Disclosure of Invention
Aiming at the defects existing in the prior art, the invention aims to provide a modified silica sol, and a preparation method and application thereof. The modified silica sol is modified by polyvinyl alcohol and hydroxypropyl methyl cellulose, so that the modified silica sol has good cohesiveness, and the surface layer slurry comprising the silica sol has high air permeability, high wet strength and cracking resistance.
To achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the invention provides a modified silica sol, wherein the raw materials of the modified silica sol comprise, by weight, 95-100 parts of silica sol, 0.1-2 parts of polyvinyl alcohol and 0.1-2 parts of hydroxypropyl methyl cellulose.
In the invention, the modified silica sol is combined with the hydroxyl groups of the polyvinyl alcohol through the silanol groups on the outer layer of the silica sol, so that the cohesiveness of the silica sol can be improved, and then the wet strength of the modified silica sol is further improved through hydroxypropyl methyl cellulose treatment; the surface layer slurry of the casting containing the modified silica sol has high wet strength and cracking resistance, so that the apparent quality of the casting is effectively improved, and the repair cost of the casting is reduced.
Preferably, the raw materials of the modified silica sol include 95-100 parts by weight of the silica sol, for example, 96 parts, 97 parts, 98 parts, 99 parts, 100 parts, etc.
Preferably, the raw material of the modified silica sol comprises 0.1 to 2 parts by weight of polyvinyl alcohol, for example, 0.2 parts, 0.4 parts, 0.6 parts, 0.8 parts, 1 part, 1.2 parts, 1.4 parts, 1.6 parts, 1.8 parts and the like.
In the invention, the content of the polyvinyl alcohol is more than 2 parts, so that the stability of the whole silica sol is reduced, and the service life of the modified silica sol is greatly reduced.
Preferably, the raw material of the modified silica sol comprises 0.1 to 2 parts by weight of hydroxypropyl methylcellulose, for example, 0.2 parts, 0.4 parts, 0.6 parts, 0.8 parts, 1 part, 1.2 parts, 1.4 parts, 1.6 parts, 1.8 parts and the like.
In the invention, the content of the hydroxypropyl methylcellulose is more than 2 parts, so that the stability of the whole silica sol is reduced, and the service life of the modified silica sol is greatly reduced.
Preferably, the silica sol has a solid content of 25 to 35%, for example, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 34%, or the like.
Preferably, the silica sol has a pH of 9.5 to 10.5, and may be, for example, 9.6, 9.7, 9.8, 9.9, 10, 10.1, 10.2, 10.3, 10.4, etc.
In the invention, the pH value of the silica sol is less than 9.5, so that the modified silica sol has poor stability and extremely poor use effect; the pH value is more than 10.5, and the alkalinity is too strong, so that the polyvinyl alcohol is decomposed, the modified silica sol cannot be obtained, and the expected use effect cannot be achieved.
Preferably, the mass ratio of polyvinyl alcohol to hydroxypropyl methylcellulose in the modified silica sol is (0.5-2): 1, and may be, for example, 0.6:1, 0.75:1, 1:1, 1.5:1, 1.8:1, etc.
In the invention, the mass ratio of the polyvinyl alcohol to the hydroxypropyl methylcellulose is less than 0.5:1, which can lead to too little hydroxypropyl methylcellulose content combined in the modified silica gel, reduce the effect of the product and can not meet the market demand; and the ratio of the raw materials is more than 2:1, so that the product is unstable and the service life is short.
In the present invention, the silica sol in the mass ratio of the silica sol, the polyvinyl alcohol and the hydroxypropyl methylcellulose means the total mass of the silica sol including the solvent.
In a preferred embodiment of the present invention, the raw materials of the modified silica sol further include 0.1 to 1 part by weight of nonionic organic phosphate, for example, 0.2 part by weight, 0.3 part by weight, 0.4 part by weight, 0.5 part by weight, 0.6 part by weight, 0.7 part by weight, 0.8 part by weight, 0.9 part by weight, and the like.
In the invention, the nonionic organic phosphate is nonionic low-foam organic phosphate, so that the compatibility among polyvinyl alcohol, hydroxypropyl methyl cellulose and silica sol can be improved.
Preferably, the raw materials of the modified silica sol further comprise 0.1 to 1 part by weight of an aqueous silicone defoamer, for example, 0.2 part by weight, 0.3 part by weight, 0.4 part by weight, 0.5 part by weight, 0.6 part by weight, 0.7 part by weight, 0.8 part by weight, 0.9 part by weight and the like.
In a second aspect, the present invention provides a method for preparing the modified silica sol according to the first aspect, the method comprising:
(1) Mixing silica sol with polyvinyl alcohol to obtain a mixed solution A;
(2) And (3) mixing the mixed solution A obtained in the step (1) with hydroxypropyl methylcellulose to obtain the modified silica sol.
