JP2000008299A - Flame resistant insulating paper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a flame resistant insulating paper having three or more multilayer structure, having the UL class of 94V-0 for flame resistance, and containing a reduced amount of flame retardants while keeping the class of the UL 94V-0 for the flame resistance. SOLUTION: This flame resistant insulating paper having a multilayer structure composed of a surface layer, inner core layers and a back layer is regulated so that the limited oxygen indexes of the surface layer and the back layer may be each >=27, and that of at least one layer of the inner core layers may be >=18 and <=24, and further regulated so that the proportion of the surface and back layers based on the flame resistant insulating paper may be 35-85 wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flame-retardant insulating paper having a flame-retardant UL standard 94V-0 (hereinafter referred to as a flame-retardant insulating paper) used for insulating electrical equipment. More specifically, a sheet made of cellulose fiber, or a base paper made of cellulose fiber and a water-containing inorganic compound, mixed with a flame retardant, or coated, or impregnated with a flame retardant sheet by impregnation as a surface layer and a back layer. One layer of the core layer is laminated with a sheet made of cellulose fiber or a mixed paper made of cellulose fiber and a water-containing inorganic compound to form a multilayer structure of three or more layers. The present invention relates to a flame-retardant insulating paper which can be manufactured at a low cost.

[0002]

2. Description of the Related Art Flame-retardant insulating paper is obtained by adding a flame-retardant function to insulating paper used for insulating electrical equipment in order to enhance the safety of electric fires. Since the Product Liability Act (PL Act) was enacted in 1995, the safety of electric fires has been questioned. This has heightened interest in electric fire safety,
Improvements in flame retardancy have been required.

[0003] As a method of imparting flame retardancy to paper, a method of applying or impregnating a flame retardant, or a method of containing a flame retardant organic substance or inorganic powder in cellulose fibers by a wet papermaking method is known. And are roughly classified into inorganic flame retardant paper and organic flame retardant paper. The inorganic flame-retardant paper is a relatively inexpensive inorganic paper mainly composed of inorganic powder, and the organic flame-retardant paper is a paper obtained by adding an organic flame retardant to paper.

However, when using inorganic paper alone, it is necessary to increase the content of inorganic powder in order to ensure flame retardancy as flame-retardant insulating paper. As a result, the strength required for insulating paper must be ensured. And it is not practical. Therefore, it is an issue to make organic flame-retardant paper flame-retardant.

Conventionally, as a method of flame-retarding insulating paper,
A method in which antimony trioxide and a halogen-containing compound are mixed with cellulose, and a method in which antimony trioxide is applied or impregnated to a sheet in which cellulose fibers or a mixture of cellulose fibers and a water-containing inorganic compound are coated or impregnated, are disclosed in JP-B-51-17606, No. 1-37502. Antimony trioxide melts in the early stage of combustion, forms a film on the surface of cellulose, blocks oxygen, lowers the temperature of the flame by an internal endothermic reaction, and exhibits self-extinguishing properties. If the temperature further rises, antimony trioxide itself gasifies, diluting the combustible gas. In addition, since this compound does not contain hydrogen ions, it promotes the dehydration and carbonization of cellulose and suppresses the production of tar-like substances necessary for continuing combustion.

When coexisting with a halogen-based flame retardant,
The decomposition temperature of the halogen-based flame retardant is appropriately lowered to exhibit the flame retardant effect. Antimony trioxide and halides have high flame retardancy due to the above synergistic effect, but environmental measures have become a problem worldwide, and in Japan, antimony trioxide has been designated as a wastewater monitoring item. I have. Also,
In Europe, there is a concern that there is a risk of carcinogenicity, so there are cases where the content in products is regulated mainly for electrical products, and it is necessary to switch to non-antimony flame retardants .

[0007] Flame-retardant insulating papers differ in the required flame retardancy depending on their use. UL standard (Underwrite
rs Laboratories Inc. ) 94V-
The flame-retardant insulating paper satisfying 0 has the highest flame retardancy among the flame-retardant insulating papers.

[0008] Further, a limit oxygen index is known as an index of flame retardancy, which is a minimum oxygen concentration (volume%) required for a material to continue burning under predetermined test conditions. It is flammable at an oxygen index of 21 or less, self-extinguishing at a limiting oxygen index of 22 to 25, and flame retardant at a limiting oxygen index of 26 or more, and UL standard 94V-0 corresponds to a limiting oxygen index of 26 or more. .

