TW202317682A - Multilayer expanded bead - Google Patents

Abstract

The object of the invention is to provide a polypropylene-based resin multilayer expanded bead capable of in-mold forming an expanded bead molding with little variation in dimensional changes due to shrinkage after molding even if water cooling time after in-mold molding is shortened. The solution of the invention is that the foam core layer of the polyolefin-based resin multilayer expanded beads of the invention is composed of ethylene-propylene random copolymer (A) with a specific ethylene content the coating layer is composed of polyolefin-based resin (B), wherein the DSC curve of the polyolefin-based resin (B) has one or more melting peak, he melting peak temperature of at least one of the melting peaks is lower than the melting point (Tm) of the random copolymer (A),the weight average molecular weight (Mw) of the random copolymer (A) is within a specific range, and the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the ethylene-propylene random copolymer (A) is within a specific range.

Description

multi-layer expanded particles

The present invention relates to multilayer expanded particles, and more specifically relates to multilayer expanded particles for in-mold molding.

Polypropylene-based resin foamed particles have excellent processability, and the expanded particle molded body obtained by in-mold molding can be shaped into complex shapes. The balance of mechanical strength, cushioning performance, and price is excellent, so it has been used as cushioning packaging materials, automobiles, etc. Components, building components, etc.

Examples of expanded particles of the polypropylene modulus include those disclosed in Patent Document 1. [Prior Art Literature] [Patent Document]

[Patent Document 1] Japanese Unexamined Patent Publication No. 2004-68016

[Problem to be solved by the invention]

However, when in-mold molding is performed at a low steam pressure using the multilayered expanded beads described in Patent Document 1, if it is desired to obtain a molded article with a complex shape or a large molded article, it is difficult for the steam to travel uniformly to the entire expanded beads in the mold. However, uneven heating may occur. As a result, the degree of shrinkage after molding differs from part to part of each expanded bead molded body, or dimensional deviation tends to occur, resulting in problems such as excessive burden on strict control of the size of the molded body.

On the other hand, in order to solve the problem of uneven heating, if the in-mold molding is performed at a higher vapor pressure, the heating time is prolonged, and the bubble particles in the mold are fully heated, the size deviation can be reduced. However, there is a possibility that the cooling time after mold forming becomes longer, and the overall molding time may also become longer.

The object of the present invention is to provide multi-layered expanded beads capable of in-mold forming an expanded bead molded body with less shrinkage after molding and less variation in dimensional change even if the cooling time after in-mold molding is shortened. [Means to solve the problem]

(但，式中之Tmc、Tc之單位均為℃)。 [5] 如前述1至4中任一項之多層發泡粒子，其中前述乙烯-丙烯無規共聚物(A)之Z平均分子量(Mz)為50萬以上100萬以下。 [6] 如前述5之多層發泡粒子，其中前述乙烯-丙烯無規共聚物(A)之Z平均分子量(Mw)相對於該乙烯-丙烯無規共聚物(A)之數平均分子量(Mz)之比(Mz/Mw)為2以上5以下。 [7] 如前述1至6中任一項之多層發泡粒子，其中前述乙烯-丙烯無規共聚物(A)之撓曲彈性模數為750MPa以上。 [8] 如前述1至7中任一項之多層發泡粒子，其中前述乙烯-丙烯無規共聚物(A)之熔體流動速率為1g/10分鐘以上20g/10分鐘以下。 [9] 如前述1至8中任一項之多層發泡粒子，其中前述多層發泡粒子之體密度為10kg/m ³以上300kg/m ³以下。 [10] 如前述1至9中任一項之多層發泡粒子，其中構成前述多層發泡粒子之發泡芯層之平均氣泡徑為20μm以上400μm以下。 [11] 一種發泡粒子成形體，其係將如前述1至10中任一項之多層發泡粒子進行模內成形而成。 [12] 如前述11之發泡粒子成形體，其中前述發泡粒子成形體之50%變形時壓縮應力為100kPa以上500kPa以下。 [發明效果] According to the present invention, multilayer expanded particles shown below are provided. [1] A multi-layer expanded particle, which is a multi-layer expanded particle having a foam core layer and a coating layer covering the foam core layer, characterized in that the foam core layer is composed of an ethylene content of 2.5% by mass or more 3.5% by mass or less of ethylene-propylene random copolymer (A), the covering layer is composed of polyolefin resin (B), and the polyolefin resin (B) measured by differential scanning calorimetry (DSC) The DSC curve of ) has more than one melting peak, and the melting peak temperature of at least one of the melting peaks is lower than the melting point (Tm) of the ethylene-propylene random copolymer (A), the ethylene-propylene random copolymer The weight average molecular weight (Mw) of the substance (A) is not less than 200,000 and not more than 300,000, and the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the ethylene-propylene random copolymer (A) (Mw /Mn) is 3.5 or more and 5 or less. [2] The multilayer expanded particle as claimed in item 1, wherein the Z average molecular weight (Mz) of the aforementioned ethylene-propylene random copolymer (A) is relative to the number average molecular weight (Mz) of the ethylene-propylene random copolymer (A) ( The ratio (Mz/Mn) of Mn) is 9.5 or more and less than 13. [3] The multilayer expanded particle according to the above-mentioned 1 or 2, wherein the melting point (Tm) of the ethylene-propylene random copolymer (A) is 130°C or more and 150°C or less. [4] The multilayer expanded particle according to any one of the aforementioned 1 to 3, wherein the crystallization temperature (Tc) of the aforementioned ethylene-propylene random copolymer (A) is the same as that of the ethylene-propylene random copolymer (A). The melting point (Tmc) satisfies the following formula (1):

