CA1139162A

CA1139162A - Method of treating glass fibres

Info

Publication number: CA1139162A
Application number: CA000330516A
Authority: CA
Inventors: Katuji Matuura
Original assignee: Daiichi Kasei Co Ltd
Current assignee: Daiichi Kasei Co Ltd
Priority date: 1978-06-26
Filing date: 1979-06-25
Publication date: 1983-01-11
Also published as: GB2027012B; US4228204A; DE2900116A1; GB2027012A; SE7905177L; SE437982B; DE2900116C2

Abstract

ABSTRACT OF THE DISCLOSURE

Method of treating glass fibers which comprises treating glass fibers with an aqueous solution of zinc salt, lead salt, tin salt or mixture thereof, thereby forming a protective coating having high chemical resistance on the surface of the glass fibers.

Description

The present invention relates to a method o~ treating glass fibers ~y which chemical resistance is imparted to the glass fibers.
Recently, long glass fibers or short glass fibers (hereinafter referred to as glass fibers) have ~een incorporated into mortars, concretes and the like to increase bending strength of cement products. As the diameter o the glass fibers decreases, the tensile strength of the glass fibers increasesO Use of glass fibers having high tensile strength affords cement products having high bending strength, so that it is recommended to use glass fiber~ having small dia-meter.
The major components of the glass f.ibers are silicon dioxide SiO2, calcium oxide CaO, magnesium oxide MgO, diboron trioxide B203, sodium oxide Na20, potassium ox.ide K20, aluminum oxide A12O3 and lithium oxide Li2O, so that the glass fibers have acid resistance at broad ranges of pH2-6. However, no glass fibers have alkali resistance at alkaline regions of pH9-14, particularly pH12-14. Alkaline earth metal oxides such as calcium oxide and magnesium oxide as well as alkali metal oxides such as sodium oxide, potassium oxide and lithium oxide are leached out from the glass fibers in the form of Ca(OH)2, Mg(OH)2, NaOH, KOH and LiOH respectively.
Therefore, cement products having good bending strength cannot be obtained in the prior art. In particular, when glass ~3'3~

fibers having small diameter are used, deterioration of the glass fi~ers is remarkable ~ecause large surface areas of the glass fibers contact the alkali components present in cement.
It has been proposea that glass fibers for use in reinforcing cements should ~e alkali resistant and it has been proposed to use glass composition containing 5 - 25% by weight of zirconium oxide ZrO~. ~owever, when glass composition containing less than 10% by wèigh~ of zirconium oxide are used, glass fibers having suficient alkali resistance cannot ~e o~tained. When glass compositions containing 10 -- 25% by weight of zirconium oxide are used, glass fibers having slight alkali resistance can be o~tained. However, it is difficult to fuse the glass composition on producing glass fibers. Also, if Eused, the temperature o~ the liquid phase is raised, so that a good spinning efficiency cannot be obtained. Further, the glass fibers cannot be formed efficiently. Furthermore, it is necessary to use a heavy-duty equipment. To overcome the drawbacks accompanied with more than 10% by weight of zir-conium oxide, it has been proposed that alkali metal oxides such as ~a2O, K2O and Li2o (hereinafter referred to as R2O) be used as flux such that the total amount of R2O is 14 - 18 by weight. Alternatively, it has been proposed that alkaline earth metal oxides such as CaO, MgO, BaO and/or boron family element oxides such as B2O3 be added to decrease a melting point of the glass composition. However, when R2O is added in an amount of 14-18% by weight, weathering occurs in an atmosphere or an aqueous solution. Also, R2O is leached out from the glass fibers by alkali components present in cement, so that strength of the glass fibers decreases. For example, after one year, bending strength of cement products decreases to 60%
of that of the cement products immediately after preparation.
Therefore, there has been reluctance to use glass compositions containing 14-18% by weight of R2O. On the other hand, when alkaline earth metal oxides and the like are incorporated into the glass composition, acid resistance of glass fibers formed therefrom decreases remarkably.
It is an object to provide a method of treating glass fibers by which improved chemical resistance is imparted to the glass fibers.
The present invention provides a method oE imparting chemical resistance to glass fibers which comprises the steps of treating glass fibers with a substantially aqueous solution of

2-25~ by weight of a metal salt selected from the group consisting of zinc salt, lead salt, tin salt and mixtures thereof, to form a protective coating having high chemical resistance on the surface of the glass fibers, then washing the treated glass fibers with water, and thereafter drying the washed glass fibers at a temperature of from 80C~200C.

