High clarity low crystallinity thermoformed polypropylene resin and process for its preparation

Abstract

The application discloses a kind of high transparency low isotacticity thermoforming polypropylene resin and its preparation process, it is related to polypropylene resin technical field, including the following process steps: polypropylene, transparent nucleating agent, antistatic agent, antioxidant, lubricant and ultraviolet absorber melt blend, extrusion into sheet, thermoforming, obtain thermoforming polypropylene resin;The thermoforming polypropylene resin also includes modified polypropylene resin;The modified polypropylene resin is obtained by mixing, co-extrusion of polypropylene, graft and peroxide.The application utilizes graft to modify polypropylene, introduces polar long branched chain segment on nonpolar polypropylene molecular chain by chemical method, produces steric hindrance, destroys the local regular arrangement of methyl, polypropylene local conformation disorder, polypropylene molecular chain movement is limited, crystallization area reduces, spherulite is refined, light scattering, Mie scattering reduces, and the transparency of the prepared polypropylene resin rises.

Description

Technical Field

[0001] This invention relates to the field of polypropylene resin technology, specifically to a high-transparency, low-isotacticity thermoforming polypropylene resin and its preparation process. Background Technology

[0002] Thermoforming is a processing technology that involves heating and softening plastic sheets, then using pressure such as vacuum, air pressure, or mechanical force to shape them into a mold, and finally cooling to obtain the finished product. It transforms sheet materials into three-dimensional products through heat-pressure molding. Commonly used materials include polypropylene (PP), polystyrene (PS), polyethylene terephthalate-1,4-cyclohexanediol (PETG), acrylonitrile-styrene-butadiene copolymer (ABS), and polyvinyl chloride (PVC). As one of the most widely used resin materials in industry, polypropylene has the characteristics of low cost, corrosion resistance, and easy recycling. Conventional polypropylene is isotactic polypropylene, with its isotacticity (the spatial regularity of methyl groups in the molecular chain) typically around 95%. However, the isotacticity of polypropylene has a significant impact on its transparency. Polypropylene with high regularity has a highly ordered molecular chain arrangement, which easily forms large spherulites. Since the size of the spherulites is close to the wavelength of visible light, it will induce light scattering, resulting in high haze and low transmittance, exhibiting low transparency. Therefore, we propose a high-transparency, low-isotacticity thermoforming polypropylene resin and its preparation process. Summary of the Invention

[0003] The purpose of this invention is to provide a high-transparency, low-isotacticity thermoforming polypropylene resin and its preparation process, so as to solve the problems mentioned in the background art.

[0004] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a high-transparency, low-isotacticity thermoforming polypropylene resin, comprising the following components: by mass percentage, 0.1% to 0.5% transparent nucleating agent and 0.3% to 0.7% additives, with the balance being polypropylene.

[0005] Furthermore, the additives include 0.1% to 0.3% antistatic agent, 0.05% to 0.10% antioxidant, 0.1% to 0.2% lubricant, and 0% to 0.1% ultraviolet absorber.

[0006] Furthermore, the isotacticity of the polypropylene is 50%–95%. Low isotactic polypropylene resin can reduce crystallinity and improve the transparency of the resulting thermoformed polypropylene resin.

[0007] Furthermore, the transparent nucleating agent is selected from one of the following sorbitol-based nucleating agents: dibenzylsorbitol, bis(3,4-dimethylbenzylmethylene)sorbitol, dibenzylidene sorbitol, or sodium benzoate. Choosing a transparent nucleating agent can refine the grain size, reduce light scattering, and decrease the haze of the material, thereby improving its transparency.

[0008] Furthermore, the antistatic agent is selected as glyceryl monostearate. The antistatic agent is used to prevent electrostatic adsorption of dust during the thermoforming process.

