Preparation method of dual-modified heavy calcium carbonate and application of dual-modified heavy calcium carbonate in silicone sealant

Abstract

The invention provides a preparation method of dual-modified ground calcium carbonate and application of the dual-modified ground calcium carbonate in silicone sealers.The preparation method comprises the steps that calcite type ground calcium carbonate fragments and water are mixed, meanwhile, a compound grinding-aid active agent is added, the active agent and hydroxyl-OH on the surface of ground calcium carbonate GCC are promoted to be subjected to a hydrolytic condensation reaction through mechanical grinding, and the ground calcium carbonate GCC is obtained; the hydrophilic GCC surface is converted into a hydrophobic surface; carrying out grading treatment on the ground wet slurry to obtain primary modified GCC; and carrying out ball-milling secondary modification on the modified GCC and a hydrophobic organosilicon compound PDMS, and carrying out chemical-physical double modification on the GCC to obtain the double modified heavy calcium carbonate. According to the invention, the silicone matrix formula and process parameters are optimized, high mechanical properties, weather resistance, construction performance and durability are still maintained under the condition of high filling amount (30-60wt%) of the dual-modified GCC to the silicone sealant, and the manufacturing cost of the silicone sealant is reduced at the same time.

Description

Technical Field

[0001] The invention belongs to the technical field of preparation and modification of inorganic fillers, and particularly relates to a preparation method of double-modified heavy calcium carbonate and application of the same in silicone sealants. Background Art

[0002] Silicone sealant is an elastic sealing material based on polysiloxane (such as 107 silicone rubber) through moisture-curing and cross-linking. Its backbone consists of Si-O bonds, and its side chains contain organic groups (such as methyl and phenyl groups), combining the weather resistance of inorganic materials with the flexibility of organic materials. Despite its excellent performance, silicone sealants still suffer from poor mechanical properties, durability, and weather resistance, as well as high manufacturing costs.

[0003] Existing silicone sealants often use calcium carbonate as a filler, but it has the following defects: ordinary heavy calcium carbonate has poor compatibility with the silicone matrix, leading to interfacial stress concentration; high oil absorption value (usually >50g / 100g), affecting rheological properties; untreated particles are prone to agglomeration, affecting dispersion uniformity.

[0004] Currently, conventional modification methods of heavy calcium (such as stearic acid treatment) still have the problem of insufficient temperature resistance (failure at >150°C) for silicone sealants.

[0005] Currently, traditional silicone sealants usually use fumed silica as filler, which is costly and has an excessively strong thickening effect, affecting workability; directly filling with heavy calcium carbonate (GCC) can easily lead to uneven dispersion and poor interfacial bonding, reducing the tensile strength and durability of the sealant. Summary of the Invention

[0006] The purpose of this section is to summarize some aspects of embodiments of the present invention and to briefly introduce some preferred embodiments.

[0007] In view of the above problems and / or the problems existing in the prior art, the present invention is proposed.

[0008] Therefore, the object of the present invention is to overcome the deficiencies in the prior art and provide a method for preparing a double-modified ground calcium carbonate.

[0009] In order to solve the above technical problems, the present invention provides the following technical solutions: a method for preparing double-modified heavy calcium carbonate, comprising:

[0010] The calcite-type heavy calcium carbonate is coarsely crushed into 5-10 cm to obtain calcite-type heavy calcium carbonate fragments;

[0011] Calcite-type heavy calcium carbonate fragments are mixed with water, and a composite grinding aid active agent is added. Mechanical grinding is used to promote a hydrolysis and condensation reaction between the active agent and the hydroxyl groups on the surface of heavy calcium carbonate (GCC), thereby converting the hydrophilic GCC surface into a hydrophobic one. The ground wet slurry is then subjected to classification treatment, followed by filter press dehydration, spray drying, grinding and sieving to obtain a first-grade modified GCC.

[0012] The obtained modified GCC is subjected to secondary modification by ball milling with the hydrophobic organosilicon compound PDMS. The long-chain molecules of PDMS entangle the modified GCC particles through van der Waals forces to form a flexible shell, thereby achieving chemical-physical dual modification of GCC. The product is then sieved through an airflow sieve and an ultrasonic vibration sieve to obtain a double-modified heavy calcium carbonate.

