Preparation method and application of composite modified calcium carbonate suitable for PVC (polyvinyl chloride) material

Abstract

The invention provides a preparation method and application of composite modified calcium carbonate suitable for a PVC (polyvinyl chloride) material. The preparation method comprises the following steps: preheating calcium carbonate powder to remove moisture and activate the surface; adding stearic acid under heating and stirring conditions to form a primary coating layer; then adding long-chain alkyl organic tin carboxylate to carry out coordination reaction with the stearic acid layer to construct a stable CaCO3-stearic acid-Sn-organic tin bridging structure; and finally cooling, sieving and packaging to obtain the composite modified calcium carbonate product. The selected long-chain alkyl organic tin carboxylate has the function of a polyvinyl chloride heat stabilizer, the compatibility of calcium carbonate and resin is improved after the long-chain alkyl organic tin carboxylate and stearic acid have a synergistic effect, and the modified calcium carbonate filler and the heat stabilizer are endowed with dual effects, so that the heat stabilization time of a polyvinyl chloride sample is prolonged; the addition amount of a traditional heat stabilizer is reduced, so that the overall formula cost is effectively reduced.

Description

TECHNICAL FIELD

[0001] The application relates to the field of surface modification of inorganic powder materials, in particular to a preparation method and application of composite modified calcium carbonate suitable for PVC materials. BACKGROUND

[0002] Calcium carbonate is an inorganic filler widely used in the plastic industry, which can reduce the cost of products and improve certain physical properties. However, due to the hydrophilic and oil-repellent characteristics of the surface of calcium carbonate, the compatibility of calcium carbonate with organic polymer materials such as polyvinyl chloride is poor, and direct filling often leads to a decrease in the mechanical properties of products; Most of the existing modification methods use stearic acid as a surface modifier. Although the cost is low and the process is simple, the modification layer is not firm because the stearic acid mainly relies on physical adsorption with calcium carbonate and is easy to fall off under high temperature and high shear conditions. Meanwhile, the function of stearic acid is single, which can only improve the interfacial compatibility and cannot endow the filler with additional properties such as thermal stability. Although some coupling agents such as titanate have good modification effect, they have the disadvantages of high price, easy hydrolysis and possible influence on the weather resistance of products; Therefore, the application provides a preparation method and application of composite modified calcium carbonate suitable for PVC materials. SUMMARY

[0003] Therefore, the application provides a preparation method and application of composite modified calcium carbonate suitable for PVC materials.

[0004] The technical scheme of the application is as follows: a preparation method of composite modified calcium carbonate suitable for PVC materials, comprising the following steps: S1, calcium carbonate powder is put into a high-speed mixer, heated to 100-120 DEG C, and continuously stirred at a speed of 800-1200 rpm for 5-10 minutes. The purpose of this step is to remove the adsorbed water and free water on the surface and pores of the calcium carbonate powder, prevent agglomeration or uneven coating in the subsequent reaction, activate the surface of the calcium carbonate particles through thermal excitation, and improve the surface energy and reactivity of the calcium carbonate particles to provide conditions for the adsorption of stearic acid molecules; The applicable calcium carbonate can be heavy calcium carbonate, light calcium carbonate or nano calcium carbonate, and the particle size range is usually 0.1-20 microns; S2, under the condition of keeping the temperature of the material, 0.5%-1.5% of stearic acid is added to the calcium carbonate powder treated in step S1, and the reaction is continued for 8-15 minutes under the condition of high-speed stirring at 1000-1500 rpm. The carboxyl part of the molten stearic acid is combined with the Ca 2+and the hydrophobic long-chain alkyl groups arrange outward to form a uniform and continuous organic coating layer on the surface of the particles, thus improving the surface wettability of the calcium carbonate; S3. Further adding long-chain alkyl organotin carboxylate accounting for 0.2% to 0.5% of the mass of the calcium carbonate to the material on the basis of the stearic acid coating layer, and stirring at a speed of 1000 to 1500 rpm for 10 to 20 minutes at 100 to 110°C; The chemical general formula of the organotin carboxylate is (R)nSn(OOC-17)4-n, wherein R is C4 to C12 alkyl, -OOC-17 is stearate, and n is 2 or 3, representing a common divalent or trivalent organotin compound. A typical implementation compound is monobutyltin tristearate or dioctyltin distearate, and the mechanism is that the Sn atom in the organotin forms a coordination bond with the oxygen atom of the carboxyl group of the stearic acid through an empty orbital, thereby combining with the stearic acid molecules that have been anchored on the surface of the CaCO3 to construct a bridging structure of “CaCO3-stearic acid-Sn-organotin”, which improves the stability of the modified layer and enables it to remain firm in a high-temperature and high-shear processing environment of polyvinyl chloride. S4. Cooling the composite-modified material to below 40°C, which can be achieved by natural cooling or air cooling to avoid degradation of the organotin carboxylate at high temperatures, and then sieving the cooled material to remove parts that are agglomerated or have abnormal particle sizes, to finally obtain a composite-modified calcium carbonate product with a uniform surface coating, which is then packaged for storage and transportation.

