阅读说明：本技术 聚丙烯系树脂颗粒、聚丙烯系树脂发泡颗粒及其制备方法和成型体 (Polypropylene resin particles, polypropylene resin expanded particles, process for producing the same, and molded article ) 是由 福泽淳 于 2018-06-04 设计创作，主要内容包括：本发明涉及聚丙烯系树脂颗粒、聚丙烯系树脂发泡颗粒及其制备方法和成型体。所述聚丙烯系树脂发泡颗粒,是由聚丙烯系树脂颗粒经发泡而得到,所述聚丙烯系树脂颗粒的制备方法至少包括将聚丙烯系树脂和包含炭黑的母炼胶熔融混炼、挤出,然后切断的步骤,所述母炼胶中炭黑的浓度为35～55重量％,并且所述母炼胶在测试条件为10kg、230℃下的熔融指数MI＝5～80g/10min；其中,相对于100重量份的聚丙烯系树脂,所述母炼胶的用量为4～10重量份。(The present invention relates to polypropylene resin particles, polypropylene resin expanded particles, a method for producing the same, and a molded article. The polypropylene resin foamed particles are obtained by foaming polypropylene resin particles, and the preparation method of the polypropylene resin particles at least comprises the steps of melting, mixing and extruding a polypropylene resin and a master batch containing carbon black, and then cutting, wherein the concentration of the carbon black in the master batch is 35-55 wt%, and the melt index MI of the master batch at 230 ℃ is 5-80 g/10min under the test conditions of 10 kg; wherein the amount of the masterbatch is 4 to 10 parts by weight per 100 parts by weight of the polypropylene resin.)

1. a process for producing polypropylene resin particles for foaming, which comprises,

the method at least comprises the steps of melting, mixing and extruding a polypropylene resin and a master batch containing carbon black, and then cutting, wherein the concentration of the carbon black in the master batch is 35-55 wt%, and the melt index MI of the master batch under the test conditions of 10kg and 230 ℃ is 5-80 g/10 min;

Wherein the amount of the masterbatch is 4 to 10 parts by weight per 100 parts by weight of the polypropylene resin.

2. the method for producing polypropylene-based resin particles for foaming according to claim 1, wherein the carbon black in the masterbatch has an average primary particle diameter of 20 to 60 nm.

3. The polypropylene-based resin particles for foaming obtained by the production method according to claim 1 or 2.

4. A process for producing expanded polypropylene resin particles, which comprises expanding the expanded polypropylene resin particles according to claim 3.

5. A polypropylene resin expanded bead obtained by the production method according to claim 4.

6. A foamed molded article obtained by filling the polypropylene resin foamed particles according to claim 5 in a mold and then molding the filled particles.

7. Moulded body according to claim 6, wherein the burn rate is less than 100mm/min in the test according to the FMVSS 302 flammability flame resistance standard.

Technical Field

the invention relates to polypropylene resin particles for foaming for manufacturing a buffer material, polypropylene resin foamed particles, a preparation method of the polypropylene resin foamed particles and a polypropylene resin foamed forming body obtained by performing in-mold forming on the polypropylene resin foamed particles, and belongs to the technical field of polymer foamed materials.

Background

The polypropylene resin in-mold foamed molded article obtained from the polypropylene resin expanded beads has any characteristics such as moldability, cushioning properties, lightweight properties, and heat insulating properties, and these characteristics are all advantages of the in-mold foamed molded article. Compared with polystyrene resin in-mold foaming molded bodies obtained by polystyrene resin foaming particles, the polypropylene resin in-mold foaming molded bodies have superior chemical resistance, heat resistance and distortion recovery rate after compression, and have superior dimensional accuracy, heat resistance and compression strength.

Owing to these characteristics, polypropylene resin in-mold foamed molded articles obtained from polypropylene resin foamed particles are often used for various applications such as cushioning materials, containers, heat insulating materials, and automobile parts.

In addition, from the viewpoint of appearance, it is sometimes required to use colored polypropylene resin expanded beads and an in-mold foamed molded article obtained from the polypropylene resin expanded beads. In particular, in the field of automobile parts and the like, black polypropylene resin expanded beads and in-mold foamed molded articles are required, and therefore carbon black is generally used as a black pigment in the in-mold foamed molded articles from the viewpoints of dyeing properties, heat resistance and the like.

Meanwhile, the polypropylene resin in-mold foamed molded article is used as a cushioning material for electronic devices, precision devices, and the like, a part tray of a robot production line, or the like, or as a wave absorber for a wave-absorbing dark room, or a wave absorber for preventing radio frequency noise, reflection of a wave, and the like in electronic devices. In these applications, an in-mold foamed molded article of a polypropylene resin is used, and carbon black needs to be added to the foamed molded article.

