GB2123748A

GB2123748A - Flame-retardant laminates

Info

Publication number: GB2123748A
Application number: GB08305113A
Authority: GB
Inventors: Yoshio Nakamura; Tomofumi Narishima
Original assignee: Sanyo Kokusaku Pulp Co Ltd
Current assignee: Sanyo Kokusaku Pulp Co Ltd
Priority date: 1982-06-30
Filing date: 1983-02-24
Publication date: 1984-02-08
Also published as: KR840001889A; JPS592843A; GB2123748B; JPS6333777B2; KR880001906B1; GB8305113D0

Abstract

Flame-retardant copper clad laminates are prepared by lamination under heat and pressure of prepregs which are obtained by coating or impregnating a base paper loaded with aluminium oxide hydrate with melamine and/or guanamine resin, or with a dispersion of aluminium hydrate in a solution of melamine and/or guanamine resin, followed by drying, and coating or impregnating the thus obtained sheets with phenolic resin rendered flame- retardant, followed by drying.

Description

SPECIFICATION Process for the preparation of flame-retardant phenolic paper base copper clad laminates The present invention relates to a process for the preparation of flame-retardant phenolic paper base copper clad laminates having improved flame retardancy, heat resistance and electrical insulating properties, which are suitable for use in printed circuit boards for consumer electronic equipment, on which electronic components are mounted.

In order to reduce the possibility of TV receivers causing outbreaks of fire, standards relating to consumer electronic equipment have been revised to contain a strict Japanese Standard No. 94 (Test for the flammability of plastic materials) under reference UL94V-0. According to this standard, flameretardant phenolic paper base laminates meet the standard in respect of flame retardancy, but they are generally inferior to well known non-flame retardant laminates in the properties which printed circuit boards should possess, such for example as heat resistance; electrical properties and resistance to warpage.

The conventional flame-retardant phenolic paper base laminates have been prepared by: (i) impregnating a base paper with a thermosetting resin solution including a condensate of melamines or the like with formaldehyde and thereafter; (ii) impregnating with a phenolic resin solution.

These laminates however, do not meet the above standard with respect to flame retarding properties.

It has been proposed to impregnate a base paper with a dilute phenolic resin solution in which metal oxides metal hydroxides and/or substantially water insoluble metal salts are dispersed and, thereafter to impregnate, with a concentrated solution of the said resin. However, the resulting laminate is still unsatisfactory in respect of flame retardancy and electrical properties. In some cases, a combination of antimony trioxide with organic halides may be used to render laminates flame-retardant.

However, the antimony trioxide may be contaminated with undesirable heavy metals such as arsenic, and lead which are inevitably retained in the base paper. During the preparation of a base paper, some of antimony trioxide containing these impurities is discharged into waste water, and may cause a pollution problem.

According to the present invention there is provided a flame retardant metal clad laminate formed by the lamination of a metal cladding layer with a substrate under heat-and pressure, which substrate comprises a base paper loaded with aluminium oxide hydrate which has been coated or impregnated with melamine and/or guanamine resin, dried, and thereafter coated or impregnated with flame retardant phenolic resin and subsequently dried.

The invention also includes a method of making a substrate for use in the production of a flame retardant metal clad laminate which method comprises (i) loading a base paper substrate with aluminium oxide hydrate, (ii) coating or impregnating said loaded substrate with a resin selected from at least melamine resin and guanamine resin, (iii) drying the substrate so treated (iv) coating or impregnating said dried substrate with a flame retardant phenolic resin (v) drying the phenolic resin treated substrate thus obtained.

The base paper may be loaded with aluminium oxide hydrate (Al203 3H20) in an amount of 5 to 30% by weight (per base paper pulp) and subsequently coated or impregnated with an aqueous or solvent solution of melamine resin and/or guanamine resin in an amount of 5 to 30% by weight (resin solid per base paper pulp), followed by drying. The resulting product, a prepreg, may then be impregnated with a predetermined amount of phenolic resin rendered flame-retardant and dried, and forming the required laminate under heat and pressure.

The thus obtained flame-retardant phenolic paper base laminates retains the satisfactory properties that the non-flame retardant laminates have. In addition, however, mentioned laminates have been found to be suitable for use in copper clad printed circuit boards having improved resistance to warpage, into which electronic parts can be mounted in high density.

The base paper used in the present invention may be formed of kraft paper, cotton linter paper, paper blending of kraft pulp and cotton linter pulp, and paper blending of kraft and/or cotton linter pulp and glass fibres. The base paper may or may not be loaded with aluminium hydrate.

Aluminiurn oxide hydrate is an inorganic substance which is insoluble in water or the solvent for phenolic resin, and contains 34.5% water of hydration. This material reieases its water of hydration at 2000C or higher as would occur in the flame exposure and this water vapour becomes an excellent flame snuffing agent. The aluminium oxide hydrate used may be a commercial grade haivng an average particle size of 5,u micron. The melamine and/or guanamine resin added to the base paper loaded aluminium hydrate is less effective in an amount of 5% or lower resin solid per base paper pulp. In an amount of 30 wt. % or higher, on the other hand, the ability to impregnate flame-retardant phenolic resin is reduced, and the impregnated paper becomes brittle or paper may even break in the treating process.

