JP2002038391A - Electrically insulating laminate base paper - Google Patents

Abstract

(57) [Problem] To provide a laminate base paper suitable for producing a laminate having good silver migration resistance and good shape and dimensional stability. SOLUTION: Hardwood unbleached pulp (LUK) having a copper value of 17 to 25 after cooking obtained by cooking wood chips.
An electrically insulating laminate base paper made from pulp obtained by bleaching P) without using molecular chlorine.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric insulating laminate base paper used for an electric insulating laminate, and more particularly, to an electric insulating laminate having good dimensional stability and excellent silver migration resistance. The present invention relates to an electrically insulating laminate base paper used for manufacturing.

[0002]

2. Description of the Related Art Ordinary laminates, especially electrical insulation laminates,
A thermosetting resin such as a phenolic resin or an epoxy resin is impregnated into the base paper of the electrically insulating laminated board, and heated and dried to form a semi-cured resin prepreg, and a plurality of the prepregs are laminated.
It is manufactured by hot pressing with metal foil. Such an electrically insulating laminate is relatively inexpensive and almost satisfies the performance for use in ordinary electric or electronic equipment, and thus is used mainly in household electric appliances.

[0003] However, with the recent reduction in the size and weight of electric products, the mounting density of electric components has increased, and the conductor patterns of printed wiring boards have become thinner. Furthermore, in a printed wiring board using paper as a base material, the conductor pattern has been made double-sided, and silver through holes for the purpose of electrical connection between the front and back sides have been used. For this reason, not only the workability, dimensional stability, and punchability of the electrical insulating laminate, but also the deterioration of the electrical insulation due to the silver migration phenomenon becomes a problem, and the performance of preventing silver migration (hereinafter referred to as silver migration resistance). Demands for improvements are becoming more stringent.

Conventionally, the pulp used for the base paper of the electrically insulating laminate is unbeaten bleached kraft pulp (L) from hardwood.
BKP) is generally used, but depending on the application, softwood bleached kraft pulp may be blended to increase the strength of the electrically insulating laminate base paper, unbleached pulp may be blended for the purpose of cost reduction, or In some cases, sulphite pulp (SP) is used to increase whiteness. Such pulp is made by a known paper machine, and the density of the obtained electrically insulating laminate base paper is as low as 0.45 to 0.55 g / cm ³ .

[0005] In order to improve the migration of silver on a printed wiring board, the properties required for the base paper include the following: low residual ions in the base paper contributing to silver ionization and precipitation as metallic silver; thermosetting resin Has good impregnation properties. In order to solve such problems, a method using a resin varnish containing an inorganic ion exchanger (JP-A-2-33442, JP-A-5-162245) is known. In the case of paper-based phenolic resin electrical insulating laminate using base paper, since the electrical insulating laminate base paper is made from pulp fiber, it does not provide a fundamental solution and silver migration resistance is sufficient. It was not something. Further, in an electric insulating laminate using a glass nonwoven fabric as a base material, a method of impregnating an organic binder with a metal migration inhibitor added to the glass nonwoven fabric has been proposed (Japanese Patent Application Laid-Open No. 6-158492).
In the case of a base paper for an electrically insulating laminate, the cost is large and it is difficult to adopt it.

[0006] In order to reduce chlorine ions in the pulp, the digestion is advanced and the potassium permanganate value (K) of the pulp is reduced.
Of unbleached pulp having a valency of 10 or less as a raw material for papermaking using low-chlorine-bleached or chlorine-free bleached pulp (Patent No. 27)
No. 64536, Japanese Patent No. 2764537) have been proposed. However, if the K value of unbleached pulp is advanced to 10 or less, the pulp strength is reduced, and the dimensional stability of the electrically insulating laminate is deteriorated. Further, if the K value of the unbleached pulp is advanced to 10 or less, the pulp yield in the cooking step is deteriorated, so that it is difficult to employ the pulp.

Further, in order to improve the heat resistance and electrical properties of the electrically insulating laminate, a method of using pulp obtained by a chlorine-free bleaching method incorporating microbial treatment as a papermaking raw material (Japanese Patent Application Laid-Open No.
No. 34396) has been proposed, but it is not practical because microorganisms require a long treatment time and cellulose as well as lignin are degraded as nutrients for microorganisms, which greatly reduces the yield of pulp. Furthermore, JP-A-7-34
Japanese Patent Publication No. 396 discloses an example using unbleached pulp having a kappa number of 16.0. However, if the kappa number of unbleached pulp is reduced to 16.0, the pulp yield decreases. It is not a common kappa number for unbleached pulp in pulp production.

