Polyolefin-based resin foamed particles and manufacturing method therefor

Abstract

The present invention relates to polyolefin-based resin foamed particles, which can be stably produced and can achieve a high foaming ratio (i.e., low dry specific gravity) by one-stage foaming, and a manufacturing method therefor. Provided is the polyolefin-based resin foamed particles, which comprise a substrate resin containing a polyolefin-based resin as a main component, and further comprise: a component (A) which is a water-absorbing organic compound; and a component (B) which is at least one selected from the group consisting of a metal borate and melamine, wherein the content of the component (A) is 0.1-0.6 parts by weight, and the content of the component (B) is 0.1-0.6 parts by weight with respect to 100 parts by weight of the substrate resin.

Description

Polyolefin resin foamed particles and method for producing the same TECHNICAL FIELD

[0001] The present application relates to polyolefin resin foamed particles, and a method for producing the same, and belongs to the technical field of polymer foamed materials. BACKGROUND

[0002] Polyolefin resin foamed molded bodies are lighter in weight than non-foamed molded bodies, and thus are widely used for cushioning packaging materials, recyclable containers, thermal transport containers (for example, seafood transport boxes, take-out transport boxes, and the like), automobile parts (for example, tool boxes, floor core materials, and the like), and the like.

[0003] When the existing production method uses water and / or carbon dioxide as a foaming agent to produce polyolefin resin foamed particles, in order to improve the foaming property, additives such as a foaming nucleating agent, a colorant, a hydrophilic compound, and the like are generally added. For example, polypropylene resin foamed particles using zinc borate are disclosed in Patent Literature 1 and Patent Literature 2, respectively, however, the foaming property thereof is still insufficient.

[0004] Patent Literature 3 discloses a method for producing polyolefin resin foamed particles, which uses polypropylene resin particles containing polyethylene glycol and a foaming nucleating agent, and produces polyolefin resin foamed particles by foaming. However, the polyolefin resin foamed particles of Patent Literature 3 need to undergo two-stage foaming (also sometimes referred to as secondary foaming, or secondary-stage foaming) to achieve a useful foaming ratio. Two-stage foaming is uneconomical because the process is increased compared to one-stage foaming (also sometimes referred to as primary foaming, or primary-stage foaming).

[0005] Prior Art Documents

[0006] Patent Literature

[0007] Patent Literature 1: CN111378202A

[0008] Patent Literature 2: CN101679662A

[0009] Patent Literature 3: CN101896543A SUMMARY

[0010] PROBLEMS TO BE SOLVED BY THE INVENTION

[0011] The present inventors have found that, in order to achieve satisfactory foaming properties in the prior art, it is necessary to use an additive or to perform two-stage foaming, which is complicated and results in high costs. Furthermore, the present inventors have also found that, in the case of using an additive, depending on the type and amount of the additive, it is sometimes difficult to stably extrude polyolefin-based resin particles during production, and thus stable production cannot be achieved. In addition, in the case of selecting the type and amount of the additive in order to achieve stable production, it is sometimes not possible to obtain a satisfactory high foaming ratio. Therefore, there is an urgent need to develop a technology that not only enables stable extrusion of polyolefin-based resin particles during production, but also enables a high foaming ratio through one-stage foaming.

[0012] Therefore, the problem to be solved by the present application is to provide polyolefin-based resin foamed particles that enable stable production (i.e., stable extrusion of polyolefin-based resin particles) and a high foaming ratio (i.e., a low dry specific gravity) through one-stage foaming, and a method for producing the same.

[0013] Solution to the problem

[0014] The present inventors have conducted intensive research in order to solve the above problem, and as a result, have found that the above problem can be solved by using, in combination, a component (A) that is a water-absorbing organic compound and at least one component (B) selected from the group consisting of a metal salt of boric acid and melamine, and thus have completed the present application.

[0015] Specifically, the present application is based on the following configuration.

[0016] The present application provides a polyolefin-based resin foamed particle, comprising a base resin in which a polyolefin-based resin is a main component,

[0017] The aforementioned polyolefin-based resin foamed particle further comprises:

[0018] a component (A) that is a water-absorbing organic compound; and

[0019] a component (B) that is at least one selected from the group consisting of a metal salt of boric acid and melamine,

[0020] The content of the aforementioned component (A) is 0.1 to 0.6 parts by weight, and the content of the aforementioned component (B) is 0.1 to 0.6 parts by weight, with respect to 100 parts by weight of the aforementioned base resin.

[0021] In some preferred embodiments, in the polyolefin-based resin foamed particle of the present application, the content of the aforementioned component (A) is 0.2 to 0.4 parts by weight, and the content of the aforementioned component (B) is 0.2 to 0.4 parts by weight, with respect to 100 parts by weight of the aforementioned base resin.

[0022] In some preferred embodiments, in the polyolefin-based resin expanded particles of the present application, the aforementioned water-absorbing organic compound is at least one selected from the group consisting of glycerin, diglycerin, and polyethylene glycol.

[0023] In some preferred embodiments, in the polyolefin-based resin expanded particles of the present application, the aforementioned metal salt of boric acid is zinc boric acid.

[0024] In some preferred embodiments, in the polyolefin-based resin expanded particles of the present application, the aforementioned polyolefin-based resin is a polypropylene-based resin.

[0025] In some preferred embodiments, in the polyolefin-based resin expanded particles of the present application, the aforementioned base resin contains 50% by weight or more of a polypropylene-based resin.

[0026] In some preferred embodiments, the polyolefin-based resin expanded particles of the present application are one-stage expanded particles.

[0027] In some preferred embodiments, the bulk density of the polyolefin-based resin expanded particles of the present application is 27.5 g / L or less.

