CN118322398B - Foamed polypropylene particles and molded part using same - Google Patents

Abstract

The present invention relates to a foamed polypropylene particle and a molded article using the same. The particles are prepared from composite particles, the composite particles comprise a core layer and a skin layer, the skin layer is coated on the surface of the core layer, the core layer at least comprises polypropylene A and a flame retardant auxiliary agent, and the skin layer at least comprises polyolefin B, a flame retardant and a flame retardant auxiliary agent. The molded article is prepared from expanded polypropylene particles, and has molding pressure lower than 2.4bar and excellent surface quality.

Description

A kind of foamed polypropylene particles and molded parts using the same

Technical Field

The invention belongs to the field of foamed polypropylene materials, and in particular relates to foamed polypropylene particles and products using the same.

Background Art

Expanded polypropylene (EPP) particles and their molded parts have excellent mechanical properties, excellent resilience, excellent temperature resistance, and diversified structural shapes of the parts. They are suitable for weight reduction, energy absorption and cushioning, sound insulation, heat insulation and other modular components of various special-shaped structures. They are widely used in transportation parts, new energy battery transfer packaging, electronic components transfer packaging, and home appliance cushioning packaging.

When EPP is used in modules such as automobile and rail transit parts and new energy battery packaging, it is required that EPP has excellent flame retardant properties. Especially in the application fields of rail transit and new energy batteries, the high flame retardancy of EPP is more clearly required. In view of market demand, this technology provides a method for preparing foamed polypropylene particles and molded parts thereof, and obtains EPP particles with excellent flame retardant and smoke suppression properties and low molding energy consumption. The molded parts thereof have excellent appearance, that is, there are very few or very small pits or gaps on the surface of the parts.

Summary of the invention

One of the purposes of the present invention is to provide a foamed polypropylene particle and a preparation method thereof.

Another object of the present invention is to provide a molded article containing the above-mentioned foamed polypropylene particles and a method for preparing the same.

Another object of the present invention is to provide the use of the above product.

In order to achieve the above-mentioned invention object, the present application adopts the following technical solutions:

A foamed polypropylene particle is prepared by a high-temperature and high-pressure autoclave foaming method. The composite particles include a core layer and a skin layer, wherein the skin layer is coated on the surface of the core layer, the core layer includes at least 95-99.5 parts by weight of polypropylene A and 0.5-5 parts by weight of a flame retardant additive, and the skin layer includes at least 75-85 parts by weight of polyolefin B, 5-15 parts by weight of a flame retardant and 0.5-10 parts by weight of a flame retardant additive.

Polypropylene A, random copolymer polypropylene, melt index 5-10 g/10 min (230° C., 2.16 kg), melting point 130-150° C.; preferably melt index 6-9 g/10 min (230° C., 2.16 kg), melting point 136-147° C.

Polyolefin B may be one or more of PP, PE, POE, POP, OBC, EVA, EAA, with a melt index of 3-20 g/10 min (230° C., 2.16 kg) and a melting point of 102-144° C.; preferably, a melt index of 3.5-15 g/10 min (230° C., 2.16 kg) and a melting point of 107-135° C.

From the perspective of facilitating the sintering of the EPP particle skin, the difference in melting point between polypropylene A and polyolefin B is in the range of 5-20° C. From the perspective of better sintering strength, polyolefin B contains at least 60-100 parts by weight of random copolymerized polypropylene.

The flame retardant additive is one or both of modified diatomite or modified zeolite powder, with an average particle size of 1-20 microns, preferably 3-15 microns. The flame retardant additives added to the core layer and the skin layer can be the same or different.

The flame retardant is a mixture of zinc stannate and decabromodiphenylethane, wherein the mixing ratio of zinc stannate to decabromodiphenylethane is (20-60)/(40-80).

The core layer also contains a cell nucleating agent, which is one or more of silicon dioxide, zinc borate, talcum powder, and calcium carbonate, with an average particle size of 10-15 microns, accounting for 0.05-0.3% of the weight of the core layer material.