[0005] Further preferably, the calcium carbonate is heavy calcium carbonate, light calcium carbonate, or nano calcium carbonate, and the particle size range is 0.1 to 20 μm.

[0006] Further preferably, the calcium carbonate is preferably 2500-mesh heavy calcium carbonate or about 50-nm nano calcium carbonate.

[0007] Further preferably, the addition amount of the stearic acid is preferably 0.8% to 1.2% of the mass of the calcium carbonate.

[0008] Further preferably, the addition amount of the long-chain alkyl organotin carboxylate is preferably 0.2% to 0.3% of the mass of the calcium carbonate.

[0009] Further preferably, the preferred process conditions of steps S1 to S3 are a temperature of 105 to 110°C, a stirring speed of about 1100 rpm, and a single-step stirring time of 10 to 15 minutes.

[0010] Further preferably, the general formula of the long-chain alkyl organotin carboxylate is (R)nSn(OOC-17)4-n. wherein R is C4 to C12 alkyl, -OOC-17 is stearate, and n is 2 or 3.

[0011] Further preferably, the long-chain alkyl organotin carboxylate is selected from monobutyltin tristearate and dioctyltin distearate.

[0012] Further preferably, the composite modified calcium carbonate has the following performance parameters: oil absorption value less than 20 g / 100 g, activation degree greater than 95%, contact angle greater than 130°, and when 40 phr of the modified calcium carbonate is added to a 100 phr PVC system, the thermal stable decomposition time of the sample piece is extended to more than 14 minutes.

[0013] In addition, the application also provides the use of the composite modified calcium carbonate prepared by the method in PVC materials, wherein the PVC materials are selected from pipe materials, profile materials, cable materials, plate materials or injection molding products, and the composite modified calcium carbonate has the dual functions of a filler and a thermal stabilizer.

[0014] The embodiment of the application has the following advantages due to the adoption of the above technical solutions. The step-by-step composite modification method of stearic acid and long-chain alkyl organotin carboxylate is adopted in the application to form a stable "CaCO3-stearic acid-Sn-organotin" bridging structure on the surface of calcium carbonate, which overcomes the defects of the stearic acid modification layer in the prior art, such as easy falling off under high temperature and high shear conditions and single function, so that the modified layer is more firmly combined and can maintain the interface stability for a long time during the processing of polyvinyl chloride; at the same time, the long-chain alkyl organotin carboxylate selected itself has the function of a polyvinyl chloride thermal stabilizer, and after synergistic action with stearic acid, not only the compatibility of calcium carbonate and resin is improved, but also the modified calcium carbonate filler has the dual function of a thermal stabilizer, thereby extending the thermal stable time of the polyvinyl chloride sample piece, reducing the addition amount of the traditional thermal stabilizer, and further effectively reducing the overall formula cost.

[0015] The above summary is intended to illustrate the present description and is not intended to limit in any way. Further aspects, embodiments and features of the present application will be apparent from the drawings and the following detailed description. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0017] Figure 1 The flowchart of the method of the present application is shown in the figure. DETAILED DESCRIPTION

[0018] In the following, certain example embodiments are simply described. As those skilled in the art can recognize, the described embodiments can be modified in various different ways without departing from the spirit or scope of the present application. Therefore, the drawings and description are to be regarded as being illustrative in nature rather than restrictive.

