HK1024010A - Non hygroscopic thermally stable aluminium hydroxide - Google Patents

Description

Damp-heat resistant stable aluminum hydroxide

The present invention relates to a moisture resistant (non-hygroscopic) thermally stable aluminum hydroxide and its use in flame retardant thermally stable laminates for printed wiring boards.

The type of printed wiring laminate is defined by the NEMA (national electrical manufacturers association) standard, a term that is widely accepted worldwide. Generally, laminates are classified according to the reinforcing material used therein, i.e. cellulose paper or glass fiber fabric. Typically, FR-2 type laminates use only cellulose paper, CEM-1 type laminates use paper and woven glass fiber fabrics, and CEM-3 type laminates contain both woven and non-woven fabrics of glass fibers. FR-4 type laminates contain only woven fiberglass fabric.

To achieve the flame retardant V0 rating specified by American Underwriters Laboratories' Standard UL-94, it is necessary to add flame retardant chemicals to the polymer system or to introduce halogens or phosphorous into the polymer backbone. These additives can help extinguish the flame when burned. However, during flame extinction, the additives release toxic and corrosive gases. Phosphoric acid is formed during the burning of FR-2 laminates containing phosphorus compounds. During the burning of CEM-3 and FR-4 laminates containing brominated epoxy resins, toxic corrosive hydrogen bromide is produced.

It is known to those skilled in the art that aluminium hydroxide can be used to improve the flame retardant properties of synthetic polymer systems based on, for example, epoxy resins, polyesters and polyvinyl esters, since these polymers decompose at the same decomposition temperatures as aluminium hydroxide. However, the gibbsite form of aluminum hydroxide (Al (OH))₃Sometimes expressed as Al₂O₃·3H₂O) the thermal stability of some components at the temperature at which they are soldered to the printed wiring laminate is insufficient and the laminate can blister and be rendered unusable.

It is known that aluminum hydroxide in the form of gibbsite is partially converted to the monohydrate form of aluminum hydroxide, i.e., boehmite (AlOOH or Al), when heated in air₂O₃·H₂O). The latter improves the thermal stability while being detrimental to the flame retardant properties.

JP-A60/203,438 discloses a CEM-3 laminate comprising heat-treated aluminum hydroxide in the form of gibbsite, which has improved thermal stability and exceeds that of standard aluminum trihydrate, but which does not have the required flame retardant properties. As a result, brominated epoxy resins must also be used to achieve the above-mentioned UL 94V0 rating in order to achieve the desired flame retardant properties. In this case, and in other applications where excellent flame retardant properties are lacking, other inorganic materials such as talc or clay may also be used.

Uk patent application no 9700708.2 describes an excellent CEM-3 laminate which has good thermal stability, is halogen/phosphorus free and which has flame retardant properties meeting UL 94V0 requirements due to the incorporation of a thermally stable aluminium hydroxide in the laminate.

However, it has been found that these thermally stable aluminum hydroxides readily absorb moisture. The moisture absorption can significantly reduce the solder resistance of the laminate. Therefore, the thermally stable aluminum hydroxide is sometimes used somewhat immediately after the preparation. It has been found that the water absorbed by the aluminium hydroxide adheres tightly to the surface and as a result the techniques commonly applied to remove surface water (e.g. prior heat treatment at 110 c in a laminate system or azeotropic distillation with acetone) may be unsatisfactory in terms of effectiveness.

It is therefore an object of the present invention to further improve the addition process and the properties of thermally stable aluminum hydroxide with the aim of significantly reducing its hygroscopicity. It is another object of the present invention to produce a CEM-3 laminate which has good thermal stability, is halogen/phosphorus free, has flame retardant properties in accordance with UL 94V0, and has excellent solder resistance and moisture resistance.

The above object is achieved by the use of a moisture and heat resistant stable aluminium hydroxide according to claim 1 and a method for manufacturing a laminate, by which the laminate contains a novel and inventive moisture and heat resistant stable aluminium hydroxide.

The moisture-proof and heat-proof stable aluminum hydroxide is characterized in thatIn the following steps: it has Al₂O₃·nH₂O, wherein n has a value of > 2.6 to < 2.9, and the aluminum hydroxide surface is treated with silane.

The base material for the moisture and heat resistant stable aluminum hydroxide used in the present invention is the moisture and heat resistant stable aluminum hydroxide described in detail in british patent application No. 9700708.2.

The production of the thermally stable onium hydroxide may be described as the comminution of an aluminum hydroxide agglomerate having an average particle size of D50% of 40 to 80 μm, preferably 50 to 70 μm, which is crystallized from a typical sodium aluminate Bayer process solution.