The flame-retardant insulating paper or the base paper used for the flame-retardant insulating paper is manufactured by a wet papermaking method. In wet papermaking, as the basis weight of the sheet increases, the texture deteriorates, and the insulating property decreases. Further, from the drying capacity and drying efficiency of the paper machine, the basis weight of one sheet is around 300 g / m ² and the thickness is 0.1 g / m ² .
The limit is around 25 mm.

[0010] Accordingly, since a sheet having a thickness of 0.30 mm or more cannot be obtained with one sheet, it is presently manufactured by laminating two or more layers of sheets of the same quality. Because of the use of, the cost is high. Further, when the amount of the water-containing inorganic compound is increased in order to suppress the use amount of the flame retardant, there is a problem that the strength of the flame retardant insulating paper is reduced.

[0011]

DISCLOSURE OF THE INVENTION The present invention relates to a non-antimony flame retardant which has excellent safety and does not adversely affect the environment, and has a high flame retardancy satisfying UL standard 94V-0. It is intended to provide inexpensive insulating paper.

[0012]

In view of such circumstances, the present inventor has conducted intensive research on flame-retardant insulating paper using a non-antimony-based flame retardant. As a result, in the process of burning the sheet, the flame spreads on the surface of the sheet. Paying attention to propagation, if a flame retardant is applied only to the front and back surfaces of a sheet without flame retardant effect,
It has been found that the flame retardant effect of the entire seat is improved. In addition, the inventors considered that the reduction in sheet strength due to the use of a non-antimony-based flame retardant was reinforced by providing a core layer. That is, the surface layer and the back layer are each provided with a sheet having a high flame-retardant effect, and the core layer is provided with at least one sheet having a low flame-retardant effect, and by laminating,
The present inventors have found that an inexpensive flame-retardant insulating paper satisfying the UL standard 94V-0 with little reduction in paper strength can be obtained, and completed the present invention.

That is, the present invention includes the following inventions. (1) It has a multilayer structure consisting of a surface layer, a core layer, and a back layer,
And a flame-retardant insulating paper having the following configuration. (2) The ratio of the surface layer and the backing layer to the flame-retardant insulating paper is 35 to 85% by weight or less. The limiting oxygen index of the surface layer and the backing layer is 27 or more, respectively. (2) The flame-retardant insulating paper according to (1), wherein the surface layer, the core layer, and the back layer are bonded to each other. (3) The flame-retardant insulating paper according to (1), wherein the flame retardant of at least one of the surface layer, the core layer, and the back layer is a non-antimony-based flame retardant.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The flame-retardant insulating paper of the present invention is obtained by mixing a flame retardant with a base paper comprising cellulose fibers and a hydrated inorganic compound on the surface layer and the back layer, or by applying a flame retardant to the base paper. Alternatively, a highly flame-retardant sheet provided with flame retardancy by impregnation is used, and at least one of the core layers is made of cellulose fibers or a mixture of cellulose fibers and a water-containing inorganic compound. Laminated sheets with low flammability are laminated.

As the cellulose fiber as a raw material of the flame-retardant insulating paper or the flame-retardant insulating base paper, softwood unbleached kraft pulp (NU
KP), softwood semi-bleached kraft pulp (NSBKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), hardwood semibleached kraft pulp (L
Kraft pulp such as SBKP) and bleached bleached kraft pulp (LBKP); non-wood fibers such as cotton fiber, Manila hemp, jute, red hemp, flax and sisal hemp; one or more of these pulp types are suitable Can be selected and used.

If necessary, a wet paper strength agent such as polyamide polyamine epichlorohydrin generally used in papermaking, or a cationized starch such as cationized starch or polyacrylamide may be added to the above-mentioned slurry of cellulose fibers or a mixed slurry of cellulose fibers and a water-containing inorganic compound. Additives that are commonly used in papermaking, such as a dry paper strength enhancer, a retention enhancer, a thickener such as polyethylene oxide, a binder such as vinylon or an emulsion, and easily form by a normal wet papermaking method. be able to. The paper machines used are circular nets, single nets, long nets, birch formers, roto formers,
Any of a hydro former or the like may be used, and the dryer may be any of a Yankee type, a multi-cylinder type, and a through type.