[0009] Furthermore, the antioxidant is selected from one or more of antioxidant 1010, antioxidant 168, antioxidant 242, antioxidant 3114, antioxidant 1330, and antioxidant THP-EPQ;

[0010] Furthermore, the antioxidant is a mixture of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1. The antioxidant is used to inhibit oxidation caused by processing heat.

[0011] Furthermore, the lubricant is selected from one or more of calcium stearate, zinc stearate, talc, and calcium carbonate. The lubricant is used to improve melt flowability.

[0012] Furthermore, the ultraviolet absorber is selected as UV-531. The ultraviolet absorber is used to improve weather resistance.

[0013] A process for preparing a high-transparency, low-isotacticity thermoforming polypropylene resin includes the following steps:

[0014] Polypropylene, a transparent nucleating agent, an antistatic agent, an antioxidant, a lubricant, and an ultraviolet absorber are melt-blended, extruded into sheets, and thermoformed to obtain thermoformed polypropylene resin.

[0015] Furthermore, the melt blending process conditions are: temperature 180–220°C, rotation speed 200–300 rpm. Melt blending uniformly disperses the polypropylene matrix, nucleating agent, and additives.

[0016] Furthermore, the extrusion sheeting process conditions are: die temperature 200–230°C, cooling roller temperature 30–50°C, forming a sheet. The extrusion sheeting process reduces the crystallinity of the produced thermoformed polypropylene resin and improves its transparency.

[0017] Furthermore, the thermoforming process conditions are as follows: the sheet is preheated to 140–160°C, compressed under a pressure of 0.5–0.8 MPa, and then cooled at a cooling rate of 30–50°C / s. Thermoforming rapidly shapes the sheet, reducing the crystalline size of the resulting thermoformed polypropylene resin.

[0018] Furthermore, the polypropylene may be partially or wholly replaced with modified polypropylene resin.

[0019] Furthermore, the thermoforming polypropylene resin comprises the following components by mass percentage: 20%–40% modified polypropylene resin, 5%–10% nano silica, 0%–8% compatibilizer, 0.1%–0.5% transparent nucleating agent, 0.3%–0.7% additives, and the balance being polypropylene;

[0020] The compatibilizer is maleic anhydride-grafted polypropylene (PP-g-MAH).

[0021] Furthermore, the modified polypropylene resin is prepared by the following process: mixing polypropylene and graft material, adding peroxide, and co-extruding to obtain the modified polypropylene resin.

[0022] Furthermore, the modified polypropylene resin comprises the following components by weight: 100 parts polypropylene, 1 to 10 parts grafted material, and 0.1 to 1.0 parts peroxide.

[0023] Furthermore, the grafting material is one or more of the following: ethylene-octene copolymer, random copolymer polypropylene, ethylene-vinyl acetate copolymer, polymethylpentene, cyclic olefin copolymer, polyphenylene ethylene, and ethylene-tetrafluoroethylene copolymer.

[0024] The peroxide is one or a mixture of dicumyl peroxide, benzoyl peroxide, di-tert-butyl peroxide, and 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane.

[0025] Furthermore, in the co-extrusion process, the extrusion temperature is 170–190℃, the rotation speed is 250–350 rpm, and the duration is 3–5 min.

[0026] Furthermore, the graft compound is a long-chain fluorinated compound, specifically prepared by the following process:

[0027] 2,3-Dibromosuccinic acid was mixed with perfluoroalkyl ethanol, p-toluenesulfonic acid was added, and the mixture was heated to 75–80 °C and stirred for 1.5–3.0 h. Sodium bicarbonate was added for neutralization, and the mixture was washed with a hexane / ethyl acetate mixture. The mixture was dried at 40–50 °C and 0.1 MPa, and chromatographically analyzed to obtain 2,3-dibromosuccinate. 2,3-Dibromosuccinate and ethanol were mixed, potassium hydroxide was added, and the mixture was heated to 70–80 °C and refluxed for 3–4 h. The mixture was extracted with ethyl acetate, washed with water, dried, and chromatographically analyzed to obtain butynedic acid diester.

