Silicic ester modified phenol/formaldehyde novolaks and their use for the production of resin coated substrates

Abstract

This invention relates to a resin preparable by reaction of a phenol/formaldehyde novolak with tetraethyl orthosilicate in a mass ratio above 28:1, wherein the phenol of the phenol/formaldehyde novolak is substituted or unsubstituted hydroxybenzene or a mixture of two or more such phenols, and to a particulate material coated with said resin. Said particles can be used e.g. in the shell molding process for the production of shell molds and shell cores; and as proppants for use in the hydraulic fracturing process.

Claims

1. Resin prepared by an acid-catalyzed reaction of a phenol/formaldehyde novolak with tetraethyl orthosilicate in a mass ratio range from 1000:1 to 28:1, wherein the phenol of the phenol/formaldehyde novolak is substituted or unsubstituted hydroxybenzene or a mixture of two or more such phenols, wherein the phenol/formaldehyde novolak has a molar ratio of phenol to formaldehyde in the range of from 1:0.5 to 1:0.95.

2. Resin according to claim 1, wherein the mass ratio in which a phenol/formaldehyde novolak and tetraethyl orthosilicate are reacted is so adjusted that the strength of a molded article obtained from a particulate material coated with said resin is increased in comparison to a molded article obtained from a particulate material coated with a phenol/formaldehyde novolak which is not reacted with tetraethyl orthosilicate, but is otherwise identical.

3. Resin according to claim 1, wherein said resin is not part of a mixture comprising sand.

4. Resin according to claim 1 wherein said resin is not cured.

5. Resin according to claim 1, wherein the phenol is unsubstituted hydroxybenzene or a mixture of unsubstituted hydroxybenzene with one or more other phenols.

6. Resin according to claim 1, wherein the resin is prepared by the acid-catalyzed reaction of a phenol/formaldehyde novolak with tetraethyl orthosilicate in a mass ratio in the range of from less than 100:1 to 28:1.

7. Resin according to claim 1, wherein the phenol/formaldehyde novolak has a molar ratio of phenol to formaldehyde in the range of from 1:0.55 to 1:0.9.

8. Resin-coated particulate material or mixture of particulate material with a resin, the particulate material or mixture comprising inorganic particles coated by or mixed with, respectively, a resin according to claim 1.

9. Resin-coated particulate material or mixture according to claim 8, wherein the resin is curable by crosslinking, or the particulate material or mixture is a cured resin-coated particulate material or mixture, respectively.

10. Resin-coated particulate material or mixture according to claim 9, wherein the crosslinking agent is an aldehyde, and/or a resol, and/or wherein the precursor releasing a crosslinking agent when heated is a methylene donor component that generates formaldehyde when heated.

11. Resin coated particulate material or mixture according to claim 8, wherein the average particle diameter of the inorganic particles is >100 m.

12. Resin preparation comprising a resin according to claim 1 and one or more of the following constituents: a crosslinking agent and/or a precursor releasing a crosslinking agent when heated, wherein the crosslinking agent is selected from the group consisting of formaldehydes and resols, and a further resin.

13. Method of making a resin prepared by an acid-catalyzed reaction of a phenol/formaldehyde novolak with tetraethyl orthosilicate in a mass ratio range from 1000:1 to 28:1, wherein the phenol of the phenol/formaldehyde novolak is substituted or unsubstituted hydroxybenzene or a mixture of two or more such phenols, wherein the phenol/formaldehyde novolak has a molar ratio of phenol to formaldehyde in the range of from 1:0.5 to 1:0.95, the method comprising: preparing or providing a phenol/formaldehyde novolak, wherein the phenol of the phenol/formaldehyde novolak is substituted or unsubstituted hydroxybenzene or a mixture of two or more such phenols, reacting the phenol/formaldehyde novolak with tetraethyl orthosilicate in a mass ratio above 28:1, optionally distilling the product of the reaction of the phenol/formaldehyde novolak with tetraethyl orthosilicate to at least partially remove the ethanol formed during said reaction.

14. Method of making a resin-coated particulate material or mixture of particulate material with a resin, the method comprising: providing or making a resin prepared by an acid-catalyzed reaction of a phenol/formaldehyde novolak with tetraethyl orthosilicate in a mass ratio range from 1000:1 to 28:1, wherein the phenol of the phenol/formaldehyde novolak is substituted or unsubstituted hydroxybenzene or a mixture of two or more such phenols, wherein the phenol/formaldehyde novolak has a molar ratio of phenol to formaldehyde in the range of from 1:0.5 to 1:0.95, providing inorganic particles, and coating said inorganic particles with said resin.

15. Shell mold or shell core prepared by the shell molding process using a resin according to claim 1 or a resin-coated particulate material or mixture comprising a resin according to claim 1 or a resin preparation comprising a resin according to claim 1 and a crosslinking agent and/or a precursor releasing a crosslinking agent when heated.

16. Process of coating and/or binding a particulate material, wherein said particulate material is coated and/or bonded with a resin prepared by an acid-catalyzed reaction of a phenol/formaldehyde novolak with tetraethyl orthosilicate in a mass ratio from 1000:1 to 28:1, wherein the phenol of the phenol/formaldehyde novolak is substituted or unsubstituted hydroxybenzene or a mixture of two or more such phenols, wherein the phenol/formaldehyde novolak has a molar ratio of phenol to formaldehyde in the range of from 1:0.5 to 1:0.95.

17. Process according to claim 16, wherein the phenol is unsubstituted hydroxybenzene or a mixture of unsubstituted hydroxybenzene with one or more other phenols.

