Polyethylene resin foam particles, polyethylene resin molded foam articles, and methods for manufacturing the same.

Abstract

The present invention relates to polyethylene resin foamed particles in which, in one or more embodiments, the weight fraction in a sieve having a nominal opening two stages smaller than the nominal opening of a sieve having the highest weight fraction measured by using a 9-stage standard sieve having a nominal opening of 2.00 to 8.00 mm, inclusive, as specified in accordance with JIS Z 8801-1: 2006, exceeds 10.0%, and variations in the foaming ratio σ / Xp is 15.0% or less. As a result, it is possible to provide: polyethylene resin foamed particles from which a polyethylene resin in-mold foamed molded body having favorable elongation at an edge section and exhibiting little deformation can be obtained; and a polyethylene resin in-mold foamed molded body.

Description

[Technical Field]

[0001] The present invention relates to polyethylene resin foam particles used, for example, in reusable containers, cushioning materials, cushioning packaging materials, heat insulating materials, etc., and a method for producing the same, as well as a polyethylene resin molded foam body obtained by in-mold foam molding of the polyethylene resin foam particles, and a method for producing the same. [Background technology]

[0002] In-mold foamed molded products, obtained by filling a mold with thermoplastic resin foam particles and performing in-mold foaming (heat molding) with steam or the like, are widely used as cushioning materials, cushioning packaging materials, and heat insulating materials because they have characteristics such as being lightweight and having heat insulating properties. When using thermoplastic resin foam particles for in-mold foam molding, poor filling of the mold can easily lead to a deterioration in the appearance and productivity of the in-mold foamed molded product. Patent Document 1 discloses a technique for improving the filling of pre-foamed particles within the in-mold foamed molded product by controlling the particle size distribution of thermoplastic resin foam particles to a predetermined range. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2014-189743 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] However, even when the particle size distribution of the foamed particles is controlled to a predetermined range, as described in Patent Document 1, in the case of polyethylene-based foamed particles, there were problems such as insufficient fusion of the edges of the in-molded foamed body using the polyethylene-based foamed particles, and problems such as deformation occurring.

[0005] The present invention has been made in view of the above-mentioned problems, and provides polyethylene-based resin foam particles and a method for producing the same, as well as a polyethylene-based resin foam molded article and a method for producing the same, which yield an in-molded foam molded article that has good edge elongation and small deformation. [Means for solving the problem]

[0006] The present invention relates to polyethylene resin foam particles in one or more embodiments in which, when measured using nine standard sieves with nominal mesh openings of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006, the weight fraction of a sieve with a nominal mesh opening two steps smaller than the nominal mesh opening of the sieve with the highest weight fraction exceeds 10.0%, and the variation in foaming ratio σ / Xp, expressed by the following formula (1), is 15.0% or less. [Formula (1)] σ / Xp(%)=(σm / Kav)×100···(1) However, in formula (1) above, Kav is the weight-average expansion factor calculated based on formula (2) below, and σm is the standard deviation of the expansion factor calculated based on formula (3) below. [Formula (2)] Kav = Σ(Ki × Wi)···(2) [Formula (3)] σm=[Σ{Wi×(Kav-Ki) 2}] 1 / 2 ...(3) However, in equations (2) and (3) above, i represents each sieve, and Wi and Ki represent the weight fraction and foaming ratio of polyethylene resin foam particles remaining in each sieve, respectively.

[0007] The present invention, in one or more embodiments, is a method for producing polyethylene resin foam particles, comprising the step of mixing polyethylene resin foam particles (A) in an amount of 50% to 100% by weight and polyethylene resin foam particles (B) in an amount of 0% to 50% by weight, wherein polyethylene resin foam particles (A) have a weight-average magnification of 3 to 60 times, measured using a 9-stage standard sieve with a nominal mesh opening of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006, and a variation in foaming magnification σ / Xp of 15.0% or less, and polyethylene resin foam particles (B) are as specified in JIS Z This invention relates to a method for producing polyethylene resin foam particles, wherein, when sieved using nine standard sieves with nominal mesh openings of 2.00 mm to 8.00 mm as specified in 8801-1:2006, the nominal mesh opening of the sieve with the highest weight fraction is two steps smaller than the nominal mesh opening of the sieve with the highest weight fraction of polyethylene resin foam particles (A), and the variation in foaming ratio σ / Xp, expressed by the following formula (1), is 15.0% or less. [Formula (1)] σ / Xp(%)=(σm / Kav)×100···(1) However, in formula (1) above, Kav is the weight-average expansion factor calculated based on formula (2) below, and σm is the standard deviation of the expansion factor calculated based on formula (3) below. [Formula (2)] Kav = Σ(Ki × Wi)···(2) [Formula (3)] σm=[Σ{Wi×(Kav-Ki) 2}] 1 / 2 ...(3) However, in equations (2) and (3) above, i represents each sieve, and Wi and Ki represent the weight fraction and foaming ratio of polyethylene resin foam particles remaining in each sieve, respectively.

[0008] The present invention relates to a polyethylene resin in-mold foamed molded article obtained by in-mold foaming of polyethylene resin foam particles in one or more embodiments.

[0009] In one or more embodiments, the present invention includes a molding step of in-mold foaming of polyethylene-based resin foamed particles. The polyethylene-based resin foamed particles are obtained by: (a) mixing 50% by weight or more and less than 100% by weight of polyethylene-based resin foamed particles (A) with more than 0% by weight and 50% by weight or less of polyethylene-based resin foamed particles (B), and foaming the resulting mixture; (b) mixing 50% by weight or more and less than 100% by weight of polyethylene-based resin foamed particles (A) with more than 0% by weight and 50% by weight or less of polyethylene-based resin foamed particles (B); or (c) foaming polyethylene-based resin foamed particles (A). The polyethylene-based resin foamed particles (A) have a weight average expansion ratio of 3 times or more and 60 times or less measured using a nine-stage standard sieve with a nominal mesh size of 2.00 mm or more and 8.00 mm or less defined in JIS Z 8801-1:2006, and the variation in expansion ratio σ / Xp represented by the following formula (1) is 15.0% or less. The polyethylene-based resin foamed particles (B) have a nominal mesh size of the sieve with the highest weight fraction, when sieved using a nine-stage standard sieve with a nominal mesh size of 2.00 mm or more and 8.00 mm or less defined in JIS Z 8801-1:2006, two stages smaller than the nominal mesh size of the sieve with the highest weight fraction of the polyethylene-based resin foamed particles (A), and the variation in expansion ratio σ / Xp represented by the following formula (1) is 15.0% or less. The polyethylene-based resin foamed particles have a weight fraction exceeding 10.0% in a sieve with a nominal mesh size two stages smaller than the nominal mesh size of the sieve with the highest weight fraction measured using a nine-stage standard sieve with a nominal mesh size of 2.00 mm or more and 8.00 mm or less defined in JIS Z 8801-1:2006, and the variation in expansion ratio σ / Xp represented by the following formula (1) is 15.0% or less. The present invention relates to a method for manufacturing a polyethylene-based resin in-mold foamed product. [Formula (1)] σ / Xp (%) = (σm / Kav) × 100 ··· (1) However, in the above formula (1), Kav is the weight average expansion ratio calculated based on the following formula (2), and σm is the standard deviation of the expansion ratio calculated based on the following formula (3). [Formula (2)] Kav = Σ(Ki × Wi) ··· (2) [Formula (3)] σm = [Σ{Wi × (Kav - Ki) 2}] 1 / 2 ···(3) However, in the above formulas (2) and (3), i represents each sieve, and represents the weight fraction and expansion ratio of the polyethylene resin foam particles remaining on each sieve.

Advantages of the Invention

[0010] The present invention can provide polyethylene resin foam particles and a method for producing the same, which can obtain a polyethylene resin in-mold foam molded body having good elongation at the edge portion and small deformation. In addition, the present invention can provide a polyethylene resin in-mold foam molded body having good elongation at the edge portion and small deformation and a method for producing the same.

Brief Description of the Drawings

[0011] [Figure 1] It is a schematic explanatory view regarding measurement of the deformation amount of a polyethylene resin in-mold foam molded body.

Embodiments for Carrying Out the Invention

[0012] The inventor of the present invention has conducted repeated studies in order to obtain a polyethylene resin in-mold foam molded body having good elongation at the edge portion and small deformation. As a result, by adjusting both the particle size distribution of the polyethylene resin foam particles and the variation σ / Xp of the expansion ratio, specifically, the sieve with a nominal aperture two steps smaller than the nominal aperture of the sieve with the highest weight fraction measured using nine standard sieves with a nominal aperture of 2.00 mm or more and 8.00 mm or less specified in JIS Z 8801-1:2006 (hereinafter simply referred to as "the sieve with the highest weight fraction"), the weight fraction in the sieve (hereinafter simply referred to as "the sieve two steps smaller") is more than 10.0%, and the variation σ / Xp of the expansion ratio represented by the above formula (1) (hereinafter simply referred to as "σ / Xp") is 15.0% or less, it has been found that a polyethylene resin in-mold foam molded body having good elongation at the edge portion and small deformation can be obtained. In particular, it was found that polyethylene resin foam particles obtained by mixing polyethylene resin foam particles (A), which have a weight-average magnification of 3 to 60 times as measured using nine standard sieves with nominal mesh openings of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006, and polyethylene resin foam particles (B), which have a nominal mesh opening two steps smaller than polyethylene resin foam particles (A) and a σ / Xp of 15.0%, in a predetermined proportion, with polyethylene resin foam particles (B), which have a weight fraction of more than 10.0% in the sieve two steps smaller and a σ / Xp of 15.0%, and which are obtained by mixing these two steps smaller in proportion to polyethylene resin foam particles (A), result in polyethylene resin foam particles with a weight fraction of more than 10.0% in the sieve two steps smaller and a σ / Xp of 15.0% or less, are more likely to be obtained in a polyethylene resin in-mold foam molded product with good edge elongation and minimal deformation.