On the other hand, in order to improve the electrical properties of the electrically insulating laminate, a method of increasing the α-cellulose content (Japanese Patent Application Laid-Open No.
However, there is a drawback that the bending of the fibers becomes large and the shape and dimensional stability of the electrically insulating laminate are deteriorated. Further, the publication does not mention improvement in silver migration resistance. Also, a method using linter pulp is known, but since cotton seed is used as a pulp raw material, the raw material supply is unstable, and the price is expensive, fluctuates easily, and it is difficult to adopt it.

On the other hand, attempts have been made to improve the silver migration resistance by modifying the thermosetting resin to be impregnated. However, other characteristics of the electrically insulating laminate may deteriorate, In the case of a resin electric insulating laminate, a portion strongly dependent on the essential properties of the base paper has been required, and further improvement of the base paper has been required.

In addition, bleaching of pulp fiber as a raw material of an electrically insulating laminate base paper has conventionally been produced by a bleaching method using molecular chlorine. However, in bleaching using molecular chlorine, chlorinated aromatic substances such as dioxin are used. In recent years, it has been clarified that there is a possibility of generating an aromatic compound, and it is required to reduce the amount of molecular chlorine used in order to suppress the generation of a chlorinated aromatic compound. Furthermore, in bleaching using molecular chlorine, cellulose chains, which are the main components of pulp fibers, are decomposed and pulp viscosity and pulp strength are reduced. May be impaired.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to provide an electrical insulating laminate having good silver migration resistance and good electrical insulating laminate properties such as shape and dimensional stability. An object of the present invention is to provide an electrically insulating laminate base paper.

[0012]

In view of the current situation, the present inventors have conducted various studies on a method for producing pulp used for a base paper of an electrically insulating laminated board in order to suppress silver migration of a printed wiring board. According to the present invention, it has been found that the shape and dimensional stability and silver migration resistance of an electrically insulating laminate obtained using an electrically insulating laminate base paper made from pulp produced without using molecular chlorine as a papermaking raw material are extremely excellent. Was completed.

The present invention encompasses the following inventions: (1) Hardwood unbleached pulp (LUKP) having a kappa number of 17 to 25 after cooking obtained by cooking wood chips.
Is an electrically insulating laminate base paper which is bleached without using molecular chlorine to obtain a papermaking raw material.

(2) The bleached hardwood pulp is bleached using at least one selected from the group consisting of oxygen, ozone, hydrogen peroxide, chlorine dioxide, and acid in the presence of an alkali. Is an electrically insulating laminate base paper.

[0015] (3) The wood chips contain 10% by weight of wood having a fiber cross-sectional area of 200 μm ² or less in the wood.
An electrically insulating laminate base paper according to (1) or (2), which contains the above.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a conventional bleaching method using molecular chlorine, lignin in pulp is chlorinated by molecular chlorine and then extracted by alkali to remove lignin. On the other hand, a method for producing pulp in which pulp is bleached using at least one selected from the group consisting of oxygen, ozone, hydrogen peroxide, chlorine dioxide, acids, enzymes and microorganisms in the presence of alkali, so-called ECF (Elf)
emental Chlorine Free bleaching differs from the conventional bleaching method using molecular chlorine in that bleaching that eliminates the chromophore of lignin is more important than delignification reaction, so lignin remains in the pulp after bleaching . Since lignin is a high molecular compound having a phenylpropane unit as a basic skeleton, it has a molecular structure very similar to a phenol resin or an epoxy resin used in an impregnation step of an electrically insulating laminate.

In the impregnation step (prepreg production step) of the electrically insulating laminate, a phenol resin having a low degree of polymerization (hereinafter referred to as a water-soluble phenol resin) diluted and adjusted with a mixed solvent of water and methanol is impregnated first. Then, it is common to impregnate tung oil or an oil-modified phenol resin (hereinafter referred to as an oil-based phenol resin) having a high degree of polymerization diluted and adjusted with acetone or the like. Further, for the purpose of cost reduction, a method of mixing the water-soluble phenol resin and the oil-based phenol resin at a predetermined ratio and producing a prepreg in one impregnation step has been adopted. By impregnating the water-soluble phenol resin first or by preferentially penetrating the water-soluble phenol resin, the permeability of the oil-based phenol resin is also improved, and the electrical characteristics of the electric insulating laminate are improved.