18. Process according to claim 16, wherein the coating and/or bonding step further comprises a crosslinking agent and/or a precursor releasing a crosslinking agent when heated.

19. Process according to claim 18, wherein the crosslinking agent is an aldehyde, and/or a resol, and/or wherein the precursor releasing a crosslinking agent when heated is a methylene donor component that generates formaldehyde when heated.

20. Process for the production of resin coated particles; or for the production of shell molds and shell cores in the shell molding process; or of making proppants for use in the hydraulic fracturing process; or of making a resin bonded abrasive grinding, snagging or cut-off wheel, comprising the process according to claim 16.

21. Shell molding process for the production of a shell mold or a shell core, comprising: preparing or providing a resin-coated particulate material or mixture of particulate material with a resin, the particulate material or mixture comprising inorganic particles coated by or mixed with, respectively, a resin prepared by an acid-catalyzed reaction of a phenol/formaldehyde novolak with tetraethyl orthosilicate in a mass ratio range from 1000:1 to 28:1, wherein the phenol of the phenol/formaldehyde novolak is substituted or unsubstituted hydroxybenzene or a mixture of two or more such phenols, wherein the phenol/formaldehyde novolak has a molar ratio of phenol to formaldehyde in the range of from 1:0.5 to 1:0.95; producing a shell mold or a shell core comprising said resin-coated particulate material.

22. Hydraulic fracturing process, comprising: forming a fracture in a reservoir rock formation injecting a fluid into the fracture introducing a proppant into the injected fluid, said proppant comprising a resin-coated particulate material or mixture of particulate material with a resin, the particulate material or mixture comprising inorganic particles coated by or mixed with, respectively, the resin prepared by an acid-catalyzed reaction of a phenol/formaldehyde novolak with tetraethyl orthosilicate in a mass ratio range from 1000:1 to 28:1, wherein the phenol of the phenol/formaldehyde novolak is substituted or unsubstituted hydroxybenzene or a mixture of two or more such phenols, wherein the phenol/formaldehyde novolak has a molar ratio of phenol to formaldehyde in the range of from 1:0.5 to 1:0.95.

23. Process of making a resin bonded abrasive grinding, snagging or cut-off wheel, comprising: preparing or providing a resin-coated particulate material or mixture of particulate material with a resin, the particulate material or mixture comprising inorganic particles coated by or mixed with, respectively, the resin prepared by an acid-catalyzed reaction of a phenol/formaldehyde novolak with tetraethyl orthosilicate in a mass ratio range from 1000:1 to 28:1, wherein the phenol of the phenol/formaldehyde novolak is substituted or unsubstituted hydroxybenzene or a mixture of two or more such phenols, wherein the phenol/formaldehyde novolak has a molar ratio of phenol to formaldehyde in the range of from 1:0.5 to 1:0.95, wherein the inorganic particles comprise abrasive grains pressing the material to form a wheel curing the resin.

24. Resin according to claim 1, wherein the resin is prepared by an acid-catalyzed reaction of a phenol/formaldehyde novolak with tetraethyl orthosilicate and a crosslinking agent.

25. Resin according to claim 1, wherein the acid-catalyzed reaction of a phenol/formaldehyde novolak with tetraethyl orthosilicate is in a mass ratio range from 50:1 to 28:1.

26. The process according to claim 16, wherein the process comprises: producing resin coated particles; or producing shell molds and shell cores; or making proppants in a hydraulic fracturing process; or making a resin bonded abrasive grinding, snagging or cut-off wheel.

Description

EXAMPLES

I. Resin Preparation

(1) Preparation of a Phenol/Formaldehyde Novolak (Intermediate Product Resin 1):

(2) A novolak resin is manufactured according to the following procedure: 519.5 g hydroxybenzene are preloaded in a 2 liter three-necked flask equipped with stirrer, dropping funnel, condenser, thermometer and heating/cooling bath. To the hydroxybenzene 1.85 g oxalic acid are added as a catalyst and the reaction mixture is heated to a temperature of 90 C. To this mixture 240 g formaldehyde solution (49 wt.-% formaldehyde) are added over 90 minutes through the dropping funnel under reflux. After finishing of the addition of the formaldehyde solution the mixture is kept for 2 hours at reflux. Excess water and hydroxybenzene are distilled off, first under atmospheric pressure and then followed by vacuum distillation up to a temperature of 180 C. and until the free hydroxybenzene content of the product is 1 wt.-%. Afterwards the product is flaked. The product yield is 500 g. The product is referred to as Resin 1.

(3) Preparation of a Phenol/Formaldehyde Novolak with Additional Amount of Salicylic Acid (Comparison Product, Resin 1a):

(4) 100 g of a novolak manufactured according to example 1 (Resin 1) are heated to 140 C. in a glass flask and 3 g salicylic acid are added at 140 C. and stirred in for 5 minutes until dissolved completely. Afterwards the resin is flaked. The flaked resin is referred to as Resin 1a.

(5) Preparation of a TEOS Modified Phenol/Formaldehyde Novolak According to the Present Invention (Resin 1b):

(6) 100 g of a novolak manufactured according to example 1 (resin 1) are heated to 140 C. in a glass flask. 3 g salicylic acid as a catalyst are added at 140 C. and stirred in for 5 minutes until dissolved completely. Thereafter 2.5 g tetraethyl orthosilicate (2.4 wt.-% TEOS based on the total weight of novolak, salicylic acid and TEOS, corresponding to 0.71 wt.-% SiO.sub.2 based on the total weight of novolak. are added through a dropping funnel in about 15 minutes and the mixture is reacted for 30 minutes at 140 C. Vacuum is applied to remove ethanol that is formed during the reaction and afterwards the resin is flaked. The flaked resin is referred to as Resin 1b.