In these respects, since the formed members and the like often have to satisfy the appropriate flammability specifications, flame retardant or low-burn-rate materials are required. However, since an in-mold foamed molded article containing carbon black and an in-mold foamed molded article having a high expansion ratio tend to be flammable, a black in-mold foamed molded article having a high expansion ratio tends to hardly satisfy flammability specifications in many cases. Therefore, it is generally necessary to use conductive carbon black or carbon black for dyeing and to assist the use of a flame retardant in order to avoid a loss in flame retardant performance.

Further, the polypropylene resin in-mold foamed molded article is also required to have a clear appearance and a uniform color, that is, to have a clear appearance and a uniform color, by uniformly dispersing carbon black. However, carbon black and flame retardants added for flame retardancy generally have a problem of mutual inhibition. For example, in order to meet the color tone requirements, it is desirable to use as little flame retardant as possible, but the flame retardant effect is reduced. On the contrary, if the flame retardant is used in a large amount, the vividness of the color tone of the appearance of the product and the uniformity of the color are also affected.

In order to solve the problems of the clear level of the external appearance and the color uniformity, the conventional proposals have tended to use carbon black having a small particle diameter, for example, carbon black having a particle diameter of less than 20nm, in order to make the color more beautiful, but at the same time, the carbon black tends to agglomerate due to its too small particle diameter, and there is a fear of the color uniformity.

Patent document 1 discloses a polypropylene resin foam molded article to which 10% by weight or more of conductive carbon black is added, but does not describe the problems of flame retardancy and appearance color of carbon black.

Patent document 2 relates to expanded polyolefin resin particles using carbon black as a coloring agent, wherein the expanded polyolefin resin particles and a polyolefin resin foamed product obtained by in-mold expansion of the expanded particles contain 0.5 to 20 wt% of carbon black, and a small amount of a flame retardant is added to ensure flame retardancy, and although good appearance can be obtained, there is still room for improvement in appearance, such as color uniformity, due to the use of components such as a flame retardant.

Patent document 3 discloses polypropylene resin expandable beads in which a carbon black coloring material is added to a polypropylene matrix resin so that a molded article obtained by in-mold molding using the expandable beads has improved flame retardancy.

Therefore, there is still room for improvement in polypropylene resin foam pellet in-mold molded articles using carbon black, in terms of compatibility between flame retardancy and vividness of appearance color and uniformity of color.

Patent document 1: JPH07-300537A

patent document 2: JP2004-263033A

Patent document 3: JP2010-209145A

Disclosure of Invention

Problems to be solved by the invention

in order to solve the above problems, it is a main object of the present invention to provide polypropylene resin expanded beads which can be used for producing polypropylene resin expanded beads having a beautiful appearance and improved flame retardancy, and a method for producing the same, and to provide polypropylene resin beads for producing the expanded beads and a method for producing the same.

It is another object of the present invention to provide an in-mold molded article of polypropylene resin expanded beads having an improved flame retardancy, which has a beautiful appearance, a clear color tone, and a uniform color.

Means for solving the problems

As a result of diligent research directed toward solving the above problems, the present inventors have found that a molded article having an excellent appearance, a vivid color, and a uniform color and improved flame retardancy can be obtained by using a polypropylene resin foamed particle obtained by mixing a polypropylene resin with a masterbatch containing carbon black having a certain carbon black content and a certain melting property, foaming the mixture to obtain a polypropylene resin foamed particle, and then performing in-mold foam molding.

The invention comprises the following technical scheme:

[1] A method for producing polypropylene resin particles for foaming, which comprises:

The method at least comprises mixing a polypropylene-based resin and

A step of melt-kneading a masterbatch containing carbon black, extruding and cutting the masterbatch, wherein the concentration of the carbon black in the masterbatch is 35 to 55 wt%, and the melt index MI of the masterbatch at 230 ℃ is 5 to 80g/10min, preferably 6 to 60g/10min under the test conditions of 10 kg;

Wherein the amount of the masterbatch is 4 to 10 parts by weight per 100 parts by weight of the polypropylene resin.

[2] The method for producing polypropylene-based resin particles for foaming according to item [1], wherein the carbon black in the masterbatch has an average primary particle diameter of 20 to 60 nm.

[3] The polypropylene-based resin particles for foaming obtained by the production method according to [1] or [2].

[4] a method for producing polypropylene resin expanded particles, which is characterized by being obtained by expanding the polypropylene resin particles for expansion according to [3].

[5] The polypropylene-based resin expanded beads obtained by the production process according to [4].

[6] A foamed molded article obtained by filling the polypropylene-based resin foamed particles according to [5] in a mold and then performing in-mold molding.

[7] The molded article according to [6], wherein the flame retardancy is less than 100mm/min in a test in accordance with FMVSS 302 flammability flame retardancy standard.

ADVANTAGEOUS EFFECTS OF INVENTION

The polypropylene resin particles provided by the invention are particularly suitable for preparing foamed particles, and further, the molded body obtained from the polypropylene resin foamed particles provided by the invention has the advantages of beautiful appearance, bright color and uniform color, and also has improved flame retardant property.