In the invention, the silica sol further comprises the step of stirring the silica sol before mixing the silica sol with the polyvinyl alcohol; the stirring time is 20 to 40 minutes, and may be, for example, 20 minutes, 25 minutes, 30 minutes, 35 minutes, 40 minutes, or the like.
Preferably, the stirring speed is 100 to 200rpm, for example, 110rpm, 120rpm, 140rpm, 150rpm, 160rpm, 180rpm, etc.
Preferably, the mixing time in step (1) is 1 to 2 hours, for example, 1 hour, 1.5 hours, 2 hours, etc.
Preferably, the temperature of the mixing in the step (1) is 20 to 25 ℃, and for example, 21 ℃, 22 ℃, 23 ℃, 24 ℃ and the like can be used.
Preferably, the rotational speed of the mixing in step (1) is 200 to 300rpm, and may be, for example, 220rpm, 240rpm, 260rpm, 280rpm, etc.
Preferably, the mixing in the step (1) comprises mixing 40-50% of polyvinyl alcohol with silica sol, and adding the rest of polyvinyl alcohol for mixing.
Preferably, the mixing of step (1) further comprises the step of adding a nonionic organic phosphate for mixing.
Preferably, the method for adding the nonionic organic phosphate for mixing comprises the following steps:
after mixing silica sol and polyvinyl alcohol, adding nonionic organic phosphate with the formula amount of 40-50% for first mixing, and then adding the rest nonionic organic phosphate for second mixing.
In the invention, the nonionic organic phosphate is added and mixed in batches to uniformly mix the nonionic organic phosphate with the mixed solution of the polyvinyl alcohol and the silica sol, and activate and further disperse the mixed solution of the polyvinyl alcohol and the silica sol.
Preferably, the time of the first mixing is 20 to 40min, for example, 25min, 30min, 35min, etc.
Preferably, the temperature of the first mixing is 20 to 25 ℃, for example, 21 ℃, 22 ℃, 23 ℃, 24 ℃, and the like.
Preferably, the rotational speed of the first mixing is 200 to 300rpm, and may be 220rpm, 240rpm, 260rpm, 280rpm, or the like, for example.
Preferably, the time of the second mixing is 1 to 3 hours, for example, 1 hour, 1.5 hours, 2 hours, 2.5 hours, etc.
Preferably, the temperature of the second mixing is 35 to 45 ℃, and may be 36 ℃, 37 ℃, 38 ℃, 39 ℃,40 ℃, 41 ℃, 42 ℃, 43 ℃, 44 ℃ or the like, for example.
Preferably, the rotation speed of the second mixing is 300-400 rpm, for example, 320rpm, 340rpm, 350rpm, 360rpm, 370rpm, 380rpm, 390rpm, etc.
Preferably, the temperature of the mixing in the step (2) is 40 to 45 ℃, and may be, for example, 40 ℃, 41 ℃, 42 ℃, 43 ℃, 44 ℃, or the like.
Preferably, the mixing time in step (2) is 1 to 3 hours, for example, 1 hour, 1.5 hours, 2 hours, 2.5 hours, etc.
Preferably, the rotational speed of the mixing in step (2) is 300 to 400rpm, and may be 320rpm, 340rpm, 350rpm, 360rpm, 370rpm, 380rpm, 390rpm, or the like, for example.
Preferably, the step (2) further comprises the step of adding an aqueous organosilicon antifoaming agent for mixing after the mixed solution A is mixed with the hydroxypropyl methylcellulose.
Preferably, the time for adding the aqueous silicone defoamer to mix is 1 to 3 hours, for example, 1 hour, 1.5 hours, 2 hours, 2.5 hours, etc.
As a preferable technical scheme of the invention, the preparation method comprises the following steps:
(1) Mixing silica sol and polyvinyl alcohol at 20-25 ℃ for 1-2 h, and then adding optional nonionic organic phosphate for mixing to obtain a mixed solution A;
(2) Mixing the mixed solution A obtained in the step (1) with hydroxypropyl methyl cellulose for 1-3 hours at the temperature of 40-45 ℃, and then adding an optional aqueous organic silicon defoamer for continuous mixing for 1-3 hours to obtain the modified silica sol.
According to the preparation method of the modified silica sol, the polyvinyl alcohol is firstly adopted for modification, and then the hydroxypropyl methyl cellulose is adopted for modification, so that the cohesiveness of the silica sol and the wet strength of the casting surface layer slurry can be improved; the combination of the silica sol and the hydroxypropyl methylcellulose is difficult compared with polyvinyl alcohol, and if the order of the silica sol and the hydroxypropyl methylcellulose is changed, the modified silica sol has extremely poor use effect and cannot be used.
