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JP-7857279-B2 - Polypropylene resin extruded foam particles, method for producing the same, and foamed molded articles

JP7857279B2JP 7857279 B2JP7857279 B2JP 7857279B2JP-7857279-B2

Inventors

  • 天野 正樹
  • 中山 清敬

Assignees

  • 株式会社カネカ

Dates

Publication Date
20260512
Application Date
20220325
Priority Date
20210325

Claims (16)

  1. Polypropylene resin extruded foam particles, The polypropylene resin extruded foam particles contain a base resin comprising: more than 70% by weight and 98% by weight or less of a branched polypropylene resin (A) having a melting point Tm 2A of 130.0°C or higher and less than 143.0°C; and 2% by weight and less than 30% by weight of a branched polypropylene resin (B) having a melting point Tm 2B of 150.0°C or higher and less than 170.0°C (the total of the polypropylene resin (A) and the polypropylene resin (B) is 100% by weight). The melting point Tm1 of the polypropylene resin extruded foam particles in the first heating stage is 130.0°C or higher and less than 155.0°C. Polypropylene resin extruded foam particles, wherein the melt elongation of the base resin is 7.0 m/min to 8.0 m/min .
  2. Polypropylene resin extruded foam particles, The aforementioned polypropylene resin extruded foam particles have a melting point Tm 2A A polypropylene resin (A) having a branched structure with a melting point Tm is present in an amount of more than 70% by weight and less than 98% by weight, and the melting point Tm is present in an amount of more than 70% by weight and less than 98% by weight. 2B The material contains a base resin containing a branched polypropylene resin (B) having a temperature of 150.0°C or higher and less than 170.0°C, in an amount of 2% by weight or more and less than 30% by weight (the total of the polypropylene resin (A) and the polypropylene resin (B) is 100% by weight), The melting point Tm of the polypropylene resin extruded foam particles at the first heating stage. 1 The temperature is between 130.0°C and 155.0°C. The polypropylene resin extruded foam particles have a bulk density of 66 g/L to 69 g/L.
  3. The polypropylene resin extruded foam particle according to claim 1 or 2, wherein the base resin comprises more than 80% by weight and 98% by weight or less of the polypropylene resin (A), and 2% by weight or more and less than 20% by weight of the polypropylene resin (B) (the sum of the polypropylene resin (A) and the polypropylene resin (B) is 100% by weight).
  4. The polypropylene resin extruded foam particles according to claim 2 , wherein the melt elongation of the base resin is 3.0 m/min to 30.0 m/min.
  5. The polypropylene resin extruded foam particles according to any one of claims 1 to 4 , wherein the melt flow rate of the base resin is 1.0 g/10 min to 20.0 g/10 min.
  6. The polypropylene resin extruded foam particles according to claim 1 , wherein the bulk density of the polypropylene resin extruded foam particles is 30 g/L to 600 g/L.
  7. The polypropylene resin extruded foam particles according to any one of claims 1 to 6 , wherein the open-cell ratio of the polypropylene resin extruded foam particles is 10.0% or less.
  8. A polypropylene resin foam molded article obtained by molding polypropylene resin extruded foam particles according to any one of claims 1 to 7 .
  9. A method for producing polypropylene resin extruded foam particles according to any one of claims 1 to 7 , The method for producing the polypropylene resin extruded foam particles comprises a preparation step of preparing the polypropylene resin (A) having a branched structure and the polypropylene resin (B) having a branched structure, and an extrusion foaming step of preparing the polypropylene resin extruded foam particles. The preparation step includes a first melt-kneading step of melt-kneading a first mixture comprising (a) a linear polypropylene resin, (b) one or more monomers selected from the group consisting of conjugated dienes and vinyl aromatic compounds, and (c) a radical polymerization initiator. In the first melt-mixing step, the polypropylene resin (A) and the polypropylene resin (B) are prepared separately. A method for producing extruded polypropylene resin foam particles, wherein the extrusion foaming step comprises a second melt-kneading step of melt-kneading a composition comprising a second mixture containing the polypropylene resin (A) and the polypropylene resin (B), and a foaming agent.
  10. A method for producing polypropylene resin extruded foam particles according to any one of claims 1 to 7 , The method for producing the polypropylene resin extruded foam particles comprises a preparation step of preparing the polypropylene resin (A) having a branched structure and the polypropylene resin (B) having a branched structure, and an extrusion foaming step of preparing the polypropylene resin extruded foam particles. The preparation step includes a first melt-kneading step of melt-kneading a first mixture comprising (a) a linear polypropylene resin, (b) one or more monomers selected from the group consisting of conjugated dienes and vinyl aromatic compounds, and (c) a radical polymerization initiator. In the first melt-kneading step, a polypropylene resin having a branched structure is prepared by using a mixture of (a-1) a linear polypropylene resin (A') having a melting point Tm 3A of 130.0°C or higher and less than 150.0°C, and (a-2) a linear polypropylene resin (B') having a melting point Tm 3B of 150.0°C or higher and less than 170.0°C, in which the polypropylene resin (A) and the polypropylene resin (B) are crosslinked within a single molecule. A method for producing polypropylene resin extruded foam particles, comprising a second melt-kneading step of melt-kneading a composition comprising a second mixture containing a polypropylene resin having the branched structure and a foaming agent, wherein the extrusion foaming step is a second melt-kneading step.
  11. The method for producing polypropylene resin extruded foam particles according to claim 9 or 10 , wherein one or more monomers selected from the group consisting of conjugated dienes and vinyl aromatic compounds in the first melt-kneading step are isoprene and/or butadiene.
  12. A method for producing polypropylene resin extruded foam particles according to any one of claims 9 to 11, wherein the amount of one or more monomers selected from the group consisting of conjugated dienes and vinyl aromatic compounds used in the first melt-kneading step is 0.01 parts by weight to 5.00 parts by weight per 100 parts by weight of the linear polypropylene resin.
  13. A method for producing polypropylene resin extruded foam particles according to any one of claims 9 to 12 , wherein the radical polymerization initiator in the first melt kneading step is one or more selected from the group consisting of t-butyl peroxyisopropyl carbonate and t-butyl peroxybenzoate.
  14. A method for producing polypropylene resin extruded foam particles according to any one of claims 9 to 13, wherein the ratio of the amount (parts by weight) of one or more monomers selected from the group consisting of conjugated dienes and vinyl aromatic compounds to the amount (parts by weight) of the radical polymerization initiator used is 0.05 to 5.00 .
  15. A method for producing a polypropylene resin foamed molded article, comprising a molding step of molding polypropylene resin extruded foam particles produced by the method for producing polypropylene resin extruded foam particles according to any one of claims 9 to 14 .
  16. The method for producing a polypropylene resin foamed molded article according to claim 15 , wherein in the molding step, the polypropylene resin extruded foam particles are heated at a vapor pressure of 0.30 MPa or less.