Detailed Description

The following describes embodiments of the present invention, but the present invention is not limited to these embodiments. The present invention is not limited to the configurations described below, and various modifications are possible within the scope of the claims, and embodiments and examples obtained by appropriately combining the technical means disclosed in the respective embodiments and examples are also included in the technical scope of the present invention. All documents described in this specification are incorporated herein by reference.

< Polypropylene resin as matrix >

In the present invention, the raw material for producing the polypropylene resin pellets mainly contains a polypropylene resin as a matrix. The polypropylene resin used in the present invention is not particularly limited, and may be a homopolymer of polypropylene, a copolymer of polypropylene, or a mixture of both.

The copolymer of the polypropylene may be a copolymer of propylene and ethylene, propylene and an α -olefin, or propylene/ethylene/α -olefin, or the like. The copolymer of propylene and an α -olefin may be, for example, a copolymer of propylene and an α -olefin having 4 to 10 carbon atoms. Examples of the α -olefin having 4 to 10 carbon atoms include 1-butene, 1-pentene, 1-hexene, 3-dimethyl-1-butene, 4-methyl-1-pentene, 4-dimethyl-1-pentene, 1-octene, and the like.

The copolymer of the above-mentioned polypropylene in the present invention may be, without limitation, a random copolymer, a syndiotactic copolymer or a block copolymer. Examples thereof include an ethylene/propylene random copolymer, a 1-butene/propylene random copolymer, an ethylene/propylene block copolymer, and a 1-butene/propylene block copolymer. The copolymer of polypropylene in the present invention may be a propylene/vinyl chloride copolymer, a propylene/maleic anhydride copolymer, or the like. Of these polymers, ethylene/propylene random copolymers and ethylene/1-butene/propylene random copolymers are preferable from the viewpoint of having good foamability and good moldability.

Here, the "polypropylene-based resin" used in the present invention means: 100% by weight of a polymer obtained by polymerizing propylene as at least a part of the monomers has a propylene content of more than 50% by weight.

For example, in the ethylene/propylene random copolymer or the ethylene/1-butene/propylene random copolymer, the ethylene content is preferably in the range of 0.2 wt% to 10 wt% in each 100 wt% of the copolymer. In the ethylene/1-butene/propylene random copolymer, the 1-butene content is preferably in the range of 0.2 to 10% by weight based on 100% by weight of the copolymer. However, the total content of ethylene and 1-butene is preferably in the range of 0.5 to 10% by weight. The content of ethylene and 1-butene in each copolymer is less than 0.2% by weight, and the foamability and moldability tend to be lowered. On the other hand, if the amount exceeds 10% by weight, mechanical properties tend to be deteriorated.

In the present invention, the raw material for producing the polypropylene resin particles may contain other kinds of polyolefins, such as polyethylene resins, in addition to the polypropylene resin. Examples of the resin include a high-density polyethylene resin, a medium-density polyethylene resin, a low-density polyethylene resin, and a linear low-density polyethylene resin. In order to increase the expansion ratio, linear low density polyethylene (or linear low density polyethylene, sometimes abbreviated as "LLDPE") is preferably used. The other kinds of polyolefins may be used singly or in combination of two or more.

When the other types of polyolefins are used in the present invention, the content of the polypropylene-based resin is 80% by weight or more, preferably 90% by weight or more, and more preferably 95% by weight or more, based on the total weight of the polyolefin-based resin.

The melting point of the polypropylene resin used in the present invention is not particularly limited, but is preferably 125 ℃ or higher and 155 ℃ or lower, and more preferably 130 ℃ or higher and 145 ℃ or lower, for example. When the melting point of the polypropylene resin is less than 125 ℃, the heat resistance tends to be lowered, and when the melting point exceeds 155 ℃, the fusion tends to be difficult to secure in the in-mold expansion molding by the expansion method, which causes difficulty in processing.

Here, the melting point of the polypropylene resin is a value obtained by calorimetric measurement using differential scanning calorimetry (hereinafter, sometimes referred to as "DSC method"). Specifically, a quantitative polypropylene resin, for example, 5 to 6mg of the resin is melted by raising the temperature of the resin from 40 ℃ to 220 ℃ at a temperature raising rate of 10 ℃/min, then crystallized by lowering the temperature of the resin from 220 ℃ to 40 ℃ at a temperature lowering rate of 10 ℃/min, and then raised again from 40 ℃ to 220 ℃ at a temperature raising rate of 10 ℃/min to obtain a DSC curve, and the melting peak temperature at the 2 nd temperature raising on the DSC curve is defined as the melting point value.