[0028] Butynedioic acid diester was dissolved in xylene, cyclopentadiene was added, and the mixture was heated to 120-130°C and stirred for 6-8 hours. The solvent was removed under reduced pressure, and the mixture was purified by vacuum distillation to obtain norbornene monomer.

[0029] Toluene, norbornene monomer, and catalyst are mixed, ethylene is introduced, the temperature is raised to 88–93 °C, and the reaction is carried out for 100–150 min to obtain the grafted product.

[0030] Furthermore, the molar ratio of 2,3-dibromosuccinic acid to perfluoroalkyl ethanol is 1:(1.1 to 1.5).

[0031] The mass ratio of 2,3-dibromosuccinic acid to p-toluenesulfonic acid is 100:(6-12).

[0032] Furthermore, the ratio of 2,3-dibromosuccinate to ethanol is 10–15 g / 100 mL;

[0033] The molar ratio of 2,3-dibromosuccinate to sodium hydroxide is 1:(2.2-2.5).

[0034] Furthermore, the molar ratio of cyclopentadiene to butynedioic acid diester is (1.4–1.6):1;

[0035] The ratio of butynedioic acid diester to toluene is (4-5) g / 100mL.

[0036] Furthermore, the concentration of norbornene monomer in toluene is 0.2–1.0 M;

[0037] Ethylene pressure 6–10 bar;

[0038] The concentration of the catalyst in toluene is 0.1–2.0 mM;

[0039] The catalyst is a nickel catalyst or a metallocene catalyst.

[0040] Furthermore, cyclopentadiene is obtained by pyrolyzing dicyclopentadiene at 170°C.

[0041] In the above technical solution, the peroxide decomposes during high-temperature co-extrusion to generate free radicals. Tertiary hydrogen atoms in the co-extruded polypropylene molecular chain segments are stripped, generating polypropylene monomer free radicals, which react with the grafting material to obtain the grafted product, denoted as modified polypropylene. Introducing polar, long-branched segments into the non-polar polypropylene molecular chain through chemical methods creates steric hindrance, interferes with the directional arrangement of methyl groups on the polypropylene molecular chain, disrupts the original isotactic sequence regularity of polypropylene, and generates local stereochemical defects, resulting in local conformational disorder.

[0042] Meanwhile, polar branched segments hinder the close arrangement of polypropylene molecular chains, reduce the size of crystalline regions, disrupt crystal regularity, decrease crystallinity, increase amorphous regions, and reduce light scattering, resulting in a decrease in isotacticity test values ​​(since isotacticity is usually characterized by its correlation with crystallinity). Furthermore, they can refine spherulite size and suppress the formation of large spherulites, thereby reducing the haze and increasing the transparency of the resulting polypropylene resin. Additionally, during the melt blending of low-isotactic polypropylene resin, the branched segments in the low-isotactic polypropylene resin increase the entanglement between molecular chains, promoting the dissociation of locally regular segments of the polypropylene molecular chains through shear forces, further demonstrating a decrease in isotacticity, resulting in reduced haze and increased transparency of the resulting polypropylene resin.

[0043] 2,3-Dibromosuccinic acid reacts with perfluoroalkyl ethanol in the presence of p-toluenesulfonic acid, and the resulting product (denoted as 2,3-dibromosuccinate) is saponified with potassium hydroxide to form KBr, yielding butynedioic acid diester. Butynedioic acid diester reacts with cyclopentadiene to generate norbornene monomer; this monomer is then introduced into an ethylene polymer to prepare a grafted product with long chains, rigid norbornene rings, and fluorine. Its rigid cyclic structure, inserted into the polypropylene chain segments, disrupts the local regularity of the methyl groups, and the steric hindrance of the side chains further interferes with the chain segment order, causing a decrease in the isotacticity of the polypropylene. Simultaneously, the norbornene ring hinders the movement of the polypropylene chain segments, and the fluorinated alkyl chains can act as weak nucleation sites, refining the spherulite size, reducing crystallinity, and decreasing light scattering and Mie scattering. The refractive index is similar to that of polypropylene, reducing interfacial scattering, resulting in lower haze and increased transparency in the prepared polypropylene resin. Meanwhile, grafting the graft onto the polypropylene molecular chain introduces long side chains, which can further enhance the impact resistance of polypropylene, reduce the surface energy of thermoformed polypropylene resin, improve its resistance to water and oil, and enhance its antifouling and self-cleaning properties.

