JPH0988000A - Method for manufacturing electrical insulating laminated board base paper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a sheet of a base paper for an electrical insulating laminated sheet good in silver migration resistance and further characteristics of the whole laminated sheet such as dimensional stability and warpage characteristics of the laminated sheet. SOLUTION: The compression dehydrating treatment of a sheet formed by carrying out the dehydrating treatment of a pulp slurry through a wire is performed with a roll press and the deterioration ratio of the pulp water retention value after the compression dehydrating treatment to that before the dehydrating treatment is regulated to <=5%. The resultant pulp is then used as a raw material and formed into a sheet of paper. The residual chloride ion concentration of the obtained base paper is regulated to <=110ppm.

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 particularly improved 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 manufacturing a laminated board.

[0002]

2. Description of the Related Art Ordinary laminates, especially laminates for electrical insulation, are obtained by impregnating a laminate base paper with a thermosetting resin such as phenol resin or epoxy resin, and heating and drying it into a prepreg of a semi-cured resin. It is manufactured by laminating a plurality of these prepregs and thermocompressing them 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 severe. Conventionally, as the pulp used for laminated board base paper, unbeaten bleached kraft pulp (LBKP) from hardwood wood has been generally used, but depending on the application, softwood bleached wood is used to increase the strength of laminated board base paper. Kraft pulp is blended, unbleached pulp is blended for cost reduction, and 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 the 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 the 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, in JP-A-63-1452, as a filter for removing ions from various solutions, an inorganic ion exchanger is supported between pulp fibers, but this method results in a large particle size. Inorganic ion-exchanger particles or inorganic ion-exchanger particles that have undergone secondary agglomeration in the wet papermaking raw material are present in the paper substrate, resulting in poor impregnation of the phenol resin varnish and poor heat resistance after molding. It cannot be adopted easily.

On the other hand, in order to improve the electrical properties of the laminate, a method of increasing the α-cellulose content (JP-A-60-7)
9952 publication), a method for increasing the α-cellulose content is to perform a high degree of bleaching with a known bleaching agent sandwiching an alkali refining and alkali extraction step, or by superheated steam prior to cooking. Pre-hydrolyze,
Or, it takes a means of refining cold alkali in the latter stage,
In such a case, if the α-cellulose content is significantly improved, the bending of the fibers becomes large, and the dimensional stability and warpage of the laminated plate deteriorate. Further, no mention is made of improvement of silver migration resistance.

It is a known fact that the use of linter pulp having a high α-cellulose content improves the insulation resistance. However, since the fibers of linter pulp are remarkably bent, the dimensional stability and the laminar stability of the laminate are improved. It has the drawback of poor warpage, and since linter pulp is made from cottonseed as a raw material, the supply of raw material is unstable and the price is expensive and volatile, making it difficult to adopt.

On the other hand, a method for improving the electric insulation by defining the amount of residual ions in the base paper (Japanese Patent Laid-Open No. 62-191597) has been reported. It was adopted and the effect was insufficient.

On the other hand, modification of the impregnated thermosetting resin has been devised to improve the resistance to silver migration, but other laminated sheet characteristics may be deteriorated, and a paper-based phenol resin laminate is used. 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.

On the other hand, as a method for compressing pulp by roll pressing to improve the dimensional stability of the laminated plate, a method of blending the treated pulp in an amount of 50% or more to reduce the average lumen opening ratio (Japanese Patent Laid-Open No. 4-163400). (Japanese Unexamined Patent Publication No. 7-26497) has been reported in which the removal rate of short fibers before and after dehydration and compression treatment is 5 to 23%. However, either due to insufficient treatment, or due to the increase of residual ions due to the blending of untreated pulp in the former, reduction of residual ions is insufficient in both cases, and the dimensional stability of the laminate is improved, but The effect of improving silver migration resistance was not satisfactory.

[0010]

SUMMARY OF THE INVENTION The present invention is directed to suppressing silver migration in printed wiring boards. An object of the present invention is to provide a 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.

[0011]

[Means for Solving the Problems] In a printed wiring board
Required for base paper to improve silver migration
The characteristics that are included are ionization of silver and deposition as metallic silver.
The amount of compounds and residual ions in the base paper that contribute to
And that the impregnation property of the thermosetting resin is good.
Especially in the silver migration phenomenon, residual ion in the base paper is
Influences the dissolution process of silver. The amount of residual ions in the base paper
The larger the amount, the faster the insulation resistance will drop in a high temperature and high humidity environment. Immediately
The silver migration resistance deteriorates. Silver resistant my gray
Chlorination is a compound that directly affects
Substances, sodium compounds, potassium compounds, calcification
Compounds, sulfuric acid compounds, etc., but especially chlorine compounds, Natri
The effect of um compounds is large. These compounds are
Sodium ion (Na⁺), Chloride ion (Cl^-)
Present in the laminated base paper as
It is thought that this has an effect on the mobility. N
a⁺And Cl^-Are caustic soda during cooking and bleaching process
Cl₂And ClO ₂Is the ion caused by the
It is difficult to make a state that does not exist.