Any size reduction technique, such as ball milling, can be used as long as it separates the grains from the coarser agglomerates with little or no overall fragmentation of the individual grains. The simultaneous broadening of the particle size distribution due to grinding and the overall disintegration of the grains improves the processability of thermally stable aluminum hydroxide in the corresponding resin system.

The material obtained from the comminution process is subsequently heat-stabilized by heating it at a temperature and for a time sufficient to reduce the water loss on ignition from 34.5% by weight (n-3) to a level corresponding to the value of n.

In Al₂O₃·nH₂In the formula of O, n preferably has a value of 2.7 to 2.8.

It is important that the particle size distribution should give a relatively small average particle size and a broad particle size distribution which improves the dispersion of the heat stable aluminum hydroxide in the resin while also minimizing the tendency of coarse particles to settle out during processing and avoiding filtration through the non-woven glass fiber fabric.

An ideal particle size distribution should allow for minimal viscosity of the resin/filler mixture to be mixed at a sufficiently high loading level sufficient to achieve the desired laminate flame retardant properties without the addition of any flame retardant.

The average particle diameter D50% of the aluminum hydroxide with the moisture and heat resistance stability is 5-10 μm. The width of the particle size distribution is represented by the ranges D10% and D90%, i.e., by the weight percentage D10% of particles having a particle size of less than 0.5 to 1.5 μm and the weight percentage D90% of particles having a particle size of less than 20 to 35 μm.

Typically, the silane treatment is first a dispersion of heat stable aluminum hydroxide in a diluent liquid commonly used in the manufacture of printed wiring laminates, preferably a ketone, more preferably acetone.

Prior to addition of the silane, the dispersion is preferably vigorously mixed using an apparatus that can apply a large amount of shear to the dispersion as would be produced using a shear head mixer.

Then, a suitable silane compound (preferably in liquid form) is added. The amount of the aluminum hydroxide is in the range of 0.1 to 2% by weight based on the heat-stable aluminum hydroxide.

Suitable silane compounds are commercially available, for example, from Huls under the trade name Dynasilan^_(Huls-brochure，Anwendung von organofunktionellen Silane，Dynasilan^_October, 1989).

Preferred silane compounds are typically aminoalkylsilanes, epoxyalkylsilanes or vinylsilanes. Particularly preferred for epoxy resin applications are aminoalkylsilanes.

The moisture and heat resistant aluminum hydroxide has a hydrophobic surface free of adsorbed moisture after silane treatment.

As described in uk patent application No. 9700708.2, a CEM-3 type press platen is typically constructed of two outer layers of woven glass fibre fabric and three inner layers of non-woven glass fabric.

According to the invention, a printed wiring laminate has a surface layer of woven glass fiber fabric impregnated with a curable resin and intermediate layers of non-woven glass fiber fabric impregnated with a curable resin, characterized in that these intermediate layers contain 200 to 275% by weight, based on the weight of the resin, of the moisture and heat resistant stable aluminum hydroxide according to claims 1 to 5.

The curable resin may be an unsaturated polyester resin, an epoxy resin, a vinyl ester or any suitable heat curable compound which decomposes on combustion within the same decomposition temperature range as the thermally stable aluminum hydroxide.

The laminate may be epoxy based and thus may be produced in a mass process. Laminates can also be produced in a continuous process using unsaturated polyesters or vinyl esters, i.e. using resins which polymerize by a mechanism of free radical polymerization. The essence of the invention is not limited to the technique of manufacturing the laminate.

If the laminate is made on an epoxy resin basis, it is generally made up of a combination of two woven glass fabrics impregnated with epoxy resin and three non-woven glass fabrics impregnated with epoxy resin containing heat stable aluminum hydroxide. The five layers are then typically laminated with one or two outer layers of copper foil, and the composite is then heated and pressed to polymerize the resin and consolidate the laminate.

Most epoxy resins for laminates for electrical or electronic use are derived from bisphenol a or cycloaliphatic species. The most commonly used hardener is dicyanodiamine.

According to the manufacturing method of the present invention, the intermediate layer is a non-woven glass fabric impregnated with a curable resin and containing 200 to 275% by weight, preferably 225 to 250% by weight of the moisture-and heat-resistant stable aluminum hydroxide according to claims 1 to 5.