[0013] As a preferred embodiment of the preparation method of the present invention, the calcite-type heavy calcium has a purity of ≥98.5%, a particle size D50 of 1.5-2.5 μm, and a specific surface area of ​​3-5 m 2 / g, control the iron content to <200ppm.

[0014] As a preferred embodiment of the preparation method of the present invention, the compound grinding aid active agent is one or more of methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, ethyltriethoxysilane, polydimethoxysilane, polydiethoxysilane, and polyether-modified silicone oil.

[0015] As a preferred embodiment of the preparation method of the present invention, the ground slurry comprises, in terms of raw material mass percentage, 0.5-2 wt % of the compounded grinding aid active agent and 30-60 wt % of water.

[0016] As a preferred embodiment of the preparation method of the present invention, the grinding time is 1 to 3 hours, the rotation speed is 400 to 800 rpm, the grinding medium is 0.1 to 0.3 mm zirconium beads, the medium filling rate is 60% to 80%, and the slurry particle size D97 ≤ 2 μm.

[0017] As a preferred embodiment of the preparation method of the present invention, the molecular weight of the PDMS is 8000-15000 g / mol, and the mass percentage of PDMS in the first-stage modified GCCC powder is 0.5-3 wt%.

[0018] As a preferred embodiment of the preparation method of the present invention, the ball milling is dry continuous ball milling, wherein the ball-to-material ratio is 10-20:1, the grinding balls are made of zirconia balls, the rotation speed is 60%-75% of the critical speed, and the grinding time is 0.5-4 hours.

[0019] Another object of the present invention is to overcome the deficiencies in the prior art and provide a double-modified ground calcium carbonate having the following characteristics:

[0020] Oil absorption value: 19±2g / 100g, GB / T 19281;

[0021] Bulk density: 0.65~0.75g / cm;

[0022] Thixotropic index TI value: 2.0-2.5, ISO 3219 standard test.

[0023] Another object of the present invention is to overcome the deficiencies in the prior art and provide a method for preparing a silicone sealant by using a double-modified GCC, comprising:

[0024] α,ω-dihydroxy polydimethylsiloxane and plasticizer dimethyl silicone oil were mixed uniformly in a planetary mixer;

[0025] Add the double-modified GCC, mix at a low speed and then gradually increase the speed until homogeneous, then add gas-phase SiO2 to adjust the thixotropy, then add the crosslinking agent methyltrimethoxysilane, the catalyst dibutyltin dilaurate, the coupling agent KH-550 / KH-560 and other additives, vacuum stir until uniform and free of particles, and vacuum degas until there are no bubbles to obtain the mixed rubber material;

[0026] After injection molding, the mixture was cured at room temperature for 24 hours, and then heated to 80° C. and cured for 2 hours to obtain a silicone sealant.

[0027] As a preferred embodiment of the application of the present invention, the content of the α,ω-dihydroxy polydimethylsiloxane is 100 parts, the content of the dimethyl silicone oil is 2-10 parts, the content of the double-modified GCC is 30-60 parts, the content of the cross-linking agent is 1-5 parts, the content of the catalyst is 0.1-0.5 parts, the content of the coupling agent is 0.5-2 parts, and the content of the gas-phase SiO2 is 0.1-1 parts.

[0028] The vacuum degree is -0.1 MPa, and the vacuuming time is 10-20 minutes.

[0029] Beneficial effects of the present invention:

[0030] (1) The present invention adds a composite grinding aid active agent in combination with a grinding process to improve the yield and activity of GCC. The active agent undergoes a hydrolysis and condensation reaction with the hydroxyl groups (-OH) on the surface of GCC to form a Si-O-Ca chemical covalent bond. At the same time, an organic silicon layer (-CH3 groups facing outward) is constructed on the surface of GCC, thereby converting the hydrophilic GCC surface into a hydrophobic one (hydrophobic effect of -CH3), improving its compatibility with organic polymers, reducing the moisture absorption of the filler, preventing agglomeration, and improving its storage stability.