(7) Preparation of a Phenol/Formaldehyde Novolak (Intermediate Product, Resin 2):

(8) A phenol/formaldehyde novolak is manufactured by reacting hydroxybenzene and a formaldehyde solution (49.5 wt.-% formaldehyde) in a molar ratio hydroxybenzene/formaldehyde of 1/0.65 using sulfuric acid as a catalyst in a 2 liter three-necked flask equipped with stirrer, dropping funnel, condenser, thermometer and heating/cooling bath. To the preloaded hydroxybenzene the sulfuric acid catalyst is added and the reaction mixture is heated to 90 C. To this mixture 240 g formaldehyde solution (49 wt.-% formaldehyde) are added over 90 minutes through the dropping funnel under reflux. After finishing of the addition of the formaldehyde solution the mixture is kept for 2 hours at reflux and the sulfuric acid is neutralized to a pH of 3.0 to 3.5 with an oxide or hydroxide of a group IA or IIA metal.

(9) Excess water and hydroxybenzene are distilled off, first under atmospheric pressure and then followed by vacuum distillation, up to a temperature of 180 C. and a free hydroxybenzene content of 1.8 wt-%. Afterwards the product is flaked. The flaked product is referred to as Resin 2.

(10) Preparation of a TEOS Modified Phenol/Formaldehyde Novolak According to the Present Invention (Resin 2a):

(11) 100 g of a novolak manufactured according to example 2 are loaded into a round bottom flask and heated to 140 C. At this temperature 1.0 g tetraethyl orthosilicate (0.99 wt.-% TEOS based on the total weight of novolak and TEOS, corresponding to 0.29 wt.-% SiO.sub.2 content based on the weight of novolak are added through a dropping funnel and reacted with the phenol/formaldehyde novolak at 140 C. for 15 minutes. At the end of the reaction the product is distilled under vacuum to remove the ethanol formed during the reaction and then flaked. The flaked product is referred to as Resin 2a.

(12) Preparation of a TEOS Modified Phenol/Formaldehyde Novolak According to the Present Invention (Resin 2b):

(13) 100 g of a novolak manufactured according to example 2 are loaded into a round bottom flask and heated to 140 C. At this temperature 2.5 g tetraethyl orthosilicate (2.4 wt.-% TEOS based on the total weight of novolak and TEOS corresponding to 0.72 wt.-% SiO.sub.2 content based on the weight of novolak are added through a dropping funnel and reacted with the phenol/formaldehyde novolak at 140 C. for 15 minutes. At the end of the reaction the product is distilled under vacuum to remove the ethanol formed during the reaction and then flaked. The flaked product is referred to as Resin 2b.

(14) Preparation of a TEOS-Modified Resin not According to the Present Invention (Comparison Product with Excess of TEOS Added, Resin 2c):

(15) 100 g of a novolak manufactured according to example 2 are loaded into a round bottom flask and heated to 140 C. At this temperature 5.0 g tetraethyl orthosilicate (4.76 wt.-% TEOS based on the total weight of novolak and TEOS; corresponding to 1.44 wt.-% SiO.sub.2 content based on the weight of novolak are added through a dropping funnel and reacted with the phenol/formaldehyde novolak at 140 C. for 15 minutes. At the end of the reaction the product is distilled under vacuum to remove the ethanol formed during the reaction and then flaked. The flaked product is referred to as Resin 2c.

(16) Preparation of a TEOS-Modified Resin not According to the Present Invention (Comparison Product with Excess of TEOS Added, Resin 2d):

(17) 100 g of a novolak manufactured according to example 2 are loaded into a round bottom flask and heated to 140 C. At this temperature 10.0 g tetraethyl orthosilicate (9.09 wt.-% TEOS based on the weight of novolak and TEOS corresponding to 2.8 wt.-% SiO.sub.2 content based on the weight of novolak are added through a dropping funnel and reacted with the phenol/formaldehyde novolak at 140 C. for 15 minutes. The product gelled and could not be flaked or tested. The gelled product is referred to as Resin 2d.

(18) Preparation of a Solution of a Phenol/Formaldehyde Novolak with Additional Amount of Salicylic Acid (Comparison Product, Resin 3a):

(19) A phenol/formaldehyde novolak solution in methanol for use in the warm coating process is manufactured according to the following procedure: 588 g hydroxybenzene is preloaded in a 2 liter three-necked flask equipped with stirrer, dropping funnel, condenser, thermometer and heating/cooling bath. To the hydroxybenzene 0.4 g oxalic acid are added as a catalyst and the reaction mixture heated to 90 C. To this mixture 293 g formaldehyde solution (50 wt.-% formaldehyde) are added through a dropping funnel under reflux and over 90 minutes. When the addition is finished the mixture is kept for 2 hours at reflux. Excess water and hydroxybenzene are distilled off, first under atmospheric pressure followed by a vacuum distillation. The final distillation temperature is 170 C. The free hydroxybenzene content of the novolak is below 2 wt.-%. To this product 26.5 g salicylic acid, 47 g water and 353 g methanol are added. The batch is cooled to below 40 C. The product yield is 485 g. The product is referred to as Resin 3a.