In the present invention, the pulp sheet is subjected to compression dehydration treatment by a roll press to remove these ions, and the residual chlorine ion concentration of the electrically insulating laminated base paper is set to 110 ppm or less. Preferably
Keep below 100ppm. There is no particular lower limit to the residual chlorine ion concentration, and the lower the better. In the present invention, Cl ₂ or Cl
Even if the exposure process is performed using O ₂ etc., it can be removed up to about 50 ppm. The residual sodium ion concentration is also preferably 110 ppm or less, more preferably 100 p
It is below pm, and there is no particular lower limit, but it can be removed up to about 50 ppm even when cooking with caustic soda is carried out.

On the other hand, many compounds other than these compounds are present in the laminated board base paper, but when the laminated board base paper is produced by a usual method, the amount thereof is originally small, and the silver migration resistance of the laminated board is hardly affected. Do not give. When observing the migration phenomenon of silver, silver migrates on the surface of the pulp fiber, inside the lumen and inside the pulp fiber.Therefore, in order to improve the silver migration resistance, residual ions inside the pulp fiber as well as on the surface of the pulp fiber should be improved. It is more effective to reduce.

It is considered that removal of fine fibers having a large surface area can reduce the residual ions in the base paper, but since silver migration often occurs along the pulp fibers, it is a fundamental solution. However, the effect of improving the silver migration resistance is small. Further, although it is possible to strengthen the washing of the pulp with a filter or the like, although the ions around the pulp fiber can be removed, the ions existing inside the pulp fiber cannot be removed, and the ion reducing effect is small. In addition, a method of minimizing the ions in the water by using an ion exchanger or a distillation method can be considered, but the pulp is produced using an actual machine line for pulping,
When making paper with a paper machine, it was necessary to treat a large amount of water, which was not practical in terms of equipment and cost.

The present invention includes the following aspects. [1] A sheet formed by dewatering pulp slurry through a wire is compression dewatered by a roll press, and a reduction rate of the pulp water retention after compression dewatering is 5% or more with respect to the pulp water retention before dewatering. A method for producing a base paper for an electrically insulating laminated board, which comprises making a paper from the above pulp as a raw material and adjusting the residual chlorine ion concentration of the obtained base paper to 110 ppm or less. [2] The method for producing an electrically insulating laminate base paper according to [1], wherein the pulp dehydrated by a roll press has a moisture content of 65% or less. [3] The method for producing a base paper for an electrically insulating laminated board according to [1] or [2], wherein white water produced by roll pressing is not used as dilution water. [4] The method for producing an electrically insulating laminated board base paper according to [1], [2] or [3], wherein the pulp slurry used in the dehydration treatment through a wire is at 30 ° C or higher. [5] The residual sodium ion concentration of the obtained base paper was adjusted to 11
The method for producing a base paper for an electrically insulating laminated board according to [1], [2], [3] or [4], which is adjusted to 0 ppm or less.

[6] A sheet formed by dehydrating pulp slurry through a wire is compressed and dehydrated by a roll press, and the reduction ratio of the pulp water retention after compression dehydration treatment to the pulp water retention before dehydration treatment is measured. Electrically insulating laminated board base paper made from 5% or more pulp as raw material and having residual chlorine ion concentration of 110 ppm or less. [7] Pulp subjected to compression dehydration treatment with a roll press is subjected to compression dehydration treatment under the condition that the moisture content of the pulp is 65% or less [6]
The electrical insulating laminated board base paper described.

The method for measuring the water retention of pulp is described in J. TAPP
I No. 26 Pulp water retention method
Since the water retention of the pulp is affected by the amount of soft cells and secondary fines in the pulp, it was measured with the pulp obtained by removing fine fibers through a 80 mesh sieve. Further, the reduction rate R of the water retention of the pulp after the treatment (after the dehydration treatment through the wire and the compression dehydration treatment by the roll press) with respect to the water retention of the untreated pulp was calculated according to the following formula. Where R ₀
Indicates the water retention of the untreated pulp, and R ₁ indicates the water retention of the treated pulp. R (%) = [(R ₀ −R ₁ ) / R ₀ ] × 100 The residual ion concentration is measured by, for example, an absorptiometric method or an atomic absorption method as described later.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The pulp slurry used in the present invention is preferably heated by steam or the like in order to efficiently remove ions in pulp fibers by pressing. The temperature of the pulp slurry is preferably 30 ° C or higher. More preferably 40
℃ or above. If the temperature is lower than 30 ° C, the effect of squeezing and removing the ions in the pulp fiber will be reduced.