(However, the units of Tmc and Tc in the formula are both °C). [5] The multilayer expanded particle according to any one of 1 to 4 above, wherein the Z-average molecular weight (Mz) of the ethylene-propylene random copolymer (A) is not less than 500,000 and not more than 1 million. [6] The multilayer expanded particle as described in the above-mentioned 5, wherein the Z-average molecular weight (Mw) of the aforementioned ethylene-propylene random copolymer (A) is relative to the number-average molecular weight (Mz) of the ethylene-propylene random copolymer (A). ) ratio (Mz/Mw) is 2 or more and 5 or less. [7] The multilayer expanded particle according to any one of 1 to 6 above, wherein the flexural modulus of elasticity of the ethylene-propylene random copolymer (A) is 750 MPa or more. [8] The multilayer expanded particle according to any one of 1 to 7 above, wherein the melt flow rate of the ethylene-propylene random copolymer (A) is not less than 1 g/10 minutes and not more than 20 g/10 minutes. [9] The multilayer expanded bead according to any one of 1 to 8 above, wherein the bulk density of the multilayer expanded bead is not less than 10 kg/m ³ and not more than 300 kg/m ³ . [10] The multilayered expanded bead according to any one of 1 to 9 above, wherein the average cell diameter of the foamed core layer constituting the multilayered expanded bead is not less than 20 μm and not more than 400 μm. [11] A molded expanded bead formed by in-mold forming the multilayered expanded bead described in any one of 1 to 10 above. [12] The expanded bead molded article according to the above 11, wherein the compressive stress at 50% deformation of the expanded bead molded article is not less than 100 kPa and not more than 500 kPa. [Invention effect]

According to the present invention, the cooling time after in-mold molding can be shortened, and even if the cooling time is shortened, multi-layered expanded particles can be formed in the mold with small shrinkage after molding and small variations in dimensional changes. .

Hereinafter, the multilayer expanded particle of the present invention will be described in detail. The multilayer expanded particle of the present invention (hereinafter also referred to as expanded particle) has a foamed core layer and a coating layer covering the foamed core layer. In addition, the foam core layer is composed of ethylene-propylene random copolymer (A) (hereinafter also referred to as copolymer (A)), and the covering layer is composed of polyolefin resin (B).

The aforementioned foam core layer is in a foamed state. The foamed state means a state in which a cell structure is formed. On the other hand, the aforementioned covering layer may be in a foamed state or in a non-foamed state, but is preferably in a non-foamed state. In addition, the non-foaming state is not only the absence of bubbles at all (as described later, it also includes the destruction of the bubbles temporarily formed when the resin particles are foamed to eliminate the bubbles), and also includes the range that does not affect the mechanical strength of the obtained molded body. Inside, those with slight air bubbles.

As an aspect in which the foam core layer is covered with the covering layer, the foam core layer may be completely covered with the covering layer, or a part of the foam core layer may be exposed. The structure in which the foam core layer is exposed is, for example, a structure in which only the peripheral surface of the cylindrical foam core layer is covered with the coating layer, and the foam core layer is exposed on the top or bottom of the cylinder.