In the present invention, a phenolic resin or an epoxy resin is contained in the pulp by bleaching a hardwood pulp having a kappa number of 17 to 25 obtained by digesting wood chips without using molecular chlorine. The presence of lignin having a molecular structure similar to that of pulp improves the affinity between pulp and phenolic resin or epoxy resin, improves resin permeability, and allows phenolic resin or epoxy resin to sufficiently cover pulp fibers Therefore, occurrence of silver migration can be suppressed. If the kappa number after the digestion is higher than 25, the amount of chemicals used for bleaching is increased, so that the economic efficiency is deteriorated and the strength of the pulp is lowered, which is not preferable. If the kappa number is less than 17, pulp strength and yield are undesirably reduced.

The pulp used in the present invention includes wood.
Fiber cross-sectional area is 200μm ^TwoThe following wood is
10% by weight or more is blended. The fiber cross-sectional area is small
This means that the fibers are thin and
The dynamic elasticity of the base paper
Dimensional stability of base paper for electrical insulation
Is improved. That is, pulp with a small fiber cross-sectional area is separated.
By bleaching without using chlorine in the form of silver, it is resistant to silver migration.
Electrical insulation with good versatility and excellent dimensional stability
A laminated base paper can be obtained.

As the pulp used in the present invention, a chemical pulp obtained by cooking wood chips by a cooking method such as kraft cooking or sulphite cooking can be used in the presence of alkali, oxygen, ozone, hydrogen peroxide, chlorine dioxide and acid. A bleaching treatment performed using at least one selected from the group consisting of the following is used. As the bleaching treatment method, a conventionally known method can be used. The above-mentioned bleaching methods can be used alone or in combination within the scope of the present invention.

For the acid treatment in the present invention, known acids such as sulfuric acid, persulfuric acid and peracetic acid can be used.

In the present invention, treatment with enzymes and microorganisms can also be used. Examples of the enzyme treatment include xylanase, lignin peroxidase, manganese-dependent peroxidase, laccase and the like. Further, the microorganism is not particularly limited as long as it has pulp bleaching ability. Phanerochaete chrysosporium, Coriolus versicolor, Coriolus versicolor, Coriolus versicolor (Corio
lus hirsutus) and Kaitake mushrooms (Lenzitesbetulin)
e) and other white rot fungi can be used. The bleaching of pulp by these strains can basically be carried out by inoculating bacteria into pulp and culturing for a predetermined period of time.
It can be appropriately selected under known conditions such as pH.

The wood species used in the present invention include:
Eucalyptus, acacia and the like can be mentioned, but of course, the tree species is not particularly limited as long as the fiber cross-sectional area in the wood is 200 μm ² or less. These eucalyptus, acacia, etc. have the same cross-sectional area of 200 μm due to differences in the growth conditions and growth characteristics related to weather conditions, land, etc.
^{Since it is 2} or more or 200 μm ² or less, the present invention relates to Eucalyptus exserta, Eucalyptus delegatensis, Eucalyptus citriodora, Eucalyptus citrus no. 1 (Eucalyptus leizhou No.
It is necessary to appropriately select and use a tree species having a fiber cross-sectional area of 200 μm ² or less, such as 1) and Acacia mearnsii.

In order to manufacture an electrical insulating laminate from the electrical laminate base paper of the present invention, the electrical insulating laminate base paper is impregnated with a thermosetting resin and dried, and two or more prepregs thus obtained are obtained. Are laminated and molded and integrated at a predetermined temperature and pressure. As the thermosetting resin, generally, a resole type phenol-formaldehyde resin is used, but is not limited thereto, and other
For example, ordinary phenol-formaldehyde resin, melamine-formaldehyde resin, and urea-formaldehyde resin can be mentioned, and they are appropriately selected and used.
The conditions of the heating and pressurizing operations at the time of thermosetting vary depending on the type and amount of the thermosetting resin and the configuration and dimensions of the laminate, but are generally at a temperature of 150 to 180 ° C. and 80 to 120 kg.
At a pressure of / cm ² for 30-60 minutes.