When the pulp slurry is heated to 30 ° C. or higher, the compression dehydration property is improved, the ions in the pulp fiber can be sufficiently squeezed and removed, and the residual ion amount can be sufficiently reduced. The wire mesh used for forming the sheet from the pulp slurry is not particularly limited, but is preferably 15 to 50 mesh. If it is less than 15 mesh, the fiber content in the drainage solution to be dehydrated increases, and the yield of pulp may decrease, and if it exceeds 50 mesh, the wire may be easily clogged and the dehydration performance may decrease. . The wire type may be any of cylinder type, twin wire type, and fourdrinier type. The basis weight of the sheet is not particularly limited, and is preferably 500 to 2500 g / m ^{2 in} terms of absolute dry weight in terms of compression dehydration property and operation of the pulp sheet.

In the present invention, a sheet formed by dehydrating pulp slurry through a wire is further compressed and dehydrated by a roll press, and the reduction rate of water retention of treated pulp relative to water retention of pulp before dehydration treatment. Is important to be 5% or more. The reduction rate is more preferably 7% or more. If it is less than 5%, the reduction of residual ions will be insufficient, and the improvement of silver migration resistance will be insufficient. There is no upper limit to the rate of decrease in water retention, but it is usually 1
It can be reduced to about 5%.

Compressing and dehydrating the pulp fibers by a roll press to reduce the water content means squeezing out the water in the pulp fibers, and the residual ions having a high concentration are efficiently removed from the pulp fibers together with the water. The water retention is an index of the amount of water inside the pulp fiber. Decrease in water retention of pulp means squeezing and removal of ions in pulp fiber. Furthermore, as shown by the decrease in water retention, compression dewatering by roll press
It also has the effect of eliminating pores in the pulp fiber wall and reducing voids where silver is apt to migrate.

Further, it is preferable that the water content be 65% or less by dehydration with a wire and compression dehydration with a roll press. As a result, a laminated board base paper having excellent dimensional stability can be obtained. More preferably, the water content is reduced to 55 by compressing and dehydrating.
% To 40%. The lower limit of water content at this time is not particularly limited, but it is usually difficult to set it to less than 40%.

It is preferable to increase the linear pressure of the roll press in order to increase the rate of decrease in water retention to 5% or more.
kg / cm or more is preferable. The linear pressure of the roll press is more preferably 150 kg / cm 2 to 250 kg / cm 2.

The number of stages of the compression dehydration treatment process of the roll press may be either one stage treatment or multistage treatment of two or more stages. Although there is no restriction on the type of roll, a grooved roll (a grooved roll), a suction roll or the like is preferable to a plain roll in order to efficiently perform the compression dehydration treatment and dehydration of pulp by a roll press. The roll-pressed pulp may be used either in the wet pulp state or in the dry dry pulp state. When untreated pulp is added, the amount of residual ions increases, so
It is more preferable to use 100% roll-pressed pulp.

The compression dehydration treatment with a roll press may be carried out after the known multistage bleaching with oxygen bleaching, chlorine, alkali, hypochlorous acid and chlorine dioxide, or may be carried out on the pulp immediately before papermaking, and is not particularly limited. Not something.

In general, white water produced by roll press or the like contains pulp raw materials and the water temperature of the white water is higher than that of fresh water, so that it can be reused in the steps such as diluting the raw materials after the treatment and the filter washing in the previous step. Although carried out for economic reasons, in the present invention, white water squeezed by a roll press,
When it is used as dilution water during the disintegration of wet pulp after roll press treatment, the residual ions removed are re-adsorbed and the residual ions increase, so white water is preferably not used.

The wood chips used in the bleached kraft pulp of the present invention are not particularly limited, and the wood oak,
It is possible to use domestically produced (especially from Hokkaido) hardwood such as linden, maple, cuttlefish, wig, hornet, and birch, or eucalyptus, acacia. In order to reduce chlorine ions, it is preferable to use TCF pulp, bleaching with an enzyme, or the like. In order to produce a laminated board from the laminated board base paper of the present invention, the laminated board base paper is impregnated with a thermosetting resin and dried, and two or more prepregs thus obtained are laminated at a predetermined temperature and pressure. Molding and integration are performed by.

