Method for preparing crosslinked polymers

Preparation method of cross-linked polymer

The present invention relates to the use of reactive prepolymerized organic compounds, with or without free radical initiators, for cross-linking by means of heat, high-energy radiation or heat and high-energy radiation.

Such substances can be reacted, such as by high-energy radiation, preferably UV light, or by free radicals at room temperature, using a combination of known peroxides and co-initiators, such as heavy metal salts, or by heating , Use thermal free radical initiators such as peroxides, azo initiators or CC active compounds for further polymerization or crosslinking. These methods of initiating the reaction can also be used in any desired combination, including the use of a mixture of generating free radicals by heat and generating free radicals by UV light, and reacting to stage B, which is a partial reaction stage, and the reaction is performed at this stage. It has been terminated but can still be triggered again later.

These reactive prepolymers should be found to be useful as pigment binders, coating compositions, compact or porous, reinforced or unreinforced molding compounds, casting compositions, electrical insulating compositions, marking pigments on surfaces hardened by sunlight, Preparation of sealant and coating composition, or as a bonding agent for printing inks, bonding agents for non-woven fabrics, adhesives, prepregs, etc.

An unsaturated polyester resin containing dihydrodicyclopentadiene (DHCPD) structural units. This resin is generally dissolved in monomeric reactive diluents such as styrene, alpha methyl styrene, vinyl toluene, allyl ortho Phthalates, acrylates, vinyl esters or the like are the subject of many patents. For example, powder coatings can also be solid substances. Due to the improper uniform polymerization ability of the double bonds of maleic acid and fumaric acid, the use of these reactive diluents has been used in the previous Technically it is deemed necessary.

DE 31 07 450 relates to unsaturated polyesters with cyclopentadiene oligomers as end groups, which can be used in ethylenically unsaturated monomers for the preparation of moulding and coating solutions; however, no reactive diluent is used No further development from this file.

EP 101 585-A relates to unsaturated polyester resin, which is modified by adding cyclopentadiene to the double bond of polyester, and then dissolving in vinyl monomer.

EP 118 786-A describes unsaturated polyester resin, which is modified by cyclopentadiene and dissolved in vinyl or allyl monomers, and cured in a two-stage process to obtain high temperature Stable molding compound.

EP 260 688-A also relates to polyester resins, which are soluble in vinyl monomers.

DE 32 30 924-A describes a special procedure for the preparation of a polyester tree containing a cyclopentadiene structure and the resin dissolved in a vinyl monomer.

EP 585 74 2-A relates to a solid substance mixture containing unsaturated polyester resin and polyurethane acrylate resin. These mixtures are suitable as powder coatings, which can be crosslinked after melting in the presence of UV light and UV initiators.

EP 0 684 284-A1 describes a synergistic mixture of unsaturated polyether ester resin and dicyclopentadiene polyester resin, which is dissolved in styrene and hardened in the presence of a peroxide catalyst.

DE-A-15 702 73 describes polyesters with 5- or 6-carbocyclic imines at the ends derived from, for example, tetrahydrophthalimide ethanol, which are soluble in unsaturated monomers.

The present invention provides the use of a reactive prepolymerized organic compound, which contains at least one easily removable hydrogen with a bond energy of not more than 397 thousand joules/mole, and at least one structural unit of ethylene-based double bond, which can be used or not freely The base initiator is cross-linked by heat, high-energy radiation or heating and high-energy radiation.

It is preferable that these hydrogens that are easily removable at the α position of the double bond (propylene) hydrogen, and especially the easily removable hydrogens of these compounds, are in the formula (I), (II), (III) and/or (IV) The structure is combined into a prepolymer.

<chemistry general="n"><img file="TW367342B_D0001.tif" /></chemistry>Here -R- is oxygen or a divalent free radical with one or more lipid, amide, urethane and/or ketone groups, or a salt bond, or according to formula (V), (VI), The structure of (VII), (VIII), (IX) and/or (X) or the combination of esters of isoprenol (Va).

<chemistry general="n"><img file="TW367342B_D0002.tif" /></chemistry>Where n=1 to 20<chemistry general="n"><img file="TW367342B_D0003.tif" /></chemistry>

The reactive prepolymerized organic compound used in the present invention may be an unsaturated polyester resin based on α and β olefin unsaturated dicarboxylic acids, and at least one of the easily removable hydrogen contained in the formulas (I) to (X) Combinations of groups, or mixtures of unsaturated polyester resins based on α and β olefin unsaturated dicarboxylic acids, and prepolymerized organic resins lacking groups with easily removable hydrogen and containing groups with easily removable hydrogen Compound.

