 1 μm to 90 μm, 3 μm to 50 μm, 5 μm. The thickness may be set to 30 μm or more. Among these, it is preferable that the average fiber diameter is thicker than 500 nm because it is easy to water and form into a sheet. It is more preferable that the average fiber diameter is larger than 1 μm, because it facilitates dehydration and sheeting in a normal papermaking process.

- Inorganic binder The inorganic binder that constitutes the composite fiber is not particularly limited as long as it adheres to the fibers and titanium oxide. However, the inorganic binder is preferably insoluble or sparingly soluble in water because the synthesis of the inorganic binder may be performed in an aqueous system and the composite fiber may be used in an aqueous system.

The inorganic binder is a solid inorganic compound, such as a metal compound. Metal compounds include metal cations (eg, Na ⁺ , Ca ²⁺ , Mg ²⁺ , Al ³⁺ , Ba ²⁺ etc.) and anions (eg, O ²⁻ , OH ⁻ , CO ₃ ²⁻ , PO ₄ ³⁻ , SO ₄ ^2- , NO ₃ -, Si ₂ O ₃ ^2- , SiO ₃ ^2- , Cl ^- , F ^- , S ^{2- ,} etc.) are combined by ionic bonds, and are generally called inorganic salts. Say. Specific examples of inorganic binders include compounds containing at least one metal selected from the group consisting of gold, silver, copper, platinum, iron, zinc, and aluminum. Also magnesium carbonate, barium carbonate, aluminum hydroxide, calcium hydroxide, barium sulfate, magnesium hydroxide, zinc hydroxide, calcium phosphate, zinc oxide, zinc stearate, sodium silicate and silica produced from mineral acids (white carbon , silica/calcium carbonate composite, silica/titanium dioxide composite), calcium sulfate, zeolite, hydrotalcite, and the like. The inorganic binders exemplified above can be used singly or in combination of two or more as long as they do not interfere with the mutual synthesis reaction in the solution containing the fibers.

At least a portion of the inorganic binder preferably contains a metal salt or metal particles containing at least one selected from the group consisting of silicic acid, magnesium, barium, aluminum, copper, iron, and zinc. The inorganic binder is more preferably barium sulfate and hydrotalcite, and particularly preferably hydrotalcite, because of their high bonding properties with titanium oxide.

In general, hydrotalcite has the structure of [M ²⁺ _1−x M ³⁺ _x (OH) ₂ ][A ⁿ⁻ _x/n ·mH ₂ O] (where M ²⁺ is a divalent metal ion and M ³⁺ is represents a trivalent metal ion, A ⁿ⁻ _x/n represents an interlayer anion, 0<x<1, n is the valence of A, and 0≦m<1. be Here, the divalent metal ion M ²⁺ is a trivalent metal ion such as Mg ²⁺ , Co ²⁺ , Ni 2+ , Zn ²⁺ , Fe ²⁺ , Ca ²⁺ , Ba ²⁺ , Cu ^{2+ ,} Mn ²⁺ , etc. Some M ³⁺ are, for example, Al ³⁺ , Fe ³⁺ , Cr ³⁺ , Ga ³⁺ , etc., and A ^n- are n-valent anions, such as OH ⁻ , Cl ⁻ , CO ₃ ⁻ , SO ₄ ⁻ . Anions may be mentioned, where x generally ranges from 0.2 to 0.33. Among these, Mg ²⁺ , Zn ²⁺ , Fe ²⁺ and Mn ²⁺ are preferable as the divalent metal ions. In particular, magnesium-based hydrotalcite is more preferable than other inorganic binders because it facilitates wastewater treatment, is stable against heat, and has a high degree of whiteness.

When the inorganic binder is hydrotalcite, the composite fiber of hydrotalcite, titanium oxide, and fiber preferably contains 10% by mass or more of magnesium, iron, manganese, or zinc in the ash, and contains 20% by mass or more. is more preferred. The metal content in the ash can be quantified by fluorescent X-ray analysis.

In one preferred embodiment, the average primary particle size of the inorganic binder can be, for example, 1 μm or less. An inorganic binder having a particle size of 100 nm or less and an inorganic binder having an average primary particle size of 50 nm or less can be used. Also, the average primary particle size of the inorganic binder can be 10 nm or more.

In addition, in the specification of the present application, the average primary particle size is a value calculated based on a scanning electron micrograph. Specifically, the area of the particle image in the electron micrograph is measured, and the primary particle diameter of the particle is obtained as the diameter of a circle having the same area. The average primary particle diameter of the particles is the 50% particle diameter in the volume-based integrated fraction calculated as the average value of the primary particle diameters obtained for 100 or more randomly selected particles. It can be calculated using an analysis device.

