GB2232988A - Resin-covered alkali-resistant glass fibres - Google Patents

Abstract

An alkali-proof glass fibre material has zirconium oxide-containing filaments or multi-filamentary glass fibre chopped strands covered with and penetrated by a thermoplastic resin by suspension polymerization. Autoclave-resistance and alkali-resistance of the fibres, also workability in the manufacturing process are all significantly improved. The material is for use in inorganic matrices (i.e. cement or calcium silicate).

Description

GLASS FIBRES, PROCESS FOR PRODUCTION THEREOF AND USE THEREOF The invention aims to provide alkali-proof glass fibre material possessing excellent mechanical properties and autoclave-resistance, wherein surfaces of filaments of the material have a large amount of alkaliproof and heat-resistant resin applied, a process for production thereof, and an inorganic matrix (among others, particularly cements, cement mortar, calcium silicate) reinforced therewith, and the use thereof for reinforcement of matrices.

Since alkali-proof glass fibres resist erosion by alkali solutions, they have been used as reinforcing materials for inorganic matrices (particularly, cement, cement mortar, calcium silicate, etc.) which contain or produce alkali substances. The alkali-resistance of alkali-proof glass fibres is strongly dependant on content of the ingredient ZrO2 in the glass composition, but is also affected by the species and the amount of organic polymer (hereinafter referred to as "sizing") applied to surfaces of the fibres, so that the species and the amount of the sizing to be applied are also important factors in seeking improvement of alkaliresistance of alkali-proof glass fibres.In determining the composition of sizing, the polymer materials to be used need to satisfy requirements such as spinning properties, workability and ease of handling in the manufacturing process of the alkali-proof glass fibrereinforced products, in addition to alkali-resistance.

Required integrity for alkali-proof glass fibres varies depending on moulding methods. For example, in the Hatschek method, soft types of glass fibre material susceptible to easy splitting/dispersion in mixing are required; whereas, in the premix method, hard types of glass fibre material require high integrity with little if any fibre-dispersion/splitting in mixing; and in the extrusion moulding method where kneading takes place, often under severer conditions, at least compared with the premix method, alkali-proof glass fibres with an extremely high integrity are required.The hard type chops hitherto used give rise to problems in that fibre-splitting occurs when mixing is conducted over a longer time as in the premix method, so that glass fibres can assume ball-forms, and in that the glass fibres can be damaged by shear force of the screw of the extruder and broken into pieces when used in the extrusion moulding method, due to their insufficient integrity. These problems and effects inhibit full utilization of reinforcing effects for the inorganic matrix.

Generally, in producing secondary products of cement, acceleration of cement-hardening is conducted in vapour at high temperatures in order tD use the moulding boxes efficiently by shortening the in-box time or to hasten the shipment. In manufacturing calcium silicate products, treatment by an autoclave is conducted to produce tobermorite crystals and xonotlite crystals by hydrothermal reaction. In manufacturing calcium silicate boards of tobermorite, the sizing agents to be used are required not to dissolve in hot alkali, since alkali-proof glass fibres are usually added to the mixture of the raw materials and the mixture subjected to gelification by heating at 95"C for about 2 hours, followed by autoclave treatment at 1800.

The previous alkali-proof glass fibres tend to lose strength when heated by such autoclave treatment.

Autoclave treatment at lower temperatures produces insufficient growth of calcium silicate crystals, which in turn results in reduced strength of matrix.

Due to use of asbestos having become strictly restricted, reinvestigation has been conducted into use of alkali-proof glass fibres in applications where heretofore their use has been considered difficult.

Improvement of properties and qualities of alkali-proof glass fibres has thus become extremely desirable.

In arriving at the present invention extensive studies and investigations have been conducted on glass fibre material, particularly chopped strands of very high integrity, with results affording improvement in alkali-resistance properties including at high temperature, when produced by applying thermoplastic resin onto filaments using a suspension polymerization process; also on use thereof as reinforcement for inorganic matrices such as cement, cement mortar, calcium silicate, etc. Substantial improvements in desirable or required properties have been determined.

Hitherto, sizing agents were applied to glass fibres in a spinning process in an amount of not more than about 3% by weight or about 0.2 in terms of achieved coating thickness. Such coatings are so thin that alkali-proof glass fibre materials are easily damaged in moulding cement, calcium silicate and other products, or are eroded by alkali in curing at high temperatures, and for either or both reasons fail to exhibit satisfactory reinforcing etc effects. Even application of larger quantities of sizing agents is not satisfactory using a two-or more-stage coating method of sizing in high concentration applied repeatedly to dried spun strands. The sizing agent was found to be attached only or mainly at surfaces of the strands and effectively failed significantly to penetrate into the inside of a multi-filament (or fibre) strand.