These prepolymerized organic compounds can also be derived from monofunctional alcohols, polyfunctional alcohols, their alkoxylation products, polyether polyols, polyester polyols, polytetrahydrofuran and/or polycaprolactone, the end of these compounds Contains structural units that are connected with esters of α and β olefin unsaturated dicarboxylic acids and have easy-to-remove hydrogen.

The reactive prepolymerized organic compound used is particularly preferred. It is liquid at room temperature, or according to DIN 53180, when its viscosity is less than 100,000 mPas at 100°C, it has a softening range of less than 130°C. At a temperature where the viscosity does not exceed 10,000 mPas, the viscosity is stable for at least 24 hours, and the compound is melted or heated during the reaction.

The reactive prepolymer used in the present invention can be used alone or together with other binders and/or organic and/or inorganic fillers as pigment binders, coating components, compact or porous, reinforced or unreinforced molds Preparation compound, casting composition, electrical insulation composition of electric casting assembly line, electric wire enamel of insulation casting assembly line in motor, reflective road marking pigment, preparation of sealant and coating composition, or as a bonding agent for pigment ink, as Adhesives or bonding agents that are neatly arranged or placed randomly, a flat surface made of organic or inorganic materials or a supporting material for fibers of any shape.

The reactive prepolymerized organic compound used in the present invention can be combined with conventional free radical initiators, CC active substances and reaction accelerators, stabilizers and further added by viscosity regulators, fluid improvers and gloss enhancers. Use of the class together.

Furthermore, the reactive prepolymerized organic compound used in the present invention can be co-crosslinked and hardened with one or more types of polyfunctional isocyanates, amino resins and polyfunctional epoxides as known in the previous section. Use together to be hardened.

The reactive prepolymerized organic compound used in the present invention contains at least one easily removable hydrogen with a bond energy of not more than 397 thousand joules/mol, and at least one structural unit of an ethylene-based double bond.

Bond energy data can be obtained from the literature and can be published, for example, from Allyn and Bacon, a division of Simon &amp; Schuster, Newton, Massachusetts, in the catalogue data of the Library of Congress ISBN-205-08453-2 (1987), by Morrison, Robert Thornton's Organic Chemistry (Table: Bond Dissociation Energy, on the inside cover), used it.

These reactants may exist in the same molecule, but the reactive prepolymer substance (organic compound) may also include a mixture of a prepolymer containing only easily removable hydrogen and a prepolymer containing only vinyl double bonds. It is also possible to use one or more hardening mechanisms in the hardening process, for example, in combination with polyfunctional isocyanates, amino resins such as melamine-, urea- or benzoguanamine-formaldehyde resins, and polyfunctional epoxides. Cross-linked. In addition, the available cross-linking mechanism can also promote the formation of a permeable network on the coating, which can often achieve its special and desired properties such as extremely high chemical resistance.

A new structure unit with at least one easily removable hydrogen with a bond energy of not more than 397 thousand joules/mol, for example, can be combined in a manner derived from the structure of the chemical formula (I) to (IV) of dihydrodicyclopentadiene<chemistry general="n"><img file="TW367342B_D0004.tif" /></chemistry>Here -R- is oxygen or one or more divalent free radicals having one or more lipid, amide, urethane and/or ketone groups, or a salt bond.

Other structural examples that combine with new substances by means of easy-to-remove hydrogen include isoalkyl, amino isoalkyl, cycloisoalkyl, cycloisoalkyl with one or more heteroatoms, and isoalkyl aromatic Radicals, or free radicals composed of the structure of the following chemical formula, where n=2 or 3 R²Is a divalent aliphatic or aromatic radical such as up to 8 carbons, or a single bond, R³Is a saturated or unsaturated divalent aliphatic, cycloaliphatic, heterocyclic or aromatic radical, or a single bond, R⁴Is H, straight chain or, for example, 1-8 carbon, aromatic group with halogen substituent or branched chain alkyl of isopentylphenyl group, R⁵Is an alkyl group, an alkyl group with a halogen substituent, an aryl group with a halogen substituent or an isopentyl phenyl group, for example<chemistry general="n"><img file="TW367342B_D0005.tif" /></chemistry><chemistry general="n"><img file="TW367342B_D0006.tif" /></chemistry>