In addition, inorganic binders having various sizes and shapes can be combined with fibers by adjusting the conditions for synthesizing the inorganic binder. For example, composite fibers in which scale-like inorganic binders are combined with fibers may be used. The shape of the inorganic binder that constitutes the conjugate fiber can be confirmed by observation with an electron microscope.

In addition, the inorganic binder may take the form of secondary particles in which fine primary particles are aggregated, and the secondary particles may be generated according to the application by an aging process. may Grinding methods include ball mills, sand grinder mills, impact mills, high pressure homogenizers, low pressure homogenizers, dyno mills, ultrasonic mills, Kanda grinders, attritors, stone mills, vibration mills, cutter mills, jet mills, disaggregators, and beaters. , short-screw extruders, twin-screw extruders, ultrasonic stirrers, domestic juicer mixers, and the like.

• Titanium oxide As the titanium oxide that constitutes the composite fiber, any purity product that is generally commercially available for industrial or experimental use can be used. Titanium oxide that has undergone surface treatment can also be used. Examples of surface treatment agents include, but are not limited to, metal oxides such as silica, alumina, and zinc oxide.

Examples of titanium oxide include titanium monoxide (TiO), titanium dioxide (TiO ₂ ), and dititanium trioxide (Ti ₂ O ₃ ). Among these, titanium dioxide is preferably used from the viewpoint of whiteness and hiding power. As titanium dioxide, titanium dioxide having any crystal structure such as rutile type, anatase type, and brookite type can be used. It is preferable because it can be demonstrated. Moreover, rutile-type titanium oxide is preferable in that it can impart opacity, wet strength, and high weather resistance suitable for a base paper for decorative laminate to the sheet obtained by making the composite fiber.

The average primary particle size of titanium oxide is preferably 50 nm or more and 400 nm or less, more preferably 100 nm or more and 300 nm or less, and even more preferably 150 nm or more and 250 nm or less. By setting the average primary particle size of the titanium oxide within this range, it is possible to produce a base paper for decorative laminate with high whiteness and concealability.

Composite fiber Composite fiber is less likely to fall off because titanium oxide is fixed to the fiber via the inorganic binder, compared to a mixture of fibers, titanium oxide, and an inorganic binder. Therefore, the base paper for decorative laminate containing this composite fiber has a high pigment yield of titanium oxide during papermaking. Further, the base paper for decorative laminate containing this conjugate fiber can exhibit high whiteness and high hiding power with a low content of titanium oxide as compared with the conventional base paper for decorative laminate to which titanium oxide is internally added.

It is preferable that 15% or more of the fiber surface of the composite fiber is covered with an inorganic binder. When the fiber surface is coated with the inorganic binder in such an area ratio, the titanium oxide can be efficiently fixed to the inorganic binder, and a conjugate fiber exhibiting the whiteness and hiding power of the titanium oxide more remarkably can be obtained. be able to. In addition, in the conjugate fiber, the coverage (area ratio) of the fiber with the inorganic binder is more preferably 50% or more, more preferably 80% or more. In addition, according to the following method for producing a composite fiber in which an inorganic binder is synthesized in a solution containing fibers and titanium oxide, a composite fiber having a coverage of 90% or more, further 95% or more can be suitably produced. The upper limit of the coverage may be appropriately set according to the desired concealing properties, and is, for example, 100%, 90%, and 80%. Observation with an electron microscope has revealed that this conjugate fiber has an inorganic binder formed on the outer surface of the fiber. The coverage refers to the coverage (area ratio) of the fiber with the inorganic binder, and can be calculated from the electron microscope image of the composite fiber.

The composite fiber preferably has a total ash content of 20% by mass or more and 80% by mass or less, more preferably 30% by mass or more and 60% by mass or less. The total ash content of the composite fibers was obtained by filtering the composite fiber slurry (3 g in terms of solid content) with suction using filter paper, drying the residue in an oven (105 ° C., 2 hours), and then burning the organic content at 525 ° C. can be calculated from the mass before and after combustion. By sheeting such conjugate fibers, a conjugate fiber sheet with a high ash content can be produced.