Examples of the water-containing inorganic compound used in the present invention include aluminum hydroxide and magnesium hydroxide. These water-containing inorganic compounds release water of crystallization by heating, and are self-digestible due to endothermic decomposition. Can be applied to paper. The carrying amount varies depending on the combination with the flame retardant, but when the carrying amount increases, the strength of the paper decreases. Therefore, the amount is suitably 10 to 40% by weight or less.

Examples of non-antimony flame retardants include guanidine phosphate, ammonium phosphate and guanidine sulfamate. Guanidine flame retardants have the effect of diluting the oxygen concentration of oxygen due to the generation of incombustible gas, and the dehydration and carbonization of cellulose. Alternatively, a flame retardant effect is exerted by providing a covering effect. Halogen-containing compounds, tin oxide,
A stannic acid compound, molybdenum oxide, ammonium molybdate, boric acid, zinc borate, or the like may be used. The supported amount of the flame retardant is appropriately supported so as to satisfy the desired limiting oxygen index of the surface layer, the core layer, and the back layer depending on the combination of the type of the flame retardant used, the type and the amount of the water-containing inorganic compound.

The flame retardant is mixed with cellulose fibers to make paper, or mixed with cellulose fibers and a water-containing inorganic compound to make wet paper. Or a base paper obtained by mixing paper with cellulose fibers, a base paper obtained by mixing paper with cellulose fibers and a water-containing inorganic compound, using a commonly used impregnation method, or applying, impregnating using a size press machine, or Coating the surface with a coater.

The flame retardant used for coating or impregnation may be, if necessary, a binder such as starch, polyvinyl alcohol, polyvinyl chloride / ethylene / vinyl acetate resin, vinylidene chloride resin, etc.
It is also possible to mix a water retention agent such as polyacrylamide, an alkyl ketene dimer or a styrene / acrylic surface sizing agent.

In the present invention, the above-described flame retardant is mixed, coated, or impregnated on the sheet as the surface layer and the back layer of the multilayer structure so that the limiting oxygen index of the sheet becomes 27 or more. Carry an appropriate amount. If the limiting oxygen index is less than 27, the nonflammable gas required to contribute to the flame retardancy of the core layer or the covering effect is insufficient, and the UL standard is 94V.
Since −0 is not satisfied, the limiting oxygen index is required to be 27 or more, and the total ratio of the surface layer and the back layer to the entire flame-retardant insulating paper is 35% by weight or more to maintain the flame retardancy.
If it exceeds 85% by weight, the amount of the flame retardant used is large, and there is no significance in providing the core layer. Further, the type of the flame retardant used for the surface layer and the back layer, and the amount of the flame retardant may be supported so as to satisfy a desired limiting oxygen index, and the surface layer and the back layer may be different. For example, when guanidine phosphate is impregnated into paper obtained by mixing 20% by weight of cellulose fiber and aluminum hydroxide on the surface layer and the back layer and the limiting oxygen index is 27 or more, guanidine phosphate may be carried at 13% by weight or more. .

In the present invention, at least one of the core layers has a limiting oxygen index of 18 or more and 24 or less. When the limiting oxygen index is 18 or less, the UL specification 94V-0 is not satisfied unless the amount of expensive flame retardants contained in the surface layer and the back layer is increased. Therefore, the limiting oxygen index is 18 or more. On the other hand, in order to limit the amount of expensive flame retardants and increase the limiting oxygen index to 24 or more, the content of the water-containing inorganic compound increases, and the strength required for insulating paper cannot be obtained. 24 or less. The loading amount of the water-containing inorganic compound contained in the core layer is not more than 40% by weight at which the strength of the paper is maintained.

A flame-retardant-containing paper used in the present invention, and
Paper containing hydrated inorganic compound, or application of flame retardant or
Sheet density after immersion is 0.95 to 1.30 g / cm^ThreeRange of
Enclose. Sheet density 0.95g / cm^ThreeLess than
Insulation required for edge paper cannot be obtained. Meanwhile, cellulose
The density is 1.3 g / c for a sheet mainly composed of fiber.
m ^ThreeWhen the calendar process is performed as described above, the calendar
-Since sheet strength deteriorates due to burning,
Is 0.95 to 1.30 g / cm^ThreeRange.