A method for measuring the kappa number and potassium permanganate value (hereinafter referred to as K value), which are indications of the residual lignin content in the pulp used in the present invention, a method for producing an electrically insulating laminate, and a resistance to silver migration The measuring method and the dimensional stability evaluation method are as follows.

Kappa Number Determination Method The kappa number of pulp is TAPPI STD T236.
It was measured according to m-60.

K value measurement method The K value of pulp is TAPPI STD T214 su-
71 was measured. However, if the K value is low,
In order to increase the accuracy of the measurement, the measurement was carried out by appropriately increasing the amount of the pulp sample. The K value is a measure of the amount of residual lignin in the pulp, and it is considered that the higher the K value, the more residual lignin, which contributes to the impregnation of the resin.

The preparation of Preparation Method electrically insulating laminate electrically insulating laminate, electrical insulating laminates base paper, a commercially available water-soluble phenolic resin (trade name Shonol BRL-
2854: Showa Polymer Co., Ltd.) and dried with a dryer to prepare a primary prepreg having a resin to base material ratio of 15:85. Resin (trade name Shaunor BLS-3)
122: manufactured by Showa Polymer Co., Ltd.) and dried to prepare a prepreg having a ratio of resin and base material of both water-soluble phenol resin and oil-modified phenol resin of 50:50. Next, 8 prepregs are stacked, 165 ° C, 100kg
/ Cm ² , for 60 minutes under pressure to obtain a phenolic resin electrically insulating laminate.

Silver migration resistance of electrically insulating laminate
Evaluation method The silver paste is applied to the electrically insulating laminate with a line width of 1 mm and a line gap of 1 mm.
Of an ion migration evaluation system (AMI-025-P: manufactured by Tabai Spec Co., Ltd.)
At a constant temperature and humidity of 60 ° C. and 85% RH.
The insulation resistance between the electrodes was measured while applying a DC voltage of V. In the evaluation, to prevent dew condensation at the start of the test,
The sample was left at 40 ° C. for 1 hour, and after the sample was sufficiently stabilized at that temperature, the humidity was set, and the measurement was started 1 hour after the humidity was set. As an evaluation criterion, the insulation resistance between the electrodes was continuously measured, and it was determined that migration occurred on the substrate having a resistance of 10 ⁶ Ω or less. From this continuous measurement data,
Time until the first migration (failure occurrence time)
Was used as a guide for evaluation. When a normal commercial circuit board is evaluated, durability of 1000 hours or more is required under the above-described conditions, but when the board is not subjected to any moisture resistance treatment as in the above-described method for manufacturing an electrically insulating laminated board. In general, those having a durability of 300 hours or more are generally judged to be good.

Evaluation Method of Dimensional Stability The evaluation method of the dimensional stability of the electrically insulating laminated board is performed by measuring the dimensional change rate by the following method. A mark is formed on the electrically insulating laminate at a span of 250 mm, and the dimension between the marks before and after heating and cooling is measured with a high-precision two-dimensional coordinate measuring device (for example, Digital Reader DR-555-D: Dainippon Screen Mfg. Co., Ltd.)
Co., Ltd.). The dimensional change rate α is obtained from Expression 1. If the electrical insulating laminate base paper is made by a regular square hand-making machine and has no anisotropy, the dimensional change rate is indicated by the average value in the vertical and horizontal directions. In the case where the paper is machined and has anisotropy, the dimensional change is indicated by the geometric mean value in the longitudinal direction, the lateral direction, and the longitudinal and lateral directions. [Equation 1] α (%) = [(L0−L1) / L0] × 100 L0: Length between gauges before heating and cooling L1: Length between gauges after heating at 160 ° C. for 1 hour and cooling Sa

[0031]

The present invention will be described more specifically with reference to examples and comparative examples below, but of course the present invention is not limited by these examples. In addition, the chemical addition rate% in Examples and Comparative Examples represents% by weight unless otherwise specified.