The content of titanium oxide in the composite fiber can be 5% by mass or more, and can be 40% by mass or more, for example, 5% by mass or more and 30% by mass or less, as ash. It is preferably 15% by mass or more and 35% by mass or less. The higher the content of titanium oxide in the conjugate fiber, the higher the degree of whiteness and hiding power can be exhibited. The content of titanium oxide in the composite fiber can be calculated by measuring the total ash content by the method described above and then quantifying the ratio of titanium oxide in the ash by X-ray fluorescence analysis.

The content of the inorganic binder in the conjugate fiber can be 10% by mass or more, can be 20% by mass or more, and can be preferably 40% by mass or more. Incidentally, the content of the inorganic binder can be calculated from the ash content with respect to the entire composite fiber. Specifically, the content of the inorganic binder is determined by (total ash - (total ash x titanium oxide content in ash))/(conversion factor). Here, the "conversion factor" is the weight reduction rate due to thermal decomposition under the condition that the inorganic binder is treated at 525°C for 2 hours. If the inorganic binder used is an unknown substance, the sheet is defiberized to separate the fibers and the inorganic content, and then only the inorganic content is recovered by fiber classification using a fractionator. C. for 2 hours, followed by further combustion at 525.degree. Inorganic substances dried at 105° C. for 2 hours can be identified by X-ray diffraction.

The strength of binding between the fibers, the inorganic binder and the titanium oxide in the conjugated fiber can be evaluated by the ash retention (%) when the conjugated fiber is made into paper. For example, the composite fiber is dispersed in water to adjust the solid content concentration to 0.2%, and after disintegration for 5 minutes with a standard disintegrator specified in JIS P 8220-1: 2012, 150 mesh according to JIS P 8222: 1998. The ash retention when sheeted using a wire can be used for evaluation.

The ash content retention of the composite fiber is preferably 80% by mass or more, more preferably 90% by mass or more. Composite fibers having an ash retention of 80% by mass or more are less likely to exfoliate the inorganic binder and titanium oxide from the composite fibers during papermaking. In addition, composite fibers having an ash retention of 80% by mass or more can be obtained in a uniformly dispersed state without agglomeration.

- Manufacturing method of titanium oxide composite fiber Titanium oxide composite fiber can be manufactured by synthesizing an inorganic binder in a slurry containing fibers and titanium oxide.
By synthesizing the inorganic binder in the slurry containing the fibers and titanium oxide, the solid inorganic binder adheres to the fibers and the titanium oxide adheres to the inorganic binder. By this manufacturing method, a titanium oxide composite fiber in which titanium oxide is efficiently fixed to the fiber can be obtained.

For example, when the inorganic binder is hydrotalcite, a composite fiber of hydrotalcite, titanium oxide and fibers can be produced by synthesizing hydrotalcite in a solution containing fibers and titanium oxide.

Hydrotalcite can be synthesized by a known method. For example, first, fibers are immersed in a carbonate aqueous solution containing carbonate ions and an alkaline aqueous solution (sodium hydroxide, etc.) that constitutes an intermediate layer in a reaction vessel, and suspended to form a slurry. Next, titanium oxide is added and dispersed in the resulting alkaline slurry. Next, an acid solution (aqueous metal salt solution containing divalent metal ions and trivalent metal ions constituting the basic layer) is added to the alkaline slurry to which titanium oxide has been added, and a coprecipitation reaction is performed by controlling the temperature, pH, etc. to synthesize hydrotalcite. Then, when hydrotalcite is formed on the fiber surface, titanium oxide dispersed in the slurry is incorporated into the hydrotalcite and adheres thereto. As a result, a high proportion of titanium oxide present in the slurry can be efficiently and uniformly fixed to the fibers.

The slurry obtained by soaking and suspending the fibers is preferably adjusted to have a pH in the range of 11-14, more preferably in the range of 12-13. When the pH of the slurry is within this range, titanium oxide, which is then added, can be uniformly dispersed in the slurry.

Various chlorides, sulfides, nitrates, and sulfates of magnesium, zinc, barium, calcium, iron, copper, silver, cobalt, nickel, and manganese are used as a source of divalent metal ions constituting the basic layer. be able to. Various chlorides, sulfides, nitrates, and sulfates of aluminum, iron, chromium, and gallium can be used as a source of trivalent metal ions constituting the basic layer.
Further, for example, when the inorganic binder is another metal compound, similarly, by synthesizing the metal compound in a solution containing the fiber and titanium oxide, a composite fiber of the metal compound, titanium oxide, and fiber can be produced. can be done.