By contrast, organic polymers can be applied substantially homogeneously and relatively thickly to inside filaments of chopped strands produced by said suspension polymerization of this invention, specifically in amounts ranging from 5% to 40% by weight. Then, coated alkali-proof glass fibres incorporated in the reinforced products suffer little if any surface damage and/or erosion by alkali of inorganic matrices even for curing at high temperatures.

When thermoplastic resin is applied to chopped strands of alkali-proof glass filaments, extremely high integrity can be achieved for filaments of chopped strands having an optional number of filaments (within the range from 10 to 800). As is evident from experimental results shown in Fig. 1, it was found that the smaller is the number of filaments held together by sizing, the larger is the flexural strength of the reinforced product. Previously, of course, the number of filaments held together in the strands was limited to about 50 by conventional spinning techniques at least for mass production purposes.Our experiments demonstrated that reinforced products produced by mixing alkali-proof multi-filament glass fibre chopped strands with 50 - 800 filaments held together therein (produced by suspension polymerization) into matrices of cement, cement mortars and calcium silicate were remarkably improved in workability at mixing, in alkali-resistance, and in autoclave-resistance properties. When the chopped strands, in which the filaments were held together with very high integrity, were vigorously stirred and mixed together with material of the matrices, the strands did not split significantly, and the fibres were substantially free from damage. When the reinforced products were cured at high temperatures, strength was lowered only a little due to application of a relatively large amount of heatresistant and alkali-proof resin to the surface of the alkali-proof filaments.

With that as background, the following aspects of invention have arisen, namely: One, alkali-proof glass fibre material comprising zirconium oxide-containing filaments or multi-filament glass fibre chopped strands that have been covered with thermoplastic resin in a suspension polymerization.

Two, a process for producing an alkali-proof glass fibre material comprising covering zirconium oxide-containing alkali-proof filaments or multifilament glass fibre chopped strands with a thermoplastic resin by suspension polymerization.

Three, an inorganic matrix reinforced with alkali-proof glass fibre material of the first above aspect.

Four, a method of reinforcing an inorganic matrix using alkali-proof glass fibre material of the first above aspect.

Preferred resulting products of this invention are found to have improved workability in moulding inorganic matrices such as cement products and calcium silicate products reinforced with alkali-proof glass fibres, good mechanical properties, alkali-proof properties and autoclave-proof properties.

Further specific description germane to implementing the invention is now given with reference to various Examples and relative to the drawing of which the single figure is a graph showing the relationship between the number of the bundled fibre filaments held together in alkali-proof glass fibre strands and flexural strength of those strands.

In implementing the present invention, there is no particular limitation for the alkali-proof glass fibre chopped strands save as already above indicated.

Required alkali-resistance is in relation to use in admixture with cement, mortar etc as inorganic matrices containing or producing alkali substances. Zirconium oxide (ZrO2) - containing alkali-proof multifilamentary glass fibre material preferably has not more than 4% alkali solubility as determined by glass fibre decrease after soaking of 2 grams of filaments of diameter 13 + 0.2 u in 100 g of a 10% aqueous solution of sodium hydroxide at 95"C for 1 hour.

Usually alkali-proof filamentary glass fibre material used in practicing the present invention contain ZrO2 in a proportion of not less than 5 mol%.

However, the ZrO2 proportion is preferably not less than 10 mol%, further preferably not less than 11 mol%, and particularly preferably not less than 11.5 mol%, as same is manageable herein and alkali-resistance usually tends to increase with the increase of ZrO2 content.

Examples of glass fibre materials whose filaments satisfy the above-mentioned conditions include those composed of SiO2: 50 - 76*; ZrO2: 8 - 16%; R20: 10 25t; R'O: O - 10%; CaF2: 0 - 2t; B203: 0 - 7%; P205: 0 - 5*; SnO2: 0 - 7.5%; and other metal oxides: 0 - 10%. In this composition, R represents an alkali metal, R' represents an alkaline earth metal, e.g. Zn or Mn, and other metal oxides include A1203, Fe203, TiO2, CeO2, La203, Nd203, Pr601l and the like (hereinafter and unless otherwise specified, the same symbols and definitions have the same meanings).

Suitable alkali-proof glass fibre chopped strands usually have 50 - 800 filaments of not more than 24 in diameter and usually 3 - 25 mm in length held together therein.