The reactive prepolymerized organic compound used in the present invention may be linear or contain one or more branch points, for example, the structure produced by repeating chemical formulas (XI) and (XII), where -R- is a bridging group or a single The bond, D- is a structure with easily removable hydrogen. In this context, the ethylene-based double bond can be in the radical -R-, and in other positions in the molecule or in any prepolymer material lacking D- which is mixed with the prepolymer material containing D-. The structures repeatedly generated by the chemical formulas (XI) and (XII) are just examples to illustrate the principle.

<chemistry general="n"><img file="TW367342B_D0007.tif" /></chemistry>

<chemistry general="n"><img file="TW367342B_D0008.tif" /></chemistry>

Particularly acceptable substances are those in which -R- is an ester group and can be obtained by adding dichloropentadiene (DCPD) to polyfunctional polycarboxylic acid. In this reaction, such as boron trifluoride must be used. Catalysts such as ether salts to achieve high conversion rates.

The adducts of maleic anhydride and water with DCPD of these chemical formulas (XIII) and (XIV) are very easy to obtain.

In this example of the adducts of formulas (XIII) and (XIV) and the new reactive prepolymers based on these isomers, there is no difference between fumaric acid and maleic acid, depending on the reaction Under different conditions, different ratios of isomers will be formed, and any mixture is within the scope of the present invention.

<chemistry general="n"><img file="TW367342B_D0009.tif" /></chemistry>

The readily available materials used in the present invention react with polymers having reactive carboxyl groups. Examples of this polymer are mono- and poly-functional hydroxyl compounds, mono- and poly-functional polymerized carboxylic acid esters of hydroxyl compounds, mono- and poly-functional polymerized epoxides, functional hydroxyl natural oils And resins, epoxidized natural oils and resins, mono- and poly-functional polymerized isocyanates and mono- and poly-functional polymerized amines.

Generally, dihydrodicyclopentadienol of chemical formula (XV) and isoprenol of chemical formula (Va) can be used to react with OH reactive substances to synthesize new substances.

<chemistry general="n"><img file="TW367342B_D0010.tif" /></chemistry>

Furthermore, the allylated hydrogen-containing group can be introduced in the form of cyclic unsaturated dicarboxylic acid imine and amino carboxylic acid or amino alcohol. It is represented by examples of chemical formulas (XVI) and (XVII). Other substances with easy-to-remove hydrogen and OH groups are oxomethylene tetrahydrophthalic acid and its derivatives such as methyl oxomethylene tetrahydrophthalic acid or oxomethylene of formula (XVI) Tetrahydrophthalimide<chemistry general="n"><img file="TW367342B_D0011.tif" /></chemistry>

And tetrahydrophthalic acid and its derivatives such as methyltetrahydrophthalic acid and tetrahydrophthalimide of formula (XVII)<chemistry general="n"><img file="TW367342B_D0012.tif" /></chemistry>

These compounds are suitable for synthesizing new substances by reacting with reactive OH substances.

The substance used in the present invention contains a double bond in the polymer chain, for example, maleic or fumaric acid or itaconate, and then reacts with cyclopentadiene to produce and also contains easily removable The structure of the bridge methylene tetrahydrophthaloyl group of the formula (XVIII) of hydrogen.

<chemistry general="n"><img file="TW367342B_D0013.tif" /></chemistry>

Furthermore, the cyclic dicarboxylic acid derivative containing allyl group hydrogen can be obtained by the Diels-Alder reaction of maleic acid containing polyester and other dienes such as butadiene or pentadiene.

