CN111363240B

CN111363240B - High-foaming-ratio polypropylene foam material and preparation method thereof

Info

Publication number: CN111363240B
Application number: CN202010242998.1A
Authority: CN
Inventors: 闫海阔; 周武舜
Original assignee: Ningbo Micro Foam Material Co ltd
Current assignee: Ningbo Micro Foam Material Co ltd
Priority date: 2020-03-31
Filing date: 2020-03-31
Publication date: 2022-06-10
Anticipated expiration: 2040-03-31
Also published as: CN111363240A

Abstract

The invention relates to the technical field of polypropylene foam materials, and particularly relates to a high-foaming-ratio polypropylene foam material and a preparation method thereof. The polypropylene foaming material is prepared by foaming a polypropylene composition, wherein the polypropylene composition comprises first polypropylene, second polypropylene and a nano material additive, and the melt index intervals of the second polypropylene and the first polypropylene are both 0.5-4g/min under the conditions of 190 ℃ and 2.16 kg; the second polypropylene has a higher melting point than the first polypropylene. The material can ensure that the product of the foaming material has better cut and other appearance parameters on the premise of ensuring high foaming multiplying power and inhibiting foaming to shrink as much as possible, and can ensure that the product has fine and smooth appearance and smooth surface.

Description

High-foaming-ratio polypropylene foam material and preparation method thereof

Technical Field

The invention relates to the technical field of polypropylene foam materials, and particularly relates to a high-foaming-ratio polypropylene foam material and a preparation method thereof.

Background

The polymer microporous foaming material is a material with excellent performance, and shows good mechanical property, thermal property and processing property. The polymer-based microporous foam material has the advantages of light weight, heat insulation, sound insulation, buffering, high specific strength, low price and the like, so the polymer-based microporous foam material is widely applied to the fields of packaging industry, agriculture, transportation industry, military industry, aerospace industry, daily necessities and the like. At present, the conventional polymer microcellular foaming materials include foamed Polystyrene (PS), foamed Polyethylene (PE), foamed Polyurethane (PU) and the like. In the foaming process of the polyurethane foam, isocyanate residues harmful to human bodies exist, and the foaming material cannot be recycled. Chlorofluorocarbon compounds or butane are generally used in the Polystyrene (PS) foaming process, which has adverse effects on the environment, is difficult to degrade and is prone to form "white pollution", and the united nations environmental protection organization has decided to stop using PS foamed products. The crosslinked polyethylene foam has low rigidity and the maximum service temperature is 80 ℃.

Compared with the traditional foaming material, the polypropylene foaming material has many advantages: (1) the heat resistance is excellent, the foaming PS is usually used at 80 ℃, the foaming PE can only resist 70-80 ℃, and the foaming PP can resist 120 ℃, so that the foamed PP can be used for a long time in a high-temperature environment; (2) the PP foam has excellent mechanical properties, the flexural modulus of the PP is far greater than that of the PE, so the static load capacity of the PP foam is superior to that of the PE foam, and the impact performance of the PP foam is superior to that of the PS foam; in addition, the foamed PP has remarkable heat insulation property, excellent chemical corrosion resistance and good stress cracking resistance. Based on the advantages, the PP foaming material has extremely competitive force in the application of a plurality of industrial fields, particularly in the application of the automobile industry and the food packaging industry, can replace the prior PS foam and PE foam, and has very wide application prospect. Based on the characteristics of light weight, rich raw material sources, superior cost performance ratio, excellent heat resistance, chemical corrosion resistance, easy recovery and the like of the polypropylene resin, the polypropylene resin is the universal thermoplastic resin with the fastest yield increase in the world, and although the polypropylene foamed product has good performance and application prospects, the development difficulty of the polypropylene foam is very high.

The preparation method of the polypropylene microporous foaming material is mainly divided into a chemical method and a physical method. In chemical foaming, an organic substance that decomposes at high temperature to generate gas, such as azodicarbonamide, is generally used as a foaming agent, and the organic foaming agent remains in the material after decomposition, and is difficult to be used in some use environments required by the material. The conventional physical foaming method gradually changes the thermodynamic state of gas, so that the generated cells are not uniform in size, and the properties of the foaming material are unstable.