,~

For the prac-tice of the present invention, in its preferred embodiment, an aqueous solution of zinc salt, lead salt, tin salt or mixture thereof is prepared. Zinc salts used in the present invention are for example zinc chloride ZnC12, zinc sulfate ZnS04, zinc nitrate Zn(N03)2 and the like.
Lead salts used in the present invention are for example lead - 3a -,; ;, chlorides such as lead monochloride PbCl, lead dichloride PbC12 and lead tetrachloride PbC14; lead sulEates such as plumbous sulfate PbSO4 and plum~ic sulfate Pb~SO4)2; lead nitrate Pb(NO3)2 and the like. Tin salts used in the present invention are Eor example tin chlorides such as stannous chloride SnC12 and stannic chloride S:nC14; tin sulEates such as stannous sulfate SnS04 and stannic sulfate Sn(S04)2; tin nitrates such as stannous nitrate Sn(NO3)2 and stannic nitrate Sn(NO3)~ and the like. Concentration of acid aqueous solution of zinc salt, lead salt, tin salt or mixture thereof is 2 -25% by weight, preferably 10 - 15~ by weight~
This a~ueous solution prepared as descri:bed above is applied to glass fibers by means of dipping, sp:ra~ing, painting or the like so as to treat the surface. of the glass fibers with said aqueous solution. Thereby, protective coat-ing having chemical resistance, particularly high alkali resistance is formed on the surEace of the glass fibers.
Any glass fibers may be treated with said aqueous solu-tion in the present invention. Representative glass fibers are for example as follows: (a) glass fibers having subs-tantially no alkali resistance consisting essentially oE
silicon dioxide SiO2, aluminum oxide A1203, diboron trioxide B203, magnesium oxide MgO, calcium oxide CaO, barium oxide BaO, alkali metal oxiaes R20(Na20, K20, Li20) and ferric oxide Fe203; (b) glass-fibers having slight alkali resistance .~ .

~ ~ ~t~3~ ~ ~

comprising essentially up to 10% by weight of zirconium oxide, 54 - 60% by weight of silicon dioxide, 0 - 6~ by weight of aluminum oxide, 0 - 7% by wei~ht of magnesium oxide, 5 - 9% by weight of calcium oxide, 1 ~ 6~ ~y weight of barium oxide, 12 - 20~ by weigh-t of alkali metal oxides and 0 - 4~ by weight of ferric oxide; (c1 glass fibers having slight alkali resistance comprising essentially 10 25~ by weight of zirconium oxide, 54 - 58% by weight of sil-i-con dioxide, 0 - 4~ by weight of aluminum oxide, 0 - 5~ by weight of magnesium oxide, 5 - 9~ by wei~ht of calcium oxide, 1 - 6~ by weight of barium oxide, 14 - 18% by weight o al-kali metal oxides and 0 - 5~ by weight of ferric oxide.
Common impurities may also present in a proportion of up to 1~ by weic~ht. Further additives may be included in propor~
tions of up to 1% by weight to assist in re~ining of the glass fibers. Such oxides are for example P2O5, Cr2O3, TiO, As2O3, Sb2O3, CdO, BeO and V2O5.
It is believed that the protective coating having chemical resistance, particularly high alkali resistance is formed by the following mechanism. The mechanism is explained by one example in which silicate glass fibers are treated with an aqueous solution of ~nC12. I~hen the surface of the glass fibers is treated with the aqueous solution, cations such as Na+, Li+, Ca2+, Mg2+ and Ba2~-bonded weakly to a network of Si-O react rapidly with reactive Cl anion to form salts such