[0028] The present application also provides a method for producing polyolefin-based resin expanded particles, comprising:

[0029] a step of dispersing polyolefin-based resin particles in an aqueous dispersion medium in a container, introducing a blowing agent, and allowing the aforementioned blowing agent to infiltrate the aforementioned polyolefin-based resin particles under heating and pressurization; and

[0030] a step of allowing the aforementioned polyolefin-based resin particles to expand by releasing the aforementioned polyolefin-based resin particles to a pressure region lower than the internal pressure in the aforementioned container, thereby obtaining polyolefin-based resin expanded particles,

[0031] the aforementioned polyolefin-based resin particles contain a base resin having a polyolefin-based resin as a main component, component (A), and component (B),

[0032] the aforementioned component (A) is a water-absorbing organic compound,

[0033] the content of the aforementioned component (A) is 0.1 to 0.6 parts by weight with respect to 100 parts by weight of the aforementioned base resin,

[0034] the aforementioned component (B) is at least one selected from the group consisting of a metal salt of boric acid and melamine,

[0035] the content of the aforementioned component (B) is 0.1 to 0.6 parts by weight with respect to 100 parts by weight of the aforementioned base resin.

[0036] In some preferred embodiments, in the method for producing the polyolefin-based resin expanded particles of the present application, the aforementioned water-absorbing organic compound is at least one selected from the group consisting of glycerol, diglycerol, and polyethylene glycol.

[0037] In some preferred embodiments, in the method for producing the polyolefin-based resin expanded particles of the present application, the aforementioned polyolefin-based resin is a polypropylene-based resin.

[0038] In some preferred embodiments, in the method for producing the polyolefin-based resin expanded particles of the present application, the aforementioned base resin contains 50% by weight or more of a polypropylene-based resin.

[0039] Effects of the Invention

[0040] The polyolefin-based resin expanded particles and the method for producing the same according to the present application not only enable stable extrusion of polyolefin-based resin particles, but also enable obtaining polyolefin-based resin expanded particles having a high expansion ratio. In particular, the polyolefin-based resin expanded particles and the method for producing the same according to the present application enable obtaining polyolefin-based resin expanded particles having a high expansion ratio by one-stage expansion. DETAILED DESCRIPTION

[0041] Various exemplary embodiments, features, and aspects of the present application will be described in detail below. The word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any implementation described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other implementations.

[0042] In addition, in order to better illustrate the present application, numerous specific details are given in the following detailed description of the application. It will be understood by those skilled in the art that the present application can be practiced without certain specific details. In other instances, well-known methods, procedures, apparatuses, and steps have not been described in detail so as not to obscure the underlying principles of the application.

[0043] In the present specification, a numerical range expressed using "numerical value A to numerical value B" means a range including the end point numerical values A and B. Unless otherwise specified, the units used in the present specification are international standard units.

[0044] In the present specification, unless otherwise specified, "parts by weight" and "wt%" with respect to polymers, copolymers, and resins in the present specification are with respect to solid components, and do not include solvents.

[0045] In the present application, "(meth)acrylic acid" means acrylic acid and / or methacrylic acid. In addition, "(meth)acrylate" means acrylate and / or methacrylate.

[0046] In the present specification, "polyolefin-based resin foamed particles" refer to particles obtained by foaming "polyolefin-based resin particles". As for polyolefin-based resin foamed particles manufactured using polyolefin-based resin particles, the structure of the polyolefin-based resin particles changes, but the components of the polyolefin-based resin particles do not change. Therefore, as for foamed molded bodies manufactured using polyolefin-based resin foamed particles, the structure of the polyolefin-based resin foamed particles changes, but the components of the polyolefin-based resin foamed particles do not change. Therefore, the components and their relative amounts obtained by analyzing polyolefin-based resin foamed particles or foamed molded bodies thereof can be regarded as the components and their relative amounts of polyolefin-based resin particles as raw materials of the polyolefin-based resin foamed particles or foamed molded bodies.

[0047] < Polyolefin-based resin foamed particles >

[0048] In the present application, even by one-stage foaming, polyolefin-based resin foamed particles having a sufficiently high foaming ratio can be obtained. Therefore, from the viewpoint of saving processes, the polyolefin-based resin foamed particles of the present application are preferably one-stage foamed particles. On the other hand, from the viewpoint of further increasing the foaming ratio, the polyolefin-based resin foamed particles are preferably two-stage foamed particles obtained by further foaming one-stage foamed particles, or the like.

[0049] In the case where the polyolefin-based resin foamed particles of the present application are one-stage foamed particles, the dry bulk density (i.e., the bulk density) thereof can be, for example, 27.5 g / L or less, preferably 27 g / L or less, further preferably 26 g / L or less, and particularly preferably 25 g / L or less. When the dry bulk density exceeds 27.5 g / L, although the mechanical strength increases, there is a tendency to impair the lightweight property of foamed molded bodies. In addition, in the case where the polyolefin-based resin foamed particles of the present application are one-stage foamed particles, the aforementioned dry bulk density (i.e., the bulk density) can be, for example, 20 g / L or more, preferably 22 g / L or more, and further preferably 23 g / L or more. When the dry bulk density is less than 20 g / L, there is a concern that foamed molded bodies obtained from the polyolefin-based resin foamed particles are easily shrunk or deformed, and the mechanical properties thereof are decreased.

[0050] In the case where the polyolefin-based resin foamed particles of the present application are multi-stage foamed particles, the preferred mode of the dry bulk density of one-stage foamed particles used to obtain the multi-stage foamed particles is the same as that in the case where the polyolefin-based resin foamed particles of the present application are one-stage foamed particles.

[0051] The dry specific gravity of the polyolefin-based resin foamed particles can be further reduced by further foaming the first foamed particles. For example, in the case where the polyolefin-based resin foamed particles of the present application are second foamed particles obtained by further foaming the first foamed particles, the dry specific gravity of the second foamed particles can be 20 g / L or less, preferably 18 g / L or less, and more preferably 15 g / L or less. There is no particular limitation on the lower limit of the dry specific gravity of the second foamed particles, and from the viewpoint of practicality, it is usually 10 g / L or more.

[0052] Hereinafter, each component of the polyolefin-based resin foamed particles will be described in order.

[0053] Polyolefin-based resin

[0054] The polyolefin-based resin foamed particles of the present application contain a base resin having a polyolefin-based resin as a main component. Here, "having a polyolefin-based resin as a main component" means that the polyolefin-based resin accounts for 50% by weight or more, preferably 70% by weight or more, and further preferably 90% by weight or more, of the total weight of the base resin, and can be 95% by weight or more, 98% by weight or more, 99% by weight or more, or 100% by weight.