Next, the ethylene-propylene random copolymer (A) constituting the foam core layer will be described. The copolymer (A) has an ethylene content of 2.5% by mass to 3.5% by mass, preferably 2.6% by mass to 3.3% by mass. If the content is within this range, it has moderate mechanical strength and exhibits sufficient secondary foamability under low vapor pressure, so it can be suitably used as expanded particles for in-mold molding. Furthermore, the resulting expanded particles have an excellent balance between mechanical strength and formability. If the content is too small, in-mold molding under low steam pressure may not be possible. On the other hand, when this content rate is too large, there exists a possibility that rigidity may fall too much.

Also, in the copolymer (A), the content of the propylene component is preferably at least 95% by mass, more preferably more than 96.5% by mass and less than 97.5% by mass, more preferably more than 96.7% by mass and less than 97.4% by mass. Since the copolymer (A) contains a propylene component as a main component, it is classified as a propylene-type resin.

In this specification, the ethylene content rate of the ethylene-propylene random copolymer (A) can be calculated|required by the conventional method determined using IR spectrum. Specifically, with the Handbook of Polymer Analysis (edited by the Symposium on Polymer Analysis of the Japanese Society of Analytical Chemistry, date of publication: January 1995, publisher: Kinokuniya Shoten, page number: 615~616, "II.2.3 2.3. The method described in 4 Propylene/Ethylene Copolymer") is a quantitative method obtained from the relationship between the value after correcting the absorbance of ethylene with a specific coefficient and the thickness of the film-shaped test piece.

The weight average molecular weight (Mw) of the ethylene-propylene random copolymer (A) is not less than 200,000 and not more than 300,000, preferably not less than 240,000 and not more than 280,000. The copolymer (A) having a weight average molecular weight (Mw) within this range can be molded in a mold under low vapor pressure. The resulting foam has excellent strength and a good balance between formability and mechanical strength.

In addition, the ratio (Mw/Mn) of the weight average molecular weight (Mw) of the ethylene-propylene random copolymer (A) to the number average molecular weight (Mn) of the ethylene-propylene random copolymer (A) is 3.5 or more and 5 or less . If the ratio (Mw/Mn) is within this range, even if the water cooling time is shortened, the resulting molded body will have little variation in dimensional change. The reason for this is that the crystallization of the resin is likely to occur in the early stage of cooling by water cooling, and the dimensional change is difficult to occur even if the cooling time by water cooling is shortened. Furthermore, it is possible to suppress the deviation of the secondary foaming, suppress the excessive progress of the local secondary foaming, and suppress the difficulty in uniformly advancing the steam into the mold. smaller. From this point of view, the ratio (Mw/Mn) is preferably from 3.7 to 4.8, more preferably from 3.8 to 4.5.

In addition, the Z average molecular weight (Mz) of the ethylene-propylene random copolymer (A) is preferably from 500,000 to 1 million, more preferably from 600,000 to 900,000, still more preferably from 650,000 to 750,000. Also, the ratio (Mz/Mn) of the Z average molecular weight (Mz) to the number average molecular weight (Mn) is preferably 9.5 or more and less than 13, more preferably 10 or more and 12 or less. If the ratio (Mz/Mn) is within this range, even if the cooling time is short, the variation in size of each part of the molded body due to shrinkage after molding can be reduced, and an expanded particle molded body can be obtained.

Also, the ratio (Mz/Mw) of the Z average molecular weight (Mz) to the weight average molecular weight (Mw) is preferably from 2 to 5, more preferably from 2.5 to 3.5, still more preferably from 2.6 to 3.2.

The ethylene-propylene random copolymer (A) used in the present invention can be oxidatively decomposed by using an organic peroxide such as a peroxide, for example, by making the ratio (Mw/Mn) of the ethylene-propylene random copolymer 3.5 to 5 , obtained by controlling the molecular weight.

In this specification, number average molecular weight (Mn), weight average molecular weight (Mw), and Z average molecular weight (Mz) can be measured by gel permeation chromatography. The details of the assay method are described in the Examples.

The melting point (Tm) of the ethylene-propylene random copolymer (A) is preferably from 130°C to 150°C, more preferably from 135°C to 145°C. If the melting point (Tm) is within this range, multilayer expanded particles can be molded under low steam pressure. On the other hand, the obtained molded body is excellent in heat resistance.

(但，式中之Tm、Tc之單位均為℃)。 In the ethylene-propylene random copolymer (A) used in the present invention, the crystallization temperature (Tc) and melting point (Tm) preferably satisfy the following formula (1).

(However, the units of Tm and Tc in the formula are both °C).