An important class of substances used in the present invention is maleic acid and fumaric acid containing substances of chemical formula (XIII) and (XIV) and isoprenols with alkoxylated mono- or polyols Monoester esters, each of these esters may contain 2-2000 ethylene oxide and/or propylene oxide units in the molecule, such as ethoxylated or propoxylated trimethanol propane, ethoxy Alkylated or propoxylated pentaerythritol, ethoxylated or propoxylated glycerol, polyethylene glycol monoalkyl ester, polypropylene glycol monoalkyl ester, poly Examples of ethylene oxide polyesters and polyether polyols, polypropylene oxides, polytetrahydrofuran and polycaprolactones. By combining long-chain polyethylene terephthalate units or polybutadiene glycol, the molecular pseudo-plasticity and improved elasticity of the hardened substance can be achieved. The above mentioned hydroxy compounds with monoesters containing alcohols that can easily remove hydrogen are also suitable, such as furfuryl alcohol, tetrahydrofurfuryl alcohol, dicarboxylic acids containing dicarboxylic acids such as maleic butadienoic acid, transbutadienoic acid, and itaconic acid. 1-alkylenols or substances of the chemical formulas (XVI) and (XVII) of acid, cis-methylbutenedioic acid, phthalic acid and its isomers.

Therefore, the type of epoxidizing agent and the degree of epoxidation of the new substance can control the properties of the final product, such as hardness, hydrophilicity and elasticity. In this context, the polyol can also be only partially esterified, and the remaining hydroxyl groups can leave freely, esterified or etherified with other substances containing easily removable hydrogen, or reacted with other reactive substances. Examples of compounds suitable for this purpose are isocyanates and epoxides. For example, hydroxy-containing natural oils such as foundry oils are also important. Other important types of substances include unsaturated polyester resins, based on unsaturated α and β carboxylic acids such as maleic acid, fumaric acid, itaconic acid, and/or structures containing hydrogen that can be easily removed Units of cis-methacrylic acid. As mentioned above, unsaturated polyester resins containing DCPD units have monomeric reactive diluents such as styrene, α methyl styrene, vinyl toluene, allyl phthalate, acrylate, Vinyl esters or the like as solutions are the subject of many patents. For example, in the case of powder coatings, which can also be solid materials, the use of these reactive diluents has a The previous technology was deemed necessary.

The unsaturated polyester resin used for this purpose in the present invention is a resin known per se, which contains a structural unit with easily removable hydrogen. The polyester used in the present invention is synthesized by a known polyester preparation technology, and is generally formed by polycondensation of a polyfunctional hydroxyl compound with a polyfunctional acid and/or its anhydride at a higher temperature. From the esters of these substances as starting materials, it is better to produce polyester by transesterification at higher temperature, because in some cases, this transesterification can make it easier and more convenient than Direct esterification is faster. It is also possible to obtain a bonding agent with an amide structure using (partially or fully) multifunctional amines. For example, it is also possible to adjust the molecular weight by partially using monofunctional starters. The starting materials listed below are only examples to illustrate the invention.

Examples of suitable starting materials are: di- and polycarboxylic acids, such as adipic acid, suberic acid, phthalic acid isomers, tetrahydrophthalic acid, methylenetetrahydrophthalic acid, Hexahydrophthalic acid, fumaric acid, maleic acid, itaconic acid, cis-methylbutenedioic acid, trimellitic acid, pyromellitic acid, di- and polyols such as Ethylene glycol, polyethylene glycol, propylene glycol, isopropanediol, butanediol isomers, hexanediol, neopentyl glycol, trimethanol propane, glycerol, pentaerythritol , Bisphenol A, hydrogenated bisphenol A, OH-polyfunctional polymers such as polybutadiene with modified hydroxyl groups, or polyurethane prepolymers with hydroxyl groups and epoxy resins, multifunctional natural substances or their Derivatives such as linseed oil fatty acid. Substances that alkoxylate functional OH groups are also important. Examples include the ethoxylation and propoxylation products of the above-mentioned polyols.

According to DE-A-15 70 323, the use of amide and amide structures is known in the prior art. The polyester amide or polyester imine can meet actual requirements, for example, in terms of thermal stability, and many examples show that it is superior to pure polyester. Within the scope of the present invention, the synthesis of polyester with special requirements such as hardness, elasticity, viscosity and/or softening point can be completed in accordance with rules well known to experienced workers. For example, experienced workers will pay attention to how to change the elasticity of the hardened polyester resin with the chain length of polyols or polycarboxylic acids. For example, polyester resins synthesized with hexanediol or adipic acid are more elastic than these based on phthalic acid and ethylene glycol. Furthermore, the properties are controlled by the addition of polyfunctional substances, which produce branched chains on the polyester molecule, such as trimellitic acid or trimethanol propane, which is well known to experienced workers. In this context, the introduction of the easily removable hydrogen structure compound into the polyester can be accomplished by, for example, the addition of a co-condensation initiator with removed hydrogen. Such easily and inexpensively available starting materials are the maleic anhydride of chemical formula (XIII) and (XIV) and the adduct of water and DCPD, which can be used together with other compounds to synthesize polyester.