The method for synthesizing the metal compound is not particularly limited, and it can be synthesized by a known method, which may be either a gas-liquid method or a liquid-liquid method. An example of the gas-liquid method is the carbon dioxide method. For example, magnesium carbonate can be synthesized by reacting magnesium hydroxide and carbon dioxide. Calcium carbonate can also be synthesized by a carbon dioxide method in which calcium hydroxide and carbon dioxide are reacted. For example, calcium carbonate may be synthesized by a soluble salt reaction method, a lime-soda method, or a soda method. Examples of the liquid-liquid method include neutralization of acids (hydrochloric acid, sulfuric acid, etc.) and bases (sodium hydroxide, potassium hydroxide, etc.), reaction of inorganic salts with acids or bases, and reaction of inorganic salts with each other. A method of causing a reaction can be mentioned. For example, barium sulfate can be obtained by reacting barium hydroxide and sulfuric acid. Aluminum hydroxide can be obtained by reacting aluminum chloride or aluminum sulfate with sodium hydroxide. An inorganic binder in which calcium and aluminum are combined can be obtained by reacting calcium carbonate and aluminum sulfate.

Further, when synthesizing the inorganic binder in this manner, any other metal or metal compound different from titanium oxide can coexist in the reaction solution. It can be efficiently incorporated into a binder and compounded.

Further, when two or more types of inorganic binders are combined with fibers, a step of synthesizing one type of inorganic binder in the presence of fibers and titanium oxide is performed, followed by a step of synthesizing another type of inorganic binder. may be performed, and two or more kinds of inorganic binders may be synthesized at the same time if they do not interfere with each other's synthesis reactions or if multiple kinds of target inorganic binders are synthesized in one synthesis reaction.

When producing the conjugate fiber, various known auxiliary agents can be added. Such additives can be added in an amount of preferably 0.001% by mass or more and 20% by mass or less, more preferably 0.1% by mass or more and 10% by mass or less, relative to the inorganic binder.

The temperature of the inorganic binder synthesis reaction can be, for example, 30° C. or higher and 100° C. or lower, preferably 40° C. or higher and 80° C. or lower, more preferably 50° C. or higher and 70° C. or lower, and particularly preferably about 60° C. . If the temperature is too high or too low, the reaction efficiency tends to decrease and the cost tends to increase.

Furthermore, the synthesis reaction can be controlled by the reaction time, specifically by adjusting the residence time of the reactants in the reaction vessel. In addition, in the present invention, the reaction can be controlled by stirring the reaction solution in the reaction vessel or by making the neutralization reaction a multi-stage reaction.

[Base paper for decorative laminate]
In order to obtain a base paper for decorative laminate that has suitable hiding properties, conventional base paper for decorative laminates has been used that contains 30% by mass or more of titanium oxide. However, the base paper for decorative laminate of the present invention has a titanium oxide content of 28% by mass or less and an opacity (JIS P8149:2000, the higher the opacity, the higher the hiding power of the base paper for decorative laminate) is 91% or more. The content of titanium oxide is preferably 26% by mass or less, more preferably 24% by mass or less, and even more preferably 22% by mass or less. Also, the opacity is preferably 94% or more, more preferably 95% or more, and even more preferably 97% or more.

The base paper for decorative laminate may have a single-layer structure or a multi-layer structure in which multiple layers are laminated, and in the multi-layer structure, the composition of each layer may be the same or different.
The basis weight of the base paper for decorative laminate can be appropriately adjusted according to the desired whiteness, hiding power, etc., but it is preferably 50 g/m ² or more and 180 g/m ² or less, and 70 g/m ² or more and 150 g/m ² or less. It is more preferable to have

A base paper for decorative laminate, which is one embodiment of the present invention, contains titanium oxide composite fibers. Since the titanium oxide composite fiber has titanium oxide fixed to the fiber, the pigment yield is high when the composite fiber is made into a base paper for decorative laminate. In addition, the obtained base paper for decorative laminate has high concealability and little difference in whiteness between the front and back surfaces. When the decorative laminate base paper contains conjugate fibers, only one type of conjugate fiber may be used, or two or more types may be mixed and used.

The composition of the base paper for decorative laminate is not particularly limited as long as it satisfies the above titanium content and opacity. For example, conjugate fibers and non-composite fibers can be included. The term "fibers that do not form a composite" means fibers to which an inorganic binder is not adhered. By including fibers that do not form a composite, the strength of the resulting sheet can be improved. It is preferable that the mass ratio (dry weight) of the composite fiber and the fiber not forming a composite be in the range of 80/20 to 100/0.