(20) Preparation of a Solution of a Resin According to the Present Invention (TEOS Modified Phenol/Formaldehyde Novolak, Resin 3b):

(21) A phenol/formaldehyde novolak solution for the warm coating process is manufactured according to the following procedure: 588 g hydroxybenzene is preloaded in a 2 liter three-necked flask equipped with stirrer, dropping funnel, condenser, thermometer and heating/cooling bath. To the hydroxybenzene 0.4 g oxalic acid as a catalyst are added and the reaction mixture heated to 90 C. To this mixture 293 g formaldehyde solution (50 wt.-% formaldehyde) are added through a dropping funnel under reflux and over 90 minutes. When the addition is finished the mixture is kept for 2 hours at reflux. Excess water and hydroxybenzene are distilled off, first under atmospheric pressure followed by a vacuum distillation. The final distillation temperature is 170 C. The free hydroxybenzene content of the phenol/formaldehyde novolak is below 2 wt.-%, To this product 26.5 g salicylic acid are added and mixed until dissolved. To this product 14.7 g tetraethyl orthosilicate (TEOS) are added within 60 minutes under reflux. After a holding time of 60 minutes 47 g water and 353 g methanol are added. The batch is cooled to below 40 C. The product yield is 1000 g. The product is referred to as Resin 3b. The tetraethyl orthosilicate content based on solid matter (excluding water and methanol) is 2.45 wt.-% corresponding to a SiO.sub.2 content of 0.72 wt.-% based on solid phenol/formaldehyde novolak.

(22) Preparation of a Phenol/Formaldehyde Novolak with Additional Amount of Salicylic Acid (Comparison Product, Resin 4a):

(23) 100 g Corrodur 7839, a sulfuric acid catalyzed and plasticized phenol/formaldehyde novolak from Huettenes Albertus Chemische Werke GmbH in Germany is loaded into a round bottom flask and heated to 140 C. At this temperature 3 g salicylic acid are added and mixed well until completely dissolved. Afterwards the product is flaked. The flaked product is referred to as Resin 4a

(24) Preparation of a Resin According to the Present Invention (TEOS Modified Phenol/Formaldehyde Novolak, Resin 4b):

(25) 100 g of Corrodur 7839, a sulfuric acid catalyzed and plasticized phenol/formaldehyde novolak from Huettenes Albertus Chemische Werke GmbH in Germany is heated to 140 C. in a glass flask and 3 g salicylic acid as a catalyst are added. The mix is stirred for 5 minutes until the salicylic acid is dissolved completely. After this 3.0 g tetraethyl orthosilicate (2.8 wt.-% TEOS based on the total weight of novolak, salicylic acid and TEOS, corresponding to 0.80 wt.-% SiO.sub.2 content based on the total weight of novolak, salicylic acid and TEOS are added through the dropping funnel and the mixture reacted for 30 minutes at 140 C. Vacuum is applied to remove ethanol that is formed during the reaction and afterwards the resin is flaked. The flaked product is referred to as Resin 4b

(26) Preparation of Resins According to the Present Invention (TEOS Modified Phenol/Formaldehyde Novolak, Resins 5a, 5b, 5c):

(27) Resins 5a, 5b and 5c are prepared in a manner analogous to resin 1 but with different molar ratios hydroxybenzene/formaldehyde. Resin 5a had a molar ratio of 1/0.6, resin 5b of 1/0.7 and resin 5c of 1/0.8. All samples are modified with 2.4% tetraethyl orthosilicate according to procedure used in the manufacturing of resin 1b.

(28) The characteristics of the resins 1a, 1b, 2, 2a, 2b, 2c, 3a, 3b, 4a and 4b are compiled in table 1:

(29) TABLE-US-00001 TABLE 1 Resin characteristics pH Free Solid Melt (10% Resin hydroxy- Water content viscosity Viscosity suspension benzene content [%] 2 g, [mPas] [mPas] in isopropanol/ Mw [%] [%] 3 h, 135 C. @ 120 C. @25 C. water: 75/25) [g/mol] Resin 1a 1.0 0 8.9 Solid 3.4 1396 Resin 1b 1.5 0 12.8 Solid 3.4 1538 Resin 2 1.8 0 2.2 Solid 3.3 Resin 2a 1.3 0 2.5 Solid 3.7 Resin 2b 1.2 0 2.6 Solid 3.6 Resin 2c 1.3 0 3.3 Solid 3.6 Resin 3a <1.5 4-6 60-65 Liquid 200-400 Resin 3b <1.5 4-6 60-65 Liquid 200-400 Resin 4a 1.0 0.1 >99 solid 3.0 Resin 4b 1.0 0.1 >99 solid 3.0

II Coating Methods

(30) The resins prepared as described above are used to coat different substrates (particulate materials). Analysis of the substrates prior to the coating gives the following characteristics (table 2):

(31) TABLE-US-00002 TABLE 2 Substrate analysis ADV LOI AFS pH Conductivity [AFS Fines No. Substrate Name, Type [%] No. value [S] method] [%] 1 H33, new quartz sand 0.18 52.5 7.4 12 10.5 0.3 2 Bauxite sand (synthetic Bauxite) 0.0 49.9 8.7 2.6 0.0 3 Reclaimed quartz sand Type V 0.07 66.5 7.8 65 67 0.2 4 Cerabeads 650 (Mullite) 0.04 66.5 7.8 7 152 0.36 5 Nugent 480, quartz sand 0.27 48.6 8.1 3.4 6 AQ 90-500, quartz sand 0.11 82.6 6.0 0.1

(32) Substrate coating processes are carried out according to the following methods:

(33) Coating Method 1a (Resins 1a, 1b and 5a, 5b and 5c; Hot Coating Process):

(34) 3000 g of the substrate (No. 1, 3 or 4 of table 2, preheated to 150 C.) are transferred to a mixer that is preheated to 120 C. 60 g of the selected resin (1a, 1b) and the 3000 g substrate are mixed for 60 seconds until all resin particles are molten and mixed uniformly with the substrate. Afterwards 18 g of a hexamethylenetetramine solution (35 wt.-% in water) are added and mixed for an additional 60 seconds. Finally 6 g calcium stearate powder are added and mixed for 15 seconds. Then the resin coated substrate is disco charged onto a tray, cooled to room temperature and sieved through a sieve to separate lumps and coarser particles from the coated substrate. The resin coated substrate (RCS) is transferred to plastic containers and kept there until used.