[0055] The polyolefin-based resin refers to a polymer obtained by polymerizing or copolymerizing an α-olefin (i.e., a mono-olefin having a double bond at the end of a molecular chain, having the formula R-CH=CH2, wherein R is an alkyl group) such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 4-methyl-1-pentene, and the like, alone or in combination, and a polystyrene resin is not included in the category of the polyolefin-based resin. Further, the polyolefin-based resin used in the present application is a polymer containing 75% by weight or more of monomer units derived from an α-olefin monomer. The content of the monomer units derived from the α-olefin monomer is preferably 80% by weight or more. Monomer units derived from other monomers copolymerizable with the α-olefin monomer can also be contained in an amount of 25% by weight or less, and preferably 20% by weight or less.

[0056] Specific examples of the α-olefin monomer include, for example, ethylene, propylene, 1-butene, isobutylene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3,4-dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene, 1-octene, 1-decene, and the like, α-olefins having 2 to 12 carbon atoms. Two or more of them can be used in combination.

[0057] Further, as specific examples of the above-mentioned other monomer copolymerizable with the α-olefin monomer, for example, there can be mentioned cyclic olefins such as cyclopentene, norbornene, 1,4,5,8-dimethano-l,2,3,4,4a,8,8a,6-octahydronaphthalene, and the like; 5-methylene-2-norbornene; 5-ethylidene-2-norbornene; 1,4-hexadiene; methyl-1,4-hexadiene; 7-methyl-l,6-octadiene; and the like. These can be used alone or in combination of two or more.

[0058] As specific examples of the polyolefin-based resin used in the present application, for example, there can be mentioned high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, and the like, polyethylene-based resins having ethylene as a main component; and polypropylene-based resins having propylene as a main component. These polyolefin-based resins can be used alone or in combination of two or more. Among these, as the polyolefin-based resin, from the viewpoint of imparting excellent mechanical strength, heat resistance, and the like to the foamed molded body, it is preferable to use a polypropylene-based resin.

[0059] When a polypropylene-based resin is used as the polyolefin-based resin, from the viewpoint of imparting excellent mechanical strength, heat resistance, and the like to the foamed molded body, the above-mentioned base resin contains 50% by weight or more of a polypropylene-based resin, preferably contains 80% by weight or more, further preferably contains 90% by weight or more, and more preferably contains 95% by weight or more of a polypropylene-based resin.

[0060] Here, the "polypropylene-based resin" used in the present application means a polymer obtained by polymerization using propylene as at least a part of the monomers, and the content rate of the monomer units derived from propylene is more than 50% by weight in 100% by weight. There is no particular limitation as long as propylene is included as a main component of the monomers, and for example, there can be mentioned a propylene homopolymer, an α-olefin-propylene random copolymer, an α-olefin-propylene block copolymer, and the like. These can be used alone or in combination of two or more. As the copolymer of propylene and α-olefin, for example, there can be mentioned a copolymer of propylene and an α-olefin having 4 to 10 carbon atoms. As the above-mentioned α-olefin having 4 to 10 carbon atoms, for example, there can be mentioned 1-butene, 1-pentene, 1-hexene, 3,3-dimethyl-l-butene, 4-methyl-l-pentene, 4,4-dimethyl-l-pentene, 1-octene, and the like.

[0061] The polypropylene-based resin used in the present application preferably has a melting point of 130°C or higher and 165°C or lower, and more preferably 135°C or higher and 155°C or lower. When the melting point of the polypropylene-based resin is lower than 130°C, there is a tendency that heat resistance and mechanical strength are insufficient. Further, when the melting point exceeds 165°C, there is a tendency that it is difficult to ensure fusion of the particles at the time of manufacturing the foamed molded body. The aforementioned melting point refers to the peak temperature of the endothermic peak in the DSC curve obtained when 1 to 10 mg of the polypropylene-based resin is warmed at a temperature increase rate of 10°C / minute from 40°C to 220°C, then cooled at a temperature decrease rate of 10°C / minute to 40°C, and then warmed again at a temperature increase rate of 10°C / minute to 220°C. That is, the melting point is the peak temperature measurement value obtained as described above at the time of the second warming (2nd run) of the DSC curve.

[0062] The polypropylene-based resin used in the present application preferably has a melt flow rate (hereinafter referred to as "MFR value") of 0.5 g / 10 minutes or higher and 30 g / 10 minutes or lower, and more preferably 2 g / 10 minutes or higher and 20 g / 10 minutes or lower. When the MFR value is lower than 0.5 g / 10 minutes, it is sometimes difficult to obtain polyolefin-based resin foamed particles with a high foaming ratio, and when it exceeds 30 g / 10 minutes, there is a tendency that the bubbles of the polyolefin-based resin foamed particles easily collapse and the coalescence rate of the polyolefin-based resin foamed particles becomes high. Note that the MFR value of the polypropylene-based resin can be a value determined in accordance with JIS K7210 under conditions of a temperature of 230°C and a load of 2.16 kg.

[0063] The polyolefin-based resin used in the present application can be obtained using a Ziegler catalyst, a metallocene catalyst, or the like.

[0064] In addition, in the present application, the base material resin can also include other resins other than the polyolefin-based resin. As the other resins, base material resins generally used in the art can be used, and for example, polystyrene-based resins, acrylic resins, polyurethane resins, phenol-aldehyde resins, urea-aldehyde resins, and the like can be listed.

[0065] Component (A)

[0066] The component (A) contained in the polyolefin-based resin foamed particles of the present application is a water-absorbing organic compound. Note that the component (A) of the present application is a different component from the component (B), in other words, the component (A) does not include melamine. As for the water-absorbing organic compound as the component (A), as long as it is an organic compound capable of interacting with water to absorb water or dissolve in water, there is no particular limitation on the specific structure thereof, and a hydrophilic organic compound can be used, for example, representatively. The hydrophilic organic compound refers to a compound or a derivative thereof having a hydrophilic group such as a carboxyl group, a hydroxyl group, an amino group, a sulfo group, a polyoxyethylene group, or the like in the molecule, and also includes a hydrophilic polymer. Specifically, for example, as the aforementioned water-absorbing organic compound, glycerin, diglycerin, lauric acid, sodium laurate, ethylene glycol, polyethylene glycol, isocyanuric acid, isocyanuric acid condensates, or the like can be mentioned. These water-absorbing organic compounds can be used alone or in combination of two or more.