[0044] As the amount of modified polypropylene resin used increases, the graft structure in the modified polypropylene resin may undergo microphase separation with the polypropylene chain segments, causing a deterioration in light transmittance and haze. Therefore, it is necessary to improve its compatibility and control the amount of modified polypropylene resin used. Detailed Implementation

[0045] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0046] In the following specific embodiments, the number of “parts” refers to parts by mass, unless otherwise specified.

[0047] Nano silica: average particle size 20nm, surface area 200±30m3 / g;

[0048] Polypropylene: LH1148-02N.X, isotacticity 91.8%, melt index 1.75g / 10min (2.16kg, 230℃), sourced from Dongguan Juzhengyuan Technology Co., Ltd.

[0049] The transparent nucleating agent is dibenzyl sorbitol; the additives include 0.2% antistatic agent, 0.1% antioxidant, 0.15% lubricant, and 0.05% UV absorber; the antistatic agent is glyceryl monostearate; the antioxidant is a mixture of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1; the lubricant is calcium stearate; the UV absorber is UV-531; the compatibilizer is maleic anhydride-grafted polypropylene (PP-g-MAH); the peroxide is 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane; cyclopentadiene is obtained by cracking dicyclopentadiene at 170℃; the catalyst is nickel catalyst α-diimine nickel.

[0050] Example 1: A preparation process for a high-transparency, low-isotacticity thermoforming polypropylene resin, comprising the following steps:

[0051] Step 1: Preparation of modified polypropylene resin

[0052] 2,3-Dibromosuccinic acid was mixed with perfluoroalkyl ethanol, p-toluenesulfonic acid was added, the mixture was heated to 75°C, and stirred for 3.0 h. Sodium bicarbonate was added for neutralization, and the mixture was washed with a hexane / ethyl acetate mixture, dried at 40°C and 0.1 MPa, and subjected to chromatography to obtain 2,3-dibromosuccinic acid ester. The molar ratio of 2,3-dibromosuccinic acid to perfluoroalkyl ethanol was 1:1.1; the mass ratio of 2,3-dibromosuccinic acid to p-toluenesulfonic acid was 100:6.

[0053] 2,3-Dibromosuccinate and ethanol were mixed, potassium hydroxide was added, and the mixture was heated to 70°C and refluxed for 4 hours. The mixture was extracted with ethyl acetate, washed with water, dried, and subjected to chromatography to obtain butynedic acid diester. The ratio of 2,3-dibromosuccinate to ethanol was 15 g / 100 mL, and the molar ratio of 2,3-dibromosuccinate to sodium hydroxide was 1:2.2.

[0054] Butynedioic acid diester was dissolved in xylene, cyclopentadiene was added, and the mixture was heated to 120°C and stirred for 8 hours. The solvent was removed under reduced pressure, and the mixture was purified by vacuum distillation to obtain norbornene monomer. The molar ratio of cyclopentadiene to butynedioic acid diester was 1.4:1, and the ratio of butynedioic acid diester to toluene was 5 g / 100 mL.

[0055] Toluene, norbornene monomer, and catalyst were mixed, ethylene was introduced, the temperature was raised to 88°C, and the reaction was carried out for 150 min to obtain the grafted product; the concentration of norbornene monomer in toluene was 0.2 M; the ethylene pressure was 10 bar; and the concentration of catalyst in toluene was 1 mM.