(35) The same coating method is used with substrate 1 (see table 2) and each of resins 5a, 5b, 5c.

(36) Coating Method 1b (Resins 4a, 4b; Hot Coating Process):

(37) 3000 g of the substrate (No. 1 of table 2, preheated to 150 C.) are transferred to a mixer that is preheated to 120 C. 90 g of the selected resin (4a or 4b) and the 3000 g substrate 1 are mixed for 60 seconds until all resin particles are molten and mixed uniformly with the substrate. Afterwards 27 g of a hexamethylenetetramine solution (35 wt.-% in water) are added and mixed for an additional 60 seconds. Finally 6 g calcium stearate powder are added and mixed for 15 seconds. Then the resin coated substrate is discharged onto a tray, cooled to room temperature and sieved through a sieve to separate lumps and coarser particles from the coated substrate. The resin coated substrate (RCS) is transferred to plastic containers and kept there until used.

(38) Coating Method 2 (Resins 2, 2a, 2b, 2c, Hot Coating Process):

(39) 1000 g substrate (No. 5 of table 2, preheated to 140 C.) are transferred to a substrate coating mixer and mixed while cooling down to a starting substrate temperature of 132 C. At this temperature the selected resin (2, 2a, 2b, or 2c) is added in the quantity given in table 3 and mixed with the substrate for 90 seconds. Then hexamethylenetetramine solution (30 wt.-% hexamethylenetetramine) and water are added in the quantities given in table 3 and mixed for about 60 seconds until breakup. The breakup point is defined as the moment when the mixture changes from highly viscous to free flowing. After breakup, 0.8 g calcium stearate powder are added followed by an additional 60 seconds mixing time. The resin coated substrate is then discharged from the mixer, screened through a 20 mesh sieve and cooled down before testing. The resins manufactured according to examples 2, 2a, 2b, 2c are used to coat Nugent 480 substrate (no. 5 of table 2), each with the four different resin contents given in table 3, thus yielding in total 16 different resin coated substrate (RCS) samples. Resin 2d could not be tested since it gelled during production.

(40) TABLE-US-00003 TABLE 3 Recipes for substrate coating method 2 Quantity of Resin content 30 wt.-% of the hexamethyl- coated Quantity of Quantity of enetetramine Quantity of substrate Nugent 480 Resin solution Quantity of Calcium- [%] substrate [g] [g] [g] Water [g] stearate [g] 1.4 1000 14 7.6 5.0 0.8 1.2 1000 12 6.5 5.8 0.8 1.0 1000 10 5.4 6.5 0.8 0.8 1000 8 4.3 7.3 0.8
Coating Method 3 (Resin Solutions 3a, 3b; Warm Coating Process):

(41) 400 g substrate (No. 6 of table 2, preheated to 80 C.) are transferred to a mixer followed by 27 g of a premixed solution consisting of: 24.1 g resin solution (3a or 3b), 2.4 g solid hexamethylenetetramine and 0.5 g calcium stearate. The mixing is done under vacuum to remove the methanol and carried out until breakup. The breakup point is defined as the moment when the mixture changes from highly viscous to free flowing. This takes 160 seconds at about 70 C. Mixing is continued for additional 60 seconds at 70 C. under vacuum to remove the ethanol formed during the reaction. Then 0.25 g of calcium stearate are added and the mixing is continued for additional 60 seconds. The resin-coated substrate is then discharged from the mixer onto a tray, cooled to room temperature, screened through a 20 mesh sieve and cooled down before testing.

(42) Substrate Coating Method 4 (Resins 2, 2b; Hot Coating Process):

(43) 3000 g of the substrate (No. 2 of table 2 preheated to 170 C.) are transferred to a mixer that is preheated to 100 C. 60 g of the selected resin (2, 2b) and the 3000 g substrate 2 are mixed for 90 seconds until all resin particles are molten and mixed uniformly with substrate 2. Afterwards 25.6 g of a hexamethylenetetramine solution (35 wt.-% in water) are added and mixed for 60 seconds. Finally 3 g calcium stearate powder are added and mixed for 10 seconds. Then the resin coated substrate is discharged onto a tray, cooled to room temperature and sieved through a sieve to separate lumps and coarser particles from the coated substrate. The resin coated substrate (RCS) is transferred to plastic containers and kept there until use.

III Test Methods

(44) Test methods 1 and 2: Hot and cold transverse strength (substrates coated with any of resins 1a, 1b, 4a, 4b, 5a, 5b, 5c)

(45) Test specimens are produced using a 2.5 liter ROEPER core shooter by shooting the rein-coated substrate into a double cavity core box with 600 kPa shooting pressure to manufacture two GF-transverse strength test bars according to VDG P-74 (published by Verein deutscher Eisenhttenleute, 2.sup.nd edition, March 1976). The two specimens are cured for 120 seconds at 220 C. 15 seconds after the curing is finished the first specimen is tested hot in a transverse strength testing machine (hot transverse strength). The second specimen is cooled to room temperature and used to determine the cold transverse strength (method 2). All tests are run in duplicate.