[0067] In the polyolefin-based resin foamed particles of the present application, the aforementioned component (A) is preferably at least one selected from the group consisting of glycerin, diglycerin, and polyethylene glycol, and further preferably glycerin, from the viewpoint of further increasing the foaming ratio when using an inorganic gas as a foaming agent and reducing the foaming pressure of the foamed particles for obtaining a target ratio.

[0068] In the polyolefin-based resin foamed particles of the present application, the content of the aforementioned component (A) is 0.1 to 0.6 parts by weight with respect to 100 parts by weight of the aforementioned base resin. Thereby, the polyolefin-based resin particles can be stably extruded, do not generate smoke during the manufacturing process, and can achieve a high foaming ratio by one-stage foaming. From the viewpoint of further increasing the foaming ratio, the content of the aforementioned component (A) is preferably 0.2 parts by weight or more, and further preferably 0.3 parts by weight or more, with respect to 100 parts by weight of the aforementioned base resin. From the viewpoint of more stably extruding the polyolefin-based resin particles, the content of the aforementioned component (A) is preferably 0.5 parts by weight or less, and more preferably 0.4 parts by weight or less, with respect to 100 parts by weight of the aforementioned base resin.

[0069] Component (B)

[0070] The component (B) included in the polyolefin-based resin foamed particles of the present application is at least one selected from the group consisting of a metal salt of boric acid and melamine. From the viewpoint of obtaining polyolefin-based resin foamed particles having a higher foaming ratio by one-stage foaming, the component (B) is preferably a metal salt of boric acid, and further preferably zinc borate.

[0071] In the polyolefin-based resin foamed particles of the present application, the content of the aforementioned component (B) is 0.1 to 0.6 parts by weight per 100 parts by weight of the aforementioned base resin. Thus, the polyolefin-based resin particles can be stably extruded, and a high foaming ratio can be achieved by one-stage foaming. From the viewpoint of further increasing the foaming ratio, the content of the aforementioned component (B) is preferably 0.15 parts by weight or more, more preferably 0.2 parts by weight or more, and further preferably 0.3 parts by weight or more, per 100 parts by weight of the aforementioned base resin. From the viewpoint of more stably extruding the polyolefin-based resin particles, the content of the aforementioned component (B) is preferably 0.55 parts by weight or less, more preferably 0.45 parts by weight or less, and further preferably 0.4 parts by weight or less, per 100 parts by weight of the aforementioned base resin.

[0072] Other water-absorbing compounds

[0073] In the polyolefin-based resin foamed particles of the present application, other water-absorbing compounds other than the component (A) and the component (B) can be added as needed. The aforementioned other water-absorbing compounds are not particularly limited as long as they do not include the component (A) and the component (B), and examples thereof include water-soluble polymers, water-absorbing polymers, hydrophilic polymers, water-soluble organic substances, water-absorbing organic substances, hydrophilic organic substances, water-soluble inorganic substances, water-absorbing inorganic substances, and hydrophilic inorganic substances. These other water-absorbing compounds can be used alone or in combination of two or more.

[0074] In the polyolefin-based resin foamed particles of the present application, when other water-absorbing compounds are used, the content of the other water-absorbing compounds is preferably less than the total content of the component (A) and the component (B).

[0075] Foaming nucleating agent

[0076] The polyolefin-based resin foamed particles of the present application can also contain a foaming nucleating agent for forming bubble nuclei, as needed. As the foaming nucleating agent used in the present application, inorganic foaming nucleating agents such as talc, calcium stearate, calcium carbonate, silica, kaolin, titanium oxide, bentonite, barium sulfate, and the like can be used. These can be used alone or in combination of two or more. Among these foaming nucleating agents, talc, calcium carbonate, and calcium stearate are preferred because they are inexpensive and allow uniform bubbles to be obtained. The amount of the foaming nucleating agent added in the present application varies depending on the type of the foaming agent used, but in general, the amount of the foaming nucleating agent added is 0.005 parts by weight to 0.8 parts by weight, and further preferably 0.01 parts by weight to 0.2 parts by weight, relative to 100 parts by weight of the aforementioned base resin. When the amount of the foaming nucleating agent added is less than 0.005 parts by weight, there is a possibility that it is difficult to increase the foaming ratio of the polyolefin-based resin foamed particles and that the uniformity of the bubbles decreases. When the amount of the foaming nucleating agent added exceeds 0.8 parts by weight, there is a tendency that it is difficult to stably extrude the polyolefin-based resin particles.

[0077] Other additives

[0078] Other additives such as antistatic agents, coloring agents, flame retardants, heat stabilizers, light stabilizers, radiation heat transfer inhibitors, and the like can also be added to the polyolefin-based resin foamed particles, as needed, without impairing the effects of the present application. The heat stabilizers used in the present application include hindered amine compounds, phosphorus compounds, and epoxy compounds. Examples of the light stabilizers include hindered amines, phosphorus stabilizers, epoxy compounds, phenolic antioxidants, nitrogen-containing stabilizers, sulfur stabilizers, benzotriazoles, and the like.

[0079] Examples of the coloring agents used in the present application include inorganic pigments such as carbon black, kohin black, iron black, cadmium yellow, cadmium red, cobalt violet, cobalt blue, Prussian blue, ultramarine blue, chromium yellow, zinc yellow, barium yellow, and the like; and organic pigments such as polyazo, quinacridone, phthalocyanine, perinone, anthraquinone, sulfur indigo blue, dioxazine, isoindolinone, and quinophthalone. In the present application, when carbon black is contained in the polyolefin-based resin foamed particles, the carbon black is preferably mixed with the aforementioned base resin in the form of a master batch (also referred to as a master batch) containing carbon black, from the viewpoint of uniformly dispersing the carbon black in the polyolefin-based resin foamed particles and stably extruding the polyolefin-based resin particles. The content of the aforementioned coloring agent is not particularly limited as long as it does not impair the effects of the present application, and the preferred range varies depending on the type of the coloring agent. For example, when the coloring agent is carbon black, its content is preferably 0.01 to 8% by weight, relative to 100% by weight of the polyolefin-based resin foamed particles of the present application. For example, when the coloring agent is an organic pigment, its content is 0.01 to 5% by weight, relative to 100% by weight of the polyolefin-based resin foamed particles of the present application. The content of the coloring agent can be appropriately set or adjusted depending on the color and the degree of color development required for the foamed molded body.