[0056] Mix 100 parts of polypropylene and 1 part of graft material, add 0.1 parts of peroxide, co-extrude at 170℃, 250 rpm, and 5 min to obtain modified polypropylene resin.

[0057] Step 2: Preparation of thermoforming polypropylene resin:

[0058] Polypropylene, modified polypropylene resin, nano-silica, compatibilizer, transparent nucleating agent, and additives are melt-blended under the following conditions: temperature 180℃, rotation speed 200 rpm. The mixture is then extruded into sheets under the following conditions: die temperature 200℃, cooling roller temperature 30℃. Finally, the sheets are thermoformed under the following conditions: the sheets are preheated to 140℃, compressed at a pressure of 0.8 MPa, and then cooled to room temperature at a cooling rate of 30℃ / s to obtain thermoformed polypropylene resin. The polypropylene resin comprises the following components by mass percentage: 20% modified polypropylene resin, 5% nano-silica, 2% compatibilizer, 0.5% transparent nucleating agent, 0.5% additives, and the balance being polypropylene.

[0059] Example 2: A preparation process for a high-transparency, low-isotacticity thermoforming polypropylene resin, comprising the following steps:

[0060] Step 1: Preparation of modified polypropylene resin

[0061] 2,3-Dibromosuccinic acid was mixed with perfluoroalkyl ethanol, p-toluenesulfonic acid was added, the mixture was heated to 78°C, and stirred for 2.5 h. Sodium bicarbonate was added for neutralization, and the mixture was washed with a hexane / ethyl acetate mixture, dried at 45°C and 0.1 MPa, and subjected to chromatography to obtain 2,3-dibromosuccinic acid ester. The molar ratio of 2,3-dibromosuccinic acid to perfluoroalkyl ethanol was 1:1.3; the mass ratio of 2,3-dibromosuccinic acid to p-toluenesulfonic acid was 100:9.

[0062] 2,3-Dibromosuccinate and ethanol were mixed, potassium hydroxide was added, and the mixture was heated to 75°C and refluxed for 3.5 h. The mixture was then extracted with ethyl acetate, washed with water, dried, and subjected to chromatography to obtain butynedic acid diester. The ratio of 2,3-dibromosuccinate to ethanol was 12 g / 100 mL, and the molar ratio of 2,3-dibromosuccinate to sodium hydroxide was 1:2.4.

[0063] Butynedioic acid diester was dissolved in xylene, cyclopentadiene was added, and the mixture was heated to 125°C and stirred for 7 hours. The solvent was removed under reduced pressure, and the mixture was purified by vacuum distillation to obtain norbornene monomer. The molar ratio of cyclopentadiene to butynedioic acid diester was 1.5:1, and the ratio of butynedioic acid diester to toluene was 4.5 g / 100 mL.

[0064] Toluene, norbornene monomer, and catalyst were mixed, ethylene was introduced, the temperature was raised to 90°C, and the reaction was carried out for 120 min to obtain the grafted product; the concentration of norbornene monomer in toluene was 0.6 M; the ethylene pressure was 8 bar; and the concentration of catalyst in toluene was 1.5 mM.

[0065] 100 parts of polypropylene and 3 parts of grafted material were mixed, and 0.30 parts of peroxide were added. The mixture was co-extruded at a temperature of 180℃, a speed of 300 rpm, and a time of 4 min to obtain modified polypropylene resin.