The adhesive used for laminating the surface layer, the core layer and the back layer includes natural polymers such as starch and glucomannan, and synthetic polymers such as polyvinyl alcohol and vinyl acetate. In addition, the bonding method is to apply an adhesive to the front and back surfaces of the sheet to be the core layer, to laminate the sheet to be the surface layer, and the sheet to be the back layer, and then press and compress using a press roll or the like, and then dry. . Dryers used for laminating include a Yankee type, a multi-cylinder type, and a through type. In particular, when a Yankee type is used, the adhesiveness between the sheet and the adhesive is increased because the drying is performed by restraint. The sheet basis weight after lamination is 350g
/ M ² or more. The sheet basis weight after lamination is 350 g / m ²
In the following, paper making with one layer is possible in a paper machine, and there is no significance in performing lamination. Therefore, the sheet basis weight after lamination is set to 350 g / m ² or more.

[0025]

EXAMPLES The present invention will be described more specifically with reference to examples below, but the present invention is of course not limited to these. In Examples and Comparative Examples, “%” indicates “% by weight of solid content” unless otherwise specified.

Example 1 Canadian Standard Freeness (CSF) 35 is prepared from NUKP (unbleached softwood kraft pulp) by a conventional method.
A pulp slurry beaten with 0 ml was prepared. Aluminum hydroxide (manufactured by Sumitomo Chemical Co., Ltd., "CL-310") containing 0.06% by weight of soda was added to the pulp slurry to prepare a mixed slurry. Using a laboratory square-shaped hand-making machine, the slurry was subjected to a basis weight of about 120 g / m ² having a limiting oxygen index of 23 containing 23% by weight of aluminum hydroxide.
And a base paper having a basis weight of about 170 g / m ² were prepared. Guanidine phosphate (manufactured by Sanwa Chemical Co., Ltd., “Apinon 30”) having a basis weight of about 120 g / m ² having a limiting oxygen index of 23
7 ") and a basis weight of about 135 g /
It created the m ² of the sheet. The above-mentioned base paper having a basis weight of about 170 g / m ² having a limiting oxygen index of 23 and a sheet having a basis weight of about 135 g / m ² having a limiting oxygen index of 27 were converted to a sheet having a density of 1.2 g / cm ³ using a laboratory machine calendar. Created. The basis weight of about 135 g / m ² sheet of the limiting oxygen index of 27 in the surface layer and the backing layer, the middle core layer 1 of limiting oxygen index 23 having a basis weight of about 170 g / m ² using a sheet, the middle core layer 1 An adhesive was applied to the front and back surfaces by bar coating, superimposed on the surface layer and the back layer, adhered tightly using an etcher, and dried with a cylinder drier to prepare a flame-retardant insulating paper (Example 1).

Examples 2 and 3 In the same manner as in Example 1, a pulp slurry of NUKP beaten to 350 ml (CFS) was prepared, and a basis weight having a limiting oxygen index of 19 was obtained using a laboratory square hand-making machine. About 150g
/ M ² was prepared. Further, a mixed slurry in which the aluminum hydroxide was added to the pulp slurry was prepared, and a basis weight of about 110 g / having a limiting oxygen index of 23 containing aluminum hydroxide by 23% by weight using a laboratory square hand-making machine was used. created the base paper of m ^2. This limit oxygen index 2
The base paper having a basis weight of about 110 g / m ² was impregnated with guanidine phosphate in the same manner as in Example 1 to prepare a sheet having a limiting oxygen index of 29 and a basis weight of about 128 g / m ² . The above-mentioned base paper having a basis weight of about 150 g / m ² having a limiting oxygen index of 19 and a sheet having a basis weight of about 128 g / m ² having a limiting oxygen index of 29 were converted to a sheet having a density of 1.2 g / cm ³ using a laboratory machine calendar. Created. A basis weight of about 128 g /
m ² sheets are bonded to the surface layer and the back layer, and the core layer 1 is bonded to a sheet having a limiting oxygen index of 19 and a basis weight of about 150 g / m ^{2 in} the same manner as in Example 1. (Example 2) was prepared. The basis weight of the above critical oxygen index 19 of about 150
g / m ² sheet as the core layer 1 and the core layer 3, and the core layer 2
Using a sheet having a limiting oxygen index of 29 and a basis weight of about 128 g / m ² , the sheet is bonded in the same manner as in Example 1, and the surface layer and the back layer of the bonded sheet are further bonded with a basis weight of a limiting oxygen index of 29. 128
Using a sheet of g / m ² , it was bonded in the same manner as in Example 1 to prepare a flame-retardant insulating paper (Example 3).