3~

as NaCl, LiCl, CaC12, MgC12 and BaC12. The salts thus formed are leached out from the surface of the glass fibers.
Zn is substituted immediately for the cations to form a colloidal zinc protective coatiny. The protective coating thus formed is stable and has good chemical resistance against acids and alkali at ambient temperature. Also, in case of PbC12, SnC12, ZnSO4, PbS04, SnSO4, Zn(NO3)2, Pb(NO3)2 or Sn(NO3)2, a similar colloidal protective coating having good chemical resistance can be formed.
The giass fibers treated as described above are washed with water, and then dried at a temperature of 80 - 200C.
As described a~ove, according to the present invention, the colloidal protective coating containing zinc, lead, tin ox mixture thereoE is formed on the surface of the glass fibers. Accordingly, the treated glass fibers have high alkali resistance. Further, the treated glass fibers have good characteristics such as good weatherproofing, good water ~ resistance, acid resistance and elasticity. When the glass ; fibers treated by the method of the present invention are incorporated into mortars, concretes or plastics, cement products or plastic products having high bending strength and compressive strength may be formed. Furthermore, as the glass fibers treated by the method of the present invention have high i elasticity, cement products obtained therefrom have reduced cracking liability.

IL~ 52 The following examples are given as specific illustra-tions of the present invention. It should be understood, however, that the present invention is not limited to the specific details set Eorth in the examples. All percent and parts are by weight.
Exa ~
[A] ZnC12 was added to water to prepare 15% ZnC12 acidic aqueous solution having pH4. Raw glass fiber in diameter 13~ and in length 25mm is prepared using the following 10 components SiO2 53.60 CaO 20.56~
A123 14.38%
B2O3 8.42 MgO 1.91%
BaO 0.58 2 ( 2 ~ Li2~ 0.36 23 0.22%
Two grams of strand were made of four hundred of the glass fibers. The strand having 4.238Kg/400H of tensile strength was dipped into the acidic aqueous solution ~or 1.5 seconds at ambient temperature. Thereafter, he treated glass fibexs were immediately washed with water, and then dried at a temperature of 100C.
For determination of alkali resistance of the treated glass fibers, the treated glass fibers were dipped into a cement extract having pH13 for 200 hours at a temperature of 80C, washed with water and then dried. Tensile strength anfl alkali loss were measured. The results ob-tained are shown in Table 1. For comparison, tensile strength and alkali loss of raw glass fibers which were not subjected to surface-treatment were measured, and the results obtained are shown in Table 1.

Table 1 Tensile After dipping strength înto the cement Percent before dipping extract o~ alkali Specimen into the o~ment Tenslle Alkali loss Nos. extract strength loss ~) (Kg/400H) (Kg/400EI) (~) _ _ ___._~ _ _ ___ __ 1 4.55 4.03 0.03 1.5 2 4.~5 3.75 0.01 0.5 3 5 30 3.81 0.00 0.0 Example 1 .

4 4.10 3.46 0.05 2.5

5.04 3 70 0.00 0~0 average 4.688 3.750 0.018 O.9 comparative 6 4.68 immeasur- O.80 40 example 1 able As is apparent from the Table 1, tensile strength of the glass fibers treated by the method of the present in-vention does not substantially decrease and alkali loss isslight, whereas the treated glass fibers are dipped into the cement extract. This shows the fact that -the treated glass fibers have sufficient alkali resistance. On the contrary, .. , _ . . . . ... .... . . . .

glass fibers of comparative example 1 have insufficient alkali resistance.
Unexpectedly, it has now been found that tensile strength of the treated glass fibers before dipping into the cement extract is higher than that of raw glass fibers.
[B] Two parts of the treated glass fibers were mixed wi-th 100 parts of Portland cement, 300 parts of standard river sand and 60 parts of water. Then, the mixture was molded in a molding box to form a molded product of 40 x 40 x 160mm, and then let the molded product stand for 24 hours. Then, the molded product was removed from the molding box~ The molded product was cured in water for 28 days at a t:empera- ¦
ture of 20 + 2C to form a mortar product. For comparison, raw glass fibers were used in place of the treated qlass fibers to form a mortar product~ Bending strength and com-pressive strength of these mortar products were measured, and the results obtained are shown in Table 2.