The melt flow index (hereinafter referred to as "MI") of the polypropylene resin used in the present invention is preferably, but not particularly limited to, 0.5g/10 min or more, 30g/10 min or less, more preferably 2g/10 min or more, or 5g/10min or more, and 20g/10 min or less. If the MI of the polypropylene resin is less than 0.5g/10 min, it may be difficult to obtain polypropylene resin expanded beads having a high expansion ratio, and if it exceeds 30g/10 min, the cells of the polypropylene resin expanded beads may be easily broken, and the percentage of interconnected cells of the polypropylene resin expanded beads may be increased. Expanded polypropylene resin beads having a relatively large expansion ratio can be easily obtained if the melt flow index of the polypropylene resin is from 0.5g/10 min to 30g/10 min. Further, the polypropylene resin in-mold foamed molded article obtained by in-mold foaming the polypropylene resin foamed particles is also excellent in surface appearance and has a small dimensional shrinkage rate. Here, MI of the polypropylene resin is a value measured in accordance with JIS K7210 under the conditions of a temperature of 230 ℃ and a load of 2.16 kg.

The polyolefin-based resin used in the present invention can be obtained by using a catalyst such as a ziegler catalyst, a metallocene catalyst, or the like.

< masterbatch containing carbon Black >

in the present invention, a masterbatch containing carbon black is used, which is obtained by adding carbon black to a resin as a matrix, kneading the mixture, and granulating the mixture. The masterbatch containing carbon black can be produced by melt-kneading the polyolefin resin and carbon black using an extruder, kneader, banbury mixer, roll press, or the like. The use of an extruder is particularly preferred.

The resin in the masterbatch may be selected from polyolefins, such as polyethylene-based resins and polypropylene-based resins. The polyethylene resin may be a homopolymer or a copolymer of ethylene. Examples of the homopolymer include a high-density polyethylene resin, a medium-density polyethylene resin, a low-density polyethylene resin, and a linear low-density polyethylene resin. In order to increase the expansion ratio, linear low density polyethylene is preferably used. The copolymer includes a copolymer of ethylene and an alpha-olefin having 4 to 10 carbon atoms. Examples of the α -olefin having 4 to 10 carbon atoms include 1-butene, 1-pentene, 1-hexene, 3-dimethyl-1-butene, 4-methyl-1-pentene, 4-dimethyl-1-pentene, 1-octene, and the like. The polyethylene resin may be any one of the homopolymers or copolymers described above or a mixture of two or more of them.

The resin in the masterbatch is preferably selected from polypropylene-based resins from the viewpoint of compatibility, and in some preferred embodiments of the present invention, the polypropylene-based resin in the masterbatch may be selected from the ranges described above for the polypropylene-based resin as the matrix.

specific examples of the carbon black in the masterbatch include channel black, roll black, disc black, gas furnace black, oil furnace black, thermal black, and acetylene black. These carbon blacks may be used alone or in combination of 2 or more. The content or concentration of carbon black in the masterbatch is 35 to 55% by weight, preferably 40 to 50% by weight, based on the total weight of the masterbatch.

The melt index MI of the master batch is 5-80 g/10min, preferably 6-60 g/10min under the test condition of 10kg and 230 ℃.

In fact, when carbon black is added to a resin, the fluidity of the resin is affected, and particularly, when the concentration of the added carbon black is high, the effect is significant. Therefore, in the present invention, the melt flowability of the resin in the masterbatch is not considered, but the melt flowability of the whole masterbatch is considered, and it is considered that the melt flowability of the whole masterbatch when the masterbatch is added to the polypropylene-based resin affects the dispersion of the carbon black in the polypropylene-based resin.

When the melt index and the carbon black concentration of the masterbatch are within the above-defined ranges, the polypropylene-based resin expanded particles and the molded article obtained can be made to have a good degree of blackness, and the color is made uniform, while good flame retardancy can be obtained.

The carbon black in the masterbatch of the present invention preferably has an average primary particle diameter of 20 to 60nm, more preferably 20 to 40 nm. When the average primary particle diameter of the carbon black is less than 20nm, dispersibility may sometimes be problematic due to too small particle diameter, and color unevenness tends to occur, and when the average primary particle diameter of the carbon black is more than 60nm, color tone tends to be unclear due to too large particle diameter. The average primary particle diameter can be measured by a laser diffraction-scattering method.

in addition, an auxiliary agent such as a stabilizer, a dispersant, and a lubricant may be added to the masterbatch as necessary.

The masterbatch of the present invention may be prepared by a method generally used in the art, or may be obtained commercially.

In the present invention, the amount of the masterbatch is 4 to 10 parts by weight, preferably 7 to 10 parts by weight, based on 100 parts by weight of the polypropylene resin. When the amount is less than 4 parts by weight, the apparent hue of the polypropylene-based resin expanded beads or molded articles tends to be less sharp, and when the amount is more than 10 parts by weight, the apparent color of the polypropylene-based resin expanded beads or molded articles tends to be uneven.

< other ingredients >

The polypropylene resin particles of the present invention are preferably incorporated with a foam nucleating agent for promoting the formation of cell nuclei. Examples of the foam nucleating agent used in the present invention include inorganic nucleating agents such as talc, calcium stearate, calcium carbonate, silica, kaolin, titanium oxide, bentonite, barium sulfate, and zinc borate. These can be used alone, also can be used in combination of more than 2. Of these foaming nucleating agents, talc, calcium carbonate and calcium stearate are preferable, which are inexpensive and facilitate uniform cell formation. The amount of the foam nucleating agent of the present invention to be added is generally 0.005 to 2 parts by weight, more preferably 0.01 to 1 part by weight, based on 100 parts by weight of the polypropylene-based resin.