Supercritical gas foaming is also a physical foaming method, but it is greatly different from conventional physical foaming. The thermodynamic state in the supercritical gas foaming process is changed rapidly, and the nucleation rate and the number of the nucleation are greatly higher than those of the common physical foaming. Moreover, the mass transfer coefficient of the supercritical gas is high, and concentration balance can be achieved in a short time, so that the processing time is shortened. The carbon dioxide is selected as the foaming agent because the carbon dioxide is environment-friendly and green, has no pollution to the environment, can easily reach the critical condition, has strong penetrating and dissolving capacity in the polymer and is beneficial to improving the foaming effect.

In the process of foaming a polypropylene material by the supercritical gas foaming method, the applicant finds that the prepared foaming material has the problems of difficult growth of foaming cells, low foaming rate, easy shrinkage and collapse of the foamed material after foaming and the like, but no solution for the problems exists at present, and the existing technical problems have certain influence on the product quality of the polypropylene foaming material, directly cause the production essential problems of poor product quality, insufficient competitiveness and the like, and seriously influence and restrict the development of enterprises.

Disclosure of Invention

The invention aims to solve the problems that foam pores of a foaming material are difficult to grow up, the foaming ratio is low and the foaming material is easy to shrink and collapse after foaming when a supercritical gas foaming method is adopted to prepare the polypropylene foaming material, provides a polypropylene foaming material with high foaming ratio and correspondingly provides a preparation method for the polypropylene foaming material.

According to the scheme, the raw materials of the polypropylene foaming material are improved, the component composition of the foaming material is fundamentally improved from the raw materials, and the parameters such as the foaming mechanism of the foaming material and the foaming temperature of the material are further changed, so that the foaming process of the provided polypropylene composition is easier to control, and the polypropylene foaming material with higher foaming ratio and better foaming quality can be obtained by matching with the foaming method provided by the application through the foaming temperature and the foaming pressure controlled in the method. Finally, the competitiveness of the product is improved by improving the foaming quality of the foaming material.

Specifically, the invention adopts the following technical scheme: firstly, a polypropylene foaming material with a high foaming ratio is provided, and in addition, a preparation method for the polypropylene foaming material is also provided, and the polypropylene foaming material with the high foaming ratio is prepared by the method.

The polypropylene foaming material with high foaming ratio is prepared by foaming a polypropylene composition, wherein the polypropylene composition comprises a first polypropylene, a second polypropylene and a nano material additive, the melt index interval of the second polypropylene and the first polypropylene is 0.5-4g/min, and the conditions are 190 ℃ and 2.16 kg; the second polypropylene has a higher melting point than the first polypropylene.

Preferably, the second polypropylene is added in an amount of 5wt% to 20wt% of the first polypropylene.

Preferably, the first polypropylene and the second polypropylene each have a melt index of 0.5 to 4g/min, provided that the melt index is 2.16kg at 190 ℃.

Preferably, the melting point of the first polypropylene is 150-160 ℃ and the melting point of the second polypropylene is 160-170 ℃.

Preferably, the melting point of the second polypropylene is 6-10 ℃ higher than the melting point of the first polypropylene.

Preferably, the nano material additive is one or more of nano silicon dioxide, nano titanium dioxide, nano montmorillonite or carbon nano tube.

The conventional polypropylene foam materials are usually foamed by using a single component, and a part of polypropylene is foamed by mixing with other polymer components. Particularly, in the process of foaming the polypropylene material by adopting a supercritical gas foaming method, the foaming ratio cannot be increased, and the problem of easy shrinkage and collapse after foaming cannot be well solved. This has seriously plagued the development of applicants' products. At least, at present, the requirement for high expansion ratio of polypropylene foam materials is not found in the field, so that when the supercritical gas foaming method is adopted for foaming, the requirement for high expansion ratio of polypropylene does not exist for the technicians in the field, and therefore, the problem of high expansion ratio foaming of polypropylene is not solved. The problem is mainly that aiming at partial products with higher foaming ratio requirements, the foaming ratio is improved on the premise that basic mechanical properties are required to be ensured as much as possible in order to meet product requirements.

The process of polypropylene is difficult when preparing polypropylene foam. Since polypropylene is a semi-crystalline polymer, and the molecular weight distribution is narrow, the softening point and the melting point are relatively close, when the processing temperature is lower than the melting point, the polypropylene is basically in a non-flowing state, but when the processing temperature is higher than the melting point, the viscosity of the polypropylene is rapidly reduced, so that the melt is difficult to contain gas, the gas is easy to escape, and the material with higher foaming ratio is difficult to achieve.