The fibers that do not form a composite are not particularly limited, and examples thereof include the fibers exemplified in the above ".fibers". Among these, the non-composite fiber preferably contains wood pulp or a combination of wood pulp and non-wood pulp and/or synthetic fiber, and is only wood pulp. is more preferred. Softwood kraft pulp is more preferable because it has a long fiber length and is advantageous for improving strength.

The base paper for decorative laminate of the present invention preferably contains 5% by mass or more, more preferably 10% by mass or more, of softwood pulp based on the total mass of the base paper for decorative laminate, from the viewpoint of improving strength. When ordinary pulp fibers are used as the pulp fibers, the content of softwood pulp cannot be increased because the texture is deteriorated by blending a large amount of titanium oxide. However, when the base paper for decorative laminate of the present invention contains conjugate fibers, the texture is better than when titanium oxide is internally added, so the blending ratio of softwood pulp can be increased.

The decorative laminate base paper can contain additives used in the papermaking field. Such additives include wet and/or dry paper strength agents (hereinafter also referred to as paper strength agents). The paper strength enhancer can improve the strength of the base paper for decorative laminate. Examples of paper strength agents include urea formaldehyde resin, melamine formaldehyde resin, polyamide, polyamine, epichlorohydrin resin, vegetable gum, latex, polyethyleneimine, glyoxal, gum, mannogalactan polyethyleneimine, polyacrylamide resin, polyvinyl resins such as amines and polyvinyl alcohols; composite polymers or copolymers composed of two or more selected from the above resins; starches and modified starches; carboxymethyl cellulose, guar gum, urea resins and the like. The addition amount of the paper strength agent is not particularly limited. However, when the base paper for decorative laminate of the present invention contains composite fibers, titanium oxide is fixed to the fibers. can be done.

Other additives include pigments, drainage improvers, internal sizing agents, pH adjusters, defoaming agents, pitch control agents, slime control agents, bulking agents, fillers such as calcium carbonate, kaolin and talc. be done. The amount of each additive used is not particularly limited.

[Method for producing base paper for decorative laminate]
The method for producing the base paper for decorative laminate of the present invention is not particularly limited, but one example is a method for making paper from a composite fiber-containing slurry containing titanium oxide composite fibers.
The paper machine (machine) used for producing the base paper for decorative laminate is not particularly limited. and paper machines. When paper-making a multi-layer composite fiber sheet, a multi-layer paper machine may be used.

[melamine decorative paper, melamine decorative board]
A melamine decorative paper can be obtained by impregnating the base paper for decorative laminate of the present invention with a melamine resin. Also, a melamine decorative board can be obtained by laminating this melamine decorative paper to a core material. Since the base paper for decorative laminate of the present invention has high concealability, core materials made of various materials can be used.

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to these examples. In addition, unless otherwise specified in this specification, concentrations, parts, etc. are based on mass, and numerical ranges are described as including the endpoints.

"Example 1"
(1) Preparation of alkaline solution and acid solution An alkaline solution and an acid solution for synthesizing hydrotalcite (HT) were prepared.
・ Alkaline solution (Na ₂ CO ₃ concentration: 0.15 M, NaOH concentration: 2.4 M)
・ Acid solution (MgSO ₄ concentration: 0.9 M, Al ₂ (SO ₄ ) ₃ concentration: 0.15 M)

(2) Composite fiber synthesis The fibers include bleached hardwood kraft pulp (LBKP, manufactured by Nippon Paper Industries Co., Ltd.) and bleached softwood kraft pulp (NBKP, manufactured by Nippon Paper Industries Co., Ltd.) at a mass ratio of 80: 20 (average fiber length: about 1 to 2 mm) and the Canadian standard freeness was adjusted to 500 ml using a double disc refiner (DDR).
Pulp fibers were added to the alkaline solution to prepare an aqueous suspension containing pulp fibers (pulp fiber concentration: 2.0%, pH: about 12.7). This aqueous suspension (180 kg of pulp solid content) was placed in a 15 m ³ reaction tank, and 60 kg of titanium dioxide (R-3L, manufactured by Sakai Chemical Industry Co., Ltd.) was added and thoroughly stirred.

While stirring this aqueous suspension, the acid solution was added dropwise (dropping rate: 6 L/min). The reaction temperature was set to 50° C., and the dropwise addition was stopped when the pH of the reaction solution reached about 7. After completion of dropping, the reaction solution was stirred for 30 minutes, washed with water using a drum filter to remove salts, and titanium oxide fine particles and solid hydrotalcite (Mg ₆ Al ₂ (OH) ₁₆ CO _{3.4H 2 )} were collected. O) and pulp fibers (solid content of pulp: 60% by mass, hydrotalcite: 20% by mass, titanium oxide: 20% by mass) were synthesized.
Observation of the surface of the composite fiber obtained using a scanning electron microscope revealed that 15% or more of the fiber surface was covered with solid hydrotalcite. Moreover, the average primary particle size of the solid hydrotalcite was 1 μm or less.