The addition of the moist heat stable aluminium hydroxide to the curable resin may be carried out by methods known to the skilled person, i.e. usually by introducing the filler (either as a dispersion in the corresponding solvent after silane treatment according to the methods of claims 6 to 9 or as a solid recovered from the silane treatment solution after drying) into a pre-dissolved mixture of resin and hardener using equipment such as a shear head mixer. Other inorganic, thermally stable fillers such as silica, clay or talc may also be added to the formulation if desired, although these materials do not significantly increase the flame retardant properties of the laminate.

Further processing of the resin/filler mixture into an "impregnated preform" and then forming a cured laminate is a common process in the art and is described in the literature, for example, in the Handbook of Epoxide Resins, published by McGraw-Hill book company.

The cured laminate of the present invention exhibits further increased thermal stability than laminates made by the process described in uk patent application no 9700708.2. The laminate of the present invention did not exhibit blistering or bubbling for more than 90 seconds when immersed in molten solder at 260 c. The laminate also has excellent flame retardant properties, and meets UL 94V-0 requirements.

Examples

1. Production of thermally stable aluminum hydroxide

The amount of the used crystal seeds is 50kg/dm³Sodium aluminate solution of the following concentrations: na (Na)₂O-140kg/dm³，Al₂O₃-150kg/dm³Total Na₂O-150kg/dm³To produce an aggregate of fine aluminum hydroxide grains (average grain size of about 1 to 2 μm) (average grain size of about 60 μm). The operating capacity of the crystallizer used is 1m³The crystallization temperature was 75 ℃ and the retention time was 24 hours.

The yield of the alumina liquid was about 40kg/dm³The crystallized product was washed with deionized water and dried at 105 ℃ for 4 hours.

The pulverization of the aluminum hydroxide particles was carried out by a vibratory ball mill (Palla 200 type manufactured by KHD Co.). The crushing conditions were as follows: the rotating speed of the motor is 1000 rpm; the loading of the bar was-about 65% by volume; the grinding rod (made of alumina) has the size of-12 mm multiplied by 12 mm; the yield of the ball mill is about 50 kg/h. Under the above conditions, the particle size of the added aluminum hydroxide was reduced to the size shown in table 1.

The final heat stabilization treatment was carried out by heating in an electric furnace at 220 ℃ for about 2 hours to reduce the water loss at the time of ignition of the aluminum hydroxide from 34.5% by weight to about 31% by weight of the material. The properties of the resulting thermally stable material are also shown in table 1.

TABLE 1

Physical parameters

Al₂O₃.nH₂O_”n ^“ 2.7

Particle size D10% (μm) 1.0

Particle size D50% (μm) 7.5

Particle size D90% (μm) 28.0

Specific surface area (m)²/g) 6.0

Oil absorption (ml/100g) 28.0

2. Example 1 silane treatment of thermally stable aluminum hydroxide

100g of the heat-stable aluminum hydroxide from example 1 were dispersed in 500ml of acetone. The mixture was dispersed in a shear head mixer for 20 minutes. Then 0.75g of aminoalkylsilane (A1100 from Witco) was added. After stirring for another 5 minutes, the solvent was evaporated and the collected damp-heat resistant stable aluminum hydroxide had the following properties:

physical parameters

Al₂O₃.nH₂O_”n ^“ 2.7

Particle size D10% (μm) 1.0

Particle size D50% (μm) 7.5

Particle size D90% (μm) 28.0

Specific surface area (m)²/g) 5.5

Oil absorption (ml/100g) 20.0

Silane content (wt.%) 0.4

3. Manufacture of laminates (batch process)

100 parts of an epoxy resin having an epoxy equivalent of 400-500 was dissolved in 30 parts of acetone, and 4 parts of dicyanodiamine previously dissolved in 36 parts of 2-methoxyethanol were mixed. To this mixture 0.1 part of 2-methylimidazole was added to accelerate the curing of the resin (mixture A).

A woven glass fabric (model 7628, made by interbrass) was impregnated with the mixture a until the resin content was 42%, and then the resin was semi-cured at 160 ℃ for 2 minutes to obtain a dried impregnated preform.

The thermally stable aluminum hydroxide of example 1 was dispersed 250phr (parts to one hundred parts resin) in one third of its weight in acetone. The mixture was dispersed in a shear head mixer for 20 minutes. Then 0.75% by weight of an aminoalkylsilane (A1100 produced by Witco) (mixture B) relative to the heat-stable aluminum hydroxide was added.

To mixture a, add separately: a)250phr of heat-stable aluminum hydroxide and B) of the inventive moist heat-stable aluminum hydroxide in the form of a mixture B. The above two mixtures were impregnated into a non-woven glass fabric (type E105 manufactured by Owens corning) to make it 90% of the total weight. The amount of acetone used to disperse the heat stable aluminum hydroxide in acetone is commensurate with the viscosity of the final resulting mixture. The resin system described above was then semi-cured (impregnated with a B-stage resin) at 160 ℃ for 3 minutes to obtain an operable dry impregnated preform.

