JPH08209595A - Electrically insulating laminated base paper - Google Patents

Abstract

(57) [Summary] [Object] To provide a base paper for an electrically insulating laminated board having good silver migration resistance and good overall laminated board characteristics such as dimensional stability and warpage characteristics of the laminated board. [Constitution] In a laminated board base paper made from wood pulp as a raw material, the pulp is JAPAN TAP
PI No. Electrical insulation characterized by the fact that the number of pulps with a fiber length of 1 mm or more is 8% or less based on the number average fiber length distribution by the fiber length test method of pulp by the optical automatic measurement method specified in 52. Laminated board base paper.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated base paper used for an electrically insulating laminated board, and more specifically, it has good silver migration resistance without impairing laminated board characteristics such as dimensional stability and warpage. The present invention relates to a laminated board base paper used for producing a laminated board.

[0002]

2. Description of the Related Art Conventional laminates, especially laminates for electrical insulation, are obtained by impregnating a laminate base paper with a thermosetting resin such as a phenol resin or an epoxy resin, and then heat-drying it to obtain a semi-cured resin state ( This is referred to as a prepreg), and a plurality of the prepregs are laminated and manufactured by thermocompression molding together with a metal foil. Such a laminated plate is relatively inexpensive and almost satisfies the performance required for use in ordinary electric or electronic devices, and is therefore mainly used for household electric appliances.

However, due to the recent lighter, thinner, shorter, and smaller electric products, the packaging density of electric parts has increased, and the conductor patterns of printed wiring boards have become finer. Furthermore, even in printed wiring boards using paper as a base material, the conductor patterns are becoming double-sided, and silver through holes have been used for the purpose of electrical connection between the front and back. Therefore, not only the workability, dimensional stability, and punchability of the laminated plate,
The deterioration of electrical insulation due to the migration phenomenon of silver has become a problem, and demands for improvement of silver migration prevention performance (hereinafter referred to as silver migration resistance) are becoming more and more strict.

Conventionally, pulp used for laminated board base paper is
Unbeaten kraft pulp from hardwood wood (LBKP)
It is generally used, but depending on the application, it may be blended with bleached softwood kraft pulp to increase the strength of laminated board base paper, or blended with unbleached pulp for the purpose of cost reduction, or with high whiteness. Sulfite pulp (S
P) may be used. Such pulp is made by a known paper machine, and the density of the laminated base paper obtained is as low as 0.45 to 0.55 g / cm ³ .

In order to improve the migration of silver in a printed wiring board, the properties required for the base paper are that there are few residual ions in the base paper that contribute to the ionization of silver and the precipitation as metallic silver, and a thermosetting resin. The good impregnating property is. In order to solve such problems, a method of using a resin varnish containing an inorganic ion exchanger (JP-A-2-133442 and JP-A-5162245) is known. In the case of the paper-based phenolic resin laminate used, since the laminate base paper is manufactured from pulp fibers, it is not a fundamental solution and the silver migration resistance is not sufficient. Further, a method of impregnating a glass nonwoven fabric with an organic binder containing a metal migration inhibitor added to a laminate using the glass nonwoven fabric as a substrate (Japanese Patent Laid-Open No. 6-158492) has been proposed. In that case, it is difficult to adopt because of the large cost increase.

On the other hand, in order to improve the electrical properties of the laminate, a method of increasing the α-cellulose content (JP-A-60-799).
No. 52) has been proposed, but there is a drawback that the bending of the fiber becomes large and the dimensional stability and warpage of the laminated plate deteriorate.
Further, in this publication, no mention is made of improvement in silver migration resistance. Further, 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 and fluctuating, which makes it difficult to adopt.

On the other hand, modification of the impregnated thermosetting resin has been devised to improve silver migration resistance, but other laminated sheet characteristics may be deteriorated, and paper-based phenol resin laminated In the case of a board, a part that strongly depends on the essential properties of the base paper is strong, and further improvement of the base paper has been required.

[0008]

DISCLOSURE OF THE INVENTION The present invention provides an electrically insulating laminated board base paper suitable for producing a laminated board having good silver migration resistance without deteriorating laminated board characteristics such as dimensional stability and warpage. It is the one we are trying to provide.