Table 2 ..
Bending strength Compressive strength (Kg/cm ) (Kg/cm ) Example 1 Comparative Example 1 Comparative example 1 example 1 96 12 60.16 392.4 3~0.2 As is apparent from the Table 2, bending strength of the mortar product of Example 1 is consîderably higher than that of the mortar product of comparative example 1.

g 31~ Jt~ ~

Further, compressive strength of the mortar product of Example 1 is siightly higher than that of the mortar product of comparative example 1.
Exam Example l was repeated. For comparison, glass fibers were treated with 5% ZrC14 aqueous solution in accordance with Japanese Patent Publication No. 30200~1975 (comparative example 2). Tensile strength of glass fibers of Example 2 and comparative example 2 before dipping into the cement extract were measured. Further, tensile strength of them after dipping into it were measured. The results obtained are shown in Table 3.
Table 3 _____ _____ ~ .
_ Tensile Exampla 2Co~lrative example 2 strength of .~ _ _ ___ _ _ _ _.
raw glass qensile s-trength 'rensile st~ng-th S ~ fibers be~ore ~Kg/400H) (Kg/400H) Nos. surface-treat- Before AEter ~efore After ¦ ¦
ment dipping dip~ing dipping dipping (Kg/ ) into the into the into the into the cement cement cement cement extract extract extract extract _ _ .
1 3.35 4.66 3.98 3.88 2.20 2 4.53 5.04 3.72 2.98 2.65 3 4.80 4.44 4.10 2.78 2.01 4 4.50 4.10 3.24 3.66 1.98 3.91 4.58 3.42 3.~3 2.00

6 3.51 4.45 3.87 2.68 2.13

7 4.79 4.62 3.12 3.31 2.07

8 3.75 4.82 3.40 2.76 2.11

9 4.30 4.00 3.68 2.73 1.71 3.95 4.21 3.80 3.10 ~.93 average 4.139 4.492 3.663 3.131 2.079 ~ s is apparent from ~he Table 3, the glass fibers treated by the method of the present invention (Example 2) have good alkali resistance~ On the ~ontrar~, the glass fibers treated by the prior art (comparative example 2) have insufficient alkali resistance.
Example 3 Example 1 was repeated with the exception th~t glass fibers having the following components were used.

Si2 54~

- 10 R2O(K2O, Li2O~ 14%

~r2 8 BaO 6~
MgO 5%
CaO 5%
~12O3 4~
Fe O 4%
The glass fibers have 3.012~g/400H Qf tensile stren~th.
Tensile strength of glass fibers treated by the method of the present invention was measured. Fur-ther, tensile strength and alkali 105s of the glass fibers which were dipped into the cement extract were measured. The results ; obtained are shown in Table 4. For comparison, raw glass fibers which are not subjected to surface-treatment were dipped into the cement extract, and the results obtained are shown in Table 4.

~3~ "~
Tabl__4 _ Tenslle After dippinq s~x~gth into the cement Percent Specinen before dippiny extract oE alkali Nos. into the Tens:ile AlX~li :loss cement extr.act s~ength loss. (%~
(Kg/400H) (Kg/400H) (g) .
1 3.20 3.12 0.02 1.0 2 3.~5 2.90 0.03 1.5 Example 3 3 3.21 3.05 0.00 0.0 4 3.11 3.1~ 0.00 0.0 3.25 3.20 0.01 O.S
averaye 3.164 3.074 0.012 0.6 __ _ _ ____ I
co~parative 6 2 195 _ _ example ~ _ ~ . ~ ~ __. _ _ _ As is apparent from the Table 4, tensile strength of the glass fibers treated by the method of the present inven-tion does not substantially decrease and alkali loss is slight, whereas the treated glass fibers are dipped into the cement extract . This shows the fact that glass fibers containing a small amount of zirconium oxide can be treated by the method of the present invention. On the contrary, glass fibers of comparative example 3 have insufficient alkali resistance.
Unexpectedly, it has now been found that tensile strength of the treated glass fibers before dipping into the cement extract is higher than that of raw glass fibers.

Example 1 was repeated with the exception that 15oPbC12 acidic aqueous solution having pH6 was used in place of .

3~
ZnC12 acidic aqueous solution. Tensile strength of the treated glass fibers was measured. Further, tensile streng-th and alkali loss of the treated glass fi~ers which were dipped into the cement extract were measured. The results obtained are sho~n in Table 5.