[0019] The embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0020] As Figure 1 shown, the embodiments of the present application provide a method for preparing a composite modified calcium carbonate suitable for PVC materials, which comprises the following steps: S1, pre-treatment: the calcium carbonate powder to be modified is put into a high-speed mixer, heated to 100-120°C, and stirred at a speed of 800-1200 rpm for 5-10 minutes, so as to effectively remove the free water in the surface and pores of the powder, and activate the surface of the calcium carbonate particles, so as to increase the surface energy and provide conditions for subsequent adsorption and chemical action; S2, first-stage modification: under the condition of keeping the temperature of the material unchanged, 0.5%-1.5% of stearic acid, preferably 0.8%-1.2%, by mass of calcium carbonate is added to the material obtained in step S1, and the stirring is continued at a speed of 1000-1500 rpm for 8-15 minutes, so that the stearic acid is uniformly coated on the surface of the calcium carbonate particles after melting, and an initial anchoring layer is formed through the interaction of the carboxyl group and Ca2+; S3, second-stage modification: 0.2%-0.5% of long-chain alkyl organotin carboxylate, preferably 0.2%-0.3%, by mass of calcium carbonate is added to the coated material obtained in step S2, and the compound has a general formula of (R)nSn(OOC-17)4-n, wherein R is C4-C12 alkyl, -OOC-17 is stearate, and n is 2 or 3; commonly used compounds include monobutyltin tristearate or dioctyltin distearate; under the condition of 100-110°C, the stirring is continued at a speed of 1000-1500 rpm for 10-20 minutes, so that the organotin carboxylate and the carboxyl oxygen atom of the stearic acid layer are coordinated to build a firm composite interface layer; S4, cooling and discharging: the composite modified material obtained in step S3 is cooled to below 40°C, and is discharged after natural cooling or air cooling treatment, and the agglomerated particles are removed through a standard screen, and then are packaged to obtain the composite modified calcium carbonate product; The composite modified calcium carbonate obtained by the above method exhibits excellent compatibility and thermal stability in the PVC formula system, and can significantly prolong the thermal decomposition time of the PVC product while maintaining the mechanical properties; Example 1 Select 2500 mesh heavy calcium carbonate as raw material, put it into the high-speed mixer, heat to 105°C and stir at 1100 rpm for 8 minutes, complete preheating and dehydration; then add 1% of the mass of calcium carbonate stearic acid, continue to stir at 1100 rpm for 10 minutes, form a preliminary coating layer; then add 0.2% of the mass of calcium carbonate monobutyl tin tristearate, stir at 105°C for 15 minutes, get the composite modified calcium carbonate; After cooling to below 40°C, sieving and packaging, the product is prepared; Test results: oil absorption value 19 g / 100 g, activation degree 97%, contact angle 133°; Example 2 The operation is the same as example 1, the difference is that the amount of monobutyl tin tristearate added in the second stage modification is 0.3% of the mass of calcium carbonate; test results: oil absorption value 18 g / 100 g, activation degree 98%, contact angle 135°; Example 3 Select 2500 mesh heavy calcium carbonate, heat to 110°C, stir at 1100 rpm for 8 minutes to complete preheating; add 1% stearic acid, stir at 1100 rpm for 12 minutes to form a coating layer; then add 0.2% of the mass of calcium carbonate dioctyltin distearate, stir at 110°C for 15 minutes; After cooling, sieving and packaging, the modified calcium carbonate is obtained; Test results: oil absorption value 19 g / 100 g, activation degree 98%, contact angle 135°; Example 4 Select 2500 mesh heavy calcium carbonate, preheat and stearic acid modification according to steps S1 and S2, the conditions are the same as example 3, add 0.3% of the mass of calcium carbonate dioctyltin distearate in the second stage modification, stir at 110°C for 15 minutes; After cooling, sieving and packaging, the product is obtained; Test results: oil absorption value 19 g / 100 g, activation degree 99%, contact angle 132°; Comparative example 1 (unmodified calcium carbonate) Select 2500 mesh heavy calcium carbonate as raw material, without any surface treatment, directly used for testing; the oil absorption value of the