[0013] In one or more embodiments of the present invention, the nine standard sieves with nominal mesh openings of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006 are the nine stages with nominal mesh openings of 2.00 mm, 2.36 mm, 2.80 mm, 3.35 mm, 4.00 mm, 4.75 mm, 5.60 mm, 6.70 mm, and 8.00 mm. In one or more embodiments of the present invention, unless otherwise specified, "weight fraction" means the weight fraction measured using the nine standard sieves with nominal mesh openings of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006.

[0014] (Polyethylene-based foamed particles) The polyethylene resin foam particles have a weight fraction exceeding 10.0% in a two-stage smaller sieve, preferably 10.1% or more, and more preferably 10.2% or more. This makes it possible to obtain a polyethylene resin in-mold foamed molded article with good edge elongation and minimal deformation.

[0015] There is no particular upper limit to the weight fraction of polyethylene-based resin foam particles in the two-stage smaller sieve, but for example, from the viewpoint of more effectively suppressing deformation of the in-molded foamed article, it is preferably 45% or less, more preferably 30% or less, and even more preferably 20% or less. Specifically, the weight fraction of polyethylene-based resin foam particles in the two-stage smaller sieve is preferably greater than 10.0% and 40% or less, more preferably 10.1% or more and 30% or less, and even more preferably 10.2% or more and 20% or less.

[0016] In one or more embodiments of the present invention, although not particularly limited, for example, from the viewpoint of more effectively suppressing deformation of the in-molded foamed article, the weight fraction of polyethylene-based resin foam particles in the sieve with the highest weight fraction is preferably 40% or more and 80%, and more preferably 45% or more and 70%.

[0017] In one or more embodiments of the present invention, although not particularly limited, for example, from the viewpoint of more effectively suppressing deformation of the in-molded foamed article, the weight fraction of polyethylene resin foam particles in a sieve with a nominal mesh opening one step smaller than the nominal mesh opening of the sieve with the highest weight fraction (hereinafter also simply referred to as "one step smaller sieve") is preferably 0% or more and 48% or less, more preferably 5% or more and 48% or less, even more preferably 10% or more and 44.9% or less, even more preferably 15% or more and 44.9% or less, and particularly preferably 20% or more and 44.8% or less.

[0018] In one or more embodiments of the present invention, although not particularly limited, for example, from the viewpoint of suppressing deformation of the in-molded foamed article, it is preferable that the weight fraction of polyethylene resin foam particles is 40% to 80% in the sieve with the highest weight fraction, 0% to 48% in the sieve one step smaller, and 10.1% to 30% in the sieve two steps smaller. It is more preferable that the weight fraction of the sieve with the highest weight fraction is 45% to 70%, the weight fraction of the sieve one step smaller is 10% to 44.9%, and the weight fraction of the sieve two steps smaller is 10.1% to 30%. It is even more preferable that the weight fraction of the sieve with the highest weight fraction is 45% to 70%, the weight fraction of the sieve one step smaller is 20% to 44.8%, and the weight fraction of the sieve two steps smaller is 10.2% to 20%.

[0019] In one or more embodiments of the present invention, σ / Xp can be expressed by the following formula (1), and can be measured specifically as described below. [Formula (1)] σ / Xp(%)=(σm / Kav)×100···(1) However, in formula (1) above, Kav is the weight-average expansion factor calculated based on formula (2) below, and σm is the standard deviation of the expansion factor calculated based on formula (3) below. [Formula (2)] Kav = Σ(Ki × Wi)···(2) [Formula (3)] σm=[Σ{Wi×(Kav-Ki) 2}] 1 / 2 ...(3) However, in formulas (2) and (3) above, i represents each sieve, and Wi and Ki represent the weight fraction and foaming ratio of polyethylene resin foam particles remaining on each sieve when sieved using nine standard sieves with nominal mesh openings of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006, respectively.

[0020] The polyethylene resin foam particles have a σ / Xp ratio of 15.0% or less. This allows for the production of polyethylene resin in-mold foam molded articles with good edge elongation and minimal deformation. From the viewpoint of further improving the edge elongation of the in-mold foam molded article, the σ / Xp ratio of the polyethylene resin foam particles is preferably 14.5% or less, and more preferably 14.0% or less. The lower limit of the σ / Xp ratio of the polyethylene resin foam particles is not particularly limited, but for example, from the viewpoint of productivity, it may be 1% or more.

[0021] While the polyethylene resin foam particles are not particularly limited, from the viewpoint of more effectively achieving both improved elongation and suppression of deformation at the edges of the in-molded foamed product, it is preferable that the weight-average magnification (hereinafter also simply referred to as "weight-average magnification") measured using nine standard sieves with nominal mesh openings of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006 is 3 to 60 times, more preferably 7 to 50 times, even more preferably 7.5 to 48 times, and even more preferably 8 to 45 times. In one or more embodiments of the present invention, the weight-average magnification is represented by the above formula (2) and can be measured as described later.

[0022] While polyethylene resin foam particles are not particularly limited, from the viewpoint of more effectively achieving both improved elongation and suppression of deformation at the edges of the in-molded foamed product, the average particle diameter (hereinafter also simply referred to as "average particle diameter") measured using a 9-stage standard sieve with a nominal mesh opening of 2.00 mm to 8.0 mm as specified in JIS Z 8801-1:2006 is preferably 2.0 mm to 9.0 mm, more preferably 2.5 mm to 8.5 mm, and even more preferably 3.0 mm to 8.0 mm.

[0023] In one or more embodiments of the present invention, the average particle diameter is represented by the following formula (4) and can be measured as described later. [Formula (4)] Average particle diameter D(mm)=Σ(Ri Wi) / 100...(4) However, in equation (4), i represents each sieve, Ri is the arithmetic mean of the nominal mesh opening of each sieve and the nominal mesh opening of a sieve one step larger than that sieve, and Wi represents the weight fraction of polyethylene resin foam particles remaining in each sieve.

[0024] The melt index (MI) of the polyethylene resin constituting the polyethylene resin foam particles is not particularly limited. For example, from the viewpoint of easily obtaining an in-molded foamed article that is difficult to deform, it may be 0.1 g / 10 min to 5.0 g / 10 min, or 0.5 g / 10 min to 4.0 g / 10 min. In one or more embodiments of the present invention, unless otherwise specified, the melt index is a value measured in accordance with JIS K 7210-1:2014 at a temperature of 190°C and a load of 2.16 kg, and is also called the melt mass flow rate, or simply the melt flow rate.

[0025] From the viewpoint of easily obtaining a foamed molded product with minimal deformation, when a box-shaped cushioning material is molded using polyethylene-based resin foam particles, it is preferable that the deformation rate calculated according to the following formula (6) is 2.9% or less, and more preferably 2.6% or less. [Formula (6)] Deformation rate (%) = [(L1+L2) / 2-L3] / [(L1+L2) / 2] × 100···(6) However, in formula (6) above, L1 and L2 represent the dimensions at both ends in the longitudinal direction, and L3 represents the dimension at the center.

[0026] From the viewpoint of easily obtaining a foamed molded article with good edge elongation, when a plate-shaped molded article is formed, it is preferable that the spacing between polyethylene-based resin foam particles at the edge of the plate-shaped molded article is small, and when rubbed strongly with a finger, the adhesion between adjacent polyethylene-based resin foam particles peels off, but the polyethylene-based resin foam particles themselves do not detach from the molded article. It is even more preferable that the spacing between polyethylene-based resin foam particles at the edge of the plate-shaped molded article is very small, and the adhesion between adjacent polyethylene-based resin foam particles does not peel off even when rubbed strongly with a finger. It is even more preferable that there is no spacing between polyethylene-based resin foam particles at the edge of the plate-shaped molded article, and the adhesion between adjacent polyethylene-based resin foam particles does not peel off even when rubbed strongly with a finger.

[0027] (Method for manufacturing polyethylene resin foam particles) In one or more embodiments of the present invention, although not particularly limited, polyethylene resin foam particles can be produced, for example, by mixing polyethylene resin foam particles (A) in an amount of 50% to 100% by weight and polyethylene resin foam particles (B) in an amount of 0% to 50% by weight. Alternatively, polyethylene resin foam particles (A) may be mixed in an amount of 50% to less than 100% by weight with polyethylene resin foam particles (B) in an amount exceeding 0% by weight and up to 50% by weight, or polyethylene resin foam particles (A) may be mixed in an amount of 60% to 95% by weight with polyethylene resin foam particles (B) in an amount of 5% to 40% by weight, or polyethylene resin foam particles (A) may be mixed in an amount of 70% to 90% by weight with polyethylene resin foam particles (B) in an amount of 10% to 30% by weight.

[0028] The weight-average magnification of polyethylene resin foam particles (A) is preferably 3 times or more and 60 times or less, and more preferably 5 times or more and 55 times or less, and more preferably 7 times or more and 50 times or less, from the viewpoint of more effectively achieving both improved elongation and suppression of deformation at the edges of the in-molded foamed molded product.

[0029] The σ / Xp of polyethylene-based foamed particles (A) is preferably 13.0% or less, more preferably 11.0% or less, and even more preferably 9.0% or less, from the viewpoint of easily keeping the σ / Xp of polyethylene-based foamed particles (A) below 15.0%. The lower limit of the σ / Xp of polyethylene-based foamed particles (A) is not particularly limited, but for example, from the viewpoint of productivity, it may be 1% or more.

[0030] In one or more embodiments of the present invention, although not particularly limited, for example, from the viewpoint of making it easier to keep the σ / Xp of polyethylene-based resin foam particles to 15% or less, the weight fraction of polyethylene-based resin foam particles (A) in the two-stage smaller sieve is preferably 0% to 30%, more preferably 0% to 20%, and even more preferably 0% to 15%.

[0031] In one or more embodiments of the present invention, although not particularly limited, for example, from the viewpoint of making it easier to keep the σ / Xp of polyethylene-based resin foam particles to 15% or less, the weight fraction of polyethylene-based resin foam particles (A) in the sieve with the highest weight fraction is preferably 50.1% or more and 95% or less, more preferably 50.5% or more and 80% or less, and even more preferably 50.5% or more and 60% or less.