[0080] As the antistatic agent used in the present application, there is no particular limitation, and low-molecular antistatic agents such as fatty acid ester compounds, fatty ethanolamine compounds, fatty ethanolamide compounds, and the like, high-molecular antistatic agents, and the like can be exemplified. These antistatic agents can be used alone or two or more kinds can be used in combination. As a commercially available product of a mixture of octadecyl diethanolamine monostearate and octadecyl diethanolamine, Electro Stripper TS-11B (manufactured by Kawabata Kagaku K.K.) can be exemplified, and as a commercially available product of a mixture of octadecyl diethanolamine monostearate and octadecyl diethanolamine and a fatty alcohol, Electro Stripper TS-15B (manufactured by Kawabata Kagaku K.K.), and the like can be exemplified. The content of the aforementioned antistatic agent is not particularly limited as long as the effect of the present application is not impaired, and for example, 0.01 to 3% by weight, relative to 100% by weight of the polyolefin resin expanded particles of the present application, can be appropriately selected.

[0081] As the radiation heat inhibitor (a substance having a property of reflecting, scattering, or absorbing light in the near infrared or infrared region (for example, a wavelength range of 800 to 3000 nm)) used in the present application, graphite, graphene, activated carbon, carbon black, titanium dioxide, and aluminum, and the like can be exemplified.

[0082] <Method for producing polyolefin resin expanded particles>

[0083] The method for producing polyolefin resin expanded particles of the present application includes: a step of dispersing polyolefin resin particles in an aqueous dispersion medium in a container, introducing a blowing agent, and allowing the blowing agent to infiltrate into the polyolefin resin particles under heating and pressurization conditions; and

[0084] A step of allowing the polyolefin resin particles to expand by releasing the polyolefin resin particles to a pressure region lower than the internal pressure in the container, thereby obtaining polyolefin resin expanded particles.

[0085] Polyolefin resin particles

[0086] The aforementioned polyolefin resin particles used in the method for producing polyolefin resin expanded particles of the present application include a base resin having a polyolefin resin as a main component, component (A) which is a hygroscopic organic compound, the content of the component (A) being 0.1 to 0.6 parts by weight, relative to 100 parts by weight of the base resin, and component (B) which is at least one selected from the group consisting of a metal salt of boric acid and melamine, the content of the component (B) being 0.1 to 0.6 parts by weight, relative to 100 parts by weight of the base resin.

[0087] When the polyolefin resin particles of the present application are used to produce the polyolefin resin foamed particles of the present application, the structure of the polyolefin resin particles is changed, but the components of the polyolefin resin particles are not changed. Therefore, in the present specification, the components and the contents thereof, and the preferred modes in the polyolefin resin particles are the same as those described above in the polyolefin resin foamed particles.

[0088] As a method for producing the polyolefin resin particles in the present application, for example, a production process (also referred to as "a pelletizing process") described below can be mentioned. First, a polyolefin resin, component (A), component (B), and other additives as needed are melt-kneaded using an extruder, a kneader, a Banbury mixer, or the like, and then extruded, and the extrudate is cut using a cutter, a pelletizer, or the like to produce polyolefin resin particles having a desired shape such as a cylindrical shape, an elliptical shape, a spherical shape, a cubic shape, a cuboid shape, or the like. Alternatively, the above blend can be extruded directly from a die into water and then immediately cut into a particle shape and cooled.

[0089] As to the step of melt-kneading, from the viewpoint of higher extrudability of the polyolefin resin particles, an extruder such as a single-screw extruder, a twin-screw extruder, or the like is preferably used. The means for feeding the above component (A), the above component (B), and other additives as needed to the extruder is not particularly limited, and an appropriate feeding means can be used for each component according to the form thereof. For example, in the case where component (A) is a liquid, it can be directly added to the extruder, and from the viewpoint of the foaming ratio and the uniformity of foaming, it is preferable to be pressurized and injected at the middle melt section of the extruder. In the case where component (A) is a solid, from the viewpoint of saving the process and cost, it is preferable that component (A) is not first made into a master batch and then fed to the extruder, but is directly supplied to the hopper of the extruder. From the same viewpoint, it is preferable that component (B) is directly supplied to the hopper of the extruder. As to the step of cutting and the step of cooling, there is no particular limitation, and a method generally used in the art can be appropriately used.

[0090] In one preferred embodiment, a polyolefin resin, component (B), and other additives as needed are supplied to the hopper of a twin-screw extruder, at least one component (A) selected from the group consisting of glycerol, diglycerol, and polyethylene glycol is pressurized and injected at the middle melt section of the extruder, and the above components are melt-kneaded and extruded using the extruder, and then cooled and cut to obtain polyolefin resin particles.

[0091] Production process

[0092] As a method for producing the polyolefin resin foamed particles in the present application, for example, a production process described below can be mentioned.

[0093] The dispersion liquid formed from the polyolefin-based resin particles of the present application, the water-based dispersion medium, the inorganic dispersant and the dispersion aid, if necessary, is charged into a container, heated to a temperature above the softening temperature of the polyolefin-based resin particles in the presence of a foaming agent, and then the dispersion liquid in the container is released to a pressure region lower than the internal pressure of the container to foam the polyolefin-based resin particles, thereby obtaining the polyolefin-based resin foamed particles. At the time of discharging the contents of the container to a pressure region lower than the internal pressure of the container, by pressurized supply of an inorganic gas such as carbon dioxide, nitrogen or air at an arbitrary stage before the release to the low pressure region, by increasing the internal pressure and adjusting the pressure release rate during foaming, the foaming ratio and the average bubble diameter can be adjusted.