Three layers of the non-woven glass fabric impregnated preform were sandwiched between two layers of the woven glass fabric impregnated preform. The resulting composite was laminated with copper foil on both sides and then at 180 ℃ under a pressure of 50 bar for 90 minutes to obtain a copper foil-clad laminate having a thickness of 1.6 mm.

Test results

A comparison was made between a) thermally stable aluminium hydroxide prepared according to british patent No. 9700708.2 and b) moisture and heat resistant stable aluminium hydroxide prepared according to the present invention.

The laminate was completely immersed in molten solder at 260 c and tested for solder resistance. When the aluminum hydroxide begins to decompose, the laminate can be heard blistering, with the escaping moisture forming waves on the molten solder surface. The time at which the blister ripple occurred was measured.

The light-off performance is defined by the American Underwriters Laboratory UL94 standard, which classifies behavior on combustion as V-0 (best), V-1 and HB (worst). For printed wiring board applications, the laminate must meet the requirements of the V-0 category.

TABLE 2

Solder resistance and flammability test results

Test of	Laminate (ts-ATH) containing thermally stable aluminium hydroxide (GB.9700708.2)			Laminates containing aluminium hydroxide stabilized against humidity and heat (invention)
					Amounts (phr)	250	250	250	250
ts-time after ATH production (month)	1	2	6	6
					Solder resistance(s)	＞90s	40s	＜20s	＞90s
Flammability UL94	VO	-	-	VO

Claims (14)

1. A molecular formula of Al₂O₃·nH₂O, wherein n has a value of > 2.6 to < 2.9, which surface has been treated with a silane.

2. The aluminum hydroxide with stability against moist heat according to claim 1, wherein the aluminum hydroxide has a particle size of D50% in the range of 5 to 10 μm.

3. The aluminum hydroxide of claim 1 or 2 having a particle size in the range of D10% of 0.5 to 1.5 μm and D90% of 20 to 35 μm.

4. The moisture and heat stable aluminum hydroxide of claim 1 wherein the silane is selected from the group consisting of aminoalkylsilanes, epoxyalkylsilanes, and vinylsilanes.

5. The moisture and heat stable aluminum hydroxide according to claim 1 or 4 wherein the silane compound is present in the thermally stable aluminum hydroxide in an amount ranging from 0.1 to 2% by weight.

6. A method for removing moisture adhering to the aluminum hydroxide of any one of claims 1 to 5, wherein the thermally stable aluminum hydroxide is treated with a silane in the presence of a ketone solvent.

7. A process as claimed in claim 6, wherein aminoalkylsilanes, epoxyalkylsilanes or vinylsilanes are used as suitable silanes.

8. The method of claim 6 or 7, wherein the silane is added in an amount of from 0.1 to 2.0% by weight of the thermally stable aluminum hydroxide.

9. The method of claim 6, wherein acetone is used as the solvent.

10. A laminate for a printed wiring board, the laminate having a surface layer formed of a woven glass fiber fabric impregnated with a resin and an intermediate layer formed of a non-woven glass fiber fabric impregnated with a curable resin, characterized in that the intermediate layer contains 200 to 275% by weight, based on the weight of the resin, of the moisture and heat resistant stable aluminum hydroxide of claims 1 to 5.

11. A laminate according to claim 10 wherein the curable resin uses unsaturated polyester resins, epoxy resins or vinyl esters.

12. A method of manufacturing a laminate for a printed wiring board by combining a surface layer having a woven glass fiber fabric impregnated with a curable resin and an intermediate layer having a non-woven glass fiber fabric impregnated with a curable resin, characterized in that the curable resin-impregnated woven glass fiber fabric contains 200 to 275% by weight, based on the weight of the intermediate layer resin, of the moisture and heat resistant stable aluminum hydroxide according to claims 1 to 5.

13. The method of claim 12, wherein the curable resin is an unsaturated polyester resin, an epoxy resin, or a vinyl ester.

14. A method according to claim 12 or 13, wherein the moisture and heat stable aluminium hydroxide according to claims 1-5 is added as a dispersion in a ketone to a non-woven glass fabric impregnated with a curable resin, obtained by a method according to claims 6-9, or in dry solid form.

15. A printed wiring board consisting of the laminate of claims 10-11 or made according to the method of claims 12-14.