Whilst suitable thermoplastic resin to be used for covering the alkali-proof glass fibre chopped strands and filaments thereof is not particularly limited as long as it is capable of covering the filaments by suspension polymerization, same are found to have particularly excellent alkali-resistance properties. Examples of such thermoplastic resins include polystyrene, polyacrylonitrile, polymethyl acrylate, polyvinyl chloride and polyvinyl acetate.

Whilst the inorganic matrices to be reinforced with the alkali-proof glass fibres in application of the present invention are not limited as long as they are compounds not containing carbon atoms or carbon compounds other than organic compounds, same may contain or produce an alkali substance, as is the case for cements, cement mortar, calcium silicate, etc.

Alkali-proof glass fibre materials hereof can be obtained by subjecting one or more species of thermoplastic resin monomers to suspension polymerization together with multi-filamentary alkaliproof glass fibre chopped strands in a suspension polymerization system. Alkali-proof multi-filament glass fibre chopped strands as commercially available are suitable for use herein. However, it is preferable for the chopped strands to be soaked in advance in monomer(s) to be used for polymerization, for wetting purposes, which promotes better, generally complete coverage of constituent single filaments of the glass fibre chopped strands.

In suspension polymerization, alkali-proof multifilamentary glass fibre chopped strands can be in a proportion of 5 - 800 parts by weight relative to 100 parts by weight of the monomer(s), particularly preferably in a proportion within the range of 50 - 500 parts by weight on the same basis. Hydrous medium to be used in suspension polymerization is preferably in a proportion of 100 - 3000 parts by weight relative to 100 parts by weight of the monomer(s) used. When hydrous medium is used in a proportion of less than 100 parts by weight relative to 100 parts by weight of the monomer(s), the resulting mixture tends to become extremely viscous as polymerization proceeds. This results in difficulty in stirring of the mixture, heat conductivity and adjustment of the temperature, consequently difficulty in obtaining resins having homogeneous properties.When hydrous medium is used in a proportion of more than 300 parts by weight, it inevitably limits the amount of the monomer(s) to be used, and results in lowering of the productivity.

Consequently, the process becomes less economical.

Conventional suspension stabilisers may be used, for example various saponification products of polyvinyl acetate (polyvinyl alcohols), styrene-maleic acid copolymers, polysodium methacrylate, copolymers of ethyl hexyl acrylate and acrylic acid and other water-soluble polymer compounds, whether used singly or plurally in combination. The amount of water-soluble polymer compounds used normally ranges from 0.1 to 5, preferably from 0.1 to 2, parts by weight relative to 100 parts by weight of the monomer(s). Also, these suspension stabilizers can be used together with some species of surfactant such as polyvinyl alcohol. Further inorganic compounds such as calcium carbonate can also be incorporated.

For suspension polymerization, a conventional vertical reactor can be used.

In polymerization of the monomer(s), it is usual to employ a polymerization initiator, preferably radical-generating polymerization initiators as is conventional, for example benzoyl peroxide. While the amount of polymerization initiator to be used varies depending on its characteristics and the polymerization temperature, the initiator is usually in an amount of 0.005 - 3.0 parts by weight relative to 100 parts by weight of the monomer(s) used.

Reinforcement of inorganic matrices by alkaliproof glass fibres of the present invention needs no special consideration or variation to what is known.

Specific working and experimental examples are now described. Examples 1 to 4 concern premix-moulding applications.

Generally, alkali-proof multi-filament glass fibre chopped strands were bundled in accordance with the following polymerization composition, and the mixture was put in an autoclave and heated up to 80"C under stirring in a temperature-controlled water vessel, followed by about five hours' polymerization.

After termination of the reaction, the contents of the autoclave were removed onto a steel for separation into water and the reaction mixture. The reaction mixture was washed with water and dried in an electric furnace.

Resulting products were alkali-proof glass fibres, viz: Composition of polymerization materials Alkali-proof glass fibres : 150 gr Styrene : 70 gr Acrylonitrile : 30 gr Benzoylperoxide : 1 gr Water : 1300 gr Suspending agent : 0.7 gr Composition of inorganic matrix Mortar comprising: Sand : Ordinary Portland cement (S:C)=l:1 Water : Ordinary Portland cement (W:C)=0.4:1 Water reducing agent : Ordinary Portland cemente0.4:l To the mortar components of the above-mentioned ratio were added alkali-proof glass fibres as shown in Examples 1 - 4 in Table 1 cnd available glass fibres (from Nippon Electric Glass Co., Ltd.ACS06H-350Z) in a proportion of 2.0* by weight respectively, and the constituents were mixed for 30 seconds in an omnimixer.

Thereafter, the mixture was poured into a wooden moulding box (510 x 320 x 10 mm) to make plates/boards.

