A METHOD FOR IMPROVING THE MECHANICAL PROPERTIES OF A GLASS-FIBER MAT

Abstract: To improve the reduction in tensile strength due to aging as well as the recovery, a weak acid is applied to a glass-fiber mat containing a phenolic condensation resin binder before the binder is hardened.

Description: A method for improving the mechanical- properties of a glass-fiber mat The invention relates to a method for improving the me¬ chanical properties of a glass-fiber mat obtained by applying a binder containing an aqueous phenolic condensation resin to the mat and hardening the binder. Glass-fiber mats are used mainly as thermal insulating material. The binder is supposed to bind the fibers firmly together to obtain a coherent structure. The binder is at the same time supposed to ensure sufficient elasticity of the in¬ sulating material and high recovery thereof after compression so that the insulating material can be stored, transported and deformed for use at the final location. US-A 4 663 419 discloses using for a glass-fiber mat a binder containing a condensation product from phenol, formal¬ dehyde and urea condensed in the presence of a basic cata¬ lyst, and additional urea and further additives, namely silane, mineral oil, ammonia and ammonium sulfate. The binder is sprayed as an aqueous solution on the raw mat that is then pressed and put in the desired form for the insulating mate¬ rial, for example a panel or a pipe, after which it is fed to a curing oven where the binder is hardened. US-A 4 176 105 discloses a binder for a glass-fiber mat which is obtained by reaction of a phenol-formaldehyde-urea condensation resin with boric acid and urea. Per 100 parts by weight of phenol-formaldehyde-urea condensation resin 12 to 16 parts by weight of boric acid are added. When the resin hardens a boric acid complex is formed. This is intended to increase the resistance of the binder to punking at high tem¬ peratures. However, known binders leave something to be desired with respect to the mechanical strength of the glass-fiber mat, in particular the tensile strength and the recovery af¬ ter compression of the mat, especially after it has been stored for some time. The invention is therefore based on the problem of im¬ proving the mechanical properties of a glass-fiber mat. This is obtained according to the invention by adding a weak acid with a pK value of more than 4, in particular more than 5, to the glass-fiber mat before hardening the binder. The pK value is defined as the negative decadic loga¬ rithm of the acid dissociation constant at 25°C. The weak acid is preferably added in an amount of 0.5 to 10 percent by weight, in particular 1 to 5 percent by weight, based on the solids content of the phenolic condensation resin of the binder. When the acid is added in an amount of less than 0.5 percent by weight no improvement of the me¬ chanical properties is observed. On the other hand, no fur¬ ther improvement occurs, but actually a reduction of the me¬ chanical properties, when the amount of weak acid exceeds 10 percent by weight . The amount of binder, including the additives and the weak acid, after hardening is 3 to 7, preferably 4 to 6, per¬ cent by weight based on the total weight of the mat . The amount of weak acid after hardening of the binder is 0.05 to 1, preferably 0.08 to 0.6, percent by weight based on the to¬ tal weight of the mat. Suitable weak acids are in particular boric acid and carboxylic acids with a pK value of more than 4, in particu¬ lar more than 5. The carboxylic acid can be a monobasic or polybasic car¬ boxylic acid with or without hydroxyl groups, for example citric acid or a fatty acid. Fatty acids with more than 8 carbon atoms, such as lauric, palmitic, stearic or oleic acid, have proven particularly suitable, in particular fatty acids with one or more C=C double bonds such as oleic acid. The phenolic condensation resin of the binder is pref¬ erably a water-soluble condensation product from phenol and formaldehyde or from phenol, formaldehyde and urea, the con¬ densation being performed in the presence of a basic cata¬ lyst, in particular an alkaline or alkaline-earth metal hy¬ droxide, for example sodium, potassium, calcium or barium hy¬ droxide. The phenolic condensation resin can be produced for example according to US-A 4 663 419. In addition to the condensation resin the binder can contain urea and additives, in particular silane, mineral oil, ammonia and/or ammonium sulfate. For example the binder can have the composition below: 55 to 70 parts by weight of water-soluble phenolic resin (based on the solids) 45 to 30 parts by weight of urea 0.1 to 0.5 parts by weight of silane 6 to 15 parts by weight of mineral oil 1 to 5 parts by weight of ammonium sulfate 2 to 10 parts by weight of ammonia (as NH 3 ) . The silane used is preferably a silane with an amine group which can be reacted with the phenol groups of the con¬ densation resin. Of the 6 to 15 parts by weight of mineral oil, however, only 0.4 to 1.2 parts by weight generally remain in the fin¬ ished mat. The ammonia