[0094] As the water-based dispersion medium used in the present application, for example, water, ethanol, ethylene glycol and the like can be used, of which water is preferred.

[0095] The amount of the water-based dispersion medium used is not particularly limited, but from the viewpoint of productivity, relative to 100 parts by weight of the base resin, it is preferably 100 to 500 parts by weight, more preferably 130 to 300 parts by weight, and most preferably 150 parts by weight or more to 210 parts by weight or less. When it is less than 100 parts by weight, sometimes the dispersion liquid formed from the polyolefin-based resin particles, the water-based dispersion medium, the inorganic dispersant and the dispersion aid can not be stable, and when it exceeds 500 parts by weight, the productivity sometimes decreases.

[0096] The inorganic dispersant usable in the present application is not particularly limited, and a commonly used inorganic dispersant can be used. Specific examples thereof include barium sulfate, kaolin, silicoaluminate containing silica-alumina as a main component such as talc, alumina, titanium oxide, calcium phosphate, calcium carbonate, magnesium phosphate, basic magnesium carbonate, basic zinc carbonate and the like. These inorganic dispersants can be used singly or in combination of two or more.

[0097] Of these, from the viewpoint of small amount of use, dispersing effect and small load on waste water treatment, it is preferred to contain barium sulfate and silicoaluminate containing silica-alumina as a main component, calcium phosphate and magnesium phosphate.

[0098] The amount of the inorganic dispersant is not particularly limited and can be appropriately adjusted to exert a dispersion stabilizing effect, and the ratio of the inorganic dispersant to the dispersion aid can also be appropriately adjusted. With respect to 100 parts by weight of the polyolefin-based resin particles, the amount of the inorganic dispersant is preferably 0.01 parts by weight or more and 5 parts by weight or less, more preferably 0.05 parts by weight or more and 4 parts by weight or less, and most preferably 0.1 parts by weight or more and 3 parts by weight or less. If the amount is less than 0.01 parts by weight, the stability of the dispersion tends to decrease at a temperature higher than the softening temperature of the polyolefin-based resin particles, and if the amount exceeds 5 parts by weight, a large amount of the inorganic dispersant adheres to the surface of the polyolefin-based resin particles, and the fusion rate of the foamed molded body formed of the polyolefin-based resin foamed particles tends to decrease.

[0099] As the dispersion aid that can be used in the present application, a surfactant is preferably used. As the surfactant, a commonly used anionic, nonionic, cationic surfactant, amphoteric surfactant, or the like can be used. These surfactants can be used alone or in combination with two or more kinds.

[0100] Among the dispersion aids, from the viewpoint of the stability of the dispersion liquid formed of the polyolefin-based resin particles, the water-based dispersion medium, the inorganic dispersant, and the dispersion aid, an anionic surfactant is preferably used as the surfactant, and among them, an alkyl sulfonate, a n-paraffin sulfonate, an alkylbenzene sulfonate, an alkylnaphthalene sulfonate, a sulfosuccinate, an a-olefin sulfonate, an N-acylsulfonate, an alkyl sulfate, an alkyl ether sulfate, more preferably a sulfonate such as an alkyl aryl ether sulfate and an alkyl ether amine sulfate, and most preferably an alkyl sulfonate, a n-paraffin sulfonate, an a-olefin sulfonate, or an alkylbenzene sulfonate is preferred.

[0101] The amount of the above dispersion aid is not particularly limited and can be appropriately adjusted in a manner that the dispersion liquid is stabilized, and with respect to 100 parts by weight of the base resin, the amount is preferably 0.001 parts by weight or more and 0.5 parts by weight or less, more preferably 0.003 parts by weight or more and 0.3 parts by weight or less, and most preferably 0.005 parts by weight or more and 0.2 parts by weight or less. If the amount is less than 0.001 parts by weight, the stability of the dispersion tends to decrease at a temperature higher than the softening temperature of the resin particles, and if the amount exceeds 0.5 parts by weight, the foaming of the dispersion liquid tends to be violent, and it is difficult to obtain polyolefin-based resin foamed particles that are high in foaming ratio and uniform in foaming.

[0102] Note that in the foaming step, the components contained in the polyolefin-based resin particles do not substantially escape into the dispersion liquid, and the water-based dispersion medium, the inorganic dispersant, and the dispersion aid contained in the dispersion liquid do not substantially enter into the finally obtained polyolefin-based resin foamed particles. In other words, the components of the obtained polyolefin-based resin foamed particles are substantially the same as those of the polyolefin-based resin particles.

[0103] The blowing agent used in the present application is not particularly limited, and a generally used blowing agent can be used. Specifically, inorganic blowing agents such as carbon dioxide, air, oxygen, nitrogen, water, and the like can be mentioned, and when water is used, it is preferable to use water as a water-based dispersing medium. These blowing agents can be used singly or in combination of two or more. Among them, in the present application, from the viewpoint that the cell diameter of the polyolefin-based resin expanded particles does not become extremely fine and that polyolefin-based resin expanded particles having a high expansion ratio and excellent foaming properties at the time of manufacturing a foamed molded body can be obtained, carbon dioxide is used as the blowing agent.

[0104] The blowing agent in the present application can be introduced into the container at any stage until foaming, or can be introduced in multiple stages, but from the viewpoint of foaming properties, it is preferable to introduce a part of it before preheating. For example, in the case of adding a blowing agent containing carbon dioxide, a dispersion liquid formed of polyolefin-based resin particles, a water-based dispersing medium, an inorganic dispersant, and a dispersing aid is housed in a container, and solid carbon dioxide (dry ice) is filled into the container, or a dispersion liquid formed of polyolefin-based resin particles, a water-based dispersing medium, an inorganic dispersant, and a dispersing aid is stored in a container, and thereafter, gaseous or liquid carbon dioxide can be introduced into the container at any stage before temperature elevation, after temperature elevation, or before release to a low pressure region. Alternatively, a combination of these methods can be employed. From the viewpoint of foaming properties and the fact that the expansion ratio and the bubble diameter of the obtained polyolefin-based resin expanded particles are less likely to deviate, it is also one of the preferable embodiments to combine carbon dioxide and water as the blowing agent. The amount of the above-mentioned blowing agent to be added is not particularly limited, and can be appropriately adjusted depending on the expansion ratio and the like, and is preferably 0.1 parts by weight or more and 50 parts by weight or less, more preferably 2 parts by weight or more and 30 parts by weight or less, and most preferably 3 parts by weight or more and 20 parts by weight or less, with respect to 100 parts by weight of the base resin. If it is less than 0.1 parts by weight, it is difficult to achieve a high expansion ratio, and if it exceeds 50 parts by weight, the bubbles of the obtained polyolefin-based resin expanded particles are likely to be broken and tend to be coalesced.