The polypropylene resin pellets of the present invention may contain, as necessary, the following components: hydrophilic compounds, metal deactivators, ultraviolet absorbers, ultraviolet stabilizers, antioxidants, processing stabilizers, stabilizers such as metal soaps, flame retardants, antistatic agents or crosslinking agents, chain transfer agents, lubricants, plasticizers, fillers, reinforcing agents, surfactants, conductivity improvers, and the like.

The hydrophilic compound refers to a compound or a derivative thereof containing a hydrophilic group such as a carboxyl group, a hydroxyl group, an amino group, a sulfo group, or a polyoxyethylene group in the molecule, and also includes a hydrophilic polymer. Among these hydrophilic compounds, glycerin is preferred, which makes it easy to obtain expanded particles having a high expansion ratio when an inorganic gas is used as a foaming agent, and which can reduce the foaming pressure for obtaining expanded particles having a desired expansion ratio. The hydrophilic polymer is a polymer having a water absorption of 0.5 wt% or more as measured in accordance with ASTM D570, and includes so-called hygroscopic polymers; a water-absorbent polymer which is a polymer that is insoluble in water, absorbs water several times to several hundred times its own weight, and is difficult to dehydrate even when pressure is applied; and a water-soluble polymer which is a polymer dissolved in water at normal temperature or high temperature. In the present invention, the hydrophilic compound is used in an amount of 0.01 to 10 parts by weight, more preferably 0.1 to 1 part by weight, based on 100 parts by weight of the polypropylene-based resin. When the content of the hydrophilic compound is less than 0.01 parts by weight, expanded beads having a low bulk density and a high expansion ratio tend not to be obtained, and when the content is more than 10 parts by weight, the surface appearance and mechanical properties of the in-mold foamed molded article to be obtained may be impaired.

As the ultraviolet absorber, a benzotriazole-based ultraviolet absorber can be used. Specific preferable examples thereof include: 2- (2-hydroxy-3-tert-butyl-5-methylphenyl) -5-chlorobenzotriazole, 2- (2-hydroxy-5-methylphenyl) -benzotriazole, 2- (2-hydroxy-3, 5-di-tert-butylphenyl) -5-chlorobenzotriazole, 2- (2-hydroxy-3, 5-di-tert-amylphenyl) -benzotriazole, 2- (2-hydroxy-5-tert-octylphenyl) -benzotriazole and the like. These compounds may be used alone, or 2 or more of them may be used in combination. Among them, 2- (2-hydroxy-3-tert-butyl-5-methylphenyl) -5-chlorobenzotriazole, 2- (2-hydroxy-5-methylphenyl) -benzotriazole, and 2- (2-hydroxy-3, 5-di-tert-butylphenyl) -5-chlorobenzotriazole are preferable. The amount of the ultraviolet absorber used is preferably 0.01 to 1.0 part by weight, more preferably 0.1 to 0.5 part by weight, based on 100 parts by weight of the polypropylene-based resin.

As the ultraviolet stabilizer, a hindered amine light stabilizer may be used. Specific preferable examples thereof include: bis (2,2,6, 6-tetramethyl-4-piperidyl) sebacate, bis (1,2,2,6, 6-pentamethyl-4-piperidyl) sebacate, poly { [6- (1,1,3, 3-tetramethylbutyl-amino) -1,3, 5-triazine-2, 4-diyl ] [ (2,2,6, 6-tetramethyl-4-piperidyl) -imino ] }. These compounds may be used alone, or 2 or more of them may be used in combination. Among them, bis (2,2,6, 6-tetramethyl-4-piperidyl) sebacate is preferable. The amount of the ultraviolet stabilizer to be used is preferably 0.01 to 1.0 part by weight, more preferably 0.1 to 0.5 part by weight, based on 100 parts by weight of the polypropylene-based resin.

As the antioxidant, a phenol-based antioxidant can be used. Specific preferable examples thereof include: tetrakis [3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionyloxy-methylene ] methane, tris (3, 5-di-tert-butyl-4-hydroxybenzyl) isocyanate, 3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionyloxy-n-octadecane, 1, 3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane and the like. These compounds may be used alone, or 2 or more of them may be used in combination. Among them, tetrakis [3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionyloxy-methylene ] methane and tris (3, 5-di-tert-butyl-4-hydroxybenzyl) isocyanate are preferable. The amount of the antioxidant to be used is preferably 0.01 to 1.0 part by weight, more preferably 0.1 to 0.5 part by weight, based on 100 parts by weight of the polypropylene-based resin.