EXAMPLE 1 A raw material chip made of 100% eucalyptus exata material having a fiber cross-sectional area of 124 μm ^{2 in} wood was subjected to a 25% sulfuration degree, a liquid ratio of 4.5, a maximum temperature of 166 ° C., a holding time of 90 minutes, and an absolute dryness. Kraft digestion with an effective alkali addition rate of 17.0% per chip, and unbleached pulp having a kappa number of 19.0 (hereinafter referred to as LUK)
P). This LUKP was treated with oxygen in the presence of an alkali (NaOH addition rate 1.5%, oxygen pressure 0.5 mP
a), chlorine dioxide (chlorine dioxide addition rate: 0.8%), alkali (NaOH addition rate: 1.0%), chlorine dioxide (chlorine dioxide addition rate: 0.4%) were sequentially bleached in multiple stages to give a whiteness of 8
6.5% bleached pulp (hereinafter referred to as LBKP) was obtained.
At this time, the K value of LBKP was 2.1. This LBK
P is used as a raw material for papermaking, and a melamine resin (trade name: Sumiretz AC8: manufactured by Sumitomo Chemical Co., Ltd.) is internally added to pulp at 1%, and an electrically insulating laminated board having a basis weight of 125 g / m ² and a density of 0.50 g / cm ^3. Was prepared. An electrical insulation laminate was prepared from the electrical insulation laminate base paper, and the silver migration resistance and the dimensional stability were evaluated.

[0033] Example 2 Eucalyptus Eguzata material 50% of the fiber cross-sectional area 124Myuemu ² and the raw material chips sulfidity 25% fiber cross-sectional area consisting of oak material 50% 250 [mu] m ² of wood, liquor ratio 4.
5. Kraft digestion was performed at a maximum temperature of 166 ° C., a holding time of 90 minutes, and an effective alkali addition rate of 17.0% per absolutely dry chips to obtain LUKP having a kappa number of 19.5. This LUK
P is oxygen in the presence of alkali (NaOH addition rate 1.5%,
Oxygen pressure 0.5 mPa), chlorine dioxide (chlorine dioxide addition rate 0.8%), alkali (NaOH addition rate 1.0%),
Multistage bleaching was sequentially performed with chlorine dioxide (chlorine dioxide addition rate: 0.4%) to obtain LBKP having a whiteness of 86.4%. At this time, the K value of LBKP was 1.9. Using this LBKP as a papermaking raw material, a basis weight of 125 g /
An electrically insulated laminate base paper having an m ² and a density of 0.50 g / cm ³ was prepared, an electrically insulated laminate was prepared from the electrically insulated laminate base paper, and silver migration resistance and dimensional stability were evaluated.

[0034] Example 3 Eucalyptus Eguzata material 10% of the fiber cross-sectional area 124Myuemu ² and the raw material chips sulfidity 25% fiber cross-sectional area consisting of oak material 90% 250 [mu] m ² of wood, liquor ratio 4.
5. Kraft cooking was performed at a maximum temperature of 166 ° C., a holding time of 90 minutes, and an effective alkali addition rate per absolutely dry chip of 17.2% to obtain LUKP having a kappa number of 19.8. This LUK
P is oxygen in the presence of alkali (NaOH addition rate 1.5%,
Oxygen pressure 0.5 mPa), chlorine dioxide (chlorine dioxide addition rate 0.85%), alkali (NaOH addition rate 1.0
%) And chlorine dioxide (chlorine dioxide addition rate: 0.4%) in order, to obtain LBKP having a whiteness of 86.1%.
At this time, the K value of LBKP was 2.2. This LBK
Using P as a papermaking raw material, a basis weight of 12 was obtained in the same manner as in Example 1.
An electrically insulating laminate base paper having a density of 5 g / m ² and a density of 0.50 g / cm ³ was prepared, and an electrical insulating laminate was prepared from the electrical insulating laminate base paper. The silver migration resistance and the dimensional stability were evaluated. .

Example 4 A raw material chip made of 100% acacia melanchy wood having a fiber cross-sectional area of 126 μm ^{2 in} wood was subjected to a 25% sulfuration degree, a liquid ratio of 4.5, a maximum temperature of 166 ° C., a holding time of 90 minutes, and an absolute dryness. Kraft cooking was performed at an effective alkali addition rate of 17.7% per chip to obtain LUKP having a kappa number of 20.5. This L
UKP was treated with oxygen (NaOH addition rate 1.5
%, Oxygen pressure 0.5 mPa), chlorine dioxide (chlorine dioxide addition rate 0.88%), alkali (NaOH addition rate 1.0
%) And chlorine dioxide (chlorine dioxide addition rate: 0.4%) in order, to obtain LBKP having a whiteness of 86.2%.
At this time, the K value of LBKP was 2.4. This LBK
Using P as a papermaking raw material, a basis weight of 12 was obtained in the same manner as in Example 1.
An electrically insulating laminate base paper having a density of 5 g / m ² and a density of 0.50 g / cm ³ was prepared, and an electrical insulating laminate was prepared from the electrical insulating laminate base paper. The silver migration resistance and the dimensional stability were evaluated. .