With respect to melt index, if the melt index is too low, cells are difficult to grow; the dissolution means that too high bubbles are easy to escape; the polypropylene mixture with better compatibility is prepared by mixing two polypropylenes, and the compatibility problem is easy to solve because the two polypropylenes belong to the same polymer.

The addition amount of the second polypropylene is low, the foaming temperature is not greatly increased, and high foaming is difficult to prepare; the addition amount is high, the foaming temperature is greatly increased, and at the temperature, the first polypropylene is almost in a molten state and is difficult to foam.

This application is through the cooperation of two kinds of different polypropylenes to reach the polypropylene foam material that possesses higher foaming multiplying power.

Preferably, the nanomaterial additive is added in an amount of 0.5wt% to 2wt% of the first polypropylene.

Preferably, the nanomaterial additive is nano montmorillonite and/or carbon nanotube.

Finally, in order to prevent the product from shrinking/collapsing after foaming, the nano particles with a sheet structure are particularly introduced into the blend, and a nano material additive is added, so that the problem that the closed-cell polypropylene foaming material is easy to shrink when the foaming ratio is higher, such as 35 times. The main principle is that nano montmorillonite with a sheet structure or carbon nano tubes with a tubular structure are uniformly distributed in the wall of a bubble hole to form a network-shaped structure skeleton, so that the material shrinkage is effectively inhibited, and the strength of a matrix is improved. When the addition amount of the nano material is small, the effect of inhibiting shrinkage is not achieved, and when the addition amount is large, the influence on the mechanical property of the material is caused, such as the quality reduction of the material, the rough appearance and the increase of section patterns; finally, the overall performance of the product is insufficient, and the actual requirements cannot be met.

Therefore, the application makes strict design control on the adding amount. The application selects the nano montmorillonite and/or the carbon nano tube preferentially, and the two materials are added singly or in a mixing way, so that the two materials are adopted for the following reasons: because nanometer montmorillonite and carbon nanotube, one has sheet structure, and one is the tubular structure, and two kinds of structures all can form skeleton texture in the expanded material, and at the micro-angle, its skeleton texture's effect is great, can form better support to the foaming wall, and other graininess nanometer materials effect is relatively poor.

Regarding the preparation method of the polypropylene foaming material provided by the present application, the method comprises the following steps:

(1) blending and extruding all components of the polypropylene composition into a blank by adopting a screw extruder;

(2) placing the blank in a high-pressure container for saturation treatment, filling supercritical carbon dioxide into the container to saturation pressure, and heating to saturation temperature for treatment, wherein the saturation treatment temperature is 150-;

(3) and (4) releasing the pressure of the high-pressure container to obtain the polypropylene foaming material with high foaming ratio.

The invention has the beneficial effects that:

(1) firstly, the high foaming ratio of the polypropylene foaming material is ensured, and most of the foaming ratio can reach more than 30-35 times and at least can reach more than 25 times;

(2) secondly, on the premise of ensuring high foaming ratio, the shrinkage of the foamed material after foaming is inhibited to a great extent, and after the foamed material is manufactured, collapse cannot occur in the later stage, so that the obtained foam is effectively foamed;

(3) thirdly, on the premise of ensuring high foaming ratio and inhibiting foaming to shrink as much as possible, the product of the foaming material is ensured to have better cuts and other appearance parameters, and the product can be ensured to have fine and smooth appearance and smooth surface.

Detailed Description

Representative embodiments will now be further refined. It should be understood that the following description is not intended to limit the embodiments to one preferred embodiment. On the contrary, it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the embodiments as defined by the appended claims.

In the following detailed description, while these embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments, it is to be understood that these examples are not limiting, such that other examples may be used and that corresponding modifications may be made without departing from the spirit and scope of the embodiments.

The invention relates to a polypropylene foaming material with high foaming ratio, which is prepared by foaming a polypropylene composition, wherein the polypropylene composition comprises a first polypropylene, a second polypropylene and a nano material additive, the melt indexes of the second polypropylene and the first polypropylene are both 0.5-4g/min, and the conditions are 190 ℃ and 2.16 kg; the second polypropylene has a higher melting point than the first polypropylene.

The addition amount of the second polypropylene is 5 to 20 weight percent of the first polypropylene; the addition amount of the nano material additive is 0.5wt% -2wt% of the first polypropylene.