To 100 parts of the resulting composite fiber slurry (concentration: 1.2% by weight), 100 ppm of a cationic retention agent (ND300, manufactured by Hymo Co., Ltd.) and an anionic retention agent (FA300, manufactured by Hymo Co., Ltd.) were added. ) was added at 100 ppm to prepare a stock slurry. A composite fiber sheet (basis weight: 100 g/m ² ) was produced from this stock slurry using a fourdrinier paper machine at a machine speed of 10 m/min.

"Example 2"
A composite fiber sheet was produced in the same manner as in Example 1, except that the Canadian standard freeness of the pulp fibers used in the production of the composite fiber was set to 400 ml.
"Example 3"
A conjugate fiber sheet was produced in the same manner as in Example 1, except that the Canadian standard freeness of the pulp fibers used in the production of the conjugate fiber was set to 300 ml.

"Example 4"
The Canadian standard freeness of the pulp fiber used for the production of the composite fiber is set to 550 ml, and the paper material slurry is added with a wet strength agent (WS-4024, manufactured by Seiko PMC Co., Ltd.) at 0.2 wt% (relative to the composite fiber). Fiber) A composite fiber sheet was produced in the same manner as in Example 1, except that the fiber was added.

"Example 5"
A composite fiber sheet was produced in the same manner as in Example 4, except that the Canadian standard freeness of the pulp fibers used in the production of the composite fiber was set to 500 ml.
"Example 6"
A conjugate fiber sheet was produced in the same manner as in Example 4, except that the Canadian standard freeness of the pulp fibers used in the production of the conjugate fiber was set to 400 ml.
"Example 7"
A conjugate fiber sheet was produced in the same manner as in Example 6, except that the Canadian standard freeness of the pulp fibers used in the production of the conjugate fiber was set to 300 ml.

"Example 8"
80 parts of the composite fiber obtained in Example 2 (the Canadian standard freeness of pulp fiber is 400 ml) and softwood bleached kraft pulp (NBKP, manufactured by Nippon Paper Industries Co., Ltd.) (average fiber length: about 1 to 2 mm, Canadian standard filter A composite fiber sheet was produced in the same manner as in Example 4, except that 20 parts of the mixture with a water content of 400 ml was made into paper.

"Example 9"
The fiber contains bleached hardwood kraft pulp (LBKP, manufactured by Nippon Paper Industries Co., Ltd.) and bleached softwood kraft pulp (NBKP, manufactured by Nippon Paper Industries Co., Ltd.) at a mass ratio of 80:20 (average fiber length: about 1 to 2 mm). , Using a pulp fiber adjusted to a Canadian standard freeness of 400 ml using a double disc refiner (DDR), an aqueous suspension containing this pulp fiber (120 kg of pulp solid content) was placed in a 15 m ³ reaction tank, and dioxide was added. A composite fiber (50% by mass of pulp solids, 25% by mass of hydrotalcite, 25% by mass of titanium oxide) was synthesized in the same manner as in Example 1, except that 60 kg of titanium was added.

A mixture of 80 parts of the obtained composite fiber and 20 parts of bleached softwood kraft pulp (NBKP, manufactured by Nippon Paper Industries Co., Ltd.) (average fiber length: about 1 to 2 mm, Canadian standard freeness of 400 ml) was made into paper. A composite fiber sheet was produced in the same manner as in Example 4.

"Example 10"
A composite fiber sheet was produced in the same manner as in Example 9, except that 90 parts of the composite fiber and 10 parts of the bleached softwood kraft pulp were used.

"Example 11"
The mass ratio of bleached hardwood kraft pulp (LBKP, manufactured by Nippon Paper Industries Co., Ltd.) and bleached softwood kraft pulp (NBKP, manufactured by Nippon Paper Industries Co., Ltd.) in pulp fibers used for manufacturing composite fibers is set to 90:10, Canadian standard drainage A composite fiber sheet was produced in the same manner as in Example 1, except that the concentration was 400 ml.
"Example 12"
A composite fiber sheet was produced in the same manner as in Example 11, except that the Canadian standard freeness was 300 ml.