[0105] The foaming temperature can be used without particular limitation, and is a temperature generally used for foaming polyolefin-based resin particles. The aforementioned foaming temperature is preferably (melting point of the base resin or polyolefin-based resin particles - 20.0°C) to (melting point of the base resin or polyolefin-based resin particles + 10.0°C), more preferably (melting point of the base resin or polyolefin-based resin particles - 15.0°C) to (melting point of the base resin or polyolefin-based resin particles + 8.0°C), and further preferably (melting point of the base resin or polyolefin-based resin particles - 10.0°C) to (melting point of the base resin or polyolefin-based resin particles + 6.0°C). An appropriate foaming temperature can be determined, for example, by differential scanning calorimetry (DSC).

[0106] The foaming pressure is preferably 1.0 MPa (gauge pressure) to 10.0 MPa (gauge pressure), more preferably 2.0 MPa (gauge pressure) to 5.0 MPa (gauge pressure), and further more preferably 2.5 MPa (gauge pressure) to 3.5 MPa (gauge pressure). If the foaming pressure is 1.0 MPa (gauge pressure) or more, polyolefin-based resin foamed particles having a suitable density can be obtained.

[0107] The time for which the dispersion in the container is maintained near the foaming temperature and the foaming pressure (maintaining time) is not particularly limited. The maintaining time is preferably 10 minutes to 60 minutes, more preferably 12 minutes to 55 minutes, and further more preferably 15 minutes to 50 minutes.

[0108] The container used in the present application is not particularly limited as long as the polyolefin-based resin can be foamed in the container, and a pressure-resistant container can be used, for example.

[0109] Although the polyolefin-based resin one-stage foamed particles can be further subjected to a foaming process (also referred to as a multi-stage foaming process), since the polyolefin-based resin foamed particles having a high foaming ratio can be obtained by subjecting the polyolefin-based resin to one-stage foaming in the production method of the present application, it is preferable to subject the polyolefin-based resin to one-stage foaming from the viewpoint of saving the process.

[0110] The polyolefin-based resin foamed particles of the present application can be used to produce a polyolefin-based resin foamed molded body by foaming molding. For example, the polyolefin-based resin foamed particles obtained by the production method of the present application described above can be filled in a mold and heated with water vapor or the like to fuse the foamed particles to each other, thereby producing an in-mold foamed molded body.

[0111] The polyolefin-based resin in-mold foamed molded body thus obtained can have excellent in-mold formability and can be used in the fields of cushion packaging materials, recyclable containers, heat-insulating transport containers (for example, seafood transport boxes, take-out transport boxes, and the like), automobile parts (for example, tool boxes, floor core materials, and the like), and the like. The present application can also reduce environmental load at the production stage.

[0112] The present application is further illustrated by the following examples, but is not limited thereto.

[0113] Example

[0114] The evaluation methods implemented in the examples and comparative examples are described below.

[0115] <Dry Specific Gravity>

[0116] The polyolefin-based resin foamed particles obtained in each of the examples and comparative examples were dried in an oven at 80°C for 12 hours, thereby sufficiently drying the particles.

[0117] The polyolefin-based resin expanded particles after the above-described sufficient drying were added to a container (content volume V [L]) until overflowing at 23°C under a standard atmospheric pressure (0.1 MPa), the upper end surface of the container was scraped to make the upper end surface of the container flush with the surface of the expanded particles, and the weight W [g] of the polyolefin-based resin expanded particles remaining in the container was measured. The dry specific gravity (i.e., bulk density) of the polyolefin-based resin expanded particles at 23°C under a standard atmospheric pressure (0.1 MPa) was calculated according to Equation (2).

[0118] Dry specific gravity (g / L) = W ÷ V (2)

[0119] <Stability of polyolefin-based resin particles in extrusion>

[0120] The stability of the polyolefin-based resin particles in extrusion was judged according to the following criteria.

[0121] O: Continuous production was possible without any problems.

[0122] Δ: Continuous production was possible, but the size of the particles was slightly changed.

[0123] X: The resin pressure during extrusion was changed, the size of the particles obtained by extrusion was greatly changed, or the extruded resin was cut off midway, so that continuous production was not possible.

[0124] Example 1

[0125] 100 parts by weight of a polypropylene-based resin, 0.4 parts by weight of zinc borate, and 0.1 parts by weight of talc were fed into a twin-screw extruder via a hopper, and 0.3 parts by weight of glycerol was injected into the middle melt section of the twin-screw extruder, and melt-kneading was performed at a cylinder temperature of about 220°C, and extruded into a linear shape through a cylindrical die having a diameter of 1.6 mm installed at the front end of the extruder, and after water cooling, cut by a cutter to obtain polyolefin-based resin particles. The average particle weight of the polyolefin-based resin particles was 1.2 mg.

[0126] A pressure-resistant container having a capacity of 0.3 m 3 A pressure-resistant container having a capacity of 0.3 m

[0127] The content of the pressure-resistant container was heated to a foaming temperature (melting point of the aforementioned polyolefin-based resin particles + 3.0°C, the melting point being a value measured based on the second temperature rise (2nd run) of DSC as previously described). Then, carbon dioxide was added to increase the pressure of the autoclave until the bubbling pressure reached 3.20 MPa (gauge pressure), and the above-mentioned foaming temperature and pressure were maintained for 30 minutes, after which the valve at the lower portion of the pressure-resistant container was opened, and the content of the pressure-resistant container was released to an atmosphere of steam at atmospheric pressure through an opening hole (single hole) having a diameter of 3.6 mm, thereby obtaining polyolefin-based resin foamed particles. The obtained polyolefin-based resin foamed particles were sent to a drier, and moisture in the foamed particles was blown off using hot air at about 80°C.