[0031] (2) The first-stage modified GCC of the present invention is subjected to second-stage modification by ball milling with a hydrophobic organosilicon compound, PDMS. The long-chain molecules of PDMS entangle the modified GCC particles through van der Waals forces, forming a flexible shell that further shields the surface polarity of GCC, achieving a chemical-physical dual modification (step-by-step coating) of GCC. This further improves the dispersibility, compatibility, and substrate-binding strength of GCC.

[0032] (3) The present invention optimizes the silicone matrix formula and process parameters to achieve high mechanical properties, weather resistance, construction performance and durability at a high filling amount (30-60wt%) of the double-modified GCC in the silicone sealant, while reducing the manufacturing cost of the silicone sealant. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort. Among them:

[0034] Figure 1 This is a scanning electron microscope image of the double-modified GCC prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0035] In order to make the above-mentioned objects, features and advantages of the present invention more clearly understood, the following is a detailed description of the specific embodiments of the present invention in conjunction with the examples in the specification. The raw materials used in the examples of the present invention are all common commercially available products.

[0036] Example 1

[0037] Preparation of double modified GCC:

[0038] (1) Calcite-type heavy calcium fragments (5-10 cm) were used as grinding raw materials, 50 wt% of dispersion medium water and 1.5 wt% of a composite grinding aid active agent (methyltriethoxysilane: n-propyltrimethoxysilane = 1:3, the ratio is by mass) were added to the grinder, and grinding modification was performed (grinding time was 3 h, rotation speed was 800 rpm, grinding medium was 0.1-0.3 mm zirconium beads, and medium filling rate was 80%) to obtain a slurry, which was dehydrated by filter press to control the moisture content to 8 wt%, then spray-dried at 120 ° C, mechanically crushed for 30 min, and graded to obtain high-yield active GCC.

[0039] (2) Active GCC and 1.8 wt% polydimethylsiloxane (PDMS) were added to a ball mill and ball-milled for 2 h. The long-chain molecules of PDMS were wrapped around the modified GCC particles through van der Waals forces to form a flexible shell. The particles were then sieved through an airflow sieve and an ultrasonic vibration sieve (the sieving conditions were: air volume: 800 m 3 / h, negative pressure -1000Pa; stainless steel mesh; vibration frequency: 2000rpm, amplitude 1.5mm) to obtain a double-modified high value-added active GCC product. The performance test results are shown in Table 1.

[0040] The scanning electron microscope image of the double-modified GCC is shown in Figure 1 , Figure 1 The graph shows that the double-modified GCC particles have irregular block or angular morphology, with nano-scale particles attached to the particle surface, smooth edges, and good particle dispersion, indicating that the chemical-physical double modification of the present invention achieves uniform coating of GCC.

[0041] Table 1

[0042]

[0043] Example 2

[0044] Preparation of silicone sealant:

[0045] 100 parts of α,ω-dihydroxy polydimethylsiloxane and 7 parts of plasticizer dimethyl silicone oil were mixed uniformly in a planetary mixer (speed 1000 rpm, time for 30 minutes);

[0046] 50 parts of the double-modified GCC prepared in Example 1 were added to the above mixture in three portions, and after mixing at a low speed, the speed was gradually increased until homogeneous, and then 0.5 parts of gas-phase SiO2 were added to adjust the thixotropy. Then, 3 parts of methyltrimethoxysilane as a crosslinking agent, 0.25 parts of dibutyltin dilaurate as a catalyst, and 1.2 parts of KH-550 / KH-56 as a coupling agent were added. The mixture was stirred in a vacuum until uniform and free of particles, and vacuum degassed (vacuum degree of -0.1 MPa for 30 minutes) until no bubbles were present to obtain a mixed rubber material.

[0047] After injection molding, the mixture was cured at room temperature for 24 hours, and then heated to 80°C and cured for 2 hours to obtain a double-modified GCC highly filled silicone sealant, and its performance was tested.