If the foam core layer is formed from the ethylene-propylene random copolymer (A) whose crystallization temperature (Tc) and melting point (Tm) satisfy the formula (1), good foaming can be obtained even if low-pressure steam is used for in-mold forming. Bubble particle shaped body. This is considered to be because the ethylene-propylene random copolymer (A) satisfying the formula (1) tends to cause crystallization early in the cooling step during in-mold molding, and it is difficult to cause dimensional changes even if the cooling time during molding is shortened. Variety.

For the above reasons, the crystallization temperature (Tc) and the melting point (Tm) preferably satisfy the following formula (2), more preferably satisfy the following formula (3).

In the present specification, the melting point of the copolymer (A) means the maximum melting peak temperature of the DSC curve obtained by heat flux differential scanning calorimetry based on JIS K7121-1987. As the state adjustment of the test piece, "(2) The case of measuring the melting temperature after a certain heat treatment" was adopted, and the cooling rate at this time was 10°C per minute. As the heating rate when measuring the melting temperature, 10°C per minute was adopted. Also, when two or more melting peaks appear, the apex temperature of the melting peak with the largest area is defined as the melting point. Regarding expanded particles and multilayered expanded particles, the melting point (Tmf) can be measured by the same method as above. Also, when the melting peak is not clear, the position of the peak can be obtained by referring to the positive, negative, and zero points of the DSC differential curve (DDSC) near the melting point.

In this specification, the crystallization temperature (Tc) means the crystallization peak temperature obtained by heat flux differential scanning calorimetry based on JIS K7121-1987. As the state adjustment of the test piece, "(2) After performing a certain heat treatment, the case of measuring the melting temperature" was adopted, and 10°C per minute was adopted as the cooling rate. Also, when two or more crystallization exothermic peaks of the copolymer (A) appear, the peak temperature of the crystallization peak with the largest area is defined as the crystallization temperature. Regarding expanded particles and multilayer expanded particles, the crystallization temperature (Tcf) can be measured by the same method.

The flexural modulus of the ethylene-propylene random copolymer (A) is preferably at least 750 MPa, more preferably at least 800 MPa and at most 1100 MPa, more preferably at least 820 MPa and at most 1000 MPa. If the flexural elastic modulus is within this range, a molded expanded particle having particularly good rigidity can be obtained.

In this specification, this flexural modulus can be calculated|required based on JISK7171:2008.

The melt flow rate (MFR) of the ethylene-propylene random copolymer (A) is preferably not less than 1 g/10 minutes and not more than 20 g/10 minutes, more preferably not less than 2 g/10 minutes and not more than 15 g/10 minutes, and more preferably More than 3g/10 minutes and less than 10g/10 minutes. If the MFR is within this range, it is easy to form expanded particles having a multilayer structure, especially resin particles having a multilayer structure of a precursor when obtaining expanded particles. In addition, the MFR of the ethylene-propylene random copolymer (A) is a value measured by the test condition M (230 degreeC/2.16 kg load) of JISK7210:1999.

In the ethylene-propylene random copolymer (A) constituting the foam core layer in the present invention, polymer components such as thermoplastic resins and thermoplastic elastomers other than the copolymer (A) may be added. However, the resin constituting the foam core layer preferably contains 80% by weight or more of the ethylene-propylene random copolymer (A), more preferably 90% by weight or more.

In addition, additives such as antistatic agents, catalyst neutralizing agents, slip agents, nucleating agents, and coloring agents such as carbon black may be added to the foam core layer. The amount of the additive depends on the type and use of the additive, but relative to 100 parts by weight of the copolymer (A) constituting the foam core layer, it is preferably 15 parts by weight or less, more preferably 10 parts by weight or less, and more preferably 5 parts by weight. It is not more than 3 parts by weight, particularly preferably not more than 3 parts by weight.

The multi-layer expanded particle of the present invention, as mentioned above, has a foam core layer and a coating layer, and the foam core layer is covered by the coating layer. The coating layer is made of polyolefin resin (B), and the DSC curve of the polyolefin resin (B) measured by differential scanning calorimetry (DSC) has more than one melting peak, and at least one of them melts The melting peak temperature of the crest must be lower than the melting point (Tm) of the ethylene-propylene random copolymer (A). By making the coating layer satisfy this constitution, the fusion property of the expanded bead is improved, and in-mold molding can be performed at a molding temperature lower than that of a single-layer expanded bead formed of only the foamed core layer.