Furthermore, the dihydrobicyclo-pentadienol of the chemical formula (XV) in the polyester synthesis can also be used, so the same structure can be introduced to remove hydrogen.

Other substances are examples of synthetic polyesters containing structural compounds with easily removable hydrogen, such as 1-methyl alkanol, tetrahydrophthalamide alkanol of chemical formula (XVI), and chemical formula (XVII) Bridging methyltetrahydrophthalamide alkanol, isoprene alcohol, furfural, tetrahydrofurfural.

Most unsaturated polyesters are very high viscosity or solid resins. One of the features of the present invention is the use of new substances of formulas (XI) and (XII), which are not conventional polyester resins, but in some cases are low-viscosity liquids with high boiling points, which can be used as particularly suitable for new systems Reactive diluents, as well as the lack of known monomeric reactive diluents containing acrylic and ethylene acid unsaturation, such as styrene or monomeric acrylates. In the examples of monoesters of lower alcohols or diols with substances of formula (XIII) and (XIV), these substances have two or more reactive groups with easily removable hydrogen, or contain high molar concentrations Of these groups. Therefore, they are highly reactive crosslinking agents and can be used alone in many cases, but the conventional linear polyester resins or these resins with low degree of branching are best used together with other substances.

Therefore, in the process and hardening process, it can reach the important application of softening range or viscosity range without high radiation. Therefore, polyesters with high melt viscosity and high softening point can be used in the present invention, and the desired low operating viscosity can be achieved by adding these materials. It can also partially use polyesters known in the prior art. These substances themselves, and especially new reactive mixtures of unsaturated polyester resins containing non-polyester polyfunctional substances, as well as those corresponding to chemical formulas (XIII) and (XIV), use monomericity in no part Or polymerizable reactive diluent for crosslinking, its reactivity is invaluable.

After being added to a substance that will form free radicals during heating, the reactive prepolymer used in the present invention can be thermally hardened. Examples of known free radical initiators are epoxides, azo compounds, azides and CC active substances. Significant acceleration in hardening or reduction of hardening temperature can be achieved by metal co-initiators such as cobalt, manganese, iron, nickel or lead.

Furthermore, in the presence of a truncated alpha type (Norris type I) or H provider/receiver system type (Norris type II) UV initiator, the new polymer is highly sensitive to UV light.

It can also be used in the present invention to produce a substance that has improved photosensitivity. For example, because its molecule has an H-accepting group, it can be, for example, a functional hydroxyphenol ketone compound such as hydroxybenzophenone or dihydroxybenzoic acid. The way of combining phenolic ketones.

The substances used in the present invention, which can be used alone or together with other binders and/or organic and/or inorganic fillers, can be used as pigment binders, coating compositions, compact or porous, reinforced or unreinforced molds. Preparation of compounds, casting compositions, electrical insulation compositions, road marking pigments hardened by sunlight, sealants and coating compositions, or as a bonding agent for printing inks, adhesives, organized or randomly arranged, composed of organic or inorganic substances Manufactured flat or shaped fibrous support cement.

Generally new substances are liquids, so they can be used directly. If it is too viscous or solid for operation, it can also be heated and melted or used as a solution in a solvent or dispersed in water.

Example 1

661.10 grams of dicyclopentadiene (5.0 mol) and 490.30 grams of maleic anhydride (5.0 mol) are weighed in a stirring Erlenmeyer flask that can be used in heaters and distillation devices. Then gently bubbling nitrogen gas, heating the mixture to 125°C, and then adding 95.00 grams of water (5.0 mol + 5 grams) over a period of one hour from the dropping funnel. The mixture was left at 125°C for one hour to allow post-reaction. A monocarboxylic acid of formula (XIII) containing easily removable hydrogen is formed. The content in the Erlenmeyer flask was cooled to 70°C, and then 1730.00 g of trimethylolpropane and the epoxidized product of ethylene oxide with a number 165 of OH 4.00 g of dibutyltin laurate and 4.00 g of terephthalate were added Phenol was gently blown into nitrogen, and then the mixture was quickly heated to 120°C. After 6 hours, the temperature was gradually increased to 190°C to distill off the water produced by condensation to obtain a high-viscosity liquid with a number 18 acid. .