[0066] Step 2: Preparation of thermoforming polypropylene resin:

[0067] Polypropylene, modified polypropylene resin, nano-silica, compatibilizer, transparent nucleating agent, and additives are melt-blended under the following conditions: temperature 200℃, rotation speed 250 rpm. The mixture is then extruded into sheets under the following conditions: die temperature 210℃, cooling roller temperature 40℃. Finally, the sheets are thermoformed under the following conditions: the sheets are preheated to 150℃, compressed at a pressure of 0.6 MPa, and then cooled to room temperature at a cooling rate of 40℃ / s to obtain thermoformed polypropylene resin. The polypropylene resin comprises the following components by mass percentage: 30% modified polypropylene resin, 8% nano-silica, 4% compatibilizer, 0.5% transparent nucleating agent, 0.5% additives, and the balance being polypropylene.

[0068] Example 3: A preparation process for a high-transparency, low-isotacticity thermoforming polypropylene resin, comprising the following steps:

[0069] Step 1: Preparation of modified polypropylene resin

[0070] 2,3-Dibromosuccinic acid was mixed with perfluoroalkyl ethanol, p-toluenesulfonic acid was added, the mixture was heated to 80 °C, and stirred for 1.5 h. Sodium bicarbonate was added for neutralization, and the mixture was washed with a hexane / ethyl acetate mixture, dried at 50 °C and 0.1 MPa, and subjected to chromatography to obtain 2,3-dibromosuccinic acid ester. The molar ratio of 2,3-dibromosuccinic acid to perfluoroalkyl ethanol was 1:1.5; the mass ratio of 2,3-dibromosuccinic acid to p-toluenesulfonic acid was 100:12.

[0071] 2,3-Dibromosuccinate and ethanol were mixed, potassium hydroxide was added, and the mixture was heated to 80°C and refluxed for 3 hours. The mixture was then extracted with ethyl acetate, washed with water, dried, and subjected to chromatography to obtain butynedic acid diester. The ratio of 2,3-dibromosuccinate to ethanol was 10 g / 100 mL, and the molar ratio of 2,3-dibromosuccinate to sodium hydroxide was 1:2.5.

[0072] Butynedioic acid diester was dissolved in xylene, cyclopentadiene was added, and the mixture was heated to 130°C and stirred for 6 hours. The solvent was removed under reduced pressure, and the mixture was purified by vacuum distillation to obtain norbornene monomer. The molar ratio of cyclopentadiene to butynedioic acid diester was 1.6:1, and the ratio of butynedioic acid diester to toluene was 4 g / 100 mL.

[0073] Toluene, norbornene monomer, and catalyst were mixed, ethylene was introduced, the temperature was raised to 93°C, and the reaction was carried out for 100 min to obtain the grafted product; the concentration of norbornene monomer in toluene was 1.0 M; the ethylene pressure was 6 bar; and the concentration of catalyst in toluene was 2 mM.

[0074] 100 parts of polypropylene and 6 parts of grafted material were mixed, and 0.6 parts of peroxide were added. The mixture was co-extruded at a temperature of 190℃, a speed of 350 rpm, and a time of 3 min to obtain modified polypropylene resin.

[0075] Step 2: Preparation of thermoforming polypropylene resin:

[0076] Polypropylene, modified polypropylene resin, nano-silica, compatibilizer, transparent nucleating agent, and additives are melt-blended under the following conditions: temperature 220℃, rotation speed 300 rpm. The mixture is then extruded into sheets under the following conditions: die temperature 230℃, cooling roller temperature 50℃. Finally, the sheets are thermoformed under the following conditions: the sheets are preheated to 160℃, compressed at a pressure of 0.5 MPa, and then cooled to room temperature at a cooling rate of 50℃ / s to obtain thermoformed polypropylene resin. The polypropylene resin comprises the following components by mass percentage: 40% modified polypropylene resin, 10% nano-silica, 8% compatibilizer, 0.5% transparent nucleating agent, 0.5% additives, and the balance being polypropylene.