Here, the "melting point of the ethylene-propylene random copolymer (A)" means that two or more melting points appear in the DSC curve of the ethylene-propylene random copolymer (A) measured by differential scanning calorimetry (DSC). When melting the peak, the temperature at the top of the melting peak with the largest area (hereinafter also referred to as the maximum melting peak temperature). Also, the so-called "the DSC curve of the polyolefin resin (B) has more than one melting peak, and the melting peak temperature of at least one of the melting peaks is lower than the melting point of the ethylene-propylene random copolymer (A)" means Refers to the case where a melting peak appears in the DSC curve of the polyolefin resin (B), and the melting peak temperature of the melting peak is lower than the aforementioned maximum melting peak temperature of the ethylene-propylene random copolymer (A). Also, when multiple melting peaks appear on the DSC curve of the polyolefin resin (B), at least the melting peak temperature of the melting peak on the lowest temperature side of the DSC curve of the polyolefin resin (B) is lower than that of the ethylene-propylene random The maximum melting peak temperature of the copolymer (A).

In the present invention, the melting peak temperature of the polyolefin resin (B) and the maximum melting peak temperature of the ethylene-propylene random copolymer (A) satisfy the aforementioned relationship, and furthermore, the molecular weight of the resin constituting the foam core layer is specified. In this range, the fusion of the coating layer can be improved, and by controlling the secondary foamability and crystallinity during water cooling of the foam core layer, even if the water cooling time is shortened, the deviation of the dimensional change can hardly occur. Bubble particles.

Also, the term "can be in-mold molded at a molding temperature lower than the molding temperature of a single-layer expanded bead composed of only a foamed core layer" refers to a monolayer composed of an ethylene-propylene random copolymer (A). Based on the in-mold molding temperature of expanded particles with a layer structure, a molded product having the same characteristics (such as surface appearance, fusion property, and recovery) as a molded product formed of expanded particles with a single-layer structure can be produced in Molded at a molding temperature lower than the standard in-mold molding temperature.

Next, in the present invention, the polyolefin-based resin (B) constituting the covering layer will be described. The polyolefin-based resin (B) preferably has an olefin component of 50 mass % or more, more preferably 70 mass % or more, more preferably 90 mass % or more. The composition and synthesis method are not particularly limited as long as the olefin component has 50% by mass or more. Specifically, examples of the polyolefin-based resin include polypropylene-based resins, polyethylene-based resins, and the like, and further, mixtures thereof, and the like.

Examples of the polypropylene-based resin include propylene homopolymers, copolymers of propylene and other copolymerizable olefins, and the like. Examples of other olefins that can be copolymerized with propylene include α-olefins having 4 or more carbon atoms, such as ethylene and 1-butene. As this copolymer, a propylene-ethylene random copolymer, a propylene-ethylene block copolymer, a propylene-ethylene-butene random copolymer, etc. are mentioned, for example, and the mixed resin etc. of 2 or more types of these are further exemplified.

As the polyethylene-based resin, for example, high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, ultra-low-density polyethylene, ethylene-vinyl acetate copolymer, etc., further exemplified Mixed resins of two or more of these, etc.

Furthermore, the coating layer of the present invention may contain polymers such as thermoplastic resins and thermoplastic elastomers other than the polyolefin-based resin (B) within the range that does not hinder the intended purpose. However, the amount added is preferably 5 parts by mass or less with respect to 100 parts by mass of the polyolefin resin (B).

Additives such as antistatic agent, catalyst neutralizer, slip agent, colorant such as carbon black can be added to the coating layer. The amount of this additive added depends on the type of addition and the purpose of use, but relative to 100 parts by weight of the polyolefin resin (B) forming the coating layer, it is preferably 15 parts by weight or less, more preferably 10 parts by weight or less, and It is more preferably at most 5 parts by weight, particularly preferably at most 3 parts by weight.

Next, the physical properties of the multilayer expanded particles of the present invention will be described. The bulk density of the multilayer expanded particles is preferably not less than 10 kg/m ³ and not more than 300 kg/m ³ . When the bulk density is within this range, the effect of shortening the cooling time specified by the present invention will be more remarkable. That is, in the prior art, multilayer expanded particles with a bulk density within this range tend to have large dimensional changes after in-mold molding due to a relatively high expansion ratio, and the cooling time tends to be prolonged. In contrast, the effect of shortening the cooling time is more obvious for the multi-layer expanded particles of the present invention. In addition, if the multi-layer expanded particles with a bulk density within this range are used, it is possible to obtain expanded particle moldings that can be used in various applications represented by automotive interior components, core materials for car bumpers, and core materials for car seats. body. For these reasons, the bulk density of the multilayer expanded particles is more preferably 15kg/ ^m3 to 200kg/ ^m3 , more preferably 17kg/ ^m3 to 100kg/ ^m3 , and more preferably 19kg/ ^m3 or more Below 50kg/ ^m3 .