"Example 13"
The Canadian standard freeness of the pulp fiber used for manufacturing the composite fiber is set to 500 ml, and 0.2 wt% of a wet paper strength agent (Seiko PMC Co., Ltd. product, WS-4024) is added to the stock slurry (anti-composite Fiber) A composite fiber sheet was produced in the same manner as in Example 11, except that the fiber was added.
"Example 14"
A composite fiber sheet was produced in the same manner as in Example 13, except that the Canadian standard freeness of the pulp fibers used in the production of the composite fibers was set to 400 ml.
"Example 15"
A composite fiber sheet was produced in the same manner as in Example 13, except that the Canadian standard freeness of the pulp fibers used in the production of the composite fiber was set to 300 ml.

"Example 16"
As the pulp fiber used for manufacturing the composite fiber, only bleached hardwood kraft pulp (LBKP, manufactured by Nippon Paper Industries Co., Ltd.) is used, and the paper material slurry is added with a wet strength agent (Seiko PMC Co., Ltd., WS-4024). ) was added in an amount of 0.2 wt % (relative to the conjugate fiber), a composite fiber sheet was produced in the same manner as in Example 4.
"Example 17"
A composite fiber sheet was produced in the same manner as in Example 16, except that the Canadian standard freeness of the fibers used in the production of the composite fibers was 300 ml.

"Comparative Example 1"
The fiber contains bleached hardwood kraft pulp (LBKP, manufactured by Nippon Paper Industries Co., Ltd.) and bleached softwood kraft pulp (NBKP, manufactured by Nippon Paper Industries Co., Ltd.) at a mass ratio of 80:20 (average fiber length: about 1 to 2 mm). , Using pulp fibers whose Canadian standard freeness was adjusted to 300 ml using a double disc refiner (DDR), an aqueous suspension containing this pulp fiber (200 kg of pulp solid content) was placed in a 15 m ³ reaction tank, Furthermore, in the same manner as in Example 1, except that 55 kg of titanium dioxide (R-3L, manufactured by Sakai Chemical Co., Ltd.) was added, composite fibers having no inorganic binder (solid pulp content: 89% by mass, titanium oxide: mass %) was obtained.
A hand-made sheet having a basis weight of 100 g/m ² (solid content of pulp: 95% by mass, titanium oxide: 5% by mass) was produced in the same manner as in Example 4 except that this composite fiber was used.

"Comparative Example 2"
To 11.875 kg (pulp fiber concentration: 0.8%) of the pulp fiber aqueous suspension obtained in Comparative Example 1, 10.4 g of titanium oxide was added and sufficiently suspended to prepare an aqueous suspension. . A hand-made sheet with a basis weight of 100 g/m ² (solid pulp content: 95% by mass, titanium oxide: 5% by mass) to which titanium oxide was added was prepared in the same manner as in Comparative Example 1 except that this aqueous suspension was used. was made.

"Comparative Example 3"
To 7.5 kg of the pulp fiber aqueous suspension obtained in Comparative Example 1 (pulp fiber concentration: 0.8%), 33 g of titanium oxide and 21 g of synthesized hydrotalcite were added and sufficiently suspended to obtain an aqueous suspension. A suspension was prepared. In the same manner as in Example 1 except that this aqueous suspension was used, a hand-made sheet with a basis weight of 100 g/m ² containing titanium oxide and hydrotalcite (solid pulp content: 60% by mass, hydrotalcite 20% by mass of site and 20% by mass of titanium oxide).

"Comparative Example 4"
To 8.75 kg of the pulp fiber aqueous suspension obtained in Comparative Example 1 (pulp fiber concentration: 0.8%), 60 g of titanium oxide was added and sufficiently suspended to prepare an aqueous suspension. A hand-made sheet with a basis weight of 100 g/m ² (solid content of pulp: 70% by mass, titanium oxide: 30% by mass) to which titanium oxide was added was prepared in the same manner as in Comparative Example 1 except that this aqueous suspension was used. was made.

"Comparative Example 5"
To 8.125 kg (pulp fiber concentration: 0.8%) of the pulp fiber aqueous suspension obtained in Comparative Example 1, 67 g of titanium oxide was added and sufficiently suspended to prepare an aqueous suspension. A hand-made sheet with a basis weight of 100 g/m ² (solid content of pulp: 65% by mass, titanium oxide: 35% by mass) to which titanium oxide was added was prepared in the same manner as in Comparative Example 1 except that this aqueous suspension was used. was made.