The melting point of the first polypropylene is 150-160 ℃, the melting point of the second polypropylene is 160-170 ℃, and the melting point of the second polypropylene is ensured to be 6-10 ℃ higher than that of the first polypropylene.

The nano material additive is one or more of nano silicon dioxide, nano titanium dioxide, nano montmorillonite or carbon nano tube, preferably one or a mixture of the nano montmorillonite and the carbon nano tube.

The preparation method of the polypropylene foaming material comprises the following steps: (1) blending and extruding all components of the polypropylene composition into a blank by adopting a screw extruder; (2) placing the blank in a high-pressure container for saturation treatment, filling supercritical carbon dioxide into the container to saturation pressure, and heating to saturation temperature for treatment, wherein the saturation treatment temperature is 150-; (3) and (4) releasing the pressure of the high-pressure container to obtain the foaming material.

Specific examples and comparative examples are as follows.

Comparative example 1.1: preparing a foaming material by a supercritical gas foaming method from a first polypropylene with a melting point of 154 ℃ and a melt index of 1.5g/10min, wherein the saturation temperature is 151 ℃, the saturation pressure is 12MPa, the foaming ratio is 25 times, and the compression strength is 151 KPa; when foaming is carried out at a temperature of above 151 ℃, the surface of the obtained material is melted, and the foamed material with the qualified quality cannot be obtained.

Comparative example 1.2: preparing a foaming material by a supercritical gas foaming method from second polypropylene with the melting point of 162 ℃ and the melt index of 2.0g/10min, wherein the saturation temperature is 159 ℃, the saturation pressure is 12MPa, the foaming ratio is 15 times, the compression strength is 552KPa, and the compression strength is 25% of the material compression strength according to ASTM D3575.

Example 1.1: taking 100 parts of first polypropylene with a melt index of 1.5g/10min and a melting point of 154 ℃, taking 10 parts of second polypropylene with a melt index of 2.0g/10min and a melting point of 164 ℃, carrying out saturation treatment for 3h at a saturation pressure of 12MPa and a saturation temperature of 155 ℃, and carrying out pressure relief for 2s to obtain the foam material. The expansion ratio was 30 times, the surface of the material was not melted, and after 1 day, the material shrunk, and the density was 25 times, and the compressive strength was 149 KPa.

Example 1.2: on the basis of example 1.1, 1 part of nano montmorillonite clay is added, then foaming is carried out at 155 ℃ and under the pressure of 12MPa, the saturation treatment time is 20min, the foaming ratio is 30 times, shrinkage does not occur after 1 day, and the compressive strength is 95 KPa.

Example 1.3: on the basis of example 1.1, 2 parts of nano montmorillonite clay is added, then foaming is carried out at 155 ℃ and under the pressure of 12MPa, the saturation treatment time is 20min, the foaming ratio is 32 times, the nano montmorillonite clay is not shrunk after 1 day, and the compressive strength is 90 KPa. The appearance is smooth, and the decorative pattern is less.

Example 1.4: on the basis of example 1.1, the first and second polypropylenes were replaced by materials each having a melt index of 10.0g/10min, resulting in an expansion ratio of 15 times, shrinkage after 1 day, and a compressive strength of 105 KPa. The appearance is smooth, and the decorative patterns are increased.

Comparative example 2.1: preparing a foaming material by a supercritical gas foaming method from first polypropylene with the melting point of 154 ℃ and the melting index of 1.5g/10min, wherein the saturation temperature is 151 ℃, the saturation pressure is 12MPa, and the foaming ratio is 25 times; foaming is carried out at a temperature of above 151 ℃, and the surface of the material is melted.

Comparative example 2.2: preparing a foaming material by a supercritical gas foaming method from second polypropylene with the melting point of 162 ℃ and the melting index of 2.0g/10min, wherein the saturation temperature is 159 ℃, the saturation pressure is 12MPa, and the foaming ratio is 15 times.

Example 2.1: after 100 parts of the first polypropylene of comparative example 2.1 and 15 parts of the second polypropylene of comparative example 2.2 were added, the material surface was not melted under the limiting foaming conditions of 157 ℃, 12MPa, and 35 times the expansion ratio, and after 1 day, the material shrunk and was measured to have a density of 25 times.

Example 2.2: on the basis of example 2.1, 1 part of nano montmorillonite clay is added, then foaming is carried out at 157 ℃ and 12MPa, the foaming ratio is 35 times, the compressive strength is 63KPa, and shrinkage does not occur after 1 day. The appearance is smooth, and the decorative pattern is less.