As the thermosetting resin, a resol type phenol-formaldehyde resin is generally used.
The present invention is not limited to these, and examples thereof include other usual phenol-formaldehyde resins, melamine-formaldehyde resins, and urea-formaldehyde resins, which are appropriately selected and used. The conditions of heating and pressurizing operations during thermosetting vary depending on the type and amount of thermosetting resin and the structure and dimensions of the laminate, but generally 15
It is carried out at a temperature of about 0 to 180 ° C. and a pressure of about 80 to 120 kg / cm ^{2 for} about 30 to 60 minutes.

[0029]

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. In the examples and comparative examples,%
Represents% by weight unless otherwise specified. The used hardwood bleached kraft pulp (hereinafter referred to as LBKP) is produced by kraft cooking a mixed material of domestic hardwoods to produce hardwood unbleached kraft pulp (hereinafter referred to as LUKP). It was manufactured by performing multi-stage bleaching with chlorine dioxide.

Examples 1 to 3 An unbeaten LBKP slurry having a concentration of 1.8% and a temperature of 40 ° C. was dehydrated with a wire cylinder (vacuum type wire mesh 25 mesh) and a pulp sheet having a water content of 72% (solid dried in terms of solid content). 1800 g / m ² ) was obtained by weight.
Roll press (grooved roll) this pulp sheet
The compression dehydration treatment was performed in the first stage. The line pressure of the roll press is 80
kg / cm (Example 1), 150 kg / cm (Example 2), and 250 kg / cm (Example 3). The water content and water retention of the pulp thus treated were measured. The pulp after the treatment is used as a raw material for papermaking, and melamine resin (trade name: Su
mirez Resin8% AC: Sumitomo Chemical Co., Ltd.) was internally added to pulp 1%, basis weight 125 g / m ² , density 0.50 g / c
The laminate sheet of m ³ and papermaking. The residual sodium ion concentration and residual chlorine ion concentration of this laminated base paper were measured.
Further, a laminated board was prepared from the laminated board base paper and evaluated for silver migration resistance and dimensional stability.

Comparative Example 1 After measuring the water retention of pulp (water retention of untreated pulp) in the same manner as in Examples 1 to 3 without performing pulp sheet formation by a wire press and compression dehydration treatment by a roll press. Using this pulp as a papermaking raw material, the basis weight is 125 g /
A laminated base paper having m ² and a density of 0.50 g / cm ³ was produced. The residual ion concentration of this laminated base paper was measured, and a laminated plate was prepared to evaluate silver migration resistance and dimensional stability.

Comparative Example 2 An unbeaten LBKP slurry having a concentration of 1.8% and 40 ° C. was treated with a wire cylinder (vacuum type wire mesh 25
It was dehydrated with a (mesh) to obtain a pulp sheet having a moisture content of 72% (1800 g / m ^{2 as an} absolute dry weight in terms of solid content). Using the pulp thus treated, the water retention of the pulp was measured in the same manner as in Examples 1 to 3, without performing compression dehydration treatment by a roll press, and the pulp was used as a papermaking raw material to produce a basis weight of 125 g. / M ² and a density of 0.50 g / cm ³ were used to produce a laminated base paper. The residual ion concentration of this laminated base paper was measured, and a laminated plate was prepared to evaluate silver migration resistance and dimensional stability.

Comparative Example 3 An unbeaten LBKP slurry having a concentration of 1.8% and 40 ° C. was wiped.
Yar cylinder (vacuum wire mesh 2
Dehydrated with 5 mesh and 72% water content pulp sheet (solid
1800g / m in absolute dry weight in terms of shape²) Got. this
Pulp treated in this way is compressed and dehydrated by a roll press.
Without any treatment, the water content was reduced to 65% or less by drying. This
Using pulp treated as in
After measuring the water retention of the pulp by the same method,
Basis weight of 125 g / m as a raw material for papermaking ², Density 0.50 g /
cm^ThreeThe laminated base paper of No. 3 was made into paper. Residue of this laminated board base paper
Measure the ion concentration, make a laminated plate,
It was evaluated for its ration resistance and dimensional stability.

Comparative Example 4 An unbeaten LBKP slurry having a concentration of 1.8% and 25 ° C. was treated with a wire cylinder (vacuum type wire mesh 2
It was dehydrated with 5 mesh) to obtain a pulp sheet having a water content of 76% (1800 g / m ² in absolute dry weight in terms of solid content). This pulp sheet was subjected to compression dehydration treatment with a roll press (grooved roll) and a linear pressure of 250 kg / cm, and the water retention of the pulp was measured in the same manner as in Examples 1 to 3, and the pulp was used as a papermaking raw material to weigh 125 g. / M ² , density 0.50g
/ Cm ³ laminated base paper was made into paper. The residual ion concentration of this laminated base paper was measured, and a laminated plate was prepared to evaluate silver migration resistance and dimensional stability.