Description

This invention relates to polypropylene resin extruded foam particles, a method for producing the same, and a foamed molded article. Polypropylene-based foam molded articles obtained using polypropylene-based resin foam particles are characterized by their excellent flexibility in shape, cushioning properties, light weight, and heat insulation properties. These characteristics are also advantages of polypropylene-based foam molded articles. Furthermore, because the base material is polypropylene-based resin, polypropylene-based foam molded articles have excellent chemical resistance, heat resistance, compressive strength, and distortion recovery rate after compression. Due to these advantages, polypropylene-based foam molded articles are used in a variety of applications, mainly as automotive interior components and core materials for automotive bumpers, as well as heat insulation materials and cushioning packaging materials. Polypropylene resin foam particles can generally be manufactured by a method called "pressure-relieving foaming," which involves dispersing polypropylene resin particles in water within a pressure vessel along with a volatile foaming agent. To obtain polypropylene resin particles for use in the pressure-relieving foaming method, it is necessary to pelletize the polypropylene resin to a size suitable for foaming using an extruder or similar equipment before use in the method. Therefore, obtaining polypropylene resin foam particles using polypropylene resin as a raw material requires two steps: a pelletizing step and a pressure-relieving foaming step. As a result, the pressure-relieving foaming method may have the following challenges: (a) it tends to require significant capital investment, and (b) it necessitates wastewater treatment facilities due to the use of a dispersion medium such as water. In recent years, in order to overcome these challenges, it has been proposed to obtain polypropylene resin extruded foam particles by an extrusion foaming method (for example, Patent Documents 1 to 3). On the other hand, from an economic standpoint, there is a demand for polypropylene resin foam particles to be moldable using steam at lower pressures (low-pressure moldability). This low-pressure moldability can be achieved, for example, by selecting a resin with a low melting point as the base resin constituting the polypropylene resin foam particles (for example, Patent Document 4). Japanese Patent Application Publication No. 9-302131Japanese Patent Publication No. 2009-256460International Public Gazette 2018/016399Japanese Patent Publication No. 2009-144096 One embodiment of the present invention is described below, but the present invention is not limited thereto. The present invention is not limited to the configurations described below, and various modifications are possible within the scope of the claims. Furthermore, embodiments or examples obtained by combining the technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention. Moreover, new technical features can be formed by combining the technical means disclosed in each embodiment. All academic and patent documents mentioned herein are incorporated herein by reference. Furthermore, unless otherwise specified herein, "A to B" representing a numerical range means "A or greater (including A and greater than A) and B or less (including B and less than B)." [1. Technical Concept of One Embodiment] Similar to polypropylene resin foam particles obtained by the depressurization foaming method, when a resin with a low melting point is selected as the base resin constituting polypropylene resin extruded foam particles, the compressive strength of the molded article obtained by molding these polypropylene resin extruded foam particles tends to be low. On the other hand, when a resin with excellent strength and a high melting point is blended with the base resin constituting polypropylene resin extruded foam particles, the melting point of the base resin approaches the melting point of the resin in question (high melting point), and as a result, the low-pressure moldability of the polypropylene resin extruded foam particles tends to be impaired. However, after diligent research by the inventors, the following findings were discovered: (i) The melting point Tm 1 of the polypropylene resin extruded foam particles at the first heating stage, (ii) The ratio (blending ratio) of (amount of polypropylene resin (B) with a high melting point Tm 2B during the second heating stage) to (amount of polypropylene resin (A) with a low melting point Tm 2A during the second heating stage), The relationship is not a simple proportional one. This is thought to be because the balance between the low-pressure moldability of the extruded foam particles and the compressive strength of the foamed molded product is achieved under a complex relationship between polypropylene resin (A) and polypropylene res