Example 4 In the same manner as in Example 1, a pulp slurry of NUKP beaten to 350 ml (CSF) was prepared, and a basis weight of 300 g with a limiting oxygen index of 19 was obtained using a laboratory square hand making machine.
/ M ² was prepared. Further, a mixed slurry in which aluminum hydroxide was added to the above pulp slurry was prepared, and using a laboratory square hand-making machine, a basis weight of about 8 with a limiting oxygen index of 23 containing aluminum hydroxide by weight of about 8 was used.
A base paper of 0 g / m ² was prepared. Guanidine phosphate is impregnated into the base paper having a limiting oxygen index of 23 and a basis weight of about 80 g / m ^{2 in} the same manner as in Example 1, and a basis weight of a limiting oxygen index of 29 and a basis weight of about 9 are used.
A 6 g / m ² sheet was prepared. The above critical oxygen index 19
Base paper having a basis weight of about 300 g / m ² and a limiting oxygen index of 2
A sheet having a basis weight of about 96 g / m ² and a density of 1.2 g / cm ³ was prepared using a laboratory machine calendar.
Using the sheet having a critical oxygen index of 29 and a basis weight of about 96 g / m ² as the surface layer and the back layer, and the core layer 1 using a sheet having a critical oxygen index of 19 and a basis weight of about 300 g / m ² , Laminating was performed in the same manner to prepare a flame-retardant insulating paper (Example 4).

Comparative Example 1 In the same manner as in Example 1, a pulp slurry of NUKP beaten to 350 ml (CSF) was prepared, and a mixed slurry was prepared by adding the aluminum hydroxide to the pulp slurry. A base paper having a limiting oxygen index of 23 and containing a weight of about 110 g / m ^2, a weight of about 150 g / m ² , and a density of 0 was prepared using a laboratory square hand-making machine. A base paper of 0.6 g / cm ³ was prepared. About 110 g of basis weight of the above-mentioned limit oxygen index 23
/ M ² of base paper is impregnated with guanidine phosphate in the same manner as in Example 1 and has a limiting oxygen index of 27 and a basis weight of about 124 g / m ^2.
m ² , density 0.6 g / cm ³ sheet and critical oxygen index 2
A sheet having a basis weight of about 128 g / m ² and a density of 0.6 g / cm ³ was prepared. The basis weight of the above critical oxygen index 27 of about 124
g / m ² sheet as the surface layer, a sheet having a limiting oxygen index of 29 and a basis weight of about 128 g / m ² as a back layer, and a core layer 1 using a sheet having a limiting oxygen index of 23 and a basis weight of about 150 g / m ^2. And laminated in the same manner as in Example 1 to obtain a flame-retardant insulating paper (Comparative Example 1).
It was created.

Comparative Examples 2 and 3 In the same manner as in Example 1, a pulp slurry of NUKP beaten to 350 ml (CSF) was prepared, and the slurry was subjected to a limiting oxygen index of 19 using a laboratory square hand-making machine.
A base paper having a basis weight of about 110 g / m ^{2 and} a base paper having a basis weight of 150 g / m ² were prepared. Also, a mixed slurry was prepared by adding the aluminum hydroxide to the pulp slurry,
Using a laboratory square hand-making machine, a basis weight of 150 g having a limiting oxygen index of 23 containing 23% by weight of aluminum hydroxide.
/ M ² was prepared. Guanidine phosphate is impregnated into the base paper having a limiting oxygen index of 19 and a basis weight of about 110 g / m ^{2 in} the same manner as in Example 1, and a basis weight of about 12 and a limiting oxygen index of 26 is used.
A sheet of 1 g / m ² was prepared. The above critical oxygen index 1
9 having a basis weight of about 150 g / m ² base paper, and a basis weight of 150 g / m ² base paper of limiting oxygen index 23, a basis weight of about 121g / m ² limiting oxygen index of 26 sheets using a laboratory machine calender A sheet having a density of 1.2 g / cm ³ was prepared. Using the sheet having a limiting oxygen index of 26 and a basis weight of about 121 g / m ² as the surface layer and the back layer, and the core layer 1 using a sheet having a limiting oxygen index of 19 and a basis weight of about 150 g / m ² , Lamination was performed in the same manner to prepare a flame-retardant insulating paper (Comparative Example 2). Further, using a sheet having a critical oxygen index of 26 and a basis weight of about 121 g / m ² as a surface layer and a back layer, and a middle core layer 1 using a sheet having a critical oxygen index of 23 and a basis weight of about 150 g / m ^2, an example is shown. By laminating in the same manner as in Example 1, a flame-retardant insulating paper (Comparative Example 3) was prepared.