(46) Test Method 3: Hot Tensile Testing (Substrates Coated with any of Resins 2, 2a, 2b, 2c, 3a, 3b)

(47) Dog-bone style test specimens with a thickness of 6.35 mm (0.5 inch) are produced using a Dietert 365-A Hot Tensile Tester. The coated substrate is compacted by hand into the core box, struck off and cured for 180 seconds at 232 C. The hot tensile strength is determined directly in the same machine. All tests are run in triplicate.

(48) Test Method 4: Cold Transverse Strength Testing (Substrates Coated with any of Resins 2, 2a, 2b, 2c)

(49) Cold transverse strengths are determined using Shell Mold Bending Strength Tester S-30B manufactured by Tosoku Measuring Instruments Co. Two test specimens (1 cm thick by 3 cm wide by 8.5 cm long) are produced by dumping the coated substrate into a core box heated to 232 C. and curing for 180 seconds. The specimens are cooled to 20 C. in a chiller prior to determining the transverse strengths.

(50) Test Method 5: Cold Tensile Testing (Substrates Coated with any of Resins 3a and 3b)

(51) Test specimens are produced using a Dietert 362 machine to make 6.35 mm (0.25 inch) thick dog-bone style test specimen. Coated substrate is compacted by hand into the core box, struck off, cured for 180 seconds at 230 C., and cooled to room temperature before testing. The strength is determined using a Dietert 612 Tensile Tester. All tests are run in triplicate.

(52) Test Method 6: Stick Point [ C.] of the Coated Substrate

(53) The stick point of the coated substrate is determined by applying a bead of coated substrate along a brass bar heated with a temperature gradient of about 154 C. at the hot end and 65 C. at the cooler end. After 60 seconds, the substrate is blown off using air at a pressure of 69 kPa, and the temperature at the point on the bar where the coated substrate sticks is determined. The results are the average of three individual readings.

(54) Test Method 7: Thermoshock Test

(55) To compare the thermo shock resistance of cores made with resin coated substrates the following test can be performed: Firstly, a round core (diameter of about 10 cm, thickness of 1 cm) has to be made by baking the resin coated substrate in a preheated core box for 2 minutes at 220 C. When cooled down to room temperature, this core will be placed on a preheated infrared lamp from Edmund Bhler, Germany, with a temperature of 450 C. Since the core is only heated from one side and due to the thermal expansion of the substrate grains the core will crack after some time depending on binder properties. The time to crack will be recorded and gives an indication about the thermo shock properties of the resin coated substrate and the tendency of the mold or core for cracking (veining) to be expected.

(56) Test Method 8: Buderus Test

(57) 500 g of resin coated substrate are dropped through a funnel on a preheated hot plate with a temperature of 220 C. After 3 minutes baking time, the plate will be rotated by 180 and kept in this position for 7 minutes. Some loose substrate particles will immediately fall down and the weight be determined (loose substrate), some substrate particles with the coating being partly cured will fall down with a delay (peel back), and some substrate particles with the coating being cured will stick to the hot plate (cured substrate). The ratio cured substrate/loose substrate is a measure for the reactivity of the resin coated substrate. The peel-back of the substrate should be as low as possible since a high peel-back will lead to technical problems when used in foundries but also to a reduced recyclability of the loose substrate. The results are expressed as % of the total amount of tested substrate.

(58) Test Method 9: Loss on Ignition (LOI)

(59) To determine the loss on ignition (LOI) a sample (W1) of a coated substrate is weighed in a pre-weighed crucible (Wc) and tempered at 900 C. for 3 hours. After cooling to room temperature in a desiccator the crucible is weighed again (W2) and the weight of the remainders (W3) is calculated by subtracting the crucible weight according to the following formula: W3=W2Wc. The LOI in [wt.-%] is calculated by the following formula: LOI=((W1W3)/W1)100

IV Application Test Results

(60) TABLE-US-00004 TABLE 4 Transverse strength, tested hot and cold (different substrates coated with any of resins 1a and 1b by coating method 1a) Hot transverse strength Cold transverse strength [N/cm.sup.2] (test method 1) [N/cm.sup.2] (test method 2) Resin 1a Resin 1b Resin 1a Resin 1b Substrate (0 wt.-% TEOS) (2.4 wt.-% TEOS) (0 wt.-% TEOS) (2.4 wt.-% TEOS) H33 250 265 600 740 (table 2, no. 1) Reclaim V 300 330 790 885 (table 2, no. 3) Cerabeads 235 310 700 815 (table 2, no. 4)

(61) TABLE-US-00005 TABLE 5 Thermoshock test (different substrates coated with any of resins 1a and 1b by coating method 1a) Thermoshock test (Time to crack), [s] (test method 7) Resin 1a Resin 1b Substrate (0 wt.-% TEOS) (2.4 wt.-% TEOS) H33 (table 2, no. 1) 122 152 Reclaim V (table 2, no. 3) 143 147 Cerabeads (table 2, no. 4) 300 300

(62) TABLE-US-00006 TABLE 6 Buderus test (different substrates coated with any of resins 1a and 1b by coating method 1a) Cured substrate [g] Peelback [g] Loose substrate [g] (test method 8) (test method 8) (test method 8) Resin Resin Resin Resin Resin Resin 1a (0 1b (2.4 1a (0 1b (2.4 1a (0 1b (2.4 wt.-% wt.-% wt.-% wt.-% wt.-% wt.-% Substrate TEOS) TEOS) TEOS) TEOS) TEOS) TEOS) H33 345 318 3 5 152 177 (table 2, no. 1) Reclaim V 323 306 0 1 177 193 (table 2, no. 3) Cerabeads 303 294 2 3 195 203 (table 2, no. 4)