[0032] In one or more embodiments of the present invention, although not particularly limited, from the viewpoint of making it easier to keep the σ / Xp of polyethylene-based resin foam particles to 15% or less, the weight fraction of polyethylene-based resin foam particles (A) in a smaller sieve is preferably 0% or more and 49.5% or less, more preferably 10% or more and 40% or less, and even more preferably 15% or more and 35% or less.

[0033] In one or more embodiments of the present invention, although not particularly limited, for example, from the viewpoint of easily suppressing the σ / Xp of polyethylene resin foam particles to 15% or less, it is preferable that the weight fraction of polyethylene resin foam particles (A) in the sieve with the highest weight fraction is 50.1% or more and 95% or less, the weight fraction in the sieve one step smaller is 0% or more and 49.5% or less, the weight fraction in the sieve two steps smaller is 0% or more and 30% or less, it is more preferable that the weight fraction in the sieve with the highest weight fraction is 50.5% or more and 60% or less, the weight fraction in the sieve one step smaller is 10% or more and 40% or less, and the weight fraction in the sieve two steps smaller is 0% or more and 15% or less.

[0034] In one or more embodiments of the present invention, if the weight fraction of polyethylene-based foamed particles (A) in the two-stage smaller sieve exceeds 10.0%, polyethylene-based foamed particles (A) may be used at 100% by weight, or polyethylene-based foamed particles (A) may be mixed with polyethylene-based foamed particles (B) at 50% by weight or more and less than 100% by weight, and polyethylene-based foamed particles (B) at more than 0% by weight and 50% by weight or less. Alternatively, polyethylene-based foamed particles (A) may be mixed with polyethylene-based foamed particles (B) at 60% by weight or more and 95% by weight or less, and polyethylene-based foamed particles (B) may be mixed with polyethylene-based foamed particles (A) at 70% by weight or more and 90% by weight or less, and polyethylene-based foamed particles (B) at 10% by weight or more and 30% by weight or less.

[0035] In one or more embodiments of the present invention, if the weight fraction of polyethylene-based foamed particles (A) in the second-smaller sieve is 10.0% or less, polyethylene-based foamed particles (A) may be mixed in an amount of 50% or more and less than 100% by weight with polyethylene-based foamed particles (B) in an amount of more than 0% by weight and 50% by weight or less. Alternatively, polyethylene-based foamed particles (A) may be mixed in an amount of 60% or more and 95% by weight or less with polyethylene-based foamed particles (B) in an amount of 5% or more and 40% by weight or less, or polyethylene-based foamed particles (A) may be mixed in an amount of 70% or more and 90% by weight or less with polyethylene-based foamed particles (B) in an amount of 10% or more and 30% by weight or less.

[0036] For polyethylene foam particles (B), the nominal mesh opening of the sieve with the highest weight fraction is two steps smaller than the nominal mesh opening of the sieve with the highest weight fraction of polyethylene foam particles (A), and the σ / Xp is 15.0% or less.

[0037] In one or more embodiments of the present invention, although not particularly limited, for example, from the viewpoint of making it easier to keep the σ / Xp of polyethylene-based resin foam particles to 15% or less, the weight fraction of polyethylene-based resin foam particles (B) in the sieve with the highest weight fraction is preferably 55% to 95%, and more preferably 60% to 90%.

[0038] In one or more embodiments of the present invention, although not particularly limited, for example, from the viewpoint of making it easier to keep the σ / Xp of polyethylene-based resin foam particles to 15% or less, the weight fraction of polyethylene-based resin foam particles (B) in a smaller sieve is preferably 0% or more and 20% or less, and more preferably 0% or more and 10% or less.

[0039] In one or more embodiments of the present invention, although not particularly limited, from the viewpoint of making it easier to keep the σ / Xp of polyethylene-based resin foam particles to 15% or less, the weight fraction of polyethylene-based resin foam particles (B) in the two-stage smaller sieve is preferably 0% or more and 10% or less, and more preferably 0% or more and 5% or less.

[0040] In one or more embodiments of the present invention, although not particularly limited, for example, from the viewpoint of making it easier to keep the σ / Xp of polyethylene resin foam particles used for molding to 15% or less, it is preferable that the weight fraction of polyethylene resin foam particles (B) in the sieve with the highest weight fraction is 55% to 95%, the weight fraction in the sieve one step smaller is 0% to 20%, and the weight fraction in the sieve two steps smaller is 0% to 10%, and it is more preferable that the weight fraction in the sieve with the highest weight fraction is 60% to 90%, the weight fraction in the sieve one step smaller is 0% to 10%, and the weight fraction in the sieve two steps smaller is 0% to 5%.

[0041] In one or more embodiments of the present invention, although not particularly limited, for example, the weight fraction of polyethylene resin foam particles (B) in the next larger sieve may be 0% or more and 45% or less, or 5% or more and 45% or less.

[0042] The σ / Xp of polyethylene-based foamed particles (B) is not particularly limited, but from the viewpoint of making it easier to keep the σ / Xp of polyethylene-based foamed particles below 15%, it is preferably 13.0% or less, more preferably 11.0% or less, and even more preferably 9.0% or less. The lower limit of the σ / Xp of polyethylene-based foamed particles (B) is not particularly limited, but from the viewpoint of productivity, it may be 1% or more.

[0043] The weight-average ratio of polyethylene resin foam particles (B) is not particularly limited, but for example, from the viewpoint of more effectively achieving both improved elongation and suppression of deformation at the edges, it is preferably 5 to 55 times, and more preferably 7 to 50 times.

[0044] The average particle diameter of the polyethylene resin foam particles (A) is not particularly limited, but for example, from the viewpoint of more effectively achieving both improved elongation and suppression of deformation at the edges of the in-molded foamed product, it is preferably 1.0 mm to 8.0 mm, more preferably 2.0 mm to 7.0 mm, and even more preferably 3.0 mm to 6.0 mm.

[0045] The average particle diameter of the polyethylene resin foam particles (B) is not particularly limited, but for example, from the viewpoint of more effectively achieving both improved elongation and suppression of deformation at the edges of the in-molded foamed product, it is preferably 0.5 mm to 6.5 mm, more preferably 1.0 mm to 5.5 mm, and even more preferably 1.5 mm to 4.5 mm.

[0046] The ratio Da / Db of the average particle diameter Da of the polyethylene-based resin foamed particles (A) to the average particle diameter Db of the polyethylene-based resin foamed particles (B) is not particularly limited. For example, from the viewpoint of more effectively improving the elongation of the edge portion of the in-mold foamed molded body, it is preferably 1.3 or more and 1.8 or less, and more preferably 1.4 or more and 1.7 or less.

[0047] The polyethylene-based resin foamed particles (A) and the polyethylene-based resin foamed particles (B) can be obtained, for example, by subjecting polyethylene-based resin particles to single-stage foaming.

[0048] Examples of the polyethylene-based resin that is the base resin of the polyethylene-based resin particles include low-density polyethylene-based resins, medium-density polyethylene-based resins, linear low-density polyethylene-based resins, and the like. Among them, from the viewpoint of easily obtaining highly foamed polyethylene-based resin foamed particles, it is more preferable to use a low-density polyethylene-based resin and / or a linear low-density polyethylene-based resin, and it is particularly preferable to use a low-density polyethylene-based resin. The polyethylene-based resin may be used alone or in combination of two or more.

[0049] The density of the low-density polyethylene-based resin is preferably 0.920 g / cm 3 The density of the low-density polyethylene-based resin is preferably 0.920 g / cm 3 above and 0.940 g / cm 3 <below, and more preferably 0.920 g / cm 3 3 above and 0.932 g / cm

[0050] The melt index (MI) of the polyethylene-based resin is not particularly limited. For example, from the viewpoint of easily obtaining an in-mold foamed molded body that is difficult to deform, it may be 0.1 g / 10 min or more and 5.0 g / 10 min or less, or may be 0.5 g / 10 min or more and 4.0 g / 10 min or less.

[0051] The melting point of the polyethylene-based resin is not particularly limited. For example, from the viewpoint of reducing production energy and production costs, it is preferably 110°C or more and 135°C or less, and more preferably 115°C or more and 130°C or less.

[0052] The polyethylene resin (low-density polyethylene resin, medium-density polyethylene resin, linear low-density polyethylene resin, etc.) may be an ethylene homopolymer, or a copolymer containing ethylene and a comonomer other than ethylene that can copolymerize with ethylene. As the comonomer copolymerizable with ethylene, α-olefins having 3 to 18 carbon atoms can be used, such as propylene, 1-butene, 1-pentene, 1-hexene, 3,3-dimethyl-1-butene, 4-methyl-1-pentene, 4,4-dimethyl-1-pentene, and 1-octene. One of these comonomers may be used alone, or two or more may be used in combination.

[0053] When the low-density polyethylene resin is a copolymer, in order to bring the density of the copolymer within the aforementioned range, it is preferable to copolymerize it using a comonomer that can copolymerize with ethylene in an amount of approximately 1% to 12% by weight.

[0054] The polyethylene resin particles may, in addition to the polyethylene resin which is the base resin, optionally contain various additives such as inorganic substances, hydrophilic compounds, antioxidants (stabilizers), antistatic agents, colorants, flame retardants, and compatibilizers.

[0055] One method for producing the aforementioned polyethylene resin particles is to use an extruder. Specifically, for example, a method may be used in which a mixture obtained by blending polyethylene resin with additives such as inorganic substances, hydrophilic compounds, and antioxidants as needed is put into an extruder, melted and kneaded, extruded through a die, cooled, and then cut into particle shape with a cutter.

[0056] In one or more embodiments of the present invention, the one-stage foaming step is a step of obtaining polyethylene resin foam particles by foaming polyethylene resin particles by dispersing polyethylene resin particles in an aqueous dispersion medium in a sealed container, adding a foaming agent containing carbon dioxide, heating and pressurizing, and then releasing to a pressure range lower than the internal pressure of the sealed container.