_able 5 Tensile After dipping strength into the before dip- cement _xtract Percent of Nos ping into the Tensile ~ Alkali alkali . cement extract strength loss loss _ _ (Kg/400H) (Kg/400H) (g) ~ _ _ 1 3.85 2.13 0.07 3.5 2 3.60 2.~2 0.11 5.5 3 3.42 ~.11 0.18 9.0 4 3.51 ~.57 0.10 5.0 3.54 2.70 0.07 3.5 average 3.584 2.386 0.106 5.3 As is apparent from the Table 5, decrease of tensile strength of the treated glass fibers is relatively low and alkali loss is slight, whereas the treated glass fibers are dipped into the cement extract. This shows the fact that the treated glass fibers have comparatively good alkali resistance.
Example 5 Example 3 was repeated with the exception that 15%
PbC12 acidic aqueous solution having p~6 was used in place of ZnC12 acidic aqueous solution. Tensile strength of the - 13 - f . .

treated glass fibers was measured. Further, tensile strength and alkali loss of the treated glass fibers which were dip-ped into the cement extract were measured. The results obtained are shown in Table 6.

Table 6 Tensile After dipping strength into the Specimen before dipping cement extract Percent of Nos. into the Tensile Alakli alkali cement eXtract strength loss loss ~Kg/400H) (Kg/400H) (g) ~ ) -1 3.05 2.97 0.10 5.0 2 3.10 3.02 0.08 ~.U
3 3.12 3.09 0.13 6.5 4 3.00 2.72 0.12 6.0 S 3.04 - 2.80 0.~0 5.0 average 3.062 2.920 0.106 5.3 As is apparent from the Table 6, tensile strength of the glass fibers treated by the method of the present in-vention does not substantially decrease and alkali loss is slight, whereas the treated glass fibers are dipped into the cement extract. This shows the fact that the treated glass fibers have sufficient alkali resistance.
Example 6 Example 1 was repeated with the exception that 15%
SnC12 aciaic aqueous solution was used in place of ZnC12 acidic aqueous solution. Tensile strength of the treated glass fibers was measured. Further, tensile strength and - la _ alkali loss of the treated glass fibers which were clipped into the cement extract were measured. The results obtained are shown in Table 7.

Table 7 _ __ . _ _ _ Tensile After dipping strength into the before dipping cement extract Percent Specimen into the ¦ of alkali ~os. cement extract Tensile Alkali loss (Kg/400H) strength loss (%) (Kg/400H) (g~

1 ~.01 3.07 0.10 cj.o 2 3~93 2.30 0.12 6.0 3 4.11 2.59 0.17 ~.5 ~ ~.07 2.~5 0.19 ~5 4.21 2.50 0.07 3.5 average 4.066 2.622 0.13 6.5 As is apparent from the Table 7, decrease of tensile strength of the treated glass fibers is relatively low and alkali loss is slight, whereas the treated glass fibers are dipped into the cement extract. This shows the fact that the treated glass fibers have comparatively good alkali resistance.
Example 7 ~ _ .
Example 3 was repeated with the exception that 15~
SnC12 acidic aqueous solution was used in place of ZnC12 acidic aqueous solution. Tensile strength of the treated glass fibers was measured. Further, tensile strength and .

al~ali loss of the treated glass fibers which were dipped into the cement extract were measured. The results obtained are shown in Table 8.

Table 8 ___ _ _ _ Tensile After dlpping _ strength into the before dipping cement e~ tract Percent Specimen into the Tensile Alkali of alkali Nos. cement extract strength loss loss _ _ ~Kg/400~) (Kg/400H) (g) (~) 1 3.70 2.11 0.19 ~.5 2 3. no 1 . 78 0.08 3 3.12 1.~0 0.17 8.5 4 3.15 1.97 0.19 9.5 3.21 2.03 0.~0 5 average 3.236 1.958 0.146 7,3 As is apparent from the Table 8, decrease o~ tensile strength of the treated glass fibers is relatively lo~ and alkali loss is slight, whereas the treated glass fibers are dipped into the cement extract. This shows the fact that the treated glass fibers have comparatively good alkali resistance.

Example 1 was repeated with the exception that various acidic acqueous solutions shown in the following Table 9 were used. Tensile strength and alkali loss of the treated glass fibers which were dipped into the cement extact were measured, and the results obtained are shown in Table 9.

-- . . . . . .