[0128] The obtained polyolefin-based resin foamed particles were subjected to measurement of the dry specific gravity by the above-mentioned evaluation method, and the polyolefin-based resin foamed particles were evaluated for extrusion stability, and the results are shown in Table 1.

[0129] Examples 2-17 and Comparative Examples 1-9

[0130] The preparation of polyolefin-based resin particles, the preparation of polyolefin-based resin foamed particles, the measurement of dry specific gravity, and the evaluation of polyolefin-based resin foamed particles for extrusion stability were carried out in the same manner as in Example 1 except that the composition used for the preparation of polyolefin-based resin particles was changed as shown in Tables 1 and 2. Among them, the carbon black, the colorant, and the antistatic agent in Examples 15-17 were each fed into the twin-screw extruder through a hopper together with the polypropylene-based resin.

[0131] Note that the foaming temperature is the optimum foaming temperature of the polyolefin-based resin particles of each of the examples and comparative examples. Therefore, the difference in performance between each of the examples and comparative examples is attributable only to the difference in the components thereof.

[0132] Table 1

[0133] Table 2

[0134] The components shown in Tables 1 and 2 were used without particular purification or the like in the examples and comparative examples, as follows.

[0135] PP: polypropylene-based resin, E680E manufactured by China Petroleum & Chemical Corporation

[0136] Glycerin: GL997 manufactured by Kingway Group Co., Ltd.

[0137] PEG: polyethylene glycol, PEG300 manufactured by Sankyo Chemical Industries, Ltd.

[0138] Zinc borate: ZB2335 manufactured by Shandong Novelda Chemical Co., Ltd.

[0139] Talc: PK-S manufactured by Nippon Talc Co., Ltd.

[0140] Carbon black: Carbon black having an average particle diameter of 27 nm

[0141] Colorant (green): CIPigment Blue 15:3

[0142] Antistatic agent: Special cationic active agent DUSPER 125B manufactured by MIYOSHIOIL & FAT CO., LTD.

[0143] In Examples 1 to 17, the components (A) and (B) were used in combination at specific contents, and in the process of manufacturing the polyolefin-based resin expanded particles, the polyolefin-based resin particles were stably extruded, and by one-stage expansion, polyolefin-based resin expanded particles having a low dry specific gravity (i.e., high expansion ratio) were obtained.

[0144] On the other hand, in Comparative Examples 1 to 9, in which the components (A) and (B) were not used in combination at the use amount range of the present application, at least one of the dry specific gravity and the evaluation result of the extrusion stability of the polyolefin-based resin particles was poor. Among them, in Comparative Example 2, a large amount of smoke was observed during the manufacturing, and it was presumed that the reason was that the component (A) was used in an amount exceeding the use amount range of the present application.

[0145] The above detailed specific examples of the present application, but these are merely illustrative and do not limit the scope of the application. The claims recited in the scheme include the scheme obtained by various modifications and changes of the above-illustrated specific examples.

[0146] Industrial applicability

[0147] The polyolefin-based resin expanded particles and the manufacturing method thereof according to the present application can stably extrude the polyolefin-based resin particles during the manufacturing process, and further can obtain polyolefin-based resin expanded particles having a high expansion ratio. Therefore, the polyolefin-based resin expanded particles and the manufacturing method thereof according to the present application can be used for manufacturing a lightweight expanded molded body at a low cost.

Claims

1. A polyolefin resin foamed particle comprising a base resin having a polyolefin resin as a main component, The polyolefin resin foamed particles further comprise: ingredient (A) which is a water-absorbing organic compound; and Component (B) is at least one selected from the group consisting of boric acid metal salts and melamine, The content of the component (A) is 0.1 to 0.6 parts by weight, and the content of the component (B) is 0.1 to 0.6 parts by weight, relative to 100 parts by weight of the base resin.

2. The polyolefin resin foamed particles according to claim 1, wherein The content of the component (A) is 0.2 to 0.4 parts by weight, and the content of the component (B) is 0.2 to 0.4 parts by weight, relative to 100 parts by weight of the base resin. The polyolefin-based resin foamed particles according to claim 1 or 2, wherein the water-absorbing organic compound is at least one selected from the group consisting of glycerin, diglycerin, and polyethylene glycol.

4. The polyolefin resin foamed particles according to claim 1 or 2, wherein The metal borate is zinc borate. The polyolefin resin foamed particles according to claim 1 or 2, wherein The polyolefin resin is a polypropylene resin. The polyolefin resin foamed particles according to claim 5 , wherein The base resin contains 50% by weight or more of a polypropylene-based resin. The polyolefin resin foamed particles according to claim 1 or 2, which are single-stage foamed particles. The polyolefin resin foamed particles according to claim 1 or 2, which have a bulk density of 27.5 g / L or less.

9. A method for producing polyolefin resin foamed particles, comprising: The process of dispersing polyolefin resin particles in an aqueous dispersion medium in a container, introducing a foaming agent, and impregnating the polyolefin resin particles with the foaming agent under heating and pressurizing conditions; and a step of foaming the polyolefin-based resin particles by releasing the polyolefin-based resin particles into a pressure region lower than the internal pressure of the container to obtain foamed polyolefin-based resin particles; The polyolefin resin particles include a base resin mainly composed of a polyolefin resin, a component (A), and a component (B). The component (A) is a water-absorbing organic compound, The content of the component (A) is 0.1 to 0.6 parts by weight relative to 100 parts by weight of the base resin. The component (B) is at least one selected from the group consisting of boric acid metal salts and melamine, The content of the component (B) is 0.1 to 0.6 parts by weight relative to 100 parts by weight of the base resin.

10. The method for producing polyolefin resin foamed particles according to claim 9, wherein The water-absorbing organic compound is at least one selected from the group consisting of glycerol, diglycerol, and polyethylene glycol.

11. The method for producing polyolefin resin foamed particles according to claim 9, wherein The polyolefin resin is a polypropylene resin. 12 . The method for producing foamed polyolefin-based resin particles according to claim 11 , wherein the base resin contains 50% by weight or more of a polypropylene-based resin.

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