[0057] In the single-stage foaming process, specifically, for example, polyethylene resin particles, an aqueous dispersion medium, and a dispersant if necessary are placed in a sealed container. Then, if necessary, the inside of the sealed container is reduced in pressure (vacuumed), a foaming agent containing carbon dioxide is introduced, and then the mixture is heated to a temperature above the softening temperature of the polyethylene resin. If necessary, after heating, more foaming agent containing carbon dioxide is added to adjust to the desired foaming pressure, and the temperature is finely adjusted to the foaming temperature while being held for a predetermined time. Then, the polyethylene resin particles impregnated with the foaming agent are released through an orifice, for example, into a collection container (e.g., a foaming cylinder) at a pressure lower than the internal pressure of the sealed container (usually atmospheric pressure) to obtain polyethylene resin foamed particles. The opening of the orifice may have one hole, or it may have two or more holes (e.g., four holes, five holes, etc.).

[0058] The pressure inside the collection container for collecting polyethylene resin foam particles should be lower than the pressure inside the sealed container, but usually, a portion of the collection container should be open to the atmosphere and kept at atmospheric pressure. Keeping the pressure inside the collection container at atmospheric pressure is preferable because it eliminates the need for complex equipment to control the pressure.

[0059] To increase the foaming ratio of polyethylene resin foam particles, a hot water shower or steam may be blown into the collection container, bringing the released polyethylene resin foam particles into contact with the hot water or steam. In this case, the temperature inside the collection container is preferably in the range of 60°C to 120°C, and more preferably in the range of 90°C to 110°C.

[0060] The single-hole opening orifice is not particularly limited, but for example, from the viewpoint of productivity, the diameter may be 1.0 mm to 7.0 mm, or 2.0 mm to 6.0 mm. Also, the single-hole opening orifice is not particularly limited, but for example, the impact angle may be 0° to 40°, or 3° to 30°. When the impact angle is within the above range, it is easier to achieve both foaming properties and cell uniformity.

[0061] In the single-stage foaming process, by making adjustments such as reducing the impact angle of the orifice or changing the temperature inside the collection container during foaming, it becomes easier to obtain polyethylene-based foamed particles in which the weight fraction in the second-stage smaller sieve exceeds 10.0% and σ / Xp is 15.0% or less.

[0062] In the single-stage foaming process, methods other than those described above are also acceptable for introducing the foaming agent. For example, polyethylene resin particles, an aqueous dispersion medium, and a dispersant as needed may be placed in a sealed container, and then, if necessary, the container may be evacuated, and the foaming agent may be introduced while heating to a temperature above the softening temperature of the polyethylene resin. Alternatively, for example, polyethylene resin particles, an aqueous dispersion medium, and a dispersant as needed may be placed in a sealed container, and then heated to near the foaming temperature, at which point the foaming agent may be introduced.

[0063] The temperature inside the sealed container before release to the low-pressure region (foaming temperature) should be above the softening temperature of the polyethylene resin particles. However, generally, based on the melting point [Tm(°C)] of the polyethylene resin particles, it is preferable to have a temperature of Tm-30(°C) or higher and Tm+20(°C) or lower, and more preferably Tm-5(°C) or higher and Tm10(°C) or lower.

[0064] In one or more embodiments of the present invention, the melting point of the polyethylene resin or the melting point Tm of the polyethylene resin particles is the melting peak temperature at the second heating stage in the DSC curve obtained when 1 mg to 10 mg of polyethylene resin or polyethylene resin particles is heated from 10°C to 190°C at a rate of 10°C / min, then cooled to 10°C at a rate of 10°C / min, and then heated again to 190°C at a rate of 10°C / min using a differential scanning calorimetry (DSC) with a differential scanning calorimetry meter. The melting end temperature is the temperature at which the tail of the melting peak curve at the second heating stage returns to the baseline position on the high-temperature side. The melting point of polyethylene resin foam particles can be measured in the same manner.

[0065] The holding time at the foaming temperature (hereinafter sometimes referred to as "hold time") is preferably in the range of more than 0 minutes and 120 minutes or less, more preferably in the range of 2 minutes or more and 60 minutes or less, and even more preferably in the range of 10 minutes or more and 50 minutes or less.

[0066] As a blowing agent, a blowing agent containing carbon dioxide is used. Examples of blowing agents other than carbon dioxide include saturated hydrocarbons such as propane, butane, and pentane; ethers such as dimethyl ether; alcohols such as methanol and ethanol; and inorganic gases such as air, nitrogen, and water vapor (water). These blowing agents may be used individually or in combination of two or more. Among the blowing agents mentioned above, it is more preferable to use a blowing agent containing only carbon dioxide, or a blowing agent containing carbon dioxide and water vapor (water), because it has a particularly low environmental impact and no flammability risk.

[0067] While it is preferable to use only water as the aqueous dispersion medium, dispersion media containing methanol, ethanol, ethylene glycol, glycerin, etc., added to water can also be used. Furthermore, when polyethylene resin particles contain hydrophilic compounds, the water in the aqueous dispersion medium also acts as a foaming agent, contributing to an improvement in the foaming ratio.

[0068] In an aqueous dispersion medium, it is preferable to use a dispersant to prevent blocking of polyethylene resin particles. Examples of dispersants include inorganic dispersants such as tricalcium phosphate, trimagnesium phosphate, basic magnesium carbonate, calcium carbonate, barium sulfate, kaolin, talc, and clay. The dispersant may be used alone or in combination of two or more types.

[0069] Furthermore, it is preferable to use a dispersion aid together with the dispersant. Examples of dispersion aids include carboxylate salts such as N-acyl amino acid salts, alkyl ether carboxylates, and acylated peptides; sulfonate salts such as alkyl sulfonates, n-paraffin sulfonates, alkylbenzene sulfonates, alkylnaphthalene sulfonates, and sulfosuccinates; sulfate esters such as sulfated oils, alkyl sulfates, alkyl ether sulfates, alkylamide sulfates, and alkyl allyl ether sulfates; and phosphate esters such as alkyl phosphates, polyoxyethylene phosphates, and alkyl allyl ether phosphates. In addition, polycarboxylic acid type polymer surfactants such as maleic acid copolymer salts and polyacrylates, polystyrene sulfonates, and naphthalsulfonic acid formalin condensate salts can also be used. The type of salt in the dispersion aid is not particularly limited, and examples include sodium salts, potassium salts, lithium salts, etc. The dispersion aid may be used alone or in combination of two or more types.

[0070] The amount of the aforementioned dispersant and dispersion aid used varies depending on their type and the type and amount of polyethylene resin particles used, but it is generally preferable to blend the dispersant in an amount of 0.1 parts by weight to 3 parts by weight and the dispersion aid in an amount of 0.001 parts by weight to 0.1 parts by weight per 100 parts by weight of the aqueous dispersion medium.

[0071] To ensure good dispersibility in an aqueous dispersion medium, polyethylene resin particles are generally used in an amount of 20 parts by weight or more and 100 parts by weight or less per 100 parts by weight of the aqueous dispersion medium.

[0072] Polyethylene resin foam particles obtained by foaming polyethylene resin particles through a single-stage foaming process are sometimes referred to as "single-stage foamed particles."

[0073] After mixing polyethylene resin particles (A) and polyethylene resin particles (B) in predetermined amounts, further foaming may be performed as needed. In this invention, the process of further foaming the polyethylene resin foam particles, which are one-stage foamed particles, to obtain polyethylene resin foam particles with a higher foaming ratio may be referred to as the "two-stage foaming process," and the polyethylene resin foam particles obtained through such a two-stage foaming process may be referred to as "two-stage foamed particles."

[0074] Furthermore, if, after mixing predetermined amounts of polyethylene resin particles (A) and polyethylene resin particles (B), the resulting mixed particles have a weight fraction exceeding 10% on a sieve with a nominal mesh size two steps smaller, and the variation in foaming ratio σ / Xp is 15.0% or less, the mixture may undergo a two-stage foaming process, or it may be used directly as polyethylene resin particles without undergoing a two-stage foaming process.

[0075] The two-stage foaming process specifically involves drying a mixture of polyethylene resin particles (A) and polyethylene resin particles (B), which are single-stage foamed particles (or, in some cases, only polyethylene resin particles (A)), as needed, placing it in a pressure-resistant container, impregnating it with an inorganic gas containing at least one gas selected from the group consisting of air, nitrogen, and carbon dioxide to apply internal pressure, and then heating and further foaming it. The two-stage foaming process may be performed multiple times as needed.

[0076] Heating methods in the two-stage foaming process include methods using steam and methods using electricity, but from the viewpoint of ease of process, handling, and safety, the method using steam is preferred.

[0077] When heating with steam, the steam pressure is preferably adjusted to 0.005 MPa (gauge pressure) or more and 0.15 MPa (gauge pressure) or less, taking into consideration the expansion ratio of the two-stage foamed particles, and more preferably to 0.01 MPa (gauge pressure) or more and 0.1 MPa (gauge pressure) or less.

[0078] The internal pressure of the inorganic gas impregnating the first-stage foamed particles should be appropriately varied considering the foaming ratio of the second-stage foamed particles, but it is preferable that it be between 0.1 MPa (absolute pressure) and 0.6 MPa (absolute pressure).

[0079] (Polyethylene resin molded foam product) Polyethylene resin foam particles can be molded into polyethylene resin in-mold foam molded articles by, for example, known in-mold foam molding.

[0080] There are no particular restrictions on the specific method for forming polyethylene resin foam molded articles by in-mold foam molding, but for example, (I) A method in which polyethylene resin foam particles are placed in a pressure vessel, impregnated with an inorganic gas containing at least one gas selected from the group consisting of air, nitrogen, and carbon dioxide to apply internal pressure, and then filled into a mold and heated and fused with steam; (II) A method in which polyethylene resin foam particles are compressed with the pressure of an inorganic gas and filled into a mold, and then heated and fused with steam using the restorative force of the polyethylene resin foam particles; (III) Examples of methods include filling a mold with polyethylene resin foam particles without any prior treatment and then heating and fusing them with steam.

[0081] The molding conditions, such as molding pressure, in in-mold foam molding are not particularly limited and can be adjusted as appropriate using, for example, general known conditions.