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Table 9 After dipping into the cement extract Examples Kind of Tensile Percent of Nos. aqueous pH strength alkali loss _ _ _ solution (Kg/40OH) Example 8 15% ~nS04 4 3~231 1.10 Example 9 15% PbS~4 6 2,051 1.54 Example 10 15% SnS04 3 1.988 1.72 Example 11 15% Zn(NO~)2 4 3.003 0.98 Example 1~ 15~ PbtN03~2 6 2.117 1.82 Example 13 15~ Sn(N03~2 3 2.005 1.53 .
____ _ _~

AS i5 apparent from the Table 9, glass fibers treated by sulfates such as ZnSO~, PbSO~ and SnSO~ as well as nitrates such as Zn~N03)2, Pb(N03)2 and Sn(N03)2 have sub-stantially same alkali resistance as the treated glass fibers of Examples 1 - 7. Decrease of tensile strength of the treated ~lass fibers is relatively low and alkali loss is slight, whereas the treated glass fibers are dipped into the cement extract.
Examples 14 - 17 Example 1 was repeated with the exception that 15~ aci-dic mixtures shown in Table 10 were used in place of ZnC12 acidic aqueous solution. Each component present in mixture was used in same concentration. Tensile strength ana alkali loss of the treated glass fibers which were dipped into the cement extract were measured. The results o~tained are shown in Table 10.

. .

Table 10 .
_ After dipping into the cement extract Examples Kind of pH Tensile Percent of Nos. mixture strength alkali 105s _ _ _ _ (K3/400H) (~) Example 14 ZnC12 ~ 4 3,641 1.21 Example 15 ZnC12 ~ 4 3,873 1,20 Example 16 ZnC12 + 4 3.652 1.31 Zn(NO332 Ex~mple 17 Z L 3 3 621 1.17 As is apparent from the Table 10, t~,nsile strength of the glass fibers treated by the me-thod of the present invention does not substantially decrease and alkali loss is slight, whereas the treated glass fibers are dipped into the cement extract, This shows the fact that the glass fibers treated by mixture have sufficient alkali resistance.
The alkali-resistant glass fibers obtained by Examples 2 - 17 were incorporated into concretes. Concrete products thus obtained have good physical properties such as bend-ing strength, Example 18 lA~ ZnC12 was added to water to prepare 15% ZnC12 acidic aqueous solution having pH4. Raw glass iber in diameter 13~ and in length 25mm is prepared using the following com-ponents:

' Si2 54 CaO ~ 5%
A1203 4%
BaO 2 2 ( 2 ' 2 ~ 18~

Zr2 17%
Two grams of strand were made of four hundred of the glass iibers. The strand having 3.142~g/400H oE tensile strength was dipped into the acidic aqueous solution for 1.5 seconds at ambient temperature. Thereafter, the treated glass fibers were immediately washed with ~ater, and then dried at a temperature of 90C.
For determinat.ion of alkali resistance of the treated glass fibers, the treated glass fibers were dipped .into a cement extract having pH12 for 240 hours at a tempera-ture of 80C, washed with water and then dried. Tensile strength and alkali loss were measured. The results obtained are shown in Tables 11 - 12. For comparison, tensile strength and alkali loss of r~w glass -fibers whi.ch were not subjected to surface-treatment were measured, and the results obtained are shown in Tables 11 - 12.

,? ,~ , Table 11 __ _ _ _ . _ _ Example 18 Co~parative exan~le 4 Tensile strength ~ sile strength SpecLmen (Kg/ 400H) ~ /400H) _ _ _ Before c~pp.ing ~ft~r dipping ~efore clipping After c~pping into the into the into the into -the c~ ~ t extract cement extract cem~lt extract cement ex-tract 1 3.52 3.~2 3.01 2.50 2 3.40 3.63 3.05 2.26 3 3~56 3.90 3.21 2.25 4 3.51 3.52 3.42 2.05 3.73 3.85 3.08 1.92 6 3.67 3.67 3.25 2~19 7 3.91 3.50 3.16 2.01 8 3.82 3.52 3.08 1.98 9 3.81 3.60 3.10 2.2~
3.73 3.51 3.06 2.22 avera~ ~ 3.666 3.612 3.142 2.162 - I .
Table 12 Alakli loss (g) Specimen Nos. Example 18 Comparative _ _ examp-le 4 1 0.00 0.04 2 0.01 0.13 : 3 . 0.00 0.27 4 0.02 0.02 . 5 0.03 0.05 6 0.00 0.06 .
7 ~.00 0.12 8 0.0~ 0.10 9 0.~1 0.09 0.01 0.07 average 0.008 0.095 ~.~ 3~3~
As is apparent from the Tables 11 - 12, tensile strength of the glass fibers treated by the method of the present invention does not substantially decrease and alkali loss is slight, when the treated glass fibers are dipped into the cement extract. This shows that the treated glass fibers have suf~icient alkali resistance.
On the contrary, glass fibers of comparative example 4 have insufficient alkali resistance.
Unexpectedly, it has now been found that tensile strength of the treated glass fibers before dippin~ into the cement extract is higher than that of raw glass fibers.
[B] Two parts of the treated glass fibers were mixed with 100 parts of Portland cement, 300 parts of standard river sand and 60 parts of water. Then, the mixture was molded in a molding box to form a molded product of 40 x 40 x 160mm, and then let the molded product stand for 24 hours. Then, the molded product was removed from the molding box~ The molded product was cured in water for 28 days at a tempera-ture of 20 ~ 2~C to form a mortar product. ~or comparison, raw glass fibers were used in place of the treated glass fibers to form a mortar product. Bending strength and com-pressive strength of these mortar products were measured, and the results are shown in Table 13.