As the processing stabilizer, a phosphorous acid-based processing stabilizer can be used. Specific preferable examples thereof include tris (2, 4-di-t-butylphenyl) phosphite, bis (2, 4-di-t-butylphenyl) pentaerythritol diphosphite, tris (monononylphenyl) phosphite and tris (dinonylphenyl) phosphite. These compounds may be used alone, or 2 or more of them may be used in combination. Of these, tris (2, 4-di-t-butylphenyl) phosphorus is preferred. The amount of the processing stabilizer is preferably 0.01 to 1.0 part by weight, more preferably 0.1 to 0.5 part by weight, based on 100 parts by weight of the polypropylene-based resin.

The antistatic agent used in the present invention is not particularly limited, and examples thereof include low-molecular antistatic agents such as fatty acid ester compounds, aliphatic ethanolamine compounds and aliphatic ethanolamine compounds, and high-molecular antistatic agents. These antistatic agents may be used alone, or 2 or more of them may be used in combination. For example, a commercially available mixture of octadecyl diethanolamine monostearate and octadecyl diethanolamine may be exemplified by Electro Stripper TS-11B (manufactured by Kao corporation), and a commercially available mixture of octadecyl diethanolamine monostearate, octadecyl diethanolamine and aliphatic alcohol may be exemplified by Electro Stripper TS-15B (manufactured by Kao corporation). The antistatic agent is preferably contained in an amount of 0.1 to 3 parts by weight, particularly preferably 0.2 to 2 parts by weight, based on 100 parts by weight of the polypropylene-based resin. When the content of the antistatic agent is less than 0.1 parts by weight, antistatic performance tends not to be exhibited, and when it exceeds 3 parts by weight, the deformation shrinkage of the obtained foamed molded article tends to be large, and the elongation of the surface of the molded article tends to be deteriorated.

As the flame retardant, a sterically hindered amine ether flame retardant can be used, and examples thereof include: n, N ' -tris {2, 4-bis [ (1-oxocyclohexyl-2, 2,6, 6-tetramethylpiperidin-4-yl) N-butylamino ] s-triazin-6-yl } -3,3' -ethanediaminopropylamine, N ' -tris {2, 4-bis [ (1-oxocyclohexyl-2, 2,6, 6-tetramethylpiperidin-4-yl) N-butylamino ] s-triazin-6-yl } -3,3' -ethanediyliminodipropylamine, N ' -tris {2, 4-bis [ (1-octyloxy-2, 2,6, 6-tetramethylpiperidin-4-yl) N-butylamino ] s-triazin-6-yl } -3,3 '-ethylenediimidazylamine, N', N "-tris {2, 4-bis [ (1-octyloxy-2, 2,6, 6-tetramethylpiperidin-4-yl) N-butylamino ] s-triazin-6-yl } -3,3 '-ethylenediiminopropylamine, N'" -tris {2, 4-bis [ (1-methoxy-2, 2,6, 6-tetramethylpiperidin-4-yl) N-butylamino ] s-triazin-6-yl } -3,3 '-ethylenediiminopropylamine, N', N "-tris {2, 4-bis [ (1-methoxy-2, 2,6, 6-tetramethylpiperidin-4-yl) N-butylamino ] s-triazin-6-yl } -3,3' -ethylenediiminopropylamine, and the like. These compounds may be used alone, or 2 or more of them may be used in combination. The sterically hindered amine ether flame retardant in the present invention is preferably 0.01 to 0.2 parts by weight, more preferably 0.02 to 0.1 parts by weight, based on 100 parts by weight of the polypropylene resin. When the blending ratio of the sterically hindered amine ether flame retardant is less than 0.01 part by weight, sufficient flame retardancy tends to be difficult to obtain, and when it exceeds 0.2 part by weight, the cost tends to be high, which is not economical.

In a preferred embodiment of the present invention, the polypropylene-based expanded beads and the molded article obtained therefrom of the present invention have a good flame retardant effect even without using the above flame retardant.

The "flame retardancy" in the present invention is determined by a flame test method defined in FMVSS 302, and is obtained by evaluating a polypropylene resin in-mold foamed molded article obtained from polypropylene resin foamed particles. In the evaluation by the test method described later, it is preferable that the burning rate is 100mm/min or less, and it is more preferable that the burning rate is 80mm/min or less.

< Polypropylene resin pellets >

The polypropylene resin pellet of the present invention includes at least the steps of melt-kneading a polypropylene resin and a masterbatch containing carbon black, extruding, and then cutting.

Examples of the method for producing the polypropylene resin pellets of the present invention include the following production steps (also referred to as "granulation step"). First, a polypropylene-based resin and a master batch containing carbon black, and additives such as a foam nucleating agent and the like as needed are blended by a mixing method such as a dry mixing method, a masterbatch method and the like. Next, the obtained mixture is melt-kneaded and extruded by using an extruder, a kneader, a banbury mixer, or the like, and is cut by using a cutter, a pelletizer, or the like, to obtain polypropylene resin pellets having a desired shape such as a cylindrical shape, an elliptical shape, a spherical shape, a cubic shape, a rectangular parallelepiped shape, or the like. Alternatively, the blend may be extruded from a die directly into water, cut into a pellet shape immediately after extrusion, and cooled.