〔evaluation〕
The sheets obtained in Examples and Comparative Examples were subjected to the following measurements. Table 1 shows the results.
<Titanium oxide content>
The titanium oxide content (% by mass) in the sheet was calculated from the total ash content in the sheet and the titanium oxide content in the ash.
The total ash content was calculated by drying the obtained sheet in an oven (105° C., 2 hours), burning the organic matter at 525° C., and calculating the mass before and after burning.
The content of titanium oxide in the ash was quantified using an energy dispersive X-ray fluorescence spectrometer EDX-7000 (manufactured by Shimadzu Corporation).

<Inorganic binder content>
The content (mass%) of the inorganic binder (hydrotalcite) in the sheet was determined by (total ash - (total ash x content of titanium oxide in ash))/(conversion factor). Incidentally, the conversion factor is 0.6 in the case of hydrotalcite.
<Titanium oxide yield>
It was calculated from the content of titanium oxide in the formulation and the content of titanium oxide in the obtained sheet.

<Basis Weight>
Measured based on JIS P 8124:1998.
<Wet strength>
After immersing a sheet cut to 15 mm in width and 100 mm in length in the grain direction in deionized water or distilled water at 20 ° C. for 10 minutes, excess water on the surface was removed, and JIS P 8135: 1998 "Paper and paperboard - wet tensile It was measured according to "Strength test method".

<Opacity>
Measured based on JIS P 8149:2000. The larger the opacity value, the better the concealability when the melamine decorative paper is produced from the base paper for decorative laminate.
<Whiteness>
Based on JIS P 8212:1998, the W side (the side in contact with the wire of the paper machine) and the F side (the side not in contact with the wire of the paper machine) of the sheet were measured.

[Evaluation of decorative melamine board]
The produced sheet was impregnated with a melamine resin to produce a melamine decorative paper. The obtained melamine decorative paper was laminated on the surface of the core plate, and the hiding property was visually observed. The evaluation criteria were as follows.
○: The back cannot be seen through △: The back can be seen slightly ×: The back can be seen through

Since the conjugate fiber used in Comparative Example 1 did not include an inorganic binder, it was not possible to increase the content of titanium oxide. In addition, the sheet obtained in Comparative Example 1 was inferior in concealability due to the low content of titanium oxide.
The sheet obtained in Comparative Example 2 had titanium oxide internally added so as to have a titanium oxide content equivalent to that of Comparative Example 1, but had a low hiding power equivalent to that of Comparative Example 1.
The sheet obtained in Comparative Example 3 was manufactured by internally adding fibers so that the contents of fibers, inorganic binder, and titanium oxide were equivalent to those of the sheet obtained in Example. It was inferior in opacity compared to each sheet produced. From Comparative Examples 1 to 3, by using a composite fiber in which titanium oxide is combined with fibers through an inorganic binder, a sheet with excellent opacity is obtained compared to the case where titanium oxide and an inorganic binder are simply added internally. It was confirmed that it was obtained.
The sheets obtained in Comparative Examples 4 and 5 are conventional base papers for decorative laminates, and contain 30 parts by weight or more of titanium oxide by internal addition. The sheets obtained in Comparative Examples 4 and 5 had excellent hiding properties, but the yield of titanium oxide was low.

The sheets produced in the examples of the present invention have a high opacity (JIS P8149: 2000) of 91% or more, despite the low titanium oxide content of 28% by mass or less, and are excellent in hiding properties. , it was confirmed that it can be suitably used as a base paper for decorative laminates. In particular, Examples 1 to 7 and 9 to 17 had hiding power equivalent to that of the conventional base papers for decorative laminates described in Comparative Examples 4 and 5 containing 30 parts by weight or more of titanium oxide as an internal addition. In addition, the sheets produced in the examples according to the present invention had a smaller difference in whiteness between the front and back surfaces than the comparative examples in which the pigment was internally added. Furthermore, in the base paper for decorative laminate of the present invention, titanium oxide is combined with fibers via an inorganic binder, so that the pigment yield during papermaking is high.

Claims (5)

The content of titanium oxide is 28% by mass or less, and the opacity (JIS P8149: 2000) is 91% or more,
A base paper for decorative laminate, comprising pulp fibers , wherein the pulp fibers have a Canadian standard freeness of 450 ml or less . The base paper for decorative laminate according to claim 1, wherein the content of titanium oxide is 24% by mass or less. The base paper for decorative laminate according to claim 1 or 2, wherein the opacity is 94% or more. A melamine decorative paper comprising the base paper for decorative laminate according to any one of claims 1 to 3. A melamine decorative board comprising the base paper for decorative board according to any one of claims 1 to 3.