[0048] See Table 2 for comparative data of active GCC highly filled silicone sealant.

[0049] Table 2

[0050]

[0051] Comparative Example 1

[0052] This comparative example uses stearic acid for secondary modification:

[0053] (1) Calcite-type heavy calcium fragments (5-10 cm) were used as grinding raw materials. 50 wt% of water as a dispersion medium and 1.5 wt% of a composite grinding aid (methyltriethoxysilane: n-propyltrimethoxysilane = 1:3, mass ratio) were added to the grinder. The grinding modification was started to obtain a slurry. The water content was controlled at 8 wt% by filter press dehydration, and then spray-dried at 120 ° C. The mechanical powder was polydimethylsilane crushed for 30 min, and the high-yield active GCC was obtained by graded treatment.

[0054] (2) Active GCC and 3.5 wt% active agent stearic acid were added to a ball mill and ball milled for 2 h. The friction heat between the grinding balls and the raw materials was used to promote the reaction of carboxyl groups in stearic acid with a small amount of calcium ion active sites to form chemical bonds, and the unreacted stearic acid molecules were further covered on the surface of GCC by physical adsorption to form a hydrophobic layer. The GCC was then sieved by air flow screening + ultrasonic vibration screening (the sieving conditions were: air volume: 800m 3 / h, negative pressure -1000 Pa; stainless steel mesh; vibration frequency: 2000 rpm, amplitude 1.5 mm) to obtain the active GCC product.

[0055] Table 3

[0056]

[0057] As shown in Table 3 above, the comparison of the secondary modification effects of the conventional active agent stearic acid and the active agent PDMS of the present invention on GCC shows that the oil absorption value of the GCC modified with conventional stearic acid is higher, but the activity does not reach 100%.

[0058] Comparative Example 2

[0059] This comparative example does not add compound grinding aid active agent:

[0060] (1) Calcite-type heavy calcium carbonate fragments (5-10 cm) were used as grinding raw materials. 50 wt% of water, a dispersion medium, was added to the grinder, and the grinding modification was started to obtain a slurry. The water content was controlled at 8 wt% by filter press dehydration, and then spray-dried at 120 ° C., mechanically crushed for 30 min, and graded to obtain GCC powder.

[0061] (2) Active GCC and 1.8 wt% polydimethylsiloxane (PDMS) were added to a ball mill and ball-milled for 2 h. The long-chain molecules of PDMS were entangled with the modified GCC particles through van der Waals forces to form a flexible shell. The particles were then sieved through air flow sieves and ultrasonic vibration sieves (the sieving conditions were: air volume: 800 m 3 / h, negative pressure -1000Pa; stainless steel mesh; vibration frequency: 2000rpm, amplitude 1.5mm) to obtain the modified GCC product.

[0062] Table 4

[0063]

[0064]

[0065] As shown in Table 4 above, by comparing the test results of Example 1 and Comparative Example 2, it is found that the absence of the composite grinding aid active agent in Comparative Example 2 has the greatest impact on the particle size of GCC, and the activation degree is reduced to 90%.

[0066] Comparative Example 3

[0067] This comparative example is to add excessive PDMS:

[0068] (1) Calcite-type heavy calcium fragments (5-10 cm) were used as grinding raw materials. 50 wt% of water as a dispersion medium and 1.5 wt% of a composite grinding aid (methyltriethoxysilane: n-propyltrimethoxysilane = 1:3, the ratio is by mass) were added to the grinder. The grinding modification was started to obtain a slurry. The water content was controlled at 8 wt% by filter press dehydration, and then spray dried at 120 ° C, mechanically crushed for 30 min, and graded to obtain GCC powder.

[0069] (2) Active GCC and 3.6 wt% polydimethylsiloxane (PDMS) were added to a ball mill and ball-milled for 2 h. The long-chain molecules of PDMS were entangled with the modified GCC particles through van der Waals forces to form a flexible shell. The particles were then sieved through air flow sieves and ultrasonic vibration sieves (the sieving conditions were: air volume: 800 m 3 / h, negative pressure -1000Pa; stainless steel mesh; vibration frequency: 2000rpm, amplitude 1.5mm) to obtain the modified GCC product.