[0082] In polyethylene resin in-molded foamed molded articles, from the viewpoint of good edge elongation, for example, in the edge portion of an in-molded article obtained using a mold for plate-shaped molded articles, it is preferable that the spacing between particles is small, and when rubbed strongly with a finger, the adhesion between adjacent foam particles peels off but the foam particles themselves do not detach from the molded article; it is more preferable that the spacing between particles is very small, and the adhesion between adjacent foam particles does not peel off even when rubbed strongly with a finger; and it is even more preferable that there is no spacing between particles at all, and the adhesion between adjacent foam particles does not peel off even when rubbed strongly with a finger.

[0083] From the viewpoint of minimizing deformation, in polyethylene resin in-molded foamed molded articles, for example, in a box-shaped in-molded foamed article with a partition plate in the center obtained using a mold for a cushioning box for storing articles with a partition plate in the center of the molded article, the deformation amount calculated according to the following formula (5) is preferably 10 mm or less, and more preferably 9 mm or less. Furthermore, the deformation rate calculated according to the following formula (6) is preferably 2.9% or less, and more preferably 2.6% or less. A box-shaped in-molded foamed article can be used that has been manufactured using a mold for a cushioning box for storing articles with a partition plate in the center of the molded article, and has dimensions of 350 mm in the longitudinal direction × 320 mm in the short direction × 180 mm in the depth direction. [Formula (5)] Deformation amount = (L1 + L2) / 2 - L3 ... (5) [Formula (6)] Deformation rate (%) = [(L1+L2) / 2-L3] / [(L1+L2) / 2] × 100···(6) However, in equations (5) and (6) above, L1 and L2 represent the dimensions at both ends in the longitudinal direction, respectively, and L3 represents the dimension at the center. [Examples]

[0084] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0085] The polyethylene resins and additives used in the examples and comparative examples are shown below. (1) Polyethylene resin Linear low-density polyethylene [Melting point: 122℃, MI: 2.0g / 10min, Density: 0.926g / cm³] 3 ] (2) Inorganic matter Talc [Manufactured by Hayashi Chemical Co., Ltd., Talc Powder (registered trademark) PK-S] (3) Hydrophilic compound Glycerin [Manufactured by Lion Corporation, purified glycerin D] (4) Antioxidants Hindered amine light stabilizer [BASF, Tinuvin 622SF]

[0086] The measurement and evaluation methods are as follows:

[0087] (Expansion ratio) The weight Gi of the polyethylene foam particles was accurately weighed to 0.001g (rounded to the fourth decimal place), and then the volume yi (cm³) of the polyethylene foam particles was determined from the rise in the scale when the weighed polyethylene foam particles were immersed in 100ml of water at 23°C in a graduated cylinder. 3 ) read the weight Gi (g) of the polyethylene foam particles and the volume yi (cm³) of the polyethylene foam particles. 3 The apparent density di of the polyolefin resin foam particles in each sieve was determined by dividing by ( ) and converting the result to g / L units. Finally, the foaming ratio Ki = ds / di was determined from the ratio with the density ds (=926 g / L) of the base resin.

[0088] (Average particle size) 200 g of polyethylene resin foam particles were sieved using standard sieves specified in JIS Z 8801-1:2006 (nine stages with nominal mesh openings of 2.00, 2.36, 2.80, 3.35, 4.00, 4.75, 5.60, 6.70, and 8.00, in mm). The average particle size D was calculated using the following formula (4) with respect to the central particle size Ri of each sieve and the weight fraction Wi of the polyethylene resin foam particles remaining in each sieve. [Formula (4)] Average particle diameter D(mm)=Σ(Ri Wi) / 100...(4) However, in equation (4), i represents each sieve, and the central particle size Ri of each sieve is the arithmetic mean of the nominal mesh opening of each sieve and the nominal mesh opening of a sieve one step larger than that sieve.

[0089] (Weight fraction, weight-average expansion ratio, σ / Xp (variation in expansion ratio)) One kilogram of polyethylene foam particles was sieved using standard sieves specified in JIS Z 8801-1:2006 (nine nominal mesh sizes: 2.00, 2.36, 2.80, 3.35, 4.00, 4.75, 5.60, 6.70, and 8.00, in mm). The weight fraction Wi and foaming ratio Ki of the polyethylene foam particles remaining in each sieve were measured, and the weight-average foaming ratio Kav was calculated based on equation (2) below. Next, the standard deviation σm of the foaming ratio was calculated based on equation (3) using the weight fraction Wi, foaming ratio Ki, and weight-average foaming ratio Kav, and the σ / Xp (foaming ratio variation) (%) was determined based on equation (1). [Formula (2)] Kav = Σ(Ki × Wi)···(2) [Formula (3)] σm=[Σ{Wi×(Kav-Ki) 2}] 1 / 2 ...(3) [Formula (1)] σ / Xp (Variation in foaming ratio) (%) = (σm / Kav) × 100 ... (1) However, in equations (2) and (3), i represents each sieve.

[0090] (Edge stretching) For evaluating edge elongation, polyethylene resin foam particles were foam-molded in-mold using a mold for plate-shaped molded bodies. The edges of the resulting molded bodies were rubbed with a finger to observe the degree of adhesion between the foam particles at the edges and the degree of detachment from the molded body. A score of 1 to 5 was assigned based on the following indicators. 1: The particles are very far apart, and when lightly rubbed with a finger, the foam particles easily detach from the molded body. 2: The particles are spaced far apart, and when rubbed vigorously with a finger, the foam particles detach from the molded body. 3: The particles are spaced very close together, and while rubbing them hard with your fingers can break the adhesion between adjacent foam particles, the foam particles themselves do not detach from the molded material. 4. The gaps between the particles are extremely small, and even if you rub them hard with your fingers, the adhesive between adjacent foam particles will not come apart. 5: There are absolutely no gaps between the particles, and even if you rub them hard with your finger, the adhesive between adjacent foam particles does not come apart.

[0091] (Amount of deformation and rate of deformation) As a mold, a mold for a cushioning box for storing goods, which has a partition plate in the center of the molded body, was used to create a box shape with dimensions of 350 mm in the longitudinal direction × 320 mm in the short direction × 180 mm in the depth direction, with a side thickness of 16 mm, and polyethylene resin foam particles were foam-molded in the mold. As shown in Figure 1, the dimensions of both ends (L1, L2) and the center (L3) in the longitudinal direction (direction indicated by the arrows) of the obtained molded body were measured, and the amount of deformation was determined according to the following formula (5), and the deformation rate was determined according to the following formula (6). [Formula (5)] Deformation amount = (L1 + L2) / 2 - L3 ... (5) [Formula (6)] Deformation rate (%) = [(L1+L2) / 2-L3] / [(L1+L2) / 2] × 100···(6)

[0092] (Manufacturing Example 1) <Preparation of polyethylene resin particles> 20 kg of linear low-density polyethylene resin was blended with 2000 ppm of inorganic material, 2000 ppm of hydrophilic compound, and 1000 ppm of antioxidant. The resulting blend was fed into a twin-screw extruder [Toshiba Machine Co., Ltd., TEM26-SX], melted and kneaded at a resin temperature of 210°C, extruded into strands through a circular die attached to the tip of the extruder, water-cooled, and cut with a cutter to obtain cylindrical foamed polyethylene resin particles (4.5 mg / particle). <Preparation of polyethylene-based foamed particles> 100 parts by weight of the obtained polyethylene resin particles for foaming were placed in a pressure-resistant sealed container along with 185 parts by weight of pure water, 0.3 parts by weight of kaolin (BASF ASP-170) as a poorly water-soluble inorganic compound, and 0.06 parts by weight of sodium dodecylbenzenesulfonate as a surfactant. Then, while stirring, 5.5 parts by weight of carbon dioxide were introduced into the pressure-resistant sealed container, and the mixture was heated to a foaming temperature of 123.3°C. Subsequently, additional carbon dioxide was injected to increase the pressure inside the pressure-resistant sealed container to a foaming pressure of 3.0 MPa (gauge pressure). After maintaining this foaming temperature and pressure for 30 minutes, the valve at the bottom of the sealed container was opened, and the aqueous dispersion (resin particles and aqueous dispersion medium) was released into a foaming cylinder under atmospheric pressure through a Φ4.0 mm, impact angle of 20°, single-hole open orifice to obtain polyethylene resin foamed particles (single-stage foamed particles). During this process, carbon dioxide was injected to maintain the pressure inside the pressure-resistant sealed container and prevent a decrease in pressure. Furthermore, the foam cylinder was kept heated by continuously blowing steam into it, so that the released foam particles would come into contact with the steam.

[0093] (Manufacturing example 2) Except for changing the foaming temperature to 123.5℃, the orifice diameter to Φ4.5mm, and the impact angle to 5°, and stopping the supply of steam to the foaming cylinder at the start of foaming, the foaming process was carried out in the same manner as in Manufacturing Example 1 to obtain polyethylene-based resin foamed particles (single-stage foamed particles).

[0094] (Manufacturing Example 3) Except for changing the foaming temperature to 123.0°C, the foaming pressure to 3.2 MPa (gauge pressure), and the orifice diameter to Φ3.6 mm, the foaming process was carried out in the same manner as in Manufacturing Example 1 to obtain polyethylene-based resin foamed particles (single-stage foamed particles).

[0095] (Manufacturing example 4) Except for changing the foaming temperature to 123.5°C and the impact angle to 5°, and stopping the steam supply to the foaming cylinder at the start of foaming, the foaming process was carried out in the same manner as in Production Example 1 to obtain polyethylene resin foamed particles (single-stage foamed particles).

[0096] (Manufacturing example 5) Polyethylene resin foam particles (single-stage foam particles) were obtained in the same manner as in Manufacturing Example 2. Next, the single-stage foam particles were dried at 60°C for 6 hours, and then impregnated with pressurized air in a pressure-resistant sealed container to apply an internal pressure (absolute pressure) of 0.39 MPa to the single-stage foam particles. Approximately 20 L of the air-impregnated single-stage foam particles were put into a foaming machine and heated for 30 seconds at a water vapor pressure of 0.05 MPa (gauge pressure) to induce double-stage foaming, thereby obtaining polyethylene resin foam particles (double-stage foam particles).