The skin layer or the core layer may also contain other plastic additives, all of which are selected from at least one of antioxidants, lubricants, antistatic agents, and colorants; and preferably, the antioxidant is selected from at least one of hindered phenol compounds, thiopropionate compounds, and phosphite compounds; the lubricant is selected from at least one of erucamide, oleamide, monostearate glycerol, polyethylene wax, and polypropylene wax. The weight proportion of other plastic additives in the core layer or the skin layer is preferably 0-5%.

Preparation of flame retardant additives:

2,3-Dimethyl-2,3-diphenylbutane and KH-560 silane coupling agent are reacted at 120-135° C. in a nitrogen atmosphere for 4-6 hours to obtain an intermediate product 1; wherein the mass ratio of 2,3-dimethyl-2,3-diphenylbutane to KH560 is (1:1.2-2).

The intermediate product 1 and diatomaceous earth or zeolite powder are added to a high-speed mixer in a certain proportion, and mixed for 10-30 minutes at a speed of 1000-2000 rpm to obtain modified diatomaceous earth or modified zeolite powder, i.e., a flame retardant additive; wherein the mass ratio of the intermediate product 1 to the diatomaceous earth or zeolite powder is 1:(10-30).

Composite particle preparation:

(1) Polypropylene A, flame retardant additives, cell nucleating agents, and other plastic additives are mixed uniformly in a certain proportion, and then melt-granulated by an extruder to obtain a core layer masterbatch; the temperature of the heating section of the extruder is 200°C-240°C.

(2) Polyolefin B, flame retardant additives, flame retardants, and other plastic additives are uniformly mixed in a certain proportion, and then melt-granulated by an extruder to obtain a skin masterbatch; the temperature of the heating section of the extruder is 200°C-240°C.

(3) adding the core layer masterbatch and the skin layer masterbatch to the core layer extruder and the skin layer extruder of the twin-single screw co-extruder unit respectively, and after plasticization, filaments are discharged through the co-extrusion die to obtain composite particles with the skin layer covering the core layer; the temperature of the heating section of the extruder is 200° C.-240° C.

Preferably, the weight percentage of the skin layer in the composite particles is 5-20%; the length of the composite particles is preferably 1.0-3.0 mm, and the unit weight is 0.5-2.0 mg.

Preparation of foamed particles: Add composite particles, dispersant and water into an autoclave, seal and add CO ₂ . Stir continuously, raise the temperature of the autoclave to a foaming temperature of 138°C-155°C, adjust the pressure in the autoclave to a foaming pressure of 1.5-4.0MPa, maintain under this temperature and pressure condition for 10-60min, release the pressure and discharge the material into a normal pressure environment, and finally obtain foamed polypropylene particles with a bulk density of 25-120g/L. The melting peak endothermic enthalpy value of the foamed particles in the first DSC melting curve that is higher than the inherent melting point is 12-24J/g.

A molded part of foamed polypropylene particles is obtained by sintering the foamed polypropylene particles as described above through steam. The specific steps are: the foamed particles are pressurized by air and then steam molded.

The molding pressure of the molded product is lower than 2.4 bar, and the surface quality is excellent; the density of the molded product is 28-30 g/L, and the oxygen index is not lower than 30%.

Beneficial effects:

A mixed flame retardant of zinc stannate and decabromodiphenylethane is used to form an excellent synergistic flame retardant effect in the cortex of the foamed particles; and in the flame retardant process, zinc stannate catalyzes the decomposed polymer into carbon, thereby improving the flame retardant effect and suppressing smoke; in addition, 2,3-dimethyl-2,3-diphenylbutane and porous diatomaceous earth or zeolite in the flame retardant additive synergistically flame retardant to a certain extent, and the porous material absorbs the generated smoke and melt, reducing the formation of molten droplets and achieving a smoke suppression effect.