calcium carbonate is 30 g / 100 g, the activation degree is 0%, and the contact angle is 20°, which shows that its surface hydrophilic and oil repellent properties are obvious, and it is difficult to be uniformly compatible with polyvinyl chloride resin; in the PVC formula system (100 phr PVC, 40 phr calcium carbonate powder), when the molding sample is heated in the oven at 190°C, discoloration begins to appear at 10 minutes, indicating that its thermal stability is poor; Comparative example 2 (only stearic acid modification) Select 2500 mesh heavy calcium carbonate as raw material, put into high-speed mixer heated to 105℃, stirring at 1100 rpm for 8 minutes to complete the preheating; to which add 1% of the mass of calcium carbonate stearic acid, continue to stir at 1100 rpm for 10 minutes, form a stearic acid coating, then directly cooled to below 40℃, sieving and packaging, to obtain stearic acid modified calcium carbonate; test results show: oil absorption value is 20g / 100g, activation degree 94%, contact angle 120°; in the formula of 100 phr PVC + 40 phr modified calcium carbonate, the sample is heated at 190℃ for 11-12 minutes to decompose, compared with the unmodified sample, it is improved, but the modified layer is easy to partially fall off at high temperature, and the thermal stability is still not ideal; Comparative Example 3 (only organic tin modification) Select 2500 mesh heavy calcium carbonate as raw material, put into high-speed mixer heated to 105℃, stirring at 1100 rpm for 8 minutes to complete the preheating; to which add 1% of the mass of calcium carbonate stearic acid, continue to stir at 1100 rpm for 10 minutes, form a stearic acid coating, then directly cooled to below 40℃, sieving and packaging, to obtain stearic acid modified calcium carbonate; test results show: oil absorption value is 20g / 100g, activation degree 94%, contact angle 120°; in the formula of 100 phr PVC + 40 phr modified calcium carbonate, the sample is heated at 190℃ for 11-12 minutes to decompose, compared with the unmodified sample, it is improved, but the modified layer is easy to partially fall off at high temperature, and the thermal stability is still not ideal; Test Example To verify the effect of the composite modification method of the present application, the performance of the composite modified calcium carbonate prepared in Examples 1-4 is compared with the samples obtained in Comparative Examples 1-3, and the test items include oil absorption value, activation degree, contact angle and thermal stability in PVC formula system; 1. Oil absorption value test The standard method of GB / T16913 is adopted, dioctyl phthalate (DOP) is used as oil absorption agent, the sample is placed in a standard oil absorption instrument, DOP is added dropwise under the specified conditions until the material appears obvious agglomeration, the DOP consumption is recorded and converted into the oil absorption value (g / 100g) per 100g of sample; 2. Activation degree test The sedimentation method is adopted, a certain amount of calcium carbonate sample is accurately weighed and added to a xylene solution, after oscillation for a certain time under constant temperature conditions, the sample is placed, the dispersion and sedimentation of calcium carbonate in xylene is measured, and the modified activation degree (%) of the surface of calcium carbonate is calculated; 3. Contact angle test The contact angle measuring instrument is adopted, the sample is pressed into a flat sheet with a diameter of 30mm and a thickness of 2mm under the tablet press; deionized water is added on the surface of the sample, the static contact angle of the water droplet on the sample surface is measured by using an optical imaging system, and the average value is taken as the final result; 4. Thermal stability test The sample was prepared according to the conventional formula of PVC, specifically 100 phr PVC resin, 40 phr modified or unmodified calcium carbonate powder, supplemented with conventional plasticizer and lubricant; first mixed uniformly on an open mill, then formed into a 30 mm x 30 mm x 2 mm sample sheet by a laminating machine; the sample sheet was placed in a 190℃ oven, and every 1 minute a sample sheet was taken out, the color b value change was detected using an ECL Ci60 color difference meter, when the b value changed ≥0.5 from the initial value, it was determined that decomposition began; the corresponding time was recorded as the thermal stability time.