[0070] Table 5

[0071]

[0072]

[0073] As can be seen from Table 5 above, by comparing the test results of Example 1 and Comparative Example 3, it is found that increasing the amount of PDMS added in Comparative Example 3 has a significant effect on the oil absorption value and particle size of GCC. The main reason is that the excess surfactant causes secondary aggregation of particles due to micelle formation or charge neutralization; at the same time, the excess surfactant covers the active sites on the GCC surface, changing its surface polarity, resulting in an increase in oil absorption value.

[0074] Comparative Example 4

[0075] The grinding aid active agent is only methyltriethoxysilane:

[0076] (1) Calcite-type heavy calcium fragments (5-10 cm) were used as grinding raw materials. 50 wt% of water as a dispersion medium and 1.5 wt% of methyltriethoxysilane as a grinding aid were added to the grinder for grinding and modification to obtain a slurry. The slurry was dehydrated by filter pressing to control the moisture content to 8 wt%, then spray-dried at 120°C, mechanically crushed for 30 min, and graded to obtain high-yield active GCC.

[0077] (2) Active GCC and 1.8 wt% polydimethylsiloxane (PDMS) were added to a ball mill and ball-milled for 2 h. The long-chain molecules of PDMS were wrapped around the modified GCC particles through van der Waals forces to form a flexible shell. The particles were then sieved through an airflow sieve and an ultrasonic vibration sieve (the sieving conditions were: air volume: 800 m 3 / h, negative pressure -1000Pa; stainless steel mesh; vibration frequency: 2000rpm, amplitude 1.5mm) to obtain a double-modified high-value-added active GCC product.

[0078] Comparative Example 5

[0079] The grinding aid active agent is only n-propyltrimethoxysilane:

[0080] (1) Calcite-type heavy calcium fragments (5-10 cm) were used as grinding raw materials. 50 wt% of water as a dispersion medium and 1.5 wt% of n-propyltrimethoxysilane as a grinding aid were added to the grinder for grinding and modification to obtain a slurry. The slurry was dehydrated by filter pressing to control the moisture content to 8 wt%, then spray-dried at 120°C, mechanically crushed for 30 min, and graded to obtain high-yield active GCC.

[0081] (2) Active GCC and 1.8 wt% polydimethylsiloxane (PDMS) were added to a ball mill and ball-milled for 2 h. The long-chain molecules of PDMS were wrapped around the modified GCC particles through van der Waals forces to form a flexible shell. The particles were then sieved through an airflow sieve and an ultrasonic vibration sieve (the sieving conditions were: air volume: 800 m 3 / h, negative pressure -1000Pa; stainless steel mesh; vibration frequency: 2000rpm, amplitude 1.5mm) to obtain a double-modified high-value-added active GCC product.

[0082] Referring to the preparation process of the silicone sealant in Example 2, silicone sealants were prepared using the GCC products in Comparative Examples 1, 2, 3, 4 and 5. The performance test results are shown in Table 6.

[0083] Table 6

[0084]

[0085] As shown in Table 6 above, the dual-modified GCC of the present invention significantly improves the tensile strength of the silicone sealant (1.8 MPa) while maintaining a high elongation at break (370%) and an excellent extrusion rate (180 g / min), demonstrating a balance of high strength, good flexibility, and workability. GCC treated without a grinding aid (e.g., Comparative Example 2) exhibits poor performance, particularly in tensile strength and extrusion rate. Comparative Examples 4 and 5, which utilize a single grinding aid, exhibit intermediate performance, demonstrating that GCC treated with a compound grinding aid effectively improves the overall performance of silicone sealants.

[0086] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, and all of these should be included in the scope of the present invention.