Comparative Example 4 In the same manner as in Example 1, a pulp slurry of NUKP beaten to 350 ml (CSF) was prepared, and a mixed slurry was prepared by adding the aluminum hydroxide to the pulp slurry. 23% by weight of aluminum hydroxide was mixed with the above mixed slurry using a laboratory square hand-making machine.
A base paper having a limiting oxygen index of 23 and a basis weight of about 110 g / m ² , and a base paper having a basis weight of about 150 g / m ² were prepared. In this base paper having a basis weight of about 110 g / m ² having a limiting oxygen index of 23,
Guanidine phosphate was impregnated in the same manner as in Example 1 to prepare a sheet having a limiting oxygen index of 26 and a basis weight of about 121 g / m ² , and a sheet having a limiting oxygen index of 29 and a basis weight of about 128 g / m ² . Basis weight of about 150 g / m ² base paper of the limiting oxygen index of 23, the limiting oxygen index of 26 basis weight of about 121g / m ² of the sheet, and a basis weight of about 128 g / m ² sheets lab limiting oxygen index 29 Density 1.2g /
A sheet of cm ³ was made. With the sheet having a basis weight of about 121 g / m ² having the limiting oxygen index 26 as a surface layer and the sheet having a limiting oxygen index 29 having a basis weight of about 128 g / m ² as a back layer, the core layer 1 having a basis weight of a limiting oxygen index 23 is provided. A sheet having an amount of about 150 g / m ² was bonded in the same manner as in Example 1 to prepare a flame-retardant insulating paper (Comparative Example 4).

COMPARATIVE EXAMPLE 5 In the same manner as in Example 1, a pulp slurry of NUKP beaten to 350 ml (CSF) was prepared, and this slurry was subjected to a limiting oxygen index of 19 using a laboratory square hand-making machine.
A base paper having a basis weight of about 360 g / m ² was prepared. Further, in the same manner as in Example 1, a mixed slurry was prepared by adding aluminum hydroxide to the above pulp slurry, and a limiting oxygen containing 23% by weight of aluminum hydroxide was prepared using a laboratory square hand-making machine. A base paper having an index of 23 and a basis weight of about 55 g / m ² was prepared. The basis weight of this critical oxygen index 23 is about 55 g
/ M ² base paper was impregnated with guanidine phosphate in the same manner as in Example 1 to prepare a sheet having a limiting oxygen index of 30 and a basis weight of about 70 g / m ² . Basis weight of the above critical oxygen index 19 of about 3
Base paper of 60 g / m ² and basis weight 7 with a limiting oxygen index of 30
A sheet having a density of 1.2 g / cm ³ was prepared from the sheet of 0 g / m ² using a lab machine calendar. The above-mentioned sheet having a limiting oxygen index of 29 and a basis weight of about 70 g / m ² is used for the surface layer and the back layer, and the core layer 1 is provided with a limiting oxygen index of 19 and a basis weight of about 360 g / m 2.
With ² of the sheet, it stuck in the same manner as in Example 1,
A flame-retardant insulating paper (Comparative Example 5) was prepared.

Comparative Example 6 In the same manner as in Example 1, a pulp slurry of NUKP beaten to 350 ml (CSF) was prepared, and a mixed slurry prepared by adding the aluminum hydroxide to the pulp slurry was prepared. A base paper having a limiting oxygen index of 23 and a basis weight of about 130 g / m ² containing 23% by weight of aluminum hydroxide was prepared from the above slurry using a laboratory square hand making machine. The basis weight of this critical oxygen index 23 is about 130 g / m ^2.
Is impregnated with guanidine phosphate in the same manner as in Example 1, and has a limiting oxygen index of 27 and a basis weight of about 145 g / m ^2.
Created a sheet. A sheet having a density of 1.2 g / cm ³ was prepared from a sheet having a critical oxygen index of 27 and a basis weight of about 145 g / m ² using a laboratory machine calendar. Using three sheets having a basis weight of about 145 g / m ² having the above-mentioned limiting oxygen index of 27, they were bonded in the same manner as in Example 1 to prepare a flame-retardant insulating paper (Comparative Example 6).