[0077] Comparative Example 1: A preparation process for a high-transparency, low-isotacticity thermoforming polypropylene resin, comprising the following steps:

[0078] Step 1: Preparation of modified polypropylene resin

[0079] Dimethyl butyne dicarboxylate was dissolved in xylene, cyclopentadiene was added, and the mixture was heated to 120°C and stirred for 8 hours. The solvent was removed under reduced pressure, and the mixture was purified by vacuum distillation to obtain norbornene monomer. The molar ratio of cyclopentadiene to dimethyl butyne dicarboxylate was 1.4:1, and the ratio of dimethyl butyne dicarboxylate to toluene was 5 g / 100 mL.

[0080] Toluene, norbornene monomer, and catalyst were mixed, ethylene was introduced, the temperature was raised to 88°C, and the reaction was carried out for 150 min to obtain the grafted product; the concentration of norbornene monomer in toluene was 0.2 M; the ethylene pressure was 10 bar; and the concentration of catalyst in toluene was 1 mM.

[0081] Mix 100 parts of polypropylene and 1 part of graft material, add 0.1 parts of peroxide, co-extrude at 170℃, 250 rpm, and 5 min to obtain modified polypropylene resin.

[0082] Step 2: The preparation of thermoforming polypropylene resin is the same as in Example 1, to obtain thermoforming polypropylene resin.

[0083] Comparative Example 2: A preparation process for a high-transparency, low-isotacticity thermoforming polypropylene resin, comprising the following process steps:

[0084] Step 1: Preparation of modified polypropylene resin

[0085] Mix 100 parts of polypropylene and 1 part of graft (maleic anhydride), add 0.1 parts of peroxide, co-extrude at 170℃, 250 rpm, and 5 min to obtain modified polypropylene resin.

[0086] Step 2: The preparation of thermoforming polypropylene resin is the same as in Example 1, to obtain thermoforming polypropylene resin.

[0087] Comparative Example 3: A preparation process for a high-transparency, low-isotacticity thermoforming polypropylene resin, comprising the following process steps:

[0088] Polypropylene, a transparent nucleating agent, and additives are melt-blended under the following conditions: temperature 180℃, rotation speed 200 rpm. The mixture is then extruded into sheets under the following conditions: die temperature 200℃, cooling roller temperature 30℃. Finally, the sheets are thermoformed under the following conditions: the sheets are preheated to 140℃, compressed at a pressure of 0.8 MPa, and then cooled to room temperature at a cooling rate of 30℃ / s to obtain thermoformed polypropylene resin. The polypropylene resin comprises the following components by mass percentage: 0.5% transparent nucleating agent, 0.5% additives, and the balance being polypropylene.

[0089] Experiment: The thermoforming polypropylene resins obtained in Examples 1-3 and Comparative Examples 1-3 were used to prepare samples. Their properties were tested and the test results were recorded.

[0090] Transparency test: The transmittance and haze of thermoformed polypropylene resin samples were tested with reference to GB / T 2410.

[0091] Mechanical property testing: The tensile strength and impact strength of thermoformed polypropylene resin samples were tested with reference to GB / T 1040.1 and GB / T 1043.1. In the tensile strength test, the test specimen was dumbbell-shaped and the tensile rate was 50 mm / min. In the impact strength test, the cantilever beam impact test was adopted and the specimen was an unnotched specimen.

[0092] Contact angle test: Deionized water and n-hexadecane were dropped onto the surface of the thermoformed polypropylene resin sample to test its water contact angle and oil contact angle. The liquid volume was 3 μL.

[0093] Isotacticity test: Using ISO 9113 as the reference standard, the isotacticity of polypropylene and modified polypropylene resin samples is tested, and the isotacticity change rate of modified polypropylene resin after modification is calculated.