The core layer is a foaming layer; the core layer contains 0.5-5% of a porous flame retardant additive, which easily absorbs gases such as carbon dioxide and water vapor during the foaming process, promotes the foaming and molding expansion process, and at the same time improves the flame retardant properties of the core layer material. If the content is less than 0.5%, the effect of promoting foaming and improving flame retardancy is not obvious; if the content is higher than 5%, there is a tendency to reduce the foaming properties.

The skin layer is a non-foamed or slightly foamed layer; the polyolefin B of the skin layer is more easily melted by heat than the core layer resin, and it is coated on the surface of the foamed core layer, giving the foamed particles easy sintering properties on the skin, thereby reducing the molding pressure of the foamed particles.

Porous flame retardant additives promote the foaming and molding expansion process, which is conducive to the excellent surface quality of molded parts, that is, very few or very small pits or gaps on the surface of molded parts, and at the same time improve the flame retardant effect of the material. Flame retardants are only added to the cortex of the foaming particles, which has little effect on the foam properties of the foaming core layer, while achieving excellent foam properties and high flame retardant and smoke suppression properties of the foaming particles and their molded parts.

Example

The present invention is further described below by way of examples. It should be understood that the methods described in the examples of the present invention are only used to illustrate the present invention, rather than to limit the present invention, and simple improvements to the preparation methods of the present invention under the premise of the concept of the present invention belong to the scope of protection claimed in the present invention. All raw materials and solvents used in the examples are commercially available products of corresponding purity.

Preparation Example of Foamed Polypropylene Particles:

Preparation of flame retardant additives:

2,3-Dimethyl-2,3-diphenylbutane and KH-560 silane coupling agent were reacted at 130° C. in a nitrogen atmosphere for 5 hours to obtain an intermediate product 1; wherein the mass ratio of 2,3-dimethyl-2,3-diphenylbutane to KH560 was (1:1.5).

The intermediate product 1 and diatomaceous earth or zeolite powder are added to a high-speed mixer at a mass ratio of 1:20, and mixed at a speed of 1500 rpm for 20 minutes to obtain modified diatomaceous earth or modified zeolite powder, i.e., a flame retardant additive.

Composite particle preparation:

(1) Polypropylene A, flame retardant additives, cell nucleating agents, and other plastic additives are mixed uniformly in a certain proportion, and then melt-granulated in an extruder to obtain a core layer masterbatch; the temperature of the heating section of the extruder is 225°C;

(2) Polyolefin B, flame retardant additive, flame retardant and other plastic additives are mixed evenly in a certain proportion and melt-granulated in an extruder to obtain a skin masterbatch; the temperature of the heating section of the extruder is 225°C;

(3) adding the core layer masterbatch and the skin layer masterbatch to the core layer extruder and the skin layer extruder of the twin-single screw co-extruder unit, respectively, and after plasticization, simultaneously passing through the co-extrusion die to form filaments and granulate to obtain composite particles of the skin layer covering the core layer; the temperature of the heating section of the extruder is 225° C.;

Preferably, the weight percentage of the skin layer in the composite particles is 5-20%; the length of the composite particles is preferably 1.0-3.0 mm, and the unit weight is 0.5-2.0 mg.

Preparation of foamed particles: Add composite particles, dispersant and water into the autoclave, seal it and add CO ₂ . Stir continuously, raise the temperature of the autoclave to the foaming temperature of 138°C-155°C, adjust the pressure in the autoclave to the foaming pressure of 1.5-4.0MPa, maintain it at this temperature and pressure for 10-60min, release the pressure and discharge the material into the normal pressure environment, and finally obtain foamed polypropylene particles.

The products of Examples 1-4 and Comparative Examples 1-6 were prepared according to the above preparation method.

Table 1 Main raw material manufacturers and performance parameters used in this application

Table 2 Formulation parameters of composite particles S1-S4 and D1-D6

Table 3 Parameters of foamed polypropylene particles and properties of molded parts of Examples 1-4 and Comparative Examples 1-6

Example of molding preparation:

The expanded polypropylene particles were filled into a rectangular mold (length 450 mm, width 350 mm, thickness 60 mm) after being subjected to 0.5 MPa air pressure for 6 hours and then steam molded.