is added as an aqueous, for example about 20%, solution. The mat is produced continuously, the spun glass fibers being deposited as a mat statistically distributed in all di¬ rections on a transport band. While the fibers fall onto the transport band they are sprayed with the liquid binder. Then the mat is fed to a curing oven to harden the binder. The weak acid can be added to the liquid binder and thus sprayed onto the glass fibers falling onto the transport band in a mixture with the binder. However it is also possible to spray the binder and the weak acid onto the falling glass fi¬ bers separately, i.e. to provide separate spray nozzles for the liquid binder, on the one hand, and a solution of the weak acid, on the other hand. The weak acid is applied sepa¬ rately in particular when an incompatibility exists between the weak acid and the components of the binder, e.g. with fatty acids with more than 8 carbon atoms. The inventive method improves in particular the tensile strength and the recovery of the mat after compression, espe¬ cially when the mat has been stored for some time. As has turned out, the inventive method improves in par¬ ticular the tensile strength and the recovery of mats com¬ prising glass fibers having an alkali oxide content of 8 to 25 molar percent, in particular glass fibers having a high sodium oxide content of more than 16 molar percent, for exam¬ ple glass fibers containing 16.5 to 19 molar percent sodium oxide, 0.2 to 0.5 molar percent potassium oxide and 8 to 18 molar percent boron oxide. Mats made of these glass fibers show particularly strong reduction of their mechanical prop¬ erties when they age, i.e. in particular after a long storage period, especially with respect to recovery. The following examples will serve to explain the inven¬ tion further. The examples use glass fibers with the composi¬ tion stated in Table I below. Table I A B Components Mol.% Mol. ; Si0 2 57.5 56.5 Fe 2 0 3 0.3 A1 2 0 3 0.5 1 CaO 8 8 MgO 3.5 3.5 Na 2 0 17.7 17.5 K 2 0 0.26 0.3 B 2 0 3 12 13 To determine tensile strength, aging of tensile strength and recovery of the compressed mat one performs the following tests. a) Determination of tensile strength and aging of tensile strength Two equal-sized doughnut-shaped samples are cut out of the particular mat and their weight determined. The first doughnut-shaped sample is torn apart and the tearing force in gram force per gram (gf/g) of mat indicates the tensile strength (RT original) . The second doughnut-shaped sample is put in an autoclave with a temperature of 105°C and a humid¬ ity of 100 percent for 15 minutes. The tensile strength (RT autoclave) in gf/g is then determined. ) Determination of recovery versus storage time A sample is cut out of the mat and its thickness deter¬ mined. The sample is compressed to one sixth of this thick¬ ness with a press. The compressed state is maintained for one hour, 24 hours, 12 days and one month. For each period the press is then opened and the increase in thickness of the re¬ lieved mat is measured. The compressed mats are stored at room temperature. Recovery (RE) is determined as follows. Measured thickness Recovery = x 100 Nominal thickness To determine the aging of recovery one repeats the above test, except that the mat is kept in the compressed state in a humid room at 35°C and an air humidity of 95% for one day. A retained compressed sample is stored at room temperature for the same period of time. The compression for both samples is then released and the increase in thickness of the re¬ lieved mat is measured after 7 days. Recovery after accelerated aging (RE aging) is deter¬ mined by the loss of thickness between the retained sample and the aged sample . Example 1 A binder with the following composition is produced: 55 parts by weight of phenol-formaldehyde condensation resin (weight based on solids) 45 parts by weight of urea 9.5 parts by weight of mineral oil 0.3 parts by weight of silane 20 parts by weight of ammonium hydroxide (as 20% solu¬ tion) 3 parts by weight of boric acid The binder diluted with water is sprayed onto A glass fibers falling onto a transport band. The mat mixed with binder formed on the transport band is then hardened in a curing oven. The amount of sprayed-on binder is 5.0% by weight (after hardening) based on the weight of the glass fi¬ bers. The amount of boric acid is 0.171% by weight based on the weight of the glass fibers. Comparative example 1 Example 1 is repeated except that a binder with the fol¬ lowing composition is sprayed onto the glass fibers: 55 parts by weight of phenol-formaldehyde condensation resin (weight based on solids) 45 parts by weight of urea 9.5 parts by weight of mineral oil 0.3 parts by weight of silane 3 parts by weight of ammonium sulfate 6 parts by weight of ammonium hydroxide (as circa 20% solution) Example 2 Example 1 is repeated except that the boric acid is sprayed on separately from the binder. Exa ple 3 Example 1 is repeated except that B glass fibers are used instead of A glass fibers. Tests a) , b) were performed with the