[0094] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Light transmittance (%) 89.2 91.5 90.8 86.4 84.7 82.3 Haze (%) 18.5 15.2 16.8 25.3 28.6 35.4 Tensile strength (MPa) 28.5 26.8 25.3 32.4 30.1 35.6 Impact strength (J / m) 62.2 65.7 69.4 55.5 52.2 45.6 Water contact angle (°) 118.5±1.2 122.7±1.0 125.4±0.9 95.2±1.5 88.6±1.8 82.3±2.0 Oil contact angle (°) 75.3±0.8 78.6±1.1 82.1±0.9 45.7±1.3 40.2±1.5 35.8±1.7 Isotacticity reduction (%) 6.5% 8.1% 9.7% 3.6% 2.3% /

[0095] Based on the data in the table above, the following conclusions can be clearly drawn:

[0096] The thermoforming polypropylene resins obtained in Examples 1-3 were compared with those obtained in Comparative Examples 1-3. The test results show that:

[0097] Compared with Comparative Example 3, the thermoforming polypropylene resins obtained in Examples 1-3 exhibit higher light transmittance and lower haze, higher water and oil contact angles, and better mechanical properties. This fully demonstrates that the present invention improves the transparency of the prepared thermoforming polypropylene resin and enhances its impact resistance and stain resistance.

[0098] Compared to Example 1, the grafting agents used in the modified polypropylene resins of Comparative Examples 1-2 were different, while the polypropylene in Comparative Example 3 was unmodified. The thermoforming polypropylene resins obtained in Comparative Examples 1-3 showed decreased light transmittance, impact strength, and water / oil contact angle, while exhibiting increased haze. This demonstrates that the modification process and the composition of the polypropylene resins used in this invention can promote a combined improvement in the transparency, impact resistance, and antifouling properties of the resulting thermoforming polypropylene resins.

[0099] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A process for the preparation of a high clarity low isotacticity thermoformed polypropylene resin characterized by: The preparation process comprises the following steps: polypropylene, transparent nucleating agent, antistatic agent, antioxidant, lubricant and ultraviolet absorber are melt blended, extruded into a sheet, thermoformed to obtain a thermoformed polypropylene resin; The thermoformed polypropylene resin further comprises a modified polypropylene resin; the modified polypropylene resin is obtained by mixing, co-extruding polypropylene, grafting agent and peroxide; The grafting agent is prepared by the following process: dissolve the dibutynyl acid diester in xylene, add cyclopentadiene, heat to 120-130℃, stir for 6-8h to obtain norbornene monomer; mix toluene, norbornene monomer and catalyst, pass in ethylene, heat to 88-93℃, react for 100-150min to obtain the grafting agent; The dibutynyl acid diester is prepared by the following process: mix 2,3-dibromosuccinic acid and perfluoroalkyl ethanol, add p-toluenesulfonic acid, heat to 75-80℃, stir for 1.5-3.0h to obtain 2,3-dibromosuccinate; mix 2,3-dibromosuccinate and ethanol, add potassium hydroxide, heat to 70-80℃, reflux for 3-4h to obtain dibutynyl acid diester.

2. The process for preparing a high transparency low isotacticity thermoformed polypropylene resin according to claim 1, characterized in that: The molar ratio of 2,3-dibromosuccinic acid to perfluoroalkyl ethanol is 1:(1.1-1.5).

3. The process for preparing a high clarity low isotacticity thermoformed polypropylene resin according to claim 1, characterized in that: The molar ratio of cyclopentadiene to dibutynyl acid diester is (1.4-1.6):

1.

4. The process for preparing a high clarity low isotacticity thermoformed polypropylene resin according to claim 1, characterized in that: The process conditions of thermoforming are as follows: preheat the sheet to 140-160℃, press plastic form under the pressure of 0.5-0.8MPa, then cool at the cooling rate of 30-50℃ / s.

5. The process for preparing a high clarity low isotacticity thermoformed polypropylene resin according to claim 1, characterized in that: In the co-extrusion process, the extrusion temperature is 170-190℃, the rotation speed is 250-350rpm, and the time length is 3-5min.

6. A high-transparency low-isotacticity thermoformed polypropylene resin prepared by the preparation process according to any one of claims 1-5.