[0097] (Manufacturing example 6) Except for changing the foaming pressure to 2.6 MPa (gauge pressure), the foaming process was carried out in the same manner as in Manufacturing Example 1 to obtain polyethylene resin foam particles (single-stage foam particles).

[0098] (Manufacturing example 7) Except for changing the foaming temperature to 123.5°C, the foaming pressure to 2.6 MPa (gauge pressure), the orifice diameter to Φ4.5 mm, and the impact angle to 5°, and stopping the supply of steam to the foaming cylinder at the start of foaming, the foaming process was carried out in the same manner as in Manufacturing Example 1 to obtain polyethylene-based resin foamed particles (single-stage foamed particles).

[0099] (Manufacturing example 8) Except for changing the foaming temperature to 123.0°C, the foaming pressure to 2.8 MPa (gauge pressure), and the orifice diameter to Φ3.6 mm, the foaming process was carried out in the same manner as in Manufacturing Example 1 to obtain polyethylene-based resin foamed particles (single-stage foamed particles).

[0100] (Manufacturing example 9) Polyethylene resin foam particles (single-stage foam particles) were obtained in the same manner as in Production Example 2. Next, using these single-stage foam particles, a two-stage foaming process was performed in the same manner as in Production Example 5, except that the internal pressure applied to the single-stage foam particles was set to 0.34 MPa (absolute pressure), to obtain polyethylene resin foam particles (double-stage foam particles).

[0101] (Manufacturing example 10) Except for changing the foaming pressure to 2.8 MPa (gauge pressure), the foaming process was carried out in the same manner as in Manufacturing Example 1 to obtain polyethylene-based resin foam particles (single-stage foam particles).

[0102] (Manufacturing Example 11) Except for changing the foaming temperature to 123.5°C, the foaming pressure to 2.8 MPa (gauge pressure), the orifice diameter to Φ4.5 mm, and the impact angle to 5°, and stopping the supply of steam to the foaming cylinder at the start of foaming, the foaming process was carried out in the same manner as in Manufacturing Example 1 to obtain polyethylene-based resin foamed particles (single-stage foamed particles).

[0103] The weight-average foaming ratio, σ / X, and average particle size of the polyethylene resin foam particles obtained in Production Examples 1 to 11 were measured as described above, and the results are shown in Table 1 below. Table 1 also shows the weight fraction of the polyethylene resin foam particles remaining in each sieve.

[0104] [Table 1]

[0105] (Example 1) <Mixing process> The polyethylene resin foam particles (single-stage foam particles) obtained in Production Example 1 and the polyethylene resin foam particles (single-stage foam particles) obtained in Production Example 6 were weighed in a weight ratio of 80:20, and these were placed in the same mesh bag and mixed by air blowing for 3 minutes. <Foaming Process> The mixture of single-stage foamed particles obtained above was dried at 60°C for 6 hours, and then impregnated with pressurized air in a pressure-resistant sealed container, applying an internal pressure (absolute pressure) of 0.39 MPa. Approximately 20 L of the air-impregnated polyethylene resin foamed particles were put into a foaming machine and heated for 30 seconds at a water vapor pressure of 0.05 MPa (gauge pressure) to induce double-stage foaming, thereby obtaining polyethylene resin foamed particles (double-stage foamed particles). <Preparation of polyethylene resin-based foamed molded products> The two-stage foamed particles obtained above were filled into a mold for a plate-shaped molded body and a mold for evaluating deformation using a polyolefin molded foam molding machine manufactured by Daisen Corporation, and heated and molded with steam at 0.12 MPa (gauge pressure) to obtain polyethylene resin molded foamed bodies. The obtained molded foamed bodies were left at room temperature (approximately 23°C) for 1 hour, dried in a constant temperature room at 75°C for 12 hours, and then left at room temperature for 4 hours before various evaluations were performed.

[0106] (Examples 2-7) Except for mixing the polyethylene resin foam particles shown in Table 2 below in the proportions shown in Table 2 below, the mixing and foaming processes were carried out in the same manner as in Example 1 to obtain polyethylene resin foam particles (two-stage foam particles). Using the obtained polyethylene-based resin foam particles (two-stage foam particles), a polyethylene-based resin molded foam body was produced in the same manner as in Example 1.

[0107] (Example 8) Except for using only the polyethylene-based resin foam particles (single-stage foam particles) (100% by weight) obtained in Manufacturing Example 4, the foaming process was carried out in the same manner as in Example 1 to obtain polyethylene-based resin foam particles (double-stage foam particles).

[0108] Using the obtained polyethylene-based resin foam particles (two-stage foam particles), a polyethylene-based resin molded foam body was produced in the same manner as in Example 1.

[0109] (Examples 9-10) Without performing a foaming process, a mixture of polyethylene-based foamed particles (single-stage foamed particles) was obtained by mixing the polyethylene-based foamed particles shown in Table 2 in the proportions shown in Table 2 below. Using the obtained mixture of polyethylene-based resin foam particles (single-stage foam particles), a polyethylene-based resin molded foam article was prepared in the same manner as in Example 1.

[0110] (Comparative Examples 1-5) Except for mixing the polyethylene resin foam particles shown in Table 3 in the proportions shown in Table 3 below, the mixing and foaming processes were carried out in the same manner as in Example 1 to obtain polyethylene resin foam particles (two-stage foam particles). Using the obtained polyethylene-based resin foam particles (two-stage foam particles), a polyethylene-based resin molded foam body was produced in the same manner as in Example 1.

[0111] The weight fraction, weight-average magnification, σ / X, and average particle diameter of the polyethylene resin foam particles obtained in the examples and comparative examples were measured as described above, and the results are shown in Tables 2 and 3 below.

[0112] Furthermore, the edge elongation and deformation of the polyethylene resin molded foam articles obtained in the examples and comparative examples were measured and evaluated as described above, and the results are shown in Tables 2 and 3 below.

[0113] [Table 2]

[0114] [Table 3]

[0115] In the examples, by using polyethylene-based foamed particles in which the weight fraction in the second-smaller sieve exceeds 10.0% and σ / Xp is 15.0% or less, an in-molded foamed molded article with good edge elongation and minimal deformation was obtained. In particular, as in Examples 1 to 8, even when the polyethylene-based foamed particles are two-stage foamed particles and the foaming ratio is high, if the weight fraction of the polyethylene-based foamed particles in the second-smaller nominal mesh sieve exceeds 10.0% and σ / Xp is 15.0% or less, an in-molded foamed molded article with good edge elongation and minimal deformation was obtained. In Examples 1 to 7, polyethylene-based foamed particles (A) and polyethylene-based foamed particles (B), which are single-stage foamed particles, were mixed, and the resulting mixture was foamed to obtain polyethylene-based foamed particles, which are two-stage foamed particles, and the weight fraction of polyethylene-based foamed particles (A) in the second-smaller sieve is less than 10.0%. In Example 8, polyethylene-based resin foam particles (A), which are single-stage foam particles, were foamed to obtain polyethylene-based resin foam particles, which are double-stage foam particles, and the weight fraction of polyethylene-based resin foam particles (A) in the two smaller sieves exceeded 10.0%. In Examples 9 and 10, polyethylene-based resin foam particles (A) and polyethylene-based resin foam particles (B), which are single-stage foam particles, were mixed to obtain polyethylene-based resin foam particles, and the weight fraction of polyethylene-based resin foam particles (A) in the two smaller sieves was less than 10.0%.

[0116] In Comparative Examples 1 and 4, which used polyethylene-based foamed particles with a σ / Xp ratio exceeding 15.0%, the deformation of the in-molded foamed articles was 14 mm or more, indicating significant deformation. In Comparative Examples 2, 3, and 5, where the weight fraction in the two-stage smaller sieve was less than 10.0%, the elongation of the edges of the in-molded foamed articles was poor, and the deformation was 12 mm, indicating significant deformation.

[0117] The present invention is not particularly limited, but preferably includes at least the following embodiments. [1] Polyethylene resin foam particles in which, when measured using nine standard sieves with nominal mesh openings of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006, the weight fraction of the sieve with a nominal mesh opening two steps smaller than the nominal mesh opening of the sieve with the highest weight fraction exceeds 10.0%, and the variation in foaming ratio σ / Xp, expressed by the following formula (1), is 15.0% or less. [Formula (1)] σ / Xp(%)=(σm / Kav)×100···(1) However, in formula (1) above, Kav is the weight-average expansion factor calculated based on formula (2) below, and σm is the standard deviation of the expansion factor calculated based on formula (3) below. [Formula (2)] Kav = Σ(Ki × Wi)···(2) [Formula (3)] σm=[Σ{Wi×(Kav-Ki) 2}] 1 / 2 ...(3) However, in equations (2) and (3) above, i represents each sieve, and Wi and Ki represent the weight fraction and foaming ratio of polyethylene resin foam particles remaining in each sieve, respectively. [2] Polyethylene resin foam particles as described in [1], measured using nine standard sieves with nominal mesh openings of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006, wherein the weight-average magnification expressed by formula (2) is 3 to 60 times. [3] Polyethylene resin foam particles as described in [1] or [2], measured using nine standard sieves with nominal mesh openings of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006, wherein the average particle diameter expressed by the following formula (4) is 2.0 mm to 9.0 mm. [Formula (4)] Average particle diameter D(mm)=Σ(Ri Wi) / 100...(4) However, in equation (4), i represents each sieve, Ri is the arithmetic mean of the nominal mesh opening of each sieve and the nominal mesh opening of a sieve one step larger than that sieve, and Wi represents the weight fraction of polyethylene resin foam particles remaining in each sieve. [4] Polyethylene resin foam particles as described in any of [1] to [3], wherein the weight fraction of the sieve with the highest weight fraction, measured using nine standard sieves with nominal mesh openings of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006, is 40% to 80%. [5] Polyethylene resin foam particles as described in any of [1] to [4], wherein the weight fraction of a sieve with a nominal mesh size two steps smaller than the nominal mesh size of the sieve with the highest weight fraction, measured using nine standard sieves with nominal mesh sizes of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006, is 10.1% to 45%. [6] Polyethylene resin foam particles according to any one of [1] to [5], wherein the variation in foaming ratio σ / Xp is 1% or more and 14.5% or less. [7] Polyethylene resin foam particles as described in any of [1] to [6], wherein the weight fraction of the sieve with the highest weight fraction measured using nine standard sieves with nominal mesh openings of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006 is 45% to 70%, the weight fraction of the sieve one step smaller is 0% to 48%, and the weight fraction of the sieve two steps smaller is 10.1% to 30%. [8] Polyethylene resin foam particles as described in any of [1] to [7], wherein the melt index of the polyethylene resin is 0.1 g / 10 min or more and 5.0 g / 10 min or less. [9] Polyethylene resin foam particles according to any of [1] to [8], wherein when a box-shaped cushioning material is formed, the deformation rate calculated according to the following formula (6) is 2.9% or less. [Formula (6)] Deformation rate (%) = [(L1+L2) / 2-L3] / [(L1+L2) / 2] × 100···(6) However, in equation (6), L1 and L2 represent the dimensions at both ends in the longitudinal direction, and L3 represents the dimension at the center.