The weight of each particle (also referred to as "average particle weight") of the polypropylene resin particles in the present invention may be 0.1 to 30mg, preferably 0.3 to 20mg, and more preferably 0.5 to 10 mg. When the average particle weight of the polypropylene resin particles is less than 0.1mg, the shrinkage of the in-mold foamed molded article obtained may be large, and when the average particle weight is more than 30mg, uneven foaming may be caused, and it may be difficult to fill the thin portion of the mold. Here, the average particle weight of the polypropylene-based resin particles can be measured by the following method: 500 polypropylene-based resin particles were randomly selected and divided into 5 groups of 100 particles, the weight (mg) of each group of resin particles was measured by an electronic balance, and then divided by the average particle weight of each group calculated by 100, the highest value and the lowest value among them were removed, and the average of the average particle weights of the middle 3 groups was taken as the average particle weight of the polypropylene-based resin particles. In addition, the weight of each particle of the polypropylene resin particles hardly changes even after the foaming step, and there is no problem in setting the average particle weight of the polypropylene resin particles as the average particle weight of the polypropylene resin foamed particles.

< Polypropylene resin expanded particles >

The polypropylene resin expanded beads of the present invention are obtained by expanding polypropylene resin beads.

The polypropylene resin foamed particles of the present invention can be obtained by the following steps:

Step 1) dispersing polypropylene resin particles in an aqueous dispersion medium in a closed container, and heating and pressurizing the mixture to a temperature equal to or higher than the softening temperature of the polypropylene resin particles;

Step 2) releasing the mixture obtained in step 1) to a pressure region lower than the internal pressure of the sealed container,

Wherein the step 1) further comprises a step of introducing an inorganic gas into the closed vessel, and the water contained in the aqueous dispersion medium and the inorganic gas introduced into the closed vessel are used together as a foaming agent.

In step 1), the softening temperature may be a temperature of from the melting point of the polypropylene resin beads to 25 ℃ and a temperature of +25 ℃ or lower, and is preferably a temperature of from the melting point of the polypropylene resin beads to 15 ℃ and a temperature of +15 ℃ or lower. After heating and pressurizing at the temperature to incorporate the foaming agent into the polypropylene resin particles, one end of the closed container is opened to release the polypropylene resin particles into an environment having a pressure lower than the internal pressure of the closed container, thereby producing polypropylene resin foamed particles.

The closed container for dispersing the polypropylene resin pellets is not particularly limited as long as it can withstand the internal pressure of the container and the internal temperature of the container at the time of producing the polypropylene resin pellets, and it is, for example, a hot press type container.

As the aqueous dispersion medium, water may be used, or water may be used in combination with methanol, ethanol, ethylene glycol, or glycerin, as necessary.

In order to prevent the polypropylene resin particles from adhering to each other, a dispersant is preferably used in the aqueous dispersion medium. Examples of the dispersant include inorganic dispersants such as tertiary calcium phosphate, magnesium phosphate, basic magnesium carbonate, calcium carbonate, barium sulfate, kaolin, talc, and clay. If necessary, it is also preferable to use a dispersing aid such as sodium dodecylbenzenesulfonate, sodium n-paraalkylsulfonate, sodium α -olefinsulfonate, magnesium sulfate, magnesium nitrate, magnesium chloride, aluminum sulfate, aluminum nitrate, aluminum chloride, iron sulfate, iron nitrate, iron chloride, or the like in combination. Among them, tertiary calcium phosphate and sodium n-paraffinsulfonate are more preferably used in combination.

The amounts of the dispersant and the dispersing aid used vary depending on the kind thereof and the kind and amount of the polypropylene resin used, but usually, the amount of the dispersant is preferably 0.2 to 3 parts by weight and the amount of the dispersing aid is preferably 0.001 to 0.1 part by weight, based on 100 parts by weight of the dispersion medium. In order to obtain good dispersibility in the aqueous dispersion medium, it is generally preferable to use 20 parts by weight or more and 100 parts by weight or less of the polypropylene-based resin particles per 100 parts by weight of the aqueous dispersion medium.

in the present invention, the foaming agent used in the production of the polypropylene resin foamed particles includes water in an aqueous dispersion medium, which enters the polypropylene resin particles during heating and pressurization, and in step 1), the method further includes a step of introducing an inorganic gas into the closed vessel, wherein the water contained in the aqueous dispersion medium and the inorganic gas introduced into the closed vessel function together as the foaming agent, and the inorganic gas includes carbon dioxide gas, air, nitrogen gas, and the like. They may be used singly or in combination. In the present invention, carbon dioxide gas is preferably used.