The method for measuring the bulk density of multilayer expanded particles is as follows. First, prepare a graduated cylinder with a volume of 1 L. While removing the static electricity of the multi-layer expanded particles, fill the multi-layer expanded particles to the 1L marking line of the measuring cylinder in a natural accumulation state. By converting the mass of the multilayered expanded particles in the measuring cylinder, that is, the mass of the multilayered expanded particles per 1 L volume, to the mass per 1 ^m3 volume (kg/ ^m3 ), the bulk density of the multilayered expanded particles ( kg/m ³ ).

The average cell diameter of the foam core layer constituting the multilayer expanded particles is preferably from 20 μm to 400 μm, more preferably from 40 μm to 250 μm, still more preferably from 80 μm to 200 μm, particularly preferably from 100 μm to 160 μm. When the average cell diameter is within this range, multilayer expanded particles having excellent in-mold formability are obtained, and the obtained expanded particle molded product is excellent in dimensional recovery after molding.

The average cell diameter of the aforementioned foamed core layer was measured as follows. It is determined as follows based on an enlarged photograph obtained by taking a cut section of the foam core layer in approximately two equal parts with a microscope. First, in the enlarged photograph of the cut section of the foam core layer, from one surface of the foam core layer to the other surface, draw four line segments passing through the approximate center of the cut section of the foam. However, the line segment is drawn to form radial straight lines extending from the approximate center of the cut surface of the bubble toward the surface of the cut particle in eight directions at equal intervals. Next, the total number N (pieces) of the number of bubbles intersecting the four line segments is obtained. The sum L (μm) of the lengths of the four line segments was obtained, and the value (L/N) obtained by dividing the sum L by the sum N was defined as the cell diameter of one foam core layer. This operation was carried out for 10 foam core layers, and the value obtained by summing and averaging the respective cell diameters was set as the average cell diameter of the foam core layer.

In the multilayer expanded particles of the present invention, the independent cell ratio is preferably at least 75%, more preferably at least 80%, even more preferably at least 82%, and most preferably at least 85%. If the closed cell ratio is within this range, multilayer expanded particles with excellent secondary expansion properties will be obtained, and the obtained expanded particle molded product will have good mechanical properties.

The independent cell ratio of the multilayer expanded particles was measured as follows. The multi-layer expanded particles are placed in a constant temperature room under the conditions of atmospheric pressure, relative humidity 50%, and 23°C for 10 days for health preservation. Next, in the constant temperature room, the multi-layer expanded particles with a loose volume of about 20 cm ³ after curing are used as a measurement sample, and the correct apparent volume Va is measured by the following water submersion method. After the apparent volume Va was measured, the sample for measurement was sufficiently dried, and according to the procedure C described in ASTM-D2856-70, the volume of the measured sample was measured with an air comparison type pycnometer 930 manufactured by Toshiba Beckman Co., Ltd. True volume Vx. Then, based on these equal volumes Va and Vx, the closed cell rate was calculated by the following formula (4), and the average value of N=5 was set as the closed cell rate of the multilayer expanded particles.

但， Vx：以前述方法測定之多層發泡粒子之真體積，即，構成多層發泡粒子樹脂之容積與多層發泡粒子內之獨立氣泡部分之氣泡總容積之和(cm ³) Va：將多層發泡粒子沉入裝入水的量筒中，基於水位上升量測定之多層發泡粒子之表觀體積(cm ³) W：多層發泡粒子測定用樣品之重量(g) ρ：構成多層發泡粒子之樹脂密度(g/cm ³)

However, Vx: the true volume of the multilayer expanded bead measured by the above-mentioned method, that is, the sum of the volume of the resin constituting the multilayer expanded bead and the total volume of the independent cells in the multilayer expanded bead (cm ³ ) Va: the volume of the multilayer expanded bead The apparent volume (cm ³ ) of the multilayered foamed particles measured based on the rise of the water level when the multilayered foamed particles sink into a graduated cylinder filled with water. Resin density of foam particles (g/cm ³ )

In the present invention, in the DSC curve of the first heating measured by the heat flux differential scanning calorimetry of the multilayer expanded particles, the inherent heat absorption peak of the polypropylene resin preferably appears (hereinafter also referred to as "Intrinsic peak") and the high-temperature peak of the secondary crystal formed by the temperature treatment during foaming.