[10] Polyethylene resin foam particles as described in any of [1] to [8], wherein when a plate-shaped molded body is formed, the spacing between polyethylene resin foam particles at the edge of the plate-shaped molded body is small, and when rubbed strongly with a finger, the adhesion between adjacent polyethylene resin foam particles peels off, but the foam particles themselves do not detach from the molded body.

[11] Polyethylene resin foam particles according to any one of [1] to [8], wherein when a plate-shaped molded body is formed, the spacing between polyethylene resin foam particles at the edge of the plate-shaped molded body is very small, and the adhesion between adjacent polyethylene resin foam particles does not peel off even when rubbed hard with a finger.

[12] Polyethylene resin foam particles according to any of [1] to [8], wherein when a plate-shaped molded body is formed, there are no gaps between the polyethylene resin foam particles at the edges of the plate-shaped molded body, and the adhesion between adjacent polyethylene resin foam particles does not peel off even when rubbed hard with a finger. A method for producing polyethylene resin foam particles according to any one of [1] to

[12] , The process includes a mixing step of mixing polyethylene resin foam particles (A) in an amount of 50% to 100% by weight and polyethylene resin foam particles (B) in an amount of 0% to 50% by weight. Polyethylene resin foam particles (A) have a weight-average magnification of 3 to 60 times, measured using nine standard sieves with nominal mesh openings of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006, and the variation in foaming magnification σ / Xp, expressed by the following formula (1), is 15.0% or less. A method for producing polyethylene resin foam particles, wherein when polyethylene resin foam particles (B) are sieved using nine standard sieves with nominal mesh openings of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006, the nominal mesh opening of the sieve with the highest weight fraction is two steps smaller than the nominal mesh opening of the sieve with the highest weight fraction of polyethylene resin foam particles (A), and the variation in foaming ratio σ / Xp, expressed by the following formula (1), is 15.0% or less. [Formula (1)] σ / Xp(%)=(σm / Kav)×100···(1) However, in formula (1) above, Kav is the weight-average expansion factor calculated based on formula (2) below, and σm is the standard deviation of the expansion factor calculated based on formula (3) below. [Formula (2)] Kav = Σ(Ki × Wi)···(2) [Formula (3)] σm=[Σ{Wi×(Kav-Ki) 2}] 1 / 2 ...(3) However, in equations (2) and (3) above, i represents each sieve, and indicates the weight fraction and foaming ratio of polyethylene resin foam particles remaining in each sieve.

[14] A method for producing polyethylene resin foam particles according to

[13] , comprising mixing polyethylene resin foam particles (A) in an amount of 50% or more and less than 100% by weight with polyethylene resin foam particles (B) in an amount of more than 0% by weight and 50% or less by weight.

[15] A method for producing polyethylene resin foam particles as described in

[14] , wherein the polyethylene resin foam particles (A) are measured using nine standard sieves with nominal mesh openings of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006, and the weight fraction of the sieve two steps smaller than the sieve with the highest weight fraction is less than 10.0%.

[16] A method for producing polyethylene resin foam particles as described in

[13] , comprising 100% by weight of polyethylene resin foam particles (A), wherein the polyethylene resin foam particles (A) have a weight fraction of 10.0% or more in the sieve two steps smaller than the sieve with the highest weight fraction, as measured using nine standard sieves with nominal mesh openings of 2.00 mm or more and 8.00 mm or less as specified in JIS Z 8801-1:2006.

[17] A method for producing polyethylene resin foam particles as described in any of

[13] to

[15] , wherein the ratio Da / Db of the average particle diameter Da of polyethylene resin foam particles (A) to the average particle diameter Db of polyethylene resin foam particles (B), measured using nine standard sieves with nominal mesh openings of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006, is 1.3 to 1.8.

[18] A method for producing polyethylene resin foamed particles according to any one of

[13] to

[15] and

[17] , comprising a foaming step after the mixing step in which the mixture is foamed.

[19] A method for producing polyethylene resin foam particles according to

[16] , comprising a foaming step of foaming polyethylene resin foam particles (A).

[20] A polyethylene resin molded article obtained by in-mold foam molding polyethylene resin foam particles obtained by the polyethylene resin foam particle manufacturing method described in any of [1] to

[12] , or by the polyethylene resin foam particle manufacturing method described in any of

[13] to

[19] .

[21] A polyethylene resin in-molded foam product as described in

[20] , which is a cushioning material.

[22] The polyethylene resin in-molded foamed article according to

[21] , wherein the cushioning material is box-shaped and has a deformation rate of 2.9% or less, determined according to the following formula (6). [Formula (6)] Deformation rate (%) = [(L1+L2) / 2-L3] / [(L1+L2) / 2] × 100···(6) However, in formula (6) above, L1 and L2 represent the dimensions at both ends in the longitudinal direction, and L3 represents the dimension at the center.

[23] A mixing step of mixing polyethylene resin foam particles (A) in an amount of 50% or more by weight and less than 100% by weight with polyethylene resin foam particles (B) in an amount of more than 0% by weight and 50% or less by weight. A foaming step to obtain polyethylene resin foam particles by foaming the obtained mixture, and The process includes a molding step in which the obtained polyethylene resin foam particles are foamed and molded in a mold. Polyethylene resin foam particles (A) have a weight-average magnification of 3 to 60 times, measured using nine standard sieves with nominal mesh openings of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006, and the variation in foaming magnification σ / Xp, expressed by the following formula (1), is 15.0% or less. When polyethylene resin foam particles (B) are sieved using nine standard sieves with nominal mesh openings of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006, the nominal mesh opening of the sieve with the highest weight fraction is two steps smaller than the nominal mesh opening of the sieve with the highest weight fraction of polyethylene resin foam particles (A), and the variation in foaming ratio σ / Xp, expressed by the following formula (1), is 15.0% or less. A method for manufacturing a polyethylene resin in-mold foamed molded article, wherein the polyethylene resin foam particles, measured using nine standard sieves with nominal mesh openings of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006, have a weight fraction exceeding 10.0% in a sieve with a nominal mesh opening two steps smaller than the sieve with the highest weight fraction, and the variation in foaming ratio σ / Xp, expressed by the following formula (1), is 15.0% or less. [Formula (1)] σ / Xp(%)=(σm / Kav)×100···(1) However, in formula (1) above, Kav is the weight-average expansion factor calculated based on formula (2) below, and σm is the standard deviation of the expansion factor calculated based on formula (3) below. [Formula (2)] Kav = Σ(Ki × Wi)···(2) [Formula (3)] σm=[Σ{Wi×(Kav-Ki) 2}] 1 / 2 ...(3) However, in equations (2) and (3) above, i represents each sieve, and indicates the weight fraction and foaming ratio of polyethylene resin foam particles remaining in each sieve.

[24] A mixing step to obtain polyethylene resin foam particles by mixing polyethylene resin foam particles (A) in an amount of 50% or more and less than 100% by weight with polyethylene resin foam particles (B) in an amount of more than 0% by weight and 50% or less by weight, and The process includes a molding step in which the obtained polyethylene resin foam particles are foamed and molded in a mold. Polyethylene resin foam particles (A) have a weight-average magnification of 3 to 60 times, measured using nine standard sieves with nominal mesh openings of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006, and the variation in foaming magnification σ / Xp, expressed by the following formula (1), is 15.0% or less. When polyethylene resin foam particles (B) are sieved using nine standard sieves with nominal mesh openings of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006, the nominal mesh opening of the sieve with the highest weight fraction is two steps smaller than the nominal mesh opening of the sieve with the highest weight fraction of polyethylene resin foam particles (A), and the variation in foaming ratio σ / Xp, expressed by the following formula (1), is 15.0% or less. A method for manufacturing a polyethylene resin in-mold foamed molded article, wherein the polyethylene resin foam particles, measured using nine standard sieves with nominal mesh openings of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006, have a weight fraction exceeding 10.0% in a sieve with a nominal mesh opening two steps smaller than the sieve with the highest weight fraction, and the variation in foaming ratio σ / Xp, expressed by the following formula (1), is 15.0% or less. [Formula (1)] σ / Xp(%)=(σm / Kav)×100···(1) However, in formula (1) above, Kav is the weight-average expansion factor calculated based on formula (2) below, and σm is the standard deviation of the expansion factor calculated based on formula (3) below. [Formula (2)] Kav = Σ(Ki × Wi)···(2) [Formula (3)] σm=[Σ{Wi×(Kav-Ki) 2}] 1 / 2 ...(3) However, in equations (2) and (3) above, i represents each sieve, and indicates the weight fraction and foaming ratio of polyethylene resin foam particles remaining in each sieve.

[25] The method for producing a polyethylene resin in-mold foamed molded article according to

[23] or

[24] , wherein the weight fraction of polyethylene resin foam particles (A) in the sieve two steps smaller than the sieve with the highest weight fraction is less than 10.0%.