The guanamine resin used may be an initial condensate obtained by reaction of benzoguanamine, acetoguanamine, formguanamine or the like with formaldehyde or a compound capable of forming formaldehyde.

The melamine and guanamine resin is a nitrogen compound, and is said to be flame-resistant resin. These resin, combined with the flame-retardant effect of aluminium hydrate, makes further improvements in flame retardancy heat resistance, electrical properties and resistance to warpage of laminates.

Thus, the laminates obtained by the present invention are superior in these properties to those obtained by the lamination of prepregs made by impregnating or coating kraft paper only with the phenolic resin having a high content of flame-retardants.

It has been found that there is no change in quality of the laminates obtained by impregnating or coating the base paper with a coating dispersion consisting of a solution of melamine and/or guanamine resin when aluminium oxide hydrate dispersed therein, followed by drying, and, then, impregnating or coating the thus coated sheet with phenolic resin solution which has been rendered flame-retardant (hereinafter called the flame-retardant phenolic resin).

The flame-retardant phenolic resin used is a flame retardant-containing reaction product of phenol, cresol, resorcinol, phenol having an alkyl substituent or the like with formaldehyde with the use of a catalytically active alkaline substance. Suitable flame retardants used include phosphates such as tricresyl phosphate (TCP), cresyl diphenyl phosphate (CDP), trisdipropyl phosphate, trischloro ethyl phosphate and trisdichloropropyl phosphate (CRP) as well as halides such as, for instance, tetrabromobisphenol A (TBA), tetrachlorobisphenol A and pentabromophenol.

In the present invention, the amount of the flame retardant added to the phenolic resin can be reduced considerably since the additional flame retardancy is provided to the base paper containing aluminium hydrate and melamine or guanamine resin thereinto. Thus, it is possible to prepare laminates having improved flame retardancy and resistance to warpage. The laminates of the present invention suffers no deterioration due to the reduced or limited amount of flame retardants.

Following is a description by way of example only of methods of carrying the invention into effect.

EXAMPLE 1 A 0.25 m/m thickness kraft paper loaded with 12 wt. % of aluminium oxide hydrate was impregnated with an aqueous solution of melamine resin in an amount of 12 wt. % (resin solid per base paper pulp), and dried. The sheet was further impregnated with the flame-retardant phenolic resin composed of phenolic resin with 10% of TBA, and dried.

Eight sheets of the thus impregnated paper were pressed together at 1 600C and 100 kg/cm2 for one hour to produce a laminate having a thickness of 1.4 mm.

An adhesive-backed copper foil was laminated onto the impregnated paper under the same conditions to form a copper-clad laminate and the warpage was determined.

The results are shown in Table 1.

EXAMPLE 2 A 0.25 m/m thickness kraft paper loaded with 1 2 wt. % of aluminium oxide hydrate, was impregnated with a guanamine resin solution in an amount of 12 wt. % (resin solid per base paper pulp), and dried in the same procedures as described in Example 1. The sheet was similarly impregnated with the same flame-retardant phenolic resin as used in Example 1 to obtain a laminate. The results are set forth in Table 1.

TABLE 1

Comparative Working Ex. 1 Ex. 2 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Aluminium Oxide Hydrate 12.3% 12.3% 20.6% 20.6% 10.5% Melamine Resin 12.5% 19.8% 10.7% 11.0% Guanamine Resin 12.1% Phenolic Resin Flame Retardant content TBA, 30% NONE TBA, 10% TBA, 10% TCP, 30% TBA, 5% TCP, 30% (relativ to resin) CDP, 10% Resin Content (weight %) 53 53 53 53 52 52 52 Flame resistance in second 15 burns 3 5 4 5 4 Insulation Resistance (C-96/20/65 + D-2/100) (#) 1.3 x 106 1.1 x 107 1.0 x 107 0.8 x 107 6.7 x 107 1.9 x 107 2.9 x 107 Heat Resistance in C 210 215 215 215 225 215 225 (5 min) Warpage in m/m 9 5 3 3 3 4 3 EXAMPLE 3 A sheet of kraft paper loaded with 20.6 wt. % of aluminium oxide hydrate was impregnated with an aqueous melamine resin solution in an amount of 19.8 wt. % (resin solid per base paper pulp), and dried. Prepregs were prepared using the phenolic resin rendered flame-retardancy by the addition of TCP. Thereafter, laminates were made in the same manner as described in Example 1. The results are given in Table 1.

EXAMPLE 4 The sheets of kraft paper loaded with 20.6 wt. % of aluminium oxide hydrate was impregnated with a solution of melamine resin and guanamine resin (1:1) in an amount of 10.7 wt. % and dried to form an impregnated sheet. The prepregs were made using the phenolic resin rendered flame-retardant by the addition of TBA and CDP. Thereafter, laminates were made in the same manner as described in Example 1. The results are given in Table 1.