[0009]

In view of the above situation, the present inventors have variously studied the relationship between the silver migration resistance of a laminate and the physical properties of raw materials in order to suppress silver migration of a printed wiring board. The silver migration resistance of the laminated sheet obtained by using the laminated base paper made from the raw material pulp having the distribution ratio of the pulp having the fiber length of 1 mm or more is 8% or less, which is found from the measurement of the average fiber length distribution. They have found that they are extremely excellent and have completed the present invention.

That is, the electrical insulating laminated board base paper according to the present invention is a laminated board base paper made from wood pulp as a raw material, wherein the pulp is JAPAN TAPP.
INo. The number of pulps having a fiber length of 1 mm or more is 8% or less based on the number average fiber length distribution by the fiber length test method of the pulp by the optical automatic measurement method specified in 52. is there.

In the present invention, it is important that the distribution ratio of fibers of 1 mm or more in the pulp is small. Generally, silver migration resistance is measured by measuring the insulation resistance value between through holes to which a predetermined voltage is applied under a constant temperature and humidity environment, and if a constant high insulation resistance value can be maintained,
It is judged that the silver migration resistance is good. When evaluated by the above evaluation method, the insulation resistance may decrease sharply at a relatively early stage of about several tens of hours. When observing the silver migration part of this printed wiring board, silver migrated along the pulp fiber, and in the short-circuited part, one pulp fiber straddled the through holes and silver migration occurred. I found out. Even when the short circuit was not reached, silver migrated along the pulp fiber.

At present, there is a movement to narrow the silver through hole interval from 2.5 mm to 2.0 mm pitch, and further to 1.5 mm pitch. That is, the land interval is 1.0 to 0.
If the pulp fibers in which the migration of silver occurs have a length longer than the land interval, the insulation resistance decreases sharply from 5 mm to 0.5 to 0.3 mm and further to 0.3 mm or less. It is thought to be an imitation. The present invention has found that by controlling the distribution ratio of the fiber length of 1 mm or more to a certain amount or less, it is possible to suppress a rapid decrease in insulation resistance caused by the migrated pulp fibers, that is, a short-circuit state.

Usually, when the fiber length of pulp used for laminated board base paper is measured, the number average fiber length is 0.45 mm, and the distribution ratio of the fiber length of 1 mm or more is about 10%. In the laminated board base paper of the present invention, when the distribution ratio of the fiber length of 1 mm or more is more than 8%, the insulation resistance is rapidly decreased due to one pulp fiber, and the silver migration resistance is unsatisfactory. It is enough. On the other hand, 1
When the distribution ratio of the fiber length of mm or more is 8% or less, good silver migration resistance is exhibited as described above. 1 mm
As a method for reducing the distribution ratio of the fiber length, it is possible to select wood chips. Examples of wood chips include eucalyptus exata, eucalyptus delegation, eucalyptus citriodora, eucalyptus grouse No. 1. By using acacia melancism and the like, the distribution ratio of the fiber length of 1 mm or more can be 8% or less.

On the other hand, when using domestically produced (especially from Hokkaido) hardwoods such as Japanese oak, linden, Itaya maple, harlequin, wig, hemil, and birch as wood chips, a method of reducing the distribution ratio of fiber length of 1 mm or more is used. As, using a centrifugal dehydrator, pulp fibers in the form of pulp slurry are dehydrated by applying centrifugal force through a wire,
This can be achieved by discharging the long fibers retained in the wire out of the system. This is because a pulp slurry having a concentration of 0.1 to 1.5% by weight is continuously introduced between a rotating wire supported by a breast roll and a couch roll and the breast roll, and centrifugal force generated by the rotation of the wire is used. It is carried out by squeezing water through the holes of the wire, separating it into useful pulp that passes through the wire with water, and long fibers that remain in the wire, and discharging the long fibers out of the system.

The size of the perforations in the wire has a significant effect on the removal of long fibers from the pulp slurry.
That is, for the present invention, the wire mesh should be less than 40 mesh. When 40 mesh or more is used, a pulp mat is formed on the wire and long fibers do not selectively stay on the wire, so that efficient separation becomes impossible. The centrifugal force can be appropriately selected and used in the range of 30 to 100G. Centrifugal force is 30
If it is G or less, the effect of removing long fibers is not remarkable, and if it is 100 G or more, the effect of removing long-term fibers reaches a peak. The present invention is not limited to the above-mentioned long fiber removing method, but can be achieved by removing with a normal slit screen, strengthening the cleaner, or the like.