Specifically, the DSC curve obtained when the multilayer expanded particles are heated from 23°C to 220°C at a heating rate of 10°C/min by means of heat flux differential scanning calorimetry (DSC of the first heating) of 2 mg to 10 mg Curve), as shown in Figure 1, it is preferable to have the inherent endothermic peak a (hereinafter, also referred to as "intrinsic peak") of polypropylene resin and the high temperature side of the inherent peak, which is derived from the temperature treatment during foaming One or more endothermic peaks b of the formed secondary crystals (hereinafter also simply referred to as "high temperature peaks").

Fig. 1 is an example of the DSC curve of the first heating. In Figure 1, a represents the inherent peak, b represents the high temperature peak, α represents the point corresponding to 80°C on the DSC curve, _TE represents the end temperature of melting, and the high temperature tail of the endothermic peak b represents the return to the baseline β is the point on the DSC curve corresponding to the melting end temperature TE of the high-temperature peak, γ is the point at the bottom of the valley between the inherent peak a and the high-temperature peak b, and δ is the vertical line drawn from the point γ to the graph The point where a straight line parallel to the axis intersects with the straight line (α-β).

The peak temperature of the intrinsic peak (intrinsic peak temperature) is preferably from 135°C to 145°C, more preferably from 138°C to 142°C. If the intrinsic peak temperature is within this range, highly crystalline crystals which contribute to an increase in rigidity can be easily formed by cooling after molding. The melting end temperature (γ) of the intrinsic peak corresponds to the temperature at the bottom of the valley between the intrinsic peak a and the high temperature peak b, preferably between 150°C and 160°C, more preferably between 152°C and 155°C.

The heat of fusion of the inherent peak is preferably from 50 J/g to 70 J/g, more preferably from 55 J/g to 65 J/g. By keeping the heat of fusion of the inherent peak within this range, the dimensional stability after molding is improved.

The heat of fusion of the intrinsic peak is obtained from the area of the part surrounded by the straight line (δ-γ) connecting the point δ and the point γ, the straight line (α-β) and the curve of the intrinsic peak a in the aforementioned Figure 1.

The heat of fusion of the high-temperature peak (hereinafter also referred to as the high-temperature peak heat) is preferably 10 J/g to 20 J/g, more preferably 12 J/g to 16 J/g. By setting the high-temperature wave peak heat amount within this range, it is possible to obtain a molded expanded particle body that hardly undergoes dimensional changes after molding and has excellent mechanical strength. In addition, the high temperature wave peak of the foam core layer can be adjusted by a known method, specifically, the adjustment method is disclosed in, for example, Japanese Patent Application Laid-Open No. 2001-151928.

Also, although the high-temperature peak b was observed in the DSC curve at the first heating as measured above, it was not observed in the DSC curve obtained at the second heating. In the DSC curve at the time of the second heating, only an endothermic peak unique to the propylene-based resin constituting the foam core layer was observed.

The heat of fusion of the high temperature peak is obtained from the area of the part surrounded by the curve of the straight line (δ-γ), straight line (α-β) and high temperature peak b in Figure 1.

The total melting peak heat is preferably from 50 J/g to 90 J/g, more preferably from 55 J/g to 80 J/g. The total heat of melting peak is the sum of the heat of fusion of the high temperature peak and the heat of fusion of the inherent peak. The total melting peak heat is calculated from the DSC curve obtained when the multi-layer expanded particles are heated from 23°C to 220°C at a heating rate of 10°C/min by heat flux differential scanning calorimetry of 2 mg to 10 mg. .

Next, the multilayer expanded bead molded product obtained by in-mold molding of the multilayer expanded bead of the present invention (hereinafter referred to simply as the expanded bead molded product or molded product) will be described. The density of the expanded particle molded body is preferably from 10 kg/m ³ to 300 kg/m ³ , more preferably from 11 kg/m ³ to 200 kg/m ³ , more preferably from 12 kg/m ³ to 100 kg/m ³ Below, preferably 15kg/ ^m3 or more and 50kg/ ^m3 or less. In particular, when the density of the molded expanded bead molded product is low, the molding time tends to be longer, so it is preferable to use the expanded bead of the present invention.

The compressive stress at 50% deformation of the expanded particle molded body is preferably from 100 kPa to 500 kPa, more preferably from 120 kPa to 300 kPa, and more preferably from 140 kPa to 200 kPa. The 50% deformation compressive stress of the expanded particle molded body can be measured according to JIS K6767:1999.

The fusion rate of the expanded particle molded body is preferably 70% or more. In this case, the molded article can fully exhibit desired mechanical properties such as rigidity corresponding to the resin constituting the multilayer expanded bead. From the viewpoint of improving the mechanical properties, the fusion ratio of the molded body is more preferably at least 80%, and more preferably at least 90%. The method for measuring the fusion rate is described in the examples.