obtained mats. The results are summarized in Table II below. Table II cf. Ex.l Ex.l Ex.2 Ex.3 a) Tensile strength RT original gf/g 250 250 229 219 RT autoclave gf/g 144 193 174 164 Loss 42 23 24 25 b) Recovery RE RE 1 h 145 147 - 143 24 h 139 140 - 138 12 days 128 132 - 128 1 month 129 126 - 126 RE aging 39 24 21 29 Examples 4 and 5 and comparative example 2 Test a) for determining tensile strength was performed with two further mats produced substantially according to ex¬ amples 1 and 2 and a further mat produced substantially ac¬ cording to comparative example 1, the test being modified in that a third doughnut-shaped sample was kept in the autoclave at 105°C and a humidity of 100% for 45 minutes. The results are shown in Table III below. Table III Cf. Ex.2 Ex.4 Ex.5 Tensile strength original gf/g 225 249 234 Tensile strength autoclave 15 min gf/g 135 161 164 Tensile strength autoclave 45 min gf/g 118 167 155 As Table III indicates, the tensile strength of the mat according to examples 4 and 5 clearly decreases more slowly through the artificial aging in the autoclave than the mat according to comparative example 2. Examples 6 to 9 Example 1 was repeated, using a binder with the follow¬ ing composition: 55 parts by weight of phenol-formaldehyde condensation resin (weight based on solids) 45 parts by weight of urea 9.5 parts by weight of mineral oil 3 parts by weight of ammonium sulfate 0.3 parts by weight of silane 6 parts by weight of ammonium hydroxide (as circa 20% aqueous solution) Separately from the binder the following carboxylic ac¬ ids were sprayed onto the glass fibers: citric acid (example 6) , lauric acid (example 7) , and oleic acid (example 8) The amount of sprayed-on carboxylic acid is about 0.4 percent based on the weight of the glass fibers. Tests a) and b) described above were performed with the mats according to examples 6 to 9. The test results are shown in Table IV below together with the corresponding test re¬ sults for comparative example 1. Table IV Cf. Ex.l Ex.6 Ex.7 Ex.8 a) Tensile strength RT original gf/g 250 270 276 255 RT autoclave ! gf/g 144 168 167 189 Loss 45 38 39 26 b) Recovery RE 1 h 145 148 148 148 24 h 139 142 142 144 12 days 128 123 134 139 1 month 129 127 127 134 RE aging 39 37 34 27

Claims: Claims 1. A method for improving the mechanical properties of a glass-fiber mat obtained by applying an aqueous binder con¬ taining a phenolic condensation resin to the mat and harden¬ ing the binder, characterized in that a weak acid with a pK value of more than 4.0 is added to the mat before the binder is hardened. 2. The method of claim 1, characterized in that the weak acid is added in an amount of 0.5 to 10 percent by weight based on the solids content of the phenolic condensation resin of the binder. 3. The method of claim 1 or 2, characterized in that the weak acid is applied in an amount of 0.01 to 3.0 percent by weight based on the weight of the glass fibers in the mat. 4. The method of any of the above claims, characterized in that the weak acid is boric acid or a carboxylic acid. 5. The method of claim 4, characterized in that the car¬ boxylic acid is a fatty acid with more than 8 carbon atoms. 6. The method of claim 4, characterized in that the car¬ boxylic acid is an unsaturated carboxylic acid. 7. The method of any of the above claims, characterized in that the phenolic condensation resin is the reaction prod¬ uct from phenol and formaldehyde or phenol, formaldehyde and urea in the presence of a basic catalyst. 8. The method of any of the above claims, characterized in that the binder contains not only the phenolic condensa¬ tion resin but also urea, a silane, mineral oil, ammonia and/or ammonium sulfate. 9. The method of claim 8, characterized in that the silane has an amine group. 10. The method of claim 1, characterized in that the binder is applied to the mat by spraying. 11. The method of claim 10, characterized in that the weak acid is sprayed on in a mixture with the binder. 12. The method of claim 10, characterized in that the weak acid is sprayed on separately from the binder. 13. The method of any of the above claims, characterized in that the mat comprises glass fibers having an alkali oxide content of 8 to 25 molar percent. 14. The method of claim 13, characterized in that the glass fibers contain 16.5 to 19 molar percent sodium oxide, 0.2 to 0.5 molar percent potassium oxide and 8 to 18 molar percent boron oxide. 15. The method of claim 1, characterized in that the im¬ proved mechanical property consists in reduced degradation of the tensile strength of the mat submitted to aging. 16. The method of claim 1, characterized in that the im¬ proved mechanical property consists in reduced degradation of the recovery of the compressed mat submitted to aging.

Inventors: JOACHIM JACKY, LERICQUE BERNARD, JOACHIM, JACKY, LERICQUE, BERNARD
Applicants: JOACHIM JACKY, LERICQUE BERNARD, SAINT GOBAIN ISOVER, ISOVER SAINT-GOBAIN, JOACHIM, JACKY, LERICQUE, BERNARD
Application year: 1996
Main classification: C03C25
IPC codes: C03C25, D04H1, D06M11, D06M13, D06M15