In order to produce a laminated board from the laminated board raw paper of the present invention, the laminated board raw paper is impregnated with a thermosetting resin and dried, and two or more of the thus obtained prepregs are laminated to each other to a predetermined size. Molding and integration are performed by temperature and pressure. As the thermosetting resin, a resol type phenol-formaldehyde resin is generally used, but the thermosetting resin is not limited to this, and other phenol-formaldehyde resin, melamine-formaldehyde resin, urea-formaldehyde resin may be used. They can be mentioned, and they are appropriately selected and used. The conditions of heating and pressurizing operation during thermosetting vary depending on the type and amount of the thermosetting resin, the structure and dimensions of the laminate, etc.
3 at a temperature of 180 ° C and a pressure of 80 to 120 kg / cm ^2.
It is performed for 0 to 60 minutes.

Measurement of fiber length distribution of pulp used in the present invention,
The method for manufacturing the laminated plate, the method for evaluating silver migration resistance, and the method for evaluating dimensional stability are as follows.

Method of Measuring Fiber Length of Pulp In the measurement, the present inventors adopted the number average fiber length distribution in order to accurately grasp the number of long fibers which has an important influence on the silver migration resistance by the number. . In measuring the average fiber length, a commercially available fiber length distribution measuring machine (trademark: FS-200, manufactured by Kajaani) was used in the present invention. This measuring machine is based on JAPAN TAPPI No. It is a device of the optical automatic measurement method defined by 52, and measures the length and the number of fibers in various fractions by utilizing the polarization characteristics of the fibers. The number average fiber length, length weighted average fiber length and weight weighted average fiber length are determined.

Manufacturing Method of Laminated Plate A laminated plate is manufactured by impregnating a laminated base paper with a commercially available water-soluble phenolic resin (trademark: Shonor BRL-2854, manufactured by Showa Polymer Co., Ltd.) and drying with a drier. By doing
A primary prepreg having a resin / base material ratio of 15:85 was prepared, and then this primary prepreg was impregnated with a commercially available oil-modified phenolic resin (trademark: Shonor BLS-3122, Showa Highpolymer Co., Ltd.), After drying, a prepreg having a resin / base material ratio of 50:50 in which both a water-soluble phenol resin and an oil-modified phenol resin were combined was produced. Next, eight prepregs were stacked and pressure-molded at 165 ° C. and 100 kg / cm ² for 60 minutes to obtain a phenol resin laminate.

Evaluation Method of Silver Migration Resistance of Laminated Plate A comb-shaped electrode having a line width of 1 mm and a line width of 1 mm was prepared on the laminated plate by using a silver paste, and an ion migration evaluation system (trademark: AMI-025-P, Tabai Espec Co., Ltd. was used. ))
A continuous test was carried out for 350 hours under the conditions of 60 ° C., 85% RH, and applied voltage of 50 V, and the time during which the insulation resistance rapidly dropped to 10 ⁶ Ω or less was measured by leak touch detection. Therefore, the silver migration resistance is good when there is no leak touch detection up to 350 hours, and the silver migration resistance is poor when the average value of the leak touch times of the leak-touch detected samples is small. In the evaluation, in order to prevent dew condensation at the start of the test, the sample was left at 60 ° 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.

Evaluation Method of Dimensional Stability The evaluation method of the dimensional stability of the laminated plate is performed by measuring the dimensional change rate by the following method. Laminated span 250
Marks were added in mm, and the dimension between the marks before and after heating and cooling was measured with a high-precision two-dimensional coordinate measuring device (for example, trademark: Digital Reader DR-555-D, manufactured by Dainippon Screen Mfg. Co., Ltd.). The dimensional change rate α is obtained from the equation 1. When the laminated base paper is made by a normal square hand making machine and does not have anisotropy, the dimensional stability is shown by the average value in the longitudinal direction and the transverse direction,
When the laminated base paper is made by a normal paper machine and has anisotropy, the dimensional change rate is represented by the longitudinal direction, the transverse direction, and the geometric mean value in the longitudinal direction and the transverse direction.