EXAMPLE 5 Prepared were an aqueous slurry in which 1 5% of aluminium oxide hydrate (commercial average particle size 5ym grade) was dispersed with the use of an acrylate pigment dispersant and a 15% aqueous solution of melamine resin so as to form a mixture thereof (1 :1). This liquid mixture was impregnated into a sheet of kraft paper which was in turn dried. The sheet was further impregnated with the phenolic resin rendered flame-retardancy by the addition of TCP, and dried. Thereafter, laminates were made in the same manner as described in Example 1. The results are given in Table 1.

COMPARATIVE EXAMPLE 1 Sheets of kraft paper were impregnated with the phenolic resin rendered flame-retardancy by the addition of TBA, dried, and processed into laminates under the same conditions as mentioned above.

The results are also given in Example 1.

COMPARATIVE EXAMPLE 2 Sheets of kraft paper were impregnated with phenolic resin, and pressed into laminates as mentioned above. The results are also given in Table 1.

From the results given in Table 1, it will be seen that the laminates formed of kraft plain paper impregnated with the flame-retardant phenolic resin are inferior in soldering heat resistance and insulation resistance to the non-flame retardant laminates. Copper-clad laminates obtained from the comparative examples are also poor in warpage.

However, the laminates prepared by the present invention meet the specification of Japanese Standard No. UL-94V-O and moreover, are superior in several properties to the non-flame retardant grade. In addition, the copper-clad laminates of the present invention have improved resistance to warpage, and are suitable for printed circuit boards having a high-density of electronic parts mounted thereon.

It has also been found that the impregnation of slurry of aluminium oxide hydrate dispersed in a melamine resin solution into sheets of kraft paper yield laminates having the same quality as the flameretardant laminates of Example 1.

Similar results are obtained with a base paper composed of cotton linter paper or paper blending cotton linter with kraft pulp, said base paper being loaded with aluminium oxide hydrate, or not. In the case of kraft paper contained glass fibres, similar results are obtained if aluminium oxide hydrate and melamine resin are added to the pulp portion from which the glass fibres have been removed.

The physical properties of the laminates obtained in the examples and comparative examples were determined according to the following testing methods.

Flame Resistance: UL-94 Insulation Resistance: JIS K 6911 (method similar to ASTM D 257) measured by Taper-Pin Electrodes, pin distance 15 m/m, at DC 500V.

Warpage of copper clad laminates: JIS C 6481 Heat Resistance: Upon heating at 1050C for 24 hours, the laminates were heated at a given temperature for 5 minutes, and heated a heating rate of 5 C per unit time. The heat resistance is expressed in terms of a maximum temperature at which the laminates did not blister. Refer to the solder heat resistance stipulated in JIS C 6481.

Claims

1. A flame retardant metal clad laminate formed by the lamination of a metal cladding layer with a substrate under heat and pressure, which substrate comprises a base paper loaded with aluminium oxide hydrate which has been coated or impregnated with melamine and/or guanamine resin, dried, and thereafter coated or impregnated with flame-retardant phenolic resin and subsequently dried.

2. A method of making a substrate for use in the production of a flame retardant metal clad laminate which method comprises (i) loading a base paper substrate with aluminium oxide hydrate, (ii) coating or impregnating said loaded substrate with a resin selected from at least melamine resin and guanamine resin, (iii) drying the substrate so treated (iv) coating or impregnating said dried substrate with a flame-retardant phenolic resin (v) drying the phenolic resin treated substrate thus obtained.

3. A method or laminate as claimed in claim 1 or claim 2 wherein the aluminium oxide hydrate is loaded into the base paper in an amount of 5% to 30% by weight based on the weight of the base paper.

4. A method or laminate as claimed in any preceding claim wherein the melamine and/or guanamine resin is applied to the loaded paper in a solvent in an amount of 5% to 30% by weight on the weight of the base paper.

5. A method or laminate as claimed in any preceding claim wherein the base paper is formed of kraft paper, cotton linter paper, and blends thereof.

6. A method or laminate as claimed in any preceding claim wherein the aluminium hydrate has a particle size of 4 to 6,u micron.

7. A method or laminate as claimed in any preceding claim wherein the flame retardant phenolic resin is a flame retardant containing reaction product, of phenol, cresol, resorcinol and/or alkyl or like substituted phenol, with formaldehyde.

8. A method or laminate as claimed in any preceding claim wherein the flame retardant for the phenolic resin is selected from one or more of tricresyl phosphate, cresyldiphenyl phosphate, trisdipropyl phosphate, trischloro ethyl phosphate, trisdichloro phosphate, tetrabranobisphenol A, tetrachlorodiphenol A and pentabranophenol.

9. A laminate as claimed in claim 1 or in any one of claims 3 to 8 when dependent on claim 1 wherein the metal is copper.

1 0. A method or laminate substantially as described in any one of the specific examples hereinbefore set forth.