Example 2

490.80 grams of maleic anhydride (5.0 mol) is weighed into a stirring Erlenmeyer flask that can be used for heaters and distillation devices, and then gently bubbling under nitrogen, heating the mixture to 100°C, and then 444.80 grams of isoamyl Dienol (5.1 mol) (2-methyl-butyl-1-en-4-ol) was added from the dropping funnel over a period of one hour. A slight exothermic reaction occurred. The mixture was then placed at 125°C for one hour to allow post-reaction. A monoester of prenol and maleic acid/maleic acid is formed, which contains easily removable hydrogen. The contents of the Erlenmeyer flask were cooled to 70°C, and then 1730.00 g of trimethanol propane and the epoxidized product of ethylene oxide with an OH number 165 were added. 4.00 g of dibutyltin laurate 4.00 g of hydroquinone Then gently bubbling nitrogen into the mixture and quickly heating the mixture to 120°C. After 6 hours, the temperature was gradually increased to 190°C to distill off the water produced by the condensation to obtain a high-viscosity liquid with a number 26 acid.

Example 3

490.30 grams of maleic anhydride (5.0 mol) and 913.10 grams of tetrahydrophthalimide ethanol (5.1 mol) (substance of chemical formula (XVII), where R=-C₂H₄-) Put in a stirring conical flask that can be used for heaters and distillation devices, and then gently pour nitrogen into the flask to heat the contents of the flask. It will melt above 70°C and an exothermic reaction will occur. After the reaction calmed down, heating was continued at 125°C for one hour. A monoester of maleic acid/fumaric acid tetrahydrophthalimide ethanol is formed, which contains easily removable hydrogen. The contents in the Erlenmeyer flask were cooled to 70°C, and then 1730.00 g of trimethanol propane and 4.00 g of dibutyltin laurate, an epoxidized product of ethylene oxide with a number of 165, were added. Then gently bubbling nitrogen into the mixture and quickly heating the mixture to 120°C. After 6 hours, the temperature was gradually increased to 190°C to distill off the water produced by condensation, and a soft resin with a number 31 acid was obtained.

Comparative example

490.30 grams of maleic anhydride (5.0 mol) is weighed into a stirring Erlenmeyer flask that can be used for heaters and distillation devices, and then gently bubbling nitrogen into the mixture, heating the mixture to 100°C, and then adding 775.20 grams of 1,3- Phenoxypropanol (5.1 mol) was added from the dropping funnel over a period of one hour. A slight exothermic reaction occurred during this period. The mixture was placed at 125°C for one hour to allow post-reaction. A monoester of maleic acid/fumaric acid and 1,3-phenoxypropanol is formed, which does not contain easily removable hydrogen. The contents of the Erlenmeyer flask were cooled to 70°C, and then 1730.00 g of trimethylolpropane and the epoxidized product of ethylene oxide with an OH number 165 were added. 4.00 g of dibutyltin laurate 4.00 g of hydroquinone Then gently bubbling nitrogen into the mixture and quickly heating the mixture to 120°C. After 6 hours, the temperature was gradually increased to 190°C to distill off the water produced by the condensation, and a liquid with a viscosity of 18 in acid was obtained.

Hardening test of the product of the above example and the control example

In order to make the operation easier, the compounds of Examples 1-3 and Comparative Examples were prepared into 80% solutions of methyl ethyl ketone. Based on the total amount of dissolved substances, 4% of tributyl perbenzoate and 3% of benzophenone were added to the solution.

Use a knife to cover the solution on the steel plate with a film thickness of about 80 microns. Under reduced pressure and 40°C for more than 3 hours, the solvent in the film is removed to obtain a film that does not fall off. The film was first irradiated with a medium pressure mercury lamp with an energy of 80 mW/cm² for 240 seconds. In the new example, a non-shedding skin can be obtained but the underside is still sticky, but the viscosity of the product of the control example remains unchanged. The steel plate was then placed in an oven and baked at 180°C for 30 minutes. After cooling, in this new example, a hard and alcohol-resistant film with good flexural strength can be obtained. Even after baking, the viscosity of the product of the control example does not decrease.