[0022]

[Formula 1] α (%) = [(L0−L1) / L0] × 100 L0: Length between gauge marks before heating / cooling L1: 160 ° C., length between gauge points after heat treatment, cooling It

[0023]

The present invention will be described in more detail with reference to the following examples and comparative examples, but the present invention is of course not limited thereto. Examples 1-2 Hardwood bleached kraft pulp obtained from acacia melancy as a raw material for wood chips, hereinafter referred to as LBKP (1
The distribution ratio of the fibers of mm or more is 4.9%) and LBKP obtained from the hardwood chips from Hokkaido (the distribution ratio of the fibers of 1 mm or more is 10.1%) are blended in the ratios of Table 1 and used as papermaking raw materials. did. Using this papermaking material, without beating,
Melamine resin (trademark: Sumirez AC8, Sumitomo Chemical Co., Ltd.)
1% of pulp was internally added to produce a laminated board base paper having a basis weight of 125 g / m ² and a density of 0.50 g / cm ³ . A laminate was prepared from this laminate base paper and evaluated for silver migration resistance and dimensional stability.

Example 3 LBKP obtained by using Hokkaido hardwood as a raw material for wood chips (distribution ratio of fibers of 1 mm or more is 10.1%)
From the Bauer-Mcnet tester (TAPPIT233
hm-82) was used to remove pulp fibers remaining at 28 mesh and used as a raw material for papermaking (distribution ratio of fibers of 1 mm or more was 7.5%). Examples 1-2 using this papermaking raw material
The same method as above, but with a basis weight of 125 g / m ² and a density of 0.50 g
/ Cm ³ laminated base paper was made into paper. A laminate was prepared from this laminate base paper and evaluated for silver migration resistance and dimensional stability.

Comparative Example 1 LBKP obtained from Hokkaido hardwood as a chip material (the distribution ratio of fibers of 1 mm or more is 10.1%)
Is used as a papermaking raw material, and the basis weight is 1 in the same manner as in Examples 1 and 2.
A laminated base paper having a density of 25 g / m ² and a density of 0.50 g / cm ³ was made into paper. A laminate was prepared from this laminate base paper and evaluated for silver migration resistance and dimensional stability.

Comparative Example 2 LBKP obtained from acacia melancy as a chip material (the distribution ratio of fibers of 1 mm or more is 4.9).
%) And LB obtained from Hokkaido hardwood chips
KP (the proportion of fibers having a size of 1 mm or more was 10.1%) was blended in the distribution ratio shown in Table 1 to prepare a papermaking raw material. Using this papermaking raw material, the basis weight was 125 g / m2 in the same manner as in Examples 1 and 2.
^2. A laminated base paper having a density of 0.50 g / cm ³ was made into paper. A laminate was prepared from this laminate base paper and evaluated for silver migration resistance and dimensional stability. Table 1 shows the evaluation results of these laminated board base papers.

[0027]

[Table 1]

As is clear from Table 1, the laminate produced from the electrical insulating laminate base paper of the present invention, which is produced by using the raw pulp in which the distribution ratio of the pulp fibers of 1 mm or more is 8% or less, is silver-resistant. Although the migration property was excellent and the dimensional stability was also good (Examples 1 to 3), the laminate produced from the electrical insulating laminate base paper containing the fiber length distribution ratio of more than 8% had silver migration resistance. And the dimensional stability tended to be inferior (Comparative Examples 1 and 2).

[0029]

Industrial Applicability According to the present invention, it becomes possible to put into practical use the laminated board base paper most suitable for producing a laminated board having a good silver migration resistance of a printed wiring board, which greatly contributes to the industrial world. .

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Claims (1)

[Claims] 1. A laminated board base paper made from wood pulp as a raw material, wherein the pulp is JAPAN T
APPI No. Electrical insulation characterized by the fact that the number of pulps with a fiber length of 1 mm or more is 8% or less based on the number average fiber length distribution by the fiber length test method of pulp by the optical automatic measurement method specified in 52. Laminated board base paper.