Among them, the minimum molding pressure is the minimum steam sintering pressure required for the proportion of particles with destroyed cells on the broken surface of the foamed polypropylene particle molding to be more than 95%.

Determination of performance parameters of molding parts:

Apparent quality of parts: Indicates that there are many pits or gaps on the surface of the workpiece; "□" indicates that there are few pits or gaps on the surface of the workpiece; It means that there are no or very few or very small pits or gaps on the surface of the workpiece.

LOI Limiting Oxygen Index Test: Tested in accordance with GB/T2406-1993, the sample size is 150mm*10mm*10mm; 10 samples are tested in each group of samples, and the results are averaged.

Examples 1-4 are all within the technical requirements, showing excellent low-pressure moldability, high flame retardancy and excellent appearance quality.

In comparative example 1, the flame retardant content in the cortex material is lower than the technical range, and the flame retardant performance of the material is reduced. In comparative example 2, the flame retardant of the cortex material does not contain zinc stannate, and the flame retardant effect is poor; and the cortex has a large content of decabromodiphenylethane, which is easier to precipitate, which is not conducive to the sintering of the cortex, the molding energy consumption increases, and a small number of pits appear on the surface of the product. In comparative example 3, the flame retardant of the cortex material does not contain decabromodiphenylethane, the flame retardant effect is poor, and the content of inorganic matter in the cortex material is relatively high, which is not conducive to sintering, the molding energy consumption is high, and there are a small number of pits on the surface of the product. In comparative example 4, the foaming core layer does not contain a porous flame retardant additive, the flame retardant performance of the material is reduced, and it is not conducive to the molding expansion of the particles, the molding energy consumption increases, and there are a small number of gaps and pits on the surface of the product. In comparative example 5, the content of porous flame retardant additive in the foam core layer is too high, and too much inorganic particles are filled, which is not conducive to the deformation and expansion of the material, but causes the molding expansion performance of the foam particles to deteriorate, the molding energy consumption to increase, and more gaps and a small number of pits appear on the surface of the product. In comparative example 6, the skin material does not contain porous flame retardant additives, which has a reduced effect on the flame retardant performance of the material.

Claims (9)

1. A foamed polypropylene particle characterized in that: the particles are prepared from composite particles under the following preparation conditions: foaming temperature is 146.8-155 ℃, foaming pressure is 1.5-4.0MPa, and reaction time is 10-60min; the composite particles comprise a core layer and a skin layer, wherein the skin layer is coated on the surface of the core layer, the core layer at least comprises 95-99.5 parts by weight of polypropylene A and 0.5-5 parts by weight of flame retardant auxiliary agent, and the skin layer at least comprises 75-85 parts by weight of polyolefin B, 5-12 parts by weight of flame retardant and 0.5-7 parts by weight of flame retardant auxiliary agent; the flame retardant auxiliary is selected from one or two of modified diatomite or modified zeolite powder, and has an average particle size of 1-20 microns;

The flame retardant auxiliary is prepared by the following method:

(1) Reacting 2, 3-dimethyl-2, 3-diphenyl butane with KH-560 type silane coupling agent at 120-135 ℃ under nitrogen atmosphere for 4-6h to obtain an intermediate product; wherein the mass ratio of the 2, 3-dimethyl-2, 3-diphenyl butane to KH560 is (1:1.2-2);

(2) Adding the intermediate product and diatomite or zeolite powder into a high-speed mixer according to a certain proportion, and mixing for 10-30min at the rotating speed of 1000-2000 rpm to obtain modified diatomite or modified zeolite powder, namely a flame retardant auxiliary; wherein the mass ratio of the intermediate product to the diatomite or zeolite powder is 1: (10-30).