[0021] Table 1: Result summary table

[0022] From the data in the table, it can be seen that: The unmodified calcium carbonate (Comparative Example 1) has a high oil absorption value, an activation degree of zero, and a contact angle of only 20°, and the thermal stability time in the PVC system is only 10 minutes, showing the worst performance.

[0023] Single stearic acid modification (Comparative Example 2) can increase the activation degree to 94% and the contact angle to 120°, but the modified layer is unstable at high temperature, and the thermal stability time is only extended to 11-12 minutes.

[0024] Single organotin modification (Comparative Example 3) has certain thermal stability, but the interface is not well combined, the activation degree is only 30%, and the contact angle is 90°, with limited effect.

[0025] The composite modified examples 1-4 of the present application are significantly better than the comparative examples in terms of oil absorption value, activation degree, contact angle and thermal stability: the oil absorption value is reduced to ≤19 g / 100 g, the activation degree reaches 97%-99%, the contact angle is increased to 132°-135°, and the thermal stability time of the sample sheet in the PVC system is extended to more than 14 minutes.

[0026] Therefore, by synergistic composite modification of stearic acid and long-chain alkyl organotin carboxylate, the surface stability and multifunctionality of calcium carbonate are significantly improved, proving the application advantage in PVC materials.

[0027] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of various changes or substitutions within the technical scope disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for preparing composite modified calcium carbonate suitable for PVC materials, characterized in that: Includes the following steps: S1. Preheating treatment: Put the calcium carbonate powder into a high-speed mixer, heat it to 100-120°C, and stir it at 800-1200 rpm for 5-10 minutes to remove moisture and activate the surface of calcium carbonate particles. S2, First step modification: Under the condition of maintaining the temperature, add stearic acid of 0.5% to 1.5% of the mass of calcium carbonate to the material obtained in step S1, and stir at 1000 to 1500 rpm for 8 to 15 minutes to make the molten stearic acid uniformly coat the surface of the calcium carbonate particles to form a basic coating layer. S3. Second step modification: Add 0.2% to 0.5% of long-chain alkyl organotin carboxylate by mass of calcium carbonate to the material obtained in step S2, and stir at 1000 to 1500 rpm for 10 to 20 minutes at 100 to 110°C to allow the organotin carboxylate to coordinate with the stearic acid layer to form a strong composite modified layer. S4. Cooling and Discharging: Cool the modified calcium carbonate obtained in step S3 to below 40°C, discharge it after natural cooling or air cooling, sieve it and package it to obtain the composite modified calcium carbonate product.

2. The method for preparing composite modified calcium carbonate suitable for PVC materials according to claim 1, characterized in that: The calcium carbonate is heavy calcium carbonate, light calcium carbonate, or nano calcium carbonate, with a particle size range of 0.1–20 μm.

3. The method for preparing composite modified calcium carbonate suitable for PVC materials according to claim 2, characterized in that: The calcium carbonate is preferably 2500 mesh heavy calcium carbonate or about 50 nm nano calcium carbonate.

4. The method for preparing composite modified calcium carbonate suitable for PVC materials according to claim 1, characterized in that: The amount of stearic acid added is preferably 0.8% to 1.2% of the mass of calcium carbonate.

5. The method for preparing composite modified calcium carbonate suitable for PVC materials according to claim 1, characterized in that: The preferred amount of the long-chain alkyl organotin carboxylate added is 0.2% to 0.3% of the mass of calcium carbonate.

6. The method for preparing composite modified calcium carbonate suitable for PVC materials according to claim 1, characterized in that: The preferred process conditions for steps S1 to S3 are: temperature 105 to 110°C, stirring speed approximately 1100 rpm, and stirring time for each step 10 to 15 minutes.

7. The method for preparing composite modified calcium carbonate suitable for PVC materials according to claim 1, characterized in that: The general formula of the long-chain alkyl organotin carboxylate is (R)nSn(OOC-17)4-n; Wherein: R is a C4 to C12 alkyl group, -OOC-17 is a stearate group, and n is 2 or 3.

8. The method for preparing composite modified calcium carbonate suitable for PVC materials according to claim 7, characterized in that: The long-chain alkyl organotin carboxylate is selected from monobutyltin tristearate and dioctyltin distearate.

9. The method for preparing composite modified calcium carbonate suitable for PVC materials according to claim 1, characterized in that: The composite modified calcium carbonate has the following performance parameters: oil absorption value less than 20g / 100g, activation degree greater than 95%, contact angle greater than 130°, and when 40 phr of modified calcium carbonate is added to a 100 phr PVC system, the thermal stability decomposition time of the sample is extended to more than 14 minutes.

10. The application of the composite modified calcium carbonate prepared according to any one of claims 1 to 9 in PVC materials, characterized in that: The PVC material is selected from pipes, profiles, cable materials, sheets or injection molded products, and the composite modified calcium carbonate has the dual functions of filler and heat stabilizer.

Images