The boards were cured in a temperature controlled room at 20"C for 3 days after which the moulding box was taken off and samples of 250 x 50 x 10 mm size were prepared and examined for their flexural strength, strand integrity and autoclave-proof properties. The results are as shown in Table 1.

Flexural strength was examined after keeping samples in water at 20"C for 28 days. As for strand integrity, the degree of strand-splitting after 60 seconds stirring in mortar was examined. As for autoclave-resistance properties, the state of the strands was examined after 10 hours treatment in a saturated solution of Ca(OH)2 at 180 C.

As shown in Table 1, the alkali-proof glass fibre materials of Examples 1 - 4 exhibit higher adhesion to thermoplastic resin and show better strand integrity and autoclave-resistance than prior products. The flexural strength of the produce of Example 3 is smaller. This is because the number of the glass fibre filaments in the strands was much larger than the products of other Examples and, as a result, the total contact area between the matrix and the filaments became smaller, i.e. in a matrix comprising a certain number of strands and filaments the contact area of matrix with the filaments becomes smaller along with the increase of the number of the filaments in one strand. It is believed that particular excellence of the product of Example 3 in autoclave-resistance is due to the fact that the adhesion percentage of the thermoplastic resin is large.

Examples 5 to 8 concern extrusion moulding S/C=1 W/C=0.8 Pulp/(S+C)=0.042 Alkali-proof glass fibres/ ( S+C ) =0.03 Therefrom, mortars were produced with alkaliproof glass fibre material having the same composition as for Examples 1 - 4 (from Nippon Electric Glass Co., Ltd. ACS06H-350Z), and was moulded into plate boards f 1800 x 210 x 16 mm using an extruder (Mikami Kogyo Inc.

HT-250). After the moulded products were naturally cured for 2 days, they were further cured in an autoclave at 160 C for 6 hours. From the moulded products, samples of 50 x 210 x 16 mm in size were prepared for the measurement of flexural strength.

Also, the flowability in extrusion, dispersibility, fibre-splitting properties, and fibre length of the alkali-proof fibres were measured. The results are as shown in Table 2.

Flowability was measured by observing dice pressure of the extruder; dispersibility was measured by observing the dispersion state of strands/filaments in a section of the un-cured moulded products taken just after extrusion; yarn-splitting properties were measured by observing the state of integrity of the strands/filaments after mixing in the mixer and kneader; and fibre length was estimated by measuring the length of the remaining fibres after a sample of about 1 cm cube was cut off and other constituents were dissolved in hydrochloric acid (36%).

The products of Examples 5 - 8 have good flowability and dispersibility as shown in Table 2, so are excellent as to workability. As the fibres are hardly broken at all in moulding, flexural strength is high. As far as the product of Example 7 is concerned, the flexural strength is small in the same manner as in the data of the premix method. This is considered to be cause adhesion was so large that the strands were not split in the extruder, and consequently contact area with matrix became smaller than that of the products of other Examples.

Examples 9 - 12 result from experimenting using a calcium silicate board, basically comprising: Cement : 60 parts Si02 : 40 parts Bentonite : 10 parts Water : 110 parts To the mixture composed of the aforesaid constituents were added alkali-proof glass fibres of Examples 9 - 12 (from Nippon Electric Glass Co., Ltd.

ACS06H-350Z) in a proportion of 10% by weight, and the mixtures were heated at 95"C for 2 hours for gelification. The resulting slurries were poured into a moulding box and left standing still at room temperature for 2 days, followed by 12 hours' autoclave treatment at 1800C to produce calcium silicate boards. The thusobtained boards were examined for flexural strength and integrity percentage (measured in accordance with the below-mentioned method), and the results are shown in Table 3.

As is clear from Table 3, the products of Examples 9 - 12 maintained their integrity in hot alkali solutions.

As a measure of integrity percentage - a beaker containing 500 cc of 1% NaOH was heated up to 95"C, and 50 pieces of multi-filamentary alkali-proof glass fibre chops were added, after which the mixture was heated for 30 minutes, and stirred for 1 minute in a labomixer. Integrity percentage represents the percentage of strands which retained their shape completely after the aforementioned treatments.

the number of the strands which retained Integrity their shape completely percentage = x 100 50 (the initial number of the alkali proof filament strands) A further reference experiment investigated the relationship between the number of filaments held together and flexural strength. In accordance with a conventional spinning method (Nippon Electric Glass Co., Ltd. E fibre catalogue), chopped strands of 6 mm fibre length and 13y fibre diameter with 25, 50, 100, 150 and 200 filaments respectively held together therein were prepared and added to mortar having the same composition as in the previous mould Examples in a proportion of 2.08 by weight, wherefrom the specimens were prepared under the same conditions as for the remix mould Example 1.Flexural strength after keeping the specimen in water at 20"C for 28 days was measured, and relationship between the number of the filaments held together and the flexural strength was tabulated. The results are as shown in Fig. 1.