2. The expanded polypropylene particles according to claim 1, wherein: the polypropylene A is random copolymer polypropylene, the melt index is 5-10g/10min (230 ℃,2.16 kg), and the melting point is 130-150 ℃; the polyolefin B is one or more selected from PP, PE, POE, POP, OBC, EVA, EAA, the melt index is 3-20g/10min (230 ℃,2.16 kg), and the melting point is 102-144 ℃; the flame retardant auxiliary is selected from one or two of modified diatomite or modified zeolite powder, and has an average particle size of 3-15 microns; the flame retardant is a mixture of zinc stannate and decabromodiphenyl ethane, wherein the mixing weight ratio of the zinc stannate to the decabromodiphenyl ethane is (20-60)/(40-80).

3. The expanded polypropylene particles according to claim 2, wherein: the melt index of the polypropylene A is 6-9g/10min (230 ℃,2.16 kg), and the melting point is 136-147 ℃; the melt index of the polyolefin B is 3.5-15g/10min (230 ℃,2.16 kg), and the melting point is 107-135 ℃; the average grain diameter of the flame retardant auxiliary is 3-15 microns.

4. The expanded polypropylene particles according to claim 1, wherein: the core layer also comprises a cell nucleating agent which is one or more of silicon dioxide, zinc borate, talcum powder and calcium carbonate, and the average grain diameter is 10-15 microns, and accounts for 0.05-0.3wt% of the core layer material.

5. The expanded polypropylene particles according to claim 1, wherein: the skin layer or the core layer can also contain other plastic additives, and at least one of antioxidants, lubricants, antistatic agents and colorants is selected from the group consisting of the following; the antioxidant is at least one selected from hindered phenol compounds, thiopropionate compounds and phosphite compounds; the lubricant is at least one of erucamide, oleamide, glyceryl monostearate, polyethylene wax and polypropylene wax; the weight ratio of other plastic auxiliary agents in the core layer or the skin layer is 0-5%.

6. A process for the preparation of expanded polypropylene particles according to any one of claims 1 to 5, characterized by comprising the following steps:

(1) Uniformly mixing polypropylene A, a flame retardant auxiliary, a foam cell nucleating agent and other plastic auxiliary according to a certain proportion, and performing melt granulation by an extruder to obtain a core layer master batch; the temperature of the heating section of the extruder is 200-240 ℃;

(2) The polyolefin B, the flame retardant auxiliary, the flame retardant and other plastic auxiliary are uniformly mixed according to a certain proportion, and then melted and granulated by an extruder to prepare the skin master batch; the temperature of the heating section of the extruder is 200-240 ℃;

(3) Respectively adding the core layer master batch and the skin layer master batch into a core layer extruder and a skin layer extruder of a double single screw co-extruder unit, plasticizing, and simultaneously carrying out filament discharge granulation through a co-extrusion die to obtain composite particles of the skin layer coated core layer; the temperature of the heating section of the extruder is 200-240 ℃; wherein, the weight percentage of the cortex in the composite particles is 5-20%; the length of the composite particles is 1.0-3.0mm, and the single weight is 0.5-2.0mg;

(4) Preparing foaming particles: adding the composite particles, the dispersing agent and water into an autoclave, sealing, adding CO ₂, continuously stirring, raising the temperature of the autoclave to 146.8-155 ℃, regulating the pressure in the autoclave to 1.5-4.0MPa, maintaining the pressure at the temperature and the pressure for 10-60min, discharging the materials into a normal pressure environment by decompression, and finally obtaining foamed polypropylene particles with the bulk density of 25-120g/L, wherein the endothermic enthalpy value of a melting peak of the foamed particles, which is higher than the inherent melting point in a primary DSC melting curve, is 12-24J/g.

7. A molded article characterized by: comprising expanded polypropylene particles according to any one of claims 1 to 5.

8. A process for the preparation of a molded article according to claim 7, comprising the steps of: the foamed particles are molded by steam after being carried with air.

9. Use of the expanded polypropylene particles according to any one of claims 1 to 5 in packaging applications.