Method for Measuring Residual Na ⁺ Ions in Laminated Base Paper 100 ml of 0.1 ^N hydrochloric acid is added to 3 g of base paper in terms of absolute dry base paper weight, and boiled for 1 hour. After that, it is filtered and the Na ⁺ ion in the extract is measured by an atomic absorption method,
It was converted to the Na ⁺ ion concentration in the base paper. The less residual Na ⁺ ions, the better the silver migration resistance.
It is good if it is 110 ppm or less.

Method for Measuring Residual Cl ⁻ Ions in Laminated Paper Base Paper 5 ml of absolute dry paper weight was added to 150 g of pure water and boiled for 1 hour. Then, the solution was filtered and the chloride ion in the extract was measured according to the absorptiometry of JIS K0101, and converted into the Cl ⁻ ion concentration in the base paper.
The smaller the amount of residual Cl ⁻ ions is, the better the silver migration resistance is, but if it is 110 ppm or less, it is generally good.

The preparation of Preparation Method laminate laminate, the laminate base paper, a commercially available water-soluble phenolic resin: impregnating (trade name Shonol BRL-2854 Showa Kobunshi Co., Ltd.), dried in a dryer By doing so, a primary prepreg having a resin / base material ratio of 15:85 was prepared, and then a commercially available oil-modified phenolic resin (trade name Shonor BLS-3122: Showa High Polymer Co., Ltd.) was used for this primary prepreg. Was impregnated and dried to prepare a prepreg having a ratio of a resin and a base material of 50:50 in which both a water-soluble phenol resin and an oil-modified phenol resin were combined. Next, stack 8 prepregs at 165 ° C, 100 kg / cm ² ,
A phenol resin laminate was obtained by pressure molding for 60 minutes.

Evaluation Method of Silver Migration Resistance of Laminated Plate A comb-shaped electrode having a line width of 1 mm and a line interval of 1 mm was prepared on the laminated plate with a silver paste, and an ion migration evaluation system (A
MI-025-P: manufactured by Tabai Espec Co., Ltd., the insulation resistance between the electrodes was measured in a state where a DC voltage of 50 V was applied in a constant temperature and constant humidity of 40 ° C. and 93% RH.
At the time of evaluation, 40 ° C to prevent condensation at the start of the test
The sample was allowed to stand for 1 hour at room temperature, 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 standard, the insulation resistance between electrodes was continuously measured, and it was determined that migration had occurred on the substrate having a resistance of 10 ⁶ Ω or less. From this continuous measurement data, the time until the first migration occurred (failure occurrence time) was used as a criterion for evaluation. When an ordinary commercially available circuit board is evaluated, durability of 1000 hours or more is required under the above conditions, but when the board is not subjected to moisture resistance treatment as in the above-mentioned laminated board manufacturing method, 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 laminated plate is performed by measuring the dimensional change rate by the following method. Laminated span 250
A mark is attached in 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.). The dimensional change rate α is calculated by the following formula. When the laminated base paper is made by a normal paper machine and has anisotropy, the dimensional change rate is shown in the longitudinal direction and the transverse direction. The dimensional change rate is basically good as it approaches 0%. However, L ₀ represents the length between the reference points before heating and cooling, and L ₁ represents the length between the reference points after heating and cooling at 160 ° C. for 1 hour. α (%) = [(L ₀ −L ₁ ) / L ₀ ] × 100 The results obtained in the examples are shown in Table 1.

[0040]

[Table 1]

As is clear from Table 1, the laminates produced from the laminate base paper of the present invention can have improved silver migration resistance (Examples 1 to 3). Also, the dimensional stability of the laminated plate is excellent.

[0042]

As described above, the present invention provides a laminated board base paper most suitable for producing a laminated board having good dimensional stability during processing of the laminated board and good silver migration resistance of the printed wiring board. There is an effect of providing. Therefore, its industrial significance is extremely large.

Claims (1)

[Claims] 1. A sheet formed by dewatering pulp slurry through a wire is compression dewatered by a roll press, and the reduction rate of the pulp water retention after compression dewatering is 5 relative to the pulp water retention before dewatering. % Of the pulp is used as a raw material for papermaking, and the residual chlorine ion concentration of the obtained base paper is adjusted to 110 ppm or less.