.

Table 13 Bending strength Compressive strenyth Specimen (Kg/cm ) (Kg~cm ) Nos. Example Comparative Example Comparative 18 Example 4 18 Example 4 _ __ _... _~

1 89.7 65.4 362 350 2 95.6 59.7 367 358 3 88.2 63.4 368 345 4 89.7 62.3 362 3~8 92.~ 6~.0 358 357 average 91.12 62.96 363.4 353.6 As is apparen-t from the Table 13, bending strength of the mortar product of Example ].8 is considerably hiqher than that of the mortar produc-t of comparative example 4.
Further, compressive strength of the mortar product of Example 18 is slightly higher than that of the mortar pro-duct of comparative example 4.
Although the present invention has been described with preferred embodiments, it is to be understood that variations and modifications may be resorted to as will be apparent to those skilled in the art. Such variations and modifications are to be considered within the purview and scope of the claims appended hereto.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of imparting chemical resistance to glass fibers which comprises the steps of treating glass fibers with a substantially aqueous solution of 2-25% by weight of a metal salt selected from the group consisting of zinc salt, lead salt, tin salt and mixtures thereof, to form a protective coating having high chemical resistance on the surface of the glass fibers, then washing the treated glass fibers with water and thereafter drying the washed glass fibers at a temperature of from 80°C to 200°C.

2. The method according to claim 1, wherein said glass fibers to be treated are ones containing no zirconium oxide and having substantially no alkali resistance.

3. The method according to claim 1, wherein said glass fibers to be treated are ones containing up to 25% by weight of zirconium oxide and having slight alkali resistance.

4. The method according to claim 3, wherein said glass fibers having slight alkali resistance comprise essentially up to 10% by weight of zirconium oxide, 54-60% by weight of silicon dioxide, 0.6% by weight of aluminum oxide, 0-7% by weight of magnesium oxide, 5-9% by weight of calcium oxide, 1-6% by weight of barium oxide, 12-20% by weight of alkali metal oxides and 0-4% by weight of ferric oxide.

5. The method according to claim 3, wherein said glass fibers having slight alkali resistance comprise essentially 10-25% by weight of zirconium oxide, 54-58% by weight of silicon dioxide, 0-4% by weight of aluminum oxide, 0-5% by weight of magnesium oxide, 5-9% by weight of calcium oxide, 1-6% by weight of barium oxide, 14-18% by weight of alkali metal oxides and 0-5% by weight of ferric oxide.

6. The method according to claim 1, wherein said zinc salt is selected from the group consisting of zinc chloride, zinc sulfate or zinc nitrate.

7. The method according to claim 1, wherein said lead salt is selected from the group consisting of lead chloride, lead sulfate or lead nitrate.

8. The method according to claim 1, wherein said tin salt is selected from the group consisting of tin chloride, tin sulfate or tin nitrate.

9. The method according to claim 6, wherein concentration of said zinc salt is 10-15% by weight of said aqueous solution.

10. The method according to claim 7, wherein concentration of said lead salt is 10-15% by weight of said aqueous solution.

11. The method according to claim 8, wherein concentration of said tin salt is 10-15% by weight of said aqueous solution.

12. The method according to claim 1, wherein said aqueous solution is applied to glass fibers by means of dipping, spraying or painting.