[26] A step of foaming polyethylene resin foam particles (A) to obtain polyethylene resin foam particles, and The process includes a molding step in which the obtained polyethylene resin foam particles are foamed and molded in a mold. Polyethylene resin foam particles (A) are measured using nine standard sieves with nominal mesh sizes of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006. The weight fraction of the sieve with the highest weight fraction measured using the sieve with a nominal mesh size two steps smaller than the nominal mesh size of the sieve with the highest weight fraction is greater than 10.0%, the weight-average magnification measured using nine standard sieves with nominal mesh sizes of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006 is between 3 and 60 times, and the variation in foaming magnification σ / Xp expressed by the following formula (1) is 15.0% or less. A method for manufacturing a polyethylene resin in-mold foamed molded article, wherein the polyethylene resin foam particles, measured using nine standard sieves with nominal mesh openings of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006, have a weight fraction exceeding 10.0% in a sieve with a nominal mesh opening two steps smaller than the sieve with the highest weight fraction, and the variation in foaming ratio σ / Xp, expressed by the following formula (1), is 15.0% or less. [Formula (1)] σ / Xp(%)=(σm / Kav)×100···(1) However, in formula (1) above, Kav is the weight-average expansion factor calculated based on formula (2) below, and σm is the standard deviation of the expansion factor calculated based on formula (3) below. [Formula (2)] Kav = Σ(Ki × Wi)···(2) [Formula (3)] σm=[Σ{Wi×(Kav-Ki) 2}] 1 / 2 ...(3) However, in equations (2) and (3) above, i represents each sieve, and indicates the weight fraction and foaming ratio of polyethylene resin foam particles remaining in each sieve. [Industrial applicability]

[0118] The in-mold foamed articles using polyethylene-based resin foam particles according to the present invention exhibit good elongation at the edges and minimal deformation, making them suitable for use in applications such as reusable containers, cushioning materials, cushioning packaging materials, and heat insulating materials.

Claims

1. Polyethylene resin foam particles, wherein the weight fraction of a sieve with a nominal mesh size two steps smaller than the nominal mesh size of the sieve with the highest weight fraction, measured using nine standard sieves with nominal mesh sizes of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006, is 10.1% to 30%, and the variation in foaming ratio σ / Xp, expressed by the following formula (1), is 15.0% or less. [Formula (1)] σ / Xp (%) = (σm / Kav)×100...(1) However, in formula (1) above, Kav is the weight-average expansion factor calculated based on formula (2) below, and σm is the standard deviation of the expansion factor calculated based on formula (3) below. [Formula (2)] Kav=Σ(Ki×Wi)...(2) [Formula (3)] σm=[Σ{Wi×(Kav-Ki)2}]1 / 2...(3) However, in equations (2) and (3) above, i represents each sieve, and Wi and Ki represent the weight fraction and foaming ratio of polyethylene resin foam particles remaining in each sieve, respectively.

2. Polyethylene resin foam particles according to claim 1, measured using nine standard sieves with nominal mesh openings of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006, wherein the weight-average magnification expressed by formula (2) is 3 times to 60 times.

3. Polyethylene resin foam particles according to claim 1 or 2, wherein the average particle diameter, as measured using nine standard sieves with nominal mesh openings of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006, is 2.0 mm to 9.0 mm, as expressed by the following formula (4). [Formula (4)] Average particle diameter D (mm)=Σ(Ri・Wi) / 100...(4) However, in equation (4), i represents each sieve, Ri is the arithmetic mean of the nominal mesh opening of each sieve and the nominal mesh opening of a sieve one step larger than that sieve, and Wi represents the weight fraction of polyethylene resin foam particles remaining in each sieve.

4. Polyethylene resin foam particles according to any one of claims 1 to 3, wherein the weight fraction of the sieve with the highest weight fraction, measured using nine standard sieves with nominal mesh openings of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006, is 40% to 80%.

5. A method for producing polyethylene resin foam particles according to any one of claims 1 to 4, The process includes a mixing step of mixing polyethylene resin foam particles (A) in an amount of 50% to 100% by weight and polyethylene resin foam particles (B) in an amount of 0% to 50% by weight. Polyethylene resin foam particles (A) have a weight-average magnification of 3 to 60 times, measured using nine standard sieves with nominal mesh openings of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006, and the variation in foaming magnification σ / Xp, expressed by the following formula (1), is 15.0% or less. A method for producing polyethylene resin foam particles, wherein when polyethylene resin foam particles (B) are sieved using nine standard sieves with nominal mesh openings of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006, the nominal mesh opening of the sieve with the highest weight fraction is two steps smaller than the nominal mesh opening of the sieve with the highest weight fraction of polyethylene resin foam particles (A), and the variation in foaming ratio σ / Xp, expressed by the following formula (1), is 15.0% or less. [Formula (1)] σ / Xp (%) = (σm / Kav)×100...(1) However, in formula (1) above, Kav is the weight-average expansion factor calculated based on formula (2) below, and σm is the standard deviation of the expansion factor calculated based on formula (3) below. [Formula (2)] Kav=Σ(Ki×Wi)...(2) [Formula (3)] σm=[Σ{Wi×(Kav-Ki)2}]1 / 2...(3) However, in equations (2) and (3) above, i represents each sieve, and indicates the weight fraction and foaming ratio of polyethylene resin foam particles remaining in each sieve.

6. A method for producing polyethylene resin foam particles according to claim 5, comprising mixing polyethylene resin foam particles (A) in an amount of 50% by weight or more and less than 100% by weight with polyethylene resin foam particles (B) in an amount of more than 0% by weight and 50% by weight or less.

7. A method for producing polyethylene resin foam particles according to claim 6, wherein the polyethylene resin foam particles (A) have a weight fraction of less than 10.0% in the sieve two steps smaller than the sieve with the highest weight fraction, as measured using nine standard sieves with nominal mesh openings of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006.

8. A method for producing polyethylene resin foam particles according to claim 5, comprising 100% by weight of polyethylene resin foam particles (A), wherein the polyethylene resin foam particles (A) have a weight fraction of 10.1% or more and 30% or less in the sieve two steps smaller than the sieve with the highest weight fraction, as measured using nine standard sieves with nominal mesh openings of 2.00 mm or more and 8.00 mm or less as specified in JIS Z 8801-1:2006.

9. A method for producing polyethylene resin foam particles according to any one of claims 5 to 7, wherein the ratio Da / Db of the average particle diameter Da of polyethylene resin foam particles (A) to the average particle diameter Db of polyethylene resin foam particles (B), measured using nine standard sieves with nominal mesh openings of 2.00 mm or more and 8.00 mm or less as specified in JIS Z 8801-1:2006, is 1.3 or more and 1.8 or less.

10. A method for producing polyethylene resin foamed particles according to any one of claims 5 to 9, further comprising a foaming step of performing foaming after the mixing step.

11. A polyethylene resin in-mold foamed molded body obtained by in-mold foaming of polyethylene resin foam particles according to any one of claims 1 to 4.

12. A polyethylene resin in-mold foamed molded body according to claim 11, which is a cushioning material.

13. This process includes a molding step in which polyethylene resin foam particles are foamed and molded in a mold. The polyethylene resin foam particles are obtained by (a) mixing polyethylene resin foam particles (A) in an amount of 50% or more by weight and less than 100% by weight with polyethylene resin foam particles (B) in an amount of 0% or more by weight and 50% or less by weight, and then foaming the resulting mixture; (b) mixing polyethylene resin foam particles (A) in an amount of 50% or more by weight and less than 100% by weight with polyethylene resin foam particles (B) in an amount of 0% or more by weight and 50% or less by weight; or (c) foaming polyethylene resin foam particles (A). Polyethylene resin foam particles (A) have a weight-average magnification of 3 to 60 times, measured using nine standard sieves with nominal mesh openings of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006, and the variation in foaming magnification σ / Xp, expressed by the following formula (1), is 15.0% or less. When polyethylene resin foam particles (B) are sieved using nine standard sieves with nominal mesh sizes of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006, the nominal mesh size of the sieve with the highest weight fraction is two sizes smaller than the nominal mesh size of the sieve with the highest weight fraction of polyethylene resin foam particles (A), and the variation in foaming ratio σ / Xp, expressed by the following formula (1), is 15.0% or less. A method for manufacturing a polyethylene resin in-mold foamed molded article, wherein the polyethylene resin foam particles are measured using nine standard sieves with nominal mesh openings of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006, and the weight fraction of the polyethylene resin foam particles in a sieve with a nominal mesh opening two steps smaller than the sieve with the highest weight fraction is 10.1% to 30%, and the variation in foaming ratio σ / Xp, expressed by the following formula (1), is 15.0% or less. [Formula (1)] σ / Xp (%) = (σm / Kav)×100...(1) However, in formula (1) above, Kav is the weight-average expansion factor calculated based on formula (2) below, and σm is the standard deviation of the expansion factor calculated based on formula (3) below. [Formula (2)] Kav=Σ(Ki×Wi)...(2) [Formula (3)] σm=[Σ{Wi×(Kav-Ki)2}]1 / 2...(3) However, in equations (2) and (3) above, i represents each sieve, and indicates the weight fraction and foaming ratio of polyethylene resin foam particles remaining in each sieve.

14. The method for producing a polyethylene resin in-mold foamed molded article according to claim 13, wherein, in (a) and (b) above, the polyethylene resin foam particles (A) have a weight fraction of less than 10.0% in a sieve with a nominal mesh size two steps smaller than the nominal mesh size of the sieve with the highest weight fraction, as measured using nine standard sieves with nominal mesh sizes of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006.

15. The method for producing a polyethylene resin in-mold foamed molded article according to claim 13, wherein, in (c) above, the polyethylene resin foam particles (A) have a weight fraction of 10.0% or more in a sieve with a nominal mesh size two steps smaller than the nominal mesh size of the sieve with the highest weight fraction, as measured using nine standard sieves with nominal mesh sizes of 2.00 mm to 8.00 mm as specified in JIS Z 8801-1:2006.

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