In a third aspect, the present invention provides a binder comprising a modified silica sol as described in the first aspect.
The numerical ranges recited herein include not only the recited point values, but also any point values between the recited numerical ranges that are not recited, and are limited to, and for the sake of brevity, the invention is not intended to be exhaustive of the specific point values that the recited range includes.
Compared with the prior art, the invention has the beneficial effects that:
according to the modified silica sol provided by the invention, the silica sol is modified by the polyvinyl alcohol and the hydroxypropyl methyl cellulose with a specific proportion, so that the modified silica sol has good cohesiveness, the surface layer slurry comprising the silica sol has high wet strength and cracking resistance, and the apparent mass of the casting is good; the viscosity of the modified silica sol is more than or equal to 3.3cps, the wet strength of the surface layer slurry comprising the modified silica sol is more than or equal to 6.8MPa, and no or fewer cracks exist on the surface of the casting.
Detailed Description
The technical scheme of the invention is further described by the following specific embodiments. It will be apparent to those skilled in the art that the examples are merely to aid in understanding the invention and are not to be construed as a specific limitation thereof.
The materials used in the examples and comparative examples of the present invention are as follows:
polyvinyl alcohol: PVA-1788 available from Shengyu New Material technology Co., ltd;
hydroxypropyl methylcellulose: HPMC-001 from Shandong Xinfuman chemical technology Co., ltd;
nonionic low foam organic phosphate: PPE 1040;
aqueous silicone defoamer: XPJ-S225.
Example 1
The embodiment provides a modified silica sol which comprises, by weight, 95 parts of silica sol (solid content is 30%), 2 parts of polyvinyl alcohol, 2 parts of hydroxypropyl methylcellulose, 0.5 part of nonionic low-foam organic phosphate and 0.5 part of aqueous organic silicon defoamer.
The embodiment provides a preparation method of the modified silica sol, which comprises the following specific steps:
(1) Placing the silica sol into a 1000mL flask, adding a stirrer, and stirring at 150rpm for 30min; slowly adding half amount of polyvinyl alcohol into the mixture under stirring condition, adjusting the stirring speed to be 250rpm, stirring for 30min, then slowly adding the other half amount of polyvinyl alcohol, heating to 20-25 ℃ when the temperature of a reaction system is lower than 20-25 ℃ in the reaction process, keeping the stirring speed to be 250rpm, continuously stirring for 1h, slowly adding half amount of nonionic low-foam organic phosphate, keeping the stirring speed to be 250rpm, continuously stirring for 30min, then raising the temperature to 40 ℃, adjusting the stirring speed to be 350rpm, slowly adding the other half amount of nonionic low-foam organic phosphate under stirring, and continuously stirring for 2h to obtain a mixed solution A;
(2) Slowly adding hydroxypropyl methyl cellulose into the mixed solution A obtained in the step (1), keeping the temperature constant at 40 ℃, keeping the stirring speed at 350rpm, and continuously stirring for 2 hours; slowly adding the aqueous organic silicon defoamer under the stirring condition, and continuously stirring for 2 hours to obtain the modified silica sol.
Example 2
The embodiment provides a modified silica sol which comprises, by weight, 95 parts of silica sol (solid content is 30%), 2 parts of polyvinyl alcohol, 1 part of hydroxypropyl methylcellulose, 1 part of nonionic low-foam organic phosphate and 1 part of aqueous organic silicon defoamer.
This example provides a method for preparing the modified silica sol, and the specific steps are the same as in example 1.
Example 3
The embodiment provides a modified silica sol which comprises, by weight, 95 parts of silica sol (solid content is 30%), 1 part of polyvinyl alcohol, 2 parts of hydroxypropyl methylcellulose, 1 part of nonionic low-foam organic phosphate and 1 part of aqueous organic silicon defoamer.
This example provides a method for preparing the modified silica sol, and the specific steps are the same as in example 1.
Example 4
The embodiment provides a modified silica sol which comprises, by weight, 95 parts of silica sol (solid content is 30%), 2 parts of polyvinyl alcohol, 1.5 parts of hydroxypropyl methylcellulose, 1 part of nonionic low-foam organic phosphate and 0.5 part of aqueous organic silicon defoamer.
This example provides a method for preparing the modified silica sol, and the specific steps are the same as in example 1.
Example 5
The embodiment provides a modified silica sol which comprises, by weight, 95 parts of silica sol (solid content is 30%), 1.5 parts of polyvinyl alcohol, 2 parts of hydroxypropyl methylcellulose, 1 part of nonionic low-foam organic phosphate and 0.5 part of aqueous organic silicon defoamer.