Example 2.3: on the basis of example 2.1, after 2 parts of nano montmorillonite clay is added, foaming is carried out at 157 ℃ and 12MPa, the foaming ratio is 36 times, the compression strength is 60KPa, shrinkage does not occur after 1 day, and the rebound resilience is better than that of the product in example 2.2. The appearance is smooth, and the decorative patterns are increased.

Example 2.4: on the basis of example 2.2, the first and second polypropylene were exchanged for a material with melt fingers of 8.0g/10min, resulting in an expansion ratio of 18 times, shrinkage after 1 day and a compressive strength of 82 KPa.

Comparative example 3.1: preparing a foaming material by a supercritical gas foaming method from first polypropylene with the melting point of 154 ℃ and the melting index of 1.5g/10min, wherein the saturation temperature is 151 ℃, the saturation pressure is 12MPa, and the foaming ratio is 25 times; foaming is carried out at a temperature of above 151 ℃, and the surface of the material is melted.

Comparative example 3.2: preparing a foaming material by a supercritical gas foaming method from second polypropylene with the melting point of 162 ℃ and the melting index of 2.0g/10min, wherein the saturation temperature is 159 ℃, the saturation pressure is 12MPa, and the foaming ratio is 15 times.

Example 3.1: 100 parts of the first polypropylene of comparative example 3.1 and 20 parts of the second polypropylene of comparative example 3.2 were added under the limiting foaming conditions of 158 ℃ C., a pressure of 12MPa, an expansion ratio of 25 times and a compressive strength of 335 KPa.

Example 3.2: on the basis of example 3.1, 1 part of nano montmorillonite clay is added, and the foaming conditions are 158 ℃, the pressure is 12MPa, the foaming ratio is 28 times, and the compressive strength is 256 KPa.

When the above-mentioned examples carried out by the applicant in actual production were compared, it was found that: when the first polypropylene and the second polypropylene with the melt indexes of 0.5-4g/min are added, a better foaming material can be obtained, and the melt index is too large, so that the performance of the product is adversely affected; and the melting points of the first and second polypropylenes are within 10 degrees of each other; when a nano material additive such as nano montmorillonite is added into the foaming material, the foaming ratio of the foaming material is obviously improved, and the shrinkage of the foaming material can be prevented.

The applicant found that the expansion ratio was improved by adding a second polypropylene having a higher melting point to the first polypropylene, but the expansion ratio could not be maintained and the shrinkage collapse occurred easily after one day, which resulted in the instability of the product. When the carbon nano tube or the nano montmorillonite is added into the composition, the problem of shrinkage and collapse is improved.

For purposes of explanation, specific nomenclature is used in the above description to provide a thorough understanding of the described embodiments. It will be apparent, however, to one skilled in the art that these specific details are not required in order to practice the embodiments described above. Thus, the foregoing descriptions of specific embodiments described herein are presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the embodiments to the precise form disclosed. It will be apparent to those skilled in the art that certain modifications, combinations, and variations can be made in light of the above teachings.

Claims

1. The polypropylene foaming material with high foaming ratio is prepared by foaming a polypropylene composition, and is characterized in that: the polypropylene composition comprises a first polypropylene, a second polypropylene and a nano material additive, wherein the melt indexes of the second polypropylene and the first polypropylene are both 0.5-4g/min under the conditions of 190 ℃ and 2.16 kg; the second polypropylene has a higher melting point than the first polypropylene;

the addition amount of the second polypropylene is 5 to 20 weight percent of the first polypropylene;

the melting point of the first polypropylene is 150-160 ℃, and the melting point of the second polypropylene is 160-170 ℃;

the melting point of the second polypropylene is 6-10 ℃ higher than that of the first polypropylene;

the nano material additive is one or more of nano silicon dioxide, nano titanium dioxide, nano montmorillonite or carbon nano tube.

2. The polypropylene foam according to claim 1, wherein: the addition amount of the nano material additive is 0.5wt% -2wt% of the first polypropylene.

3. The polypropylene foam according to claim 2, wherein: the nano material additive is nano montmorillonite and/or carbon nano tube.

4. The method for preparing polypropylene foam material according to any one of the preceding claims, wherein: the method comprises the following steps:

(3) and (4) releasing the pressure of the high-pressure container to obtain the foaming material.