(63) TABLE-US-00007 TABLE 7 Stick point test (different substrates coated with any of resins 1a and 1b by coating method 1a) Stick point of the coated substrate [ C.] (test method 6) Resin 1a Resin 1b Substrate (0 wt.-% TEOS) (2.4 wt.-% TEOS) H33 (table 2, no. 1) 85 87 Reclaim V (table 2, no. 3) 86 87 Cerabeads (table 2, no. 4) 87 89

(64) TABLE-US-00008 TABLE 8 Hot tensile strength (substrate 5 of table 2 coated with different amounts of any of resins 2, 2a, 2b, 2c* by coating method 2) Hot tensile strength [N/cm.sup.2] (test method 3) Amount of resin Resin 2 Resin 2a Resin 2b Resin 2c [g] on 100 g sand (0 wt.-% (0.99 wt.-% (2.44 wt.-% (4.76 wt.-% (Nugent 480) TEOS) TEOS) TEOS) TEOS) 1.4 164 192 217 200 1.2 162 182 197 179 1.0 127 142 152 149 0.8 103 109 123 109 *Resin 2d could not be tested since it gelled during production.

(65) TABLE-US-00009 TABLE 9 Cold transverse strength (substrate 5 of table 2 coated with different amounts of any of resins 2, 2a, 2b, 2c* by coating method 2) Cold Transverse strength [N/cm.sup.2], Amount of resin (test method 4) [g] Resin 2 Resin 2a Resin 2b Resin 2c on 100 g sand (0 wt.-% (0.99 wt % (2.44 wt.-% (4.76 wt.-% (Nugent 480) TEOS) TEOS) TEOS) TEOS) 1.4 17.3 21.6 22.5 20.2 1.2 14.4 18.0 18.8 18.4 1.0 11.1 12.3 16.2 14.8 0.8 8.0 10.9 12.0 11.6 *Resin 2d could not be tested since it gelled during production.

(66) TABLE-US-00010 TABLE 10 Stick point (substrate 5 of table 2 coated with different amounts of any of resins 2, 2a, 2b, 2c* by coating method 2) Stick point of the coated substrate [ C.] Amount of resin (test method 6) [g] Resin 2 Resin 2a Resin 2b Resin 2c on 100 g sand (0 wt.-% (0.99 wt-% (2.44 wt.-% (4.76 wt.-% (Nugent 480) TEOS) TEOS) TEOS) TEOS) 1.4 93 93 92 91 1.2 93 95 92 92 1.0 94 95 93 95 0.8 96 96 95 95 *Resin 2d could not be tested since it gelled during production.

(67) TABLE-US-00011 TABLE 11 Comparison of different parameters of hot coated sand (substrate 2 of table 2 coated with any of resins 2, 2b by coating method 4) Resin 2 Resin 2b (0 wt.-% (2.44 wt.-% Test Test Method TEOS) TEOS) Hot tensile strength [N/cm.sup.2] 3 220 231 Cold transverse strength [N/cm.sup.2] 2 885 1545 Stick point sand [ C.] 6 94 95 Loose sand [%] 8 37.24 39.48 Peel back [%] 8 3.44 5.58 Cured sand [%] 8 59.32 54.94

(68) TABLE-US-00012 TABLE 12 Comparison of different parameters of hot coated sand (substrate 1 of table 2 coated with any of resins 4a, 4b by coating method 1b) Resin 4a Resin 4b (0 wt.- (2.8 wt.- Test Method % TEOS) % TEOS) Hot transverse strength [N/cm.sup.2] 1 285 355 Cold transverse strength [N/cm.sup.2] 2 850 975 Peel back [%] of total sand 8 12 4 Stick point sand [ C.] 6 89 88

(69) TABLE-US-00013 TABLE 13 Comparison of different parameters of warm coated sand (substrate 6 of table 2 coated with any of resin solutions 3a, 3b by coating method 3) Resin 3a Resin 3b (0 wt.-% (2.4 wt.-% TEOS Test Method TEOS) b.o.s.r.)* Hot tensile strength 230 C. 3 324 386 [N/cm.sup.2] Cold tensile strength [N/cm2] 5 510 620 Peel back [%] of total sand 8 14.5 14.5 Stick point sand [ C.] 6 99 101 LOI @ 900 C., 3 h [%] 9 4.2 4.2 Foundry trials with nodular iron; Less sticking, casting temperature: 1380 C. less veining, Improved casting surface *b.o.s.r. = based on solid resin including salicylic acid and TEOS

(70) TABLE-US-00014 TABLE 14 Effect of the molar ratio (MR) hydroxybenzene/formaldehyde on several parameters of resin coated sands (substrate 1 of table 2, coating method 1a) coated with any of modified (2.4 wt.-% TEOS) phenol/formaldehyde novolaks 5a, 5b, 5c Resin 5a Resin 5b Resin 5c Test (MR = (MR = (MR = Test Method 1/0.6) 1/0.7) 1/0.8) Hot transverse strength 1 245 275 250 [N/cm.sup.2] Cold transverse strength 2 845 810 630 [N/cm.sup.2] Stick point sand [ C.] 6 80 86 92 Loose sand [%] 8 41.4 42.2 48.8 Peel back [%] 8 11.4 3.4 6.2 Cured sand [%] 8 47.2 54.4 45.0

V Conclusions from the Test Results

(71) Effect of tetraethyl orthosilicate modification on the performance of an oxalic acid catalyzed phenol/formaldehyde novolak on different substrates (Tables 4-7):

(72) An oxalic acid catalyzed phenol/formaldehyde novolak (resin 1) is modified by including 2.4 wt.-% TEOS (resin 1b). Three different substrates (substrates no 1, 3 and 4 of table 2) are hot-coated with either unmodified resin 1a or modified resin 1b, respectively. The modification of the resin by addition of TEOS resulted in an increase of the hot transverse strength (table 4) of test specimens in the range from 6 to 32% (depending on the substrate) and of the cold transverse strength (table 4) of test specimens in the range from 12 to 23% (depending on the substrate).