This example provides a method for preparing the modified silica sol, and the specific steps are the same as in example 1.
Example 6
This example provides a modified silica sol differing from example 1 only in that the polyvinyl alcohol was present in an amount of 0.5 parts, and other materials and amounts were the same as in example 1.
This example provides a method for preparing the modified silica sol, and the specific steps are the same as in example 1.
Example 7
This example provides a modified silica sol differing from example 1 only in that the hydroxypropyl methylcellulose was present in an amount of 0.5 parts, and the other materials and amounts were the same as in example 1.
This example provides a method for preparing the modified silica sol, and the specific steps are the same as in example 1.
Comparative example 1
This comparative example provides a modified silica sol differing from example 1 only in that the polyvinyl alcohol was 4 parts, and other raw materials and amounts were the same as in example 1.
This comparative example provides a method for preparing the modified silica sol, and the specific procedure is the same as in example 1.
Comparative example 2
This comparative example provides a modified silica sol differing from example 1 only in that the hydroxypropyl methylcellulose was 4 parts, and other materials and amounts were the same as in example 1.
This comparative example provides a method for preparing the modified silica sol, and the specific procedure is the same as in example 1.
Comparative example 3
This comparative example provides a modified silica sol differing from example 1 only in that the modified silica sol has no polyvinyl alcohol therein, and other raw materials and amounts thereof are the same as those of example 1.
This comparative example provides a method for preparing the modified silica sol, and the specific procedure is the same as in example 1.
Comparative example 4
This comparative example provides a modified silica sol differing from example 1 only in that there is no hydroxypropyl methylcellulose in the modified silica sol, and other materials and amounts are the same as in example 1.
This comparative example provides a method for preparing the modified silica sol, and the specific procedure is the same as in example 1.
Comparative example 5
This comparative example provides a silica sol supplied by Guangdong and silicon articles Inc., which was not modified with polyvinyl alcohol and hydroxypropyl methylcellulose.
Performance testing
(1) pH value: measured by a pH meter;
(2) Viscosity: measured by a viscometer;
(3) Wet strength: adopting a JB/T13038-2017 method to test;
(4) Apparent mass: mixing 1 part of the modified silica sol provided in examples 1 to 7 and comparative examples 1 to 4 with 1 part of the silica sol provided in comparative example 5 and 4.4 parts of powder liquid of refractory materials (zircon powder, manufacturer: 40 kg/bag of Yixing city ancient king technology Co., ltd.) to prepare surface layer slurry, and observing surface crack condition after casting; judgment standard: the surface has no obvious cracks, the crack content is less than 3%, and the surface is marked as 'excellent'; crack content is greater than 3%, noted as "bad".
The specific test results are shown in table 1:
TABLE 1
As can be seen from the table, the modified silica sol provided by the invention has high viscosity and excellent adhesiveness by modifying the silica sol with polyvinyl alcohol and hydroxypropyl methylcellulose in a specific ratio; and the wet strength and air permeability of the casting surface sizing agent can be improved, and the cracking resistance is improved, so that the apparent quality of the casting is good.
From examples 1 to 5, the modified silica sol is alkaline, and accords with the use habit of the investment casting industry; the viscosity of the modified silica sol is 3.3-4.2 cps, the wet strength of the surface sizing agent comprising the modified silica sol is 6.8-7.9 MPa, and the surface of the casting has no or fewer cracks; as is clear from comparison of examples 1 and examples 6 to 7, when the polyvinyl alcohol and the hydroxypropyl methylcellulose in the modified silica sol are not in a specific ratio, the wet strength is lowered and the surface quality of the casting is deteriorated; as is clear from comparison of example 1 with comparative examples 1 to 4, when the combination or the proportion is not preferable in the present invention, the wet strength of the surface layer slurry is lowered or the surface quality of the casting is deteriorated, and the cracks are more; as can be seen from comparison of example 1 and comparative example 5, the modified silica sol provided by the invention has better performance in all aspects than the common unmodified silica sol.
In summary, the modified silica sol provided by the invention is modified by the polyvinyl alcohol and the hydroxypropyl methyl fiber, so that the cohesiveness of the silica sol can be improved, the wet strength of casting surface sizing agent is improved, the defects of cracking resistance, good air permeability, shell cracking, swelling and the like are avoided, the apparent quality of castings is improved, and the production cost is reduced.
While the foregoing is directed to embodiments of the present invention, other and further details of the invention may be had by the present invention, it should be understood that the foregoing description is merely illustrative of the present invention and that no limitations are intended to the scope of the invention, except insofar as modifications, equivalents, improvements or modifications are within the spirit and principles of the invention.