From Fig. 1, it is found that, as the number of the filaments held together becomes smaller, the flexural strength becomes larger.

Table 1 Premix method data Prior product Example 1 Example 2 Example 3 Example 4 Integrity Bad Best Best Best Best Autoclave-proof property Bad Good Good Best Good Flexural strength of 160 150 170 100 175 molded product (kg/cm) Thermoplastic resin 2.0 20 20 40 10 adhesion percentage (%) Number of fiber filaments 50 50 25 200 25 in strands Fiber length (mm) 6 6 6 6 6 Glass content (wt%) 2 2 2 2 2 Table 2 Extrusion-molding data Prior product Example 5 Example 6 Example 7 Example 8 Flowability Bad Best Best Best Best Dispersibility Good Best Best Best Best Fiber-splitting property Observed None None Observed None Fiber length in molded 0.07 2 < 2 < 2 < 2 < product (mm) Flexural strength of 70 140 160 90 160 molded product (kg/cm) Glass content (wt%) 3 3 3 3 3 Table 3 Calcium silicate press-molding data Prior product Example 9 Example 10 Example 11 Example 12 Integrity percentage (%) 80 100 100 100 100 Flexural strength (kg/cm) 110 150 170 110 170 Adhesion percentage (%) 2.0 20 20 40 10 Number of fiber filaments 50 50 25 200 25 in strands Glass content (wt%) 10 10 10 10 10 Fiber length (mm) 13 13 13 13 13 While alkali-proof glass fibres have been developed as the materials in place of asbestos and have been used as architectural materials and industrial materials for about 15 years, they have not been used in some fields because of lack of long-term durability or reduction in strength caused by autoclave treatment.

According to the present invention, autoclaveresistance and alkali-resistance of the alkali-proof glass fibres and workability in the manufacturing process of the inorganic matrices reinforced with said alkali-proof glass fibres can be remarkably improved, and thus exploration of its application to a wider range of use can be expected.

Claims (13)

1. Alkali-proof glass fibre material comprising chopped strands of zirconium oxide-containing filaments or multi-filament glass fibres that have been covered with thermoplastic resin in a suspension polymerization process.

2. Alkali-proof glass fibre material as claimed in Claim 1, wherein alkali solubility of said filaments is not more than 4%.

3. Alkali-proof glass fibre material as claimed in Claim 1 or Claim 2, wherein said filaments contain zirconium oxide in a proportion of not less than 10 mol%.

4. An alkali-proof glass fibre material as claimed in any preceding Claim, wherein said filaments are composed of SiO2: 50 - 76%; ZrO2: 8 - 16%; R20: 10 25%; R'O: O - 10%; CaF2: 0 - 2%; B203: 0 - 7%; P205: 0 - 5%; SnO2: 0 - 7.5%; and other metal oxides: O - 10%, where.R represents an alkali metal, R' represents an alkaline earth metal and the other metal oxides include one or more of A1203, Fe203, TiO2, CeO2, La203, Nd2O3, Per6011.

5. A process for producing alkali-proof glass fibre material, comprising covering zirconium oxide-containing filaments or mu:.ti-filament glass fibre chopped strands with a thermoplastic resin by suspension polymerization.

6. A process as claimed in Claim 5, wherein filamentary chopped strands are used in said suspension polymerization in a proportion of 5 - 800 parts by weight relative to 100 parts by weight of monomers used for producing a thermoplastic resin.

7. A process as claimed in Claim 5 or Claim 6, wherein a hydrous medium is used in said suspension polymerization in a proportion of 100 - 3000 parts by weight relative to 100 parts by weight of the monomers used for producing a thermoplastic resin.

8. An inorganic matrix reinforced with alkali-proof glass fibre material according to Claim 1.

9. An inorganic matrix as claimed in Claim 8, wherein said inorganic matrix is cement or cement mortar or calcium silicate.

10. A method of reinforcing an inorganic matrix using alkali-proof glass fibre material according to Claim 1.

11. Alkali-proof glass fibre material substantially as herein described with reference to the Examples and the accompanying drawing.

12. Process for producing alkali-proof glass fibre material substantially as herein described with reference to the Examples and the accompanying drawing.

13. Reinforced matrix products substantially as herein described with reference to the Examples and the accompanying drawing.