Example 5 LUKP produced in the same manner as in Example 1 was treated with oxygen in the presence of an alkali (alkaline addition ratio 1.7%, oxygen pressure 0.1%).
5mPa), ozone (ozone addition rate 0.5%), alkali (NaOH addition rate 1.0%), and chlorine dioxide (chlorine dioxide addition rate 0.45%) were sequentially bleached in multiple stages to give a whiteness of 8
5.7% LBKP was obtained. At this time, the K value of LBKP was 1.1. Using this LBKP as a papermaking raw material, a basis weight of 125 g / m ² and a density of 0.5 were obtained in the same manner as in Example 1.
An electrically insulating laminate base paper of 0 g / cm ³ was produced. An electrical insulation laminate was prepared from the electrical insulation laminate base paper, and the silver migration resistance and the dimensional stability were evaluated.

Comparative Example 1 LUKP produced in the same manner as in Example 1 was treated with oxygen (NaOH addition rate 1.5%, oxygen pressure 0.1%) in the presence of alkali.
5 mPa), molecular chlorine (chlorine addition rate 1.3%), alkali (NaOH addition rate 0.9%), sodium hypochlorite (sodium hypochlorite addition rate 0.25%), chlorine dioxide (dioxide LBKP was obtained by sequentially performing multi-stage bleaching at a chlorine addition rate of 0.2%. At this time, the K value of LBKP was 0.2. In the same manner as in Example 1, an electrically insulating laminate base paper having a basis weight of 125 g / m ² and a density of 0.50 g / cm ³ was prepared as a papermaking raw material. An electrically insulated electrical insulating laminate was prepared from this electrical insulated laminate base paper, and its silver migration resistance and dimensional stability were evaluated.

[0038] Comparative Example 2 The raw material chips sulfidity 25% fiber cross-sectional area consisting of Eucalyptus grandis material 100% 260 .mu.m ² in wood,
The kraft digestion was carried out at a liquid ratio of 4.5, a maximum temperature of 166 ° C., a holding time of 90 minutes, and an effective alkali addition rate of 17.0% per absolutely dry chip to obtain LUKP having a kappa number of 19.6. This LUKP was treated with oxygen (NaOH addition rate 1.
7%, oxygen pressure 0.5 mPa), molecular chlorine (chlorine addition rate 1.5%), alkali (NaOH addition rate 0.9%),
Sodium hypochlorite (addition rate of sodium hypochlorite 0.25%), chlorine dioxide (addition rate of chlorine dioxide 0.2
%) To obtain LBKP. L at this time
The K value of BKP was 0.3. Using this pulp as a raw material for papermaking, a basis weight of 125 g /
An electrically insulated laminate base paper having m ² and a density of 0.50 g / cm ³ was produced. An electrical insulation laminate was prepared from the electrical insulation laminate base paper, and the silver migration resistance and the dimensional stability were evaluated. Table 1 shows the results obtained in the examples.

[0039]

[Table 1]

[0040]

As is evident from Table 1, the electrical insulating laminate manufactured from the base paper of the electrical insulating laminate using the pulp manufactured without using molecular chlorine as the papermaking raw material has excellent silver migration resistance. Also, the dimensional stability was good (Examples 1 to 5).

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Hitoshi Kagawa 1-10-6 Shinonome, Koto-ku, Tokyo Oji Paper Co., Ltd. Shinonome Research Center F term (reference) 4L055 AA03 AD05 AD07 AD08 AD10 EA01 EA16 EA40 FA11 FA18 GA02

Claims (3)

[Claims] 1. An electric machine characterized by bleaching hardwood unbleached pulp having a kappa number of 17 to 25 after cooking obtained by cooking wood chips without using molecular chlorine to obtain a papermaking raw material. Insulated laminate base paper. 2. The bleached hardwood unbleached pulp is bleached using at least one selected from the group consisting of oxygen, ozone, hydrogen peroxide, chlorine dioxide, and acid. Base paper for electrical insulation laminate. 3. The base paper for electrically insulating laminate according to claim 1, wherein the wood chips contain 10% by weight or more of wood having a fiber cross-sectional area of 200 μm ² or less in the wood.