(73) The largest increase of the hot tensile strength is obtained with test specimens made from an artificial substrate (Cerabeads 650 from Itochu, Japan, substrate no. 4 in table 2) coated with resin 1b. The largest increase of the cold transverse strength is obtained with test specimens made from new quartz sand (H33 from Quarzwerke Haltern, substrate no. 1 of table 2) coated with resin 1b.

(74) A strong improvement in time to crack (+24%) measured by the thermoshock test (method 7, table 5) is found for test specimens made from new silica sand type H33 coated with resin 1b.

(75) The Buderus test (method 8, table 6) shows a slight reduction (3 to 8%) in cure speed of substrates coated with resin 1b, compared to substrates coated with resin 1a.

(76) Substrates coated with resin 1b show an increase in the stick point temperature of 1 to 2 K compared to substrates that were coated with an unmodified resin 1a (table 7).

(77) Effect of the Quantity of Tetraethyl Orthosilicate Modification on a Sulfuric Acid Catalyzed Phenol/Formaldehyde Novolak (Tables 8-12):

(78) A sulfuric acid catalyzed phenol/formaldehyde novolak (resin 2) is modified with 0.99 wt.-% (resin 2a), 2.44 wt.-% (resin 2b), and 4.76 wt.-% (resin 2c, not according to the invention) tetraethyl orthosilicate, respectively. Modification by addition of 9.09 wt.-% tetraethyl orthosilicate (resin 2d, not according to the invention) has been tried but failed since this product had gelled. A new Nugent 480 silica sand (substrate no 5 of table 2) is hot coated with different amounts of resin (1.4 g, 1.2 g, 1.0 g and 0.8 g resin/100 g sand) of either the unmodified resin 2 ore one of the three above described modified resins 2a, 2b, 2c.

(79) The test specimens obtained from sand coated with a resin having 2.44 wt.-% tetraethyl orthosilicate added (resin 2b) perform best and yield the highest hot tensile strength (table 8) and cold transverse strength (table 9) results. The performance increase compared to test specimens obtained from sand coated with the unmodified resin 2 is in the range of from 19 to 32% in hot tensile strength and from 28 to 44% in cold transverse strength (in each case depending amounts of resin per 100 g of sand). A further increase in TEOS addition actually lowered the strength results of test specimens and is therefore not desirable.

(80) When resin 2 is replaced by the modified resin 2b, the amount of resin per 100 g sand can be reduced from 1.4 wt.-% (resin 2) to an extrapolated amount of 1.12 wt.-% resin (equivalent to a reduction of the amount of resin of about 20%) at the same level of hot tensile strength, and to an extrapolated amount of 1.09 wt.-% resin (equivalent to a reduction of the amount of resin of about 22 wt.-%) at the same level of cold tensile strength.

(81) Further analysis of the data and extrapolation suggests that modification of a sulfuric acid catalyzed phenol/formaldehyde novolak with 2.44 wt.-% tetraethyl orthosilicate allows for a reduction of the amount of resin per 100 g sand by approximately 20% while maintaining the same strength level of test specimens.

(82) The melt point (table 10) of the discussed resin coated sand (2b versus 2) is reduced by 1 C. which is not significant.

(83) When a Bauxite sand (substrate no. 2 of table 2) is coated with a modified resin 2b an increase in cold transverse strength of 74% is observed (table 11).

(84) In another experiment (table 12) a plasticized, sulfuric acid catalyzed phenol/formaldehyde novolak (resin 4a) that is commercially available at Huettenes-Albertus Chemische Werke GmbH is modified by reaction with tetraethyl orthosilicate (resin 4b).

(85) Test specimens obtained from sand (substrate no 1 of table 2) coated with the modified resin 4b show a hot transverse strength that is increased by 24% and a cold transverse strength that is increased by 15%, each compared to test specimens obtained from sand coated with the unmodified resin 4a. The observed peel back of the coated sand (test method 8) is reduced by 75%.

(86) Effect of Tetraethyl Orthosilicate Modification on the Performance of a Resin Solution Used in the Warm Coating Process (Table 13):

(87) An oxalic acid catalyzed novolak solution (resin solution 3a) for the warm coating process is modified (resin solution 3b) by addition of 2.4 wt.-% tetraethyl orthosilicate (calculated on the basis of dry resin, salicylic acid and TEOS and excluding the solvents methanol and water and a new quartz sand (AQ 90-500 from Sibelco, substrate no. 6 in table 2) is coated with the unmodified (resin solution 3a) as well as with the modified product (resin solution 3b) under warm coating conditions (coating method 3).

(88) Test specimens obtained from sand coated with the modified resin 3b show a hot tensile strength that is increased by 19% and a cold tensile strength that is increased by 21%, each compared to test specimens obtained from sand coated with the unmodified resin 3a. The peel back value is not affected. The stick point of the sand is increased by 2 C. (not significant).

(89) Effect of the Molar Ratio Hydroxybenzene/Formaldehyde on the Traverse Strength and the Buderus Test, Table 14):

(90) For an oxalic acid catalyzed phenol/formaldehyde novolak, at a molar ratio in the range of from 1/0.6 (resin 5a) to 1/0.8 (resin 5c), more specifically at a ratio of 1/0.7 (resins 5b), the highest hot transverse strength of test specimens obtained from substrate 1 coated by coating method 1a, as well the highest weight of cured sand and the lowest peel back value are obtained.