Claims

1. A method for preparing double-modified ground calcium carbonate, characterized in that: include, The calcite-type heavy calcium carbonate is coarsely crushed into 5-10 cm to obtain calcite-type heavy calcium carbonate fragments; Calcite-type heavy calcium carbonate fragments are mixed with water, and a compound grinding aid active agent is added at the same time. Mechanical grinding is used to promote the hydrolysis and condensation reaction between the active agent and the hydroxyl groups -OH on the surface of heavy calcium carbonate GCC, thereby converting the hydrophilic GCC surface into a hydrophobic one. The ground wet slurry is subjected to classification treatment, and then subjected to filter press dehydration, spray drying, grinding, crushing and sieving classification treatment to obtain the first-grade modified GCC; The obtained modified GCC is subjected to secondary modification by ball milling with the hydrophobic organosilicon compound PDMS. The long-chain molecules of PDMS entangle the modified GCC particles through van der Waals forces to form a flexible shell, thereby achieving chemical-physical dual modification of GCC. The product is then sieved through an airflow sieve and an ultrasonic vibration sieve to obtain a double-modified heavy calcium carbonate.

2. The preparation method according to claim 1, wherein: The calcite-type heavy calcium has a purity of ≥98.5%, a particle diameter D50 of 1.5-2.5 μm, and a specific surface area of ​​3-5 m 2 / g, control the iron content to <200ppm.

3. The preparation method according to claim 1 or 2, wherein: The composite grinding aid active agent is one or more of methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, ethyltriethoxysilane, polydimethoxysilane, polydiethoxysilane, and polyether modified silicone oil.

4. The preparation method according to claim 1 or 3, wherein: The ground slurry, wherein, based on the mass percentage of raw materials, the content of the compound grinding aid active agent is 0.5-2wt%, and the water content is 30-60wt%.

5. The preparation method according to claim 4, wherein: The mechanical grinding parameters are as follows: grinding time of 1 to 3 hours, rotation speed of 400 to 800 rpm, grinding medium of 0.1 to 0.3 mm zirconium beads, medium filling rate of 60% to 80%, and slurry particle size D97≤2 μm after grinding.

6. The preparation method according to claim 1, wherein: The molecular weight of the PDMS is 8000 to 15000 g / mol, and the mass percentage of the PDMS in the first-stage modified GCCC powder is 0.5 to 3 wt%.

7. The preparation method according to claim 1 or 6, wherein: The ball mill is a dry continuous ball mill, wherein the ball-to-material ratio is 10-20:1, the grinding balls are made of zirconia balls, the rotation speed is 60%-75% of the critical speed, and the grinding time is 0.5-4 hours.

8. The double-modified ground calcium carbonate prepared by the preparation method according to any one of claims 1 to 7, characterized in that: The double-modified heavy calcium carbonate has the following characteristics: Oil absorption value: 19±2g / 100g, GB / T 19281; Bulk density: 0.65~0.75g / cm; Thixotropic index TI value: 2.0-2.5, ISO 3219 standard test.

9. Use of the double-modified GCC according to claim 8 in the preparation of silicone sealant, characterized in that: include, α,ω-dihydroxy polydimethylsiloxane and plasticizer dimethyl silicone oil were mixed uniformly in a planetary mixer; Add the double-modified GCC, mix at a low speed and then gradually increase the speed until homogeneous, then add gas-phase SiO2 to adjust the thixotropy, then add the crosslinking agent methyltrimethoxysilane, the catalyst dibutyltin dilaurate, and the coupling agent KH-550 / KH-560, vacuum stir until uniform and free of particles, and vacuum degas until there are no bubbles to obtain a mixed rubber material; After injection molding, the mixture was cured at room temperature for 24 hours, and then heated to 80° C. and cured for 2 hours to obtain a silicone sealant.

10. The use according to claim 9, characterized in that: Based on the mass of the raw materials, the content of the α,ω-dihydroxy polydimethylsiloxane is 100 parts, the content of the dimethyl silicone oil is 2-10 parts, the content of the double-modified GCC is 30-60 parts, the content of the crosslinking agent is 1-5 parts, the content of the catalyst is 0.1-0.5 parts, the content of the coupling agent is 0.5-2 parts, and the content of the added gas-phase SiO2 is 0.1-1 parts; The vacuum degree is -0.1 MPa, and the vacuuming time is 10-20 minutes.

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