In the present invention, step 1) is a pressure-releasing foaming method, and in a preferred embodiment of the present invention, the polypropylene resin beads, the aqueous dispersion medium, if necessary, the dispersant, the dispersion aid, and the like are charged into a closed container, the closed container is evacuated if necessary, a foaming agent is introduced into the closed container, the container is heated to a temperature equal to or higher than the softening temperature of the polypropylene resin beads, or the foaming agent is introduced while the container is heated to a temperature equal to or higher than the softening temperature of the polypropylene resin, the pressure in the closed container is increased to about 1.5 to 5MPa (gauge pressure), preferably 2.0 to 3.5MPa (gauge pressure) by heating, if necessary, the foaming pressure can be adjusted to a desired foaming pressure by further adding the foaming agent, and the foaming temperature can be finely adjusted, and is generally in the range of 135 to 160 ℃, next, the polypropylene resin expanded beads are obtained by releasing the polypropylene resin beads impregnated with the foaming agent into a pressure region (usually, atmospheric pressure) lower than the internal pressure of the closed container. The polypropylene resin foamed particles obtained by the above method are also generally called polypropylene resin one-stage foamed particles.

In addition, without limitation, the polypropylene resin expanded beads of the present invention may be expanded in two or more stages after the first stage expansion, and typically, for example, the polypropylene resin expanded beads of the first stage are subjected to the following steps: the inner pressure of the inorganic gas impregnated into the particles is increased to atmospheric pressure or higher by pressurization with the inorganic gas, and then the particles are further expanded by heat treatment with water vapor having a pressure of 0.02MPa to 0.12MPa to obtain polypropylene resin secondary expanded particles.

The average cell diameter of the polypropylene resin expanded beads of the present invention is preferably 100 to 200 μm, more preferably 130 to 190 μm. When the average cell diameter is less than 100 μm, the surface appearance of the foamed molded article tends to be lowered, and the compressive strength tends to be lowered. When the average cell diameter exceeds 200 μm, the uniformity of the cell diameter tends to be lowered, and the surface appearance of the foam molded article tends to be lowered.

The bulk density of the polypropylene resin expanded beads of the present invention is preferably 20 to 55g/L, and more preferably 23 to 55 g/L. When the bulk density is less than 20g/L, the polypropylene resin foamed molded article tends to be easily shrunk or deformed, and the mechanical properties tend to be deteriorated. When the bulk density exceeds 55g/L, the foamed molded article tends to be hard and heavy, and the advantage of light weight cannot be obtained.

< Polypropylene resin foam-molded article and production method >

In the present invention, a polypropylene resin foamed molded article can be obtained by performing in-mold foaming as follows: the polypropylene resin expanded beads obtained as described above are filled in a mold and heated with steam or the like to fuse the expanded beads to each other.

As the in-mold foaming method, for example, the following methods can be used:

1) A method in which the polypropylene resin foamed particles are subjected to a pressure treatment with an inorganic gas (for example, air, nitrogen, carbon dioxide, or the like) to impregnate the polypropylene resin foamed particles with the inorganic gas, a predetermined internal pressure is applied to the polypropylene resin foamed particles, and then the polypropylene resin foamed particles are filled in a mold and heated and fused with steam; alternatively, the first and second electrodes may be,

2) A method of compressing polypropylene resin foamed pellets under a gas pressure to fill a mold with the pellets having an increased internal pressure, and heating and fusing the pellets with steam; alternatively, the first and second electrodes may be,

3) A method of filling a mold with polypropylene resin foamed particles and heating and fusing the same with steam without particularly performing a pretreatment.

For example, in the case of 1), the expanded polypropylene resin beads are filled into a sealable but not sealable molding die while applying an expansion capability by pressurizing air in a pressure-resistant container in advance to make the internal pressure of the expanded polypropylene resin beads to about 0.08MPa (absolute pressure) or more and 0.3MPa (absolute pressure) or less, and the expanded polypropylene resin beads are molded under the conditions of a heating water vapor pressure of about 0.05MPa (gauge pressure) or more and 0.4MPa (gauge pressure) or less and a heating time of about 1 second or more and 120 seconds with water vapor as a heating medium to fuse the expanded polypropylene resin beads to each other, and then cooled with water until the deformation of the in-mold expanded molded article after the in-mold expanded molded article is extracted from the molding die can be suppressed, whereby the in-mold expanded polypropylene resin molded article can be produced. From the viewpoint of surface properties, mechanical properties, dimensional stability, and the like of the obtained polypropylene resin in-mold foamed molded article, the internal pressure of the foamed particles is preferably 0.1MPa (absolute pressure) or more and 0.25MPa (absolute pressure) or less, the heating water vapor pressure is preferably 0.05MPa (gauge pressure) or more and 0.25MPa (gauge pressure) or less, and the heating time is preferably 5 seconds or more and 60 seconds or less.

The polypropylene resin in-mold foamed molded article obtained in this way can be used for heat insulating materials, cushioning packaging materials, interior parts for automobiles, and the like. The polypropylene resin foamed molded article of the present invention is particularly suitable for use as a cushioning packaging material for producing articles of various shapes.

The invention is further illustrated, but not limited, by the following examples.