Comparative Example 7 In the same manner as in Example 1, a pulp slurry of NUKP beaten to 350 ml (CSF) was prepared, and antimony trioxide and chlorinated polypropylene were added to the pulp slurry in an absolute dry weight ratio of 1: 2. The mixture was charged to prepare a mixed slurry of cellulose fibers and a flame retardant. Using a laboratory square-shaped hand-making machine, the above slurry was prepared using antimony trioxide at 9.4% by weight and having a limiting oxygen index of 26 and a basis weight of about 14.
A 2 g / m ² base paper was made. This sheet was impregnated with boric acid as a flame retardant aid to prepare a sheet having a limiting oxygen index of 27 and a basis weight of about 145 g / m ² . A sheet having a density of 1.2 g / cm ³ was prepared from a sheet having a critical oxygen index of 27 and a basis weight of about 145 g / m ² using a laboratory machine calendar. A basis weight of about 145 g /
using three sheets of m ^2, stuck in the same manner as in Example 1 to prepare a flame燃絶edge sheet (Comparative Example 7).

The limiting oxygen index of the flame-retardant insulating papers obtained in Examples 1 to 4 and Comparative Examples 1 to 7 was JIS-K-7201.
It measured according to. Flame retardancy evaluation was measured in accordance with UL standards, and UL94V-0 was evaluated as ○ when it passed and × when it failed. In addition, the dielectric breakdown of the obtained flame-retardant insulating paper was measured according to JIS-C-23.
According to JIS-P-8113, the breaking length was measured in accordance with JIS-P-8113, and the dielectric breakdown was 6.5 kv / mm or more as 、, less than that, and the breaking length was 3.8 km or more as 、, and less than ×. did.

Examples 1 to 4 and Comparative Examples 1 to 6 show the content of guanidine phosphate, and Comparative Example 7 shows the total content of antimony trioxide and chlorinated polypropylene. Was described.

Table 1 shows the measurement results of flame retardancy, dielectric breakdown, breaking length, and flame retardant content.

[Table 1]

As is clear from Table 1, the flame-retardant insulating papers obtained in Examples 1 to 4 are conventional flame-retardant insulating papers (Comparative Examples 6 and 7).
Compared with conventional flame-retardant insulating paper (comparative example), it does not contain antimony, reduces the required amount of a flame retardant, satisfies the UL standard 94V-0, and has a dielectric breakdown and breaking length. 6, 7), which is suitable for flame-retardant insulating paper. On the other hand, Comparative Example 1 is inferior in dielectric breakdown and breaking length.
Comparative Examples 2 to 4 are inferior in flame retardancy. Comparative Example 5 is inferior in flame retardancy and dielectric breakdown. Comparative Example 6 requires a large amount of an expensive flame retardant.
Comparative Example 7 has a problem containing antimony.

[0039]

As described above, the flame-retardant insulating paper of the present invention comprises:
It has excellent suitability as a flame-retardant insulating paper, and can reduce the amount of expensive flame-retardant, greatly contributes to the cost reduction of the flame-retardant insulating paper, and various electric insulating papers, for example, an electric dust collector filter, It can be widely used for electrodes of dry batteries and protective coatings for electrical equipment.

 ──────────────────────────────────────────────────続 き Continuing on the front page F term (reference) 4F100 AA19H AH01H BA03 BA07 BA10A BA10B BA13 CA08 CA08A CA08B CA08C DG10A DG10B DG10C GB90 JJ07 JJ07A JJ07B JJ07C YY00A YY00B YY00C 4H028 AA07A18A13A01A38A EA32 FA13 FA19 GA02 GA44

Claims (3)

[Claims] 1. A flame-retardant insulating paper having a multilayer structure comprising a surface layer, a core layer, and a back layer, and having the following constitution. (1) The ratio of the surface layer and the back layer to the flame-retardant insulating paper is 35 to 85% by weight or less. (2) The limiting oxygen index of each of the surface layer and the back layer is 27 or more. Include at least one layer having a limiting oxygen index of 18 or more and 24 or less. 2. The flame-retardant insulating paper according to claim 1, wherein the surface layer, the core layer, and the back layer are laminated. 3. The flame-retardant insulating paper according to claim 1, wherein the flame retardant in at least one of the surface layer, the core layer, and the back layer is a non-antimony-based flame retardant.