Next, the manufacturing method of the multilayer expanded particle of this invention is demonstrated. The multilayer expanded particles can be formed by making the resin particle coating layer made of the aforementioned polyolefin resin (B) cover the resin particle core layer made of the aforementioned ethylene-propylene random copolymer (A). Obtained by soaking.

In the present invention, the multilayer resin particle can be produced as follows, for example. The extruder for the core layer of resin particles and the extruder for the coating layer of resin particles are connected to a co-extrusion die to supply the required ethylene- The propylene random copolymer (A) is melt-kneaded with additives such as a cell regulator as needed to form a resin melt for forming a resin particle core layer. In addition, the resin melt for forming the resin particle coating layer is formed by supplying the required polyolefin resin (B) and additives as necessary to the extruder for the resin particle coating layer and melt-kneading them. Next, introduce the resin melt for forming the resin particle core layer into the co-extrusion die to form a linear flow, and at the same time introduce the resin melt for the resin particle coating layer into the co-extrusion die to form the resin particle coating The resin melt for layer formation is laminated so that the resin melt for core layer formation surrounds the linear flow of the resin particle core layer to form a resin melt with a multilayer structure. Extrude the multi-layered resin melt from the small hole of the die attached to the exit of the extruder into more than one strand, put the strand into water and cool it, cut it into an appropriate length, or extrude it from the die Multi-layered resin particles can be produced by means of cutting, cooling, etc. while going out into the water. In this specification, the multilayer structure thus formed may be referred to as a "sheath-core" structure.

Regarding the method of producing multi-layered resin particles using a co-extrusion die, details are described in, for example, Japanese Patent Publication No. 41-16125, Japanese Patent Publication No. 43-23858, Japanese Patent Publication No. 44-29522, and Japanese Patent Application Laid-Open No. 60. - Bulletin No. 185816, etc.

To the resin melt for forming the resin particle core layer, it is preferable to add a cell regulator in order to adjust the cell diameter of the foamed core layer. Examples of the cell regulator include inorganic substances such as talc, calcium carbonate, borax, zinc borate, aluminum hydroxide, and alum. The amount added is preferably from 0.001 to 10 parts by weight, more preferably from 0.01 to 5 parts by weight, based on 100 parts by weight of the copolymer (A) forming the resin particle core layer. In addition, when adding the bubble regulator to the copolymer (A), the bubble regulator can be directly formulated, but it is generally preferable to add it as a masterbatch of the bubble regulator in consideration of dispersibility and the like.

The weight of the multi-layered resin particles is sufficient to ensure the uniform filling of the multi-layered foamed particles in the mold, preferably 0.02 mg to 20 mg, more preferably 0.1 mg to 6 mg.

The multilayered expanded particles of the present invention can be produced by, for example, the so-called dispersion medium release foaming method using the aforementioned multilayered resin particles. In the dispersion medium release foaming method, the multilayer resin particles are dispersed in a dispersion medium such as water in a sealed container such as an autoclave together with a physical foaming agent, and the dispersion medium is heated to a temperature above the softening temperature of the resin particles. , so that the foaming agent is impregnated in the multi-layered resin particles. Next, while keeping the pressure in the airtight container at a pressure above the vapor pressure of the foaming agent, one end of the water surface in the airtight container is opened, and the dispersion medium of the expandable multilayered resin particles containing the foaming agent and water etc. Together, they are released from the closed container to a pressure environment lower than the pressure in the closed container, usually at atmospheric pressure, and foamed to obtain multilayer expanded particles. Furthermore, the foamed multi-layered resin particles containing the physical foaming agent can also be taken out from the airtight container, heated with a heating medium such as steam, and foamed. On the other hand, when producing multi-layered resin particles with the aforementioned extruder, the foaming agent is pressed into the extruder for forming the core layer of the resin particles to produce a foamable molten resin composition. Next, the expandable molten resin composition is laminated with the molten resin for forming the coating layer of the resin particles to produce a molten resin composition having a sheath-core structure. Then, the expanded particles can be obtained by extruding the molten resin composition of the sheath-core structure from the die, foaming, and cutting into particles.

In the dispersion medium release foaming method, the pressure difference between the high pressure and the low pressure when releasing from a high pressure without foaming to a low pressure with bubbles is preferably 500 kPa or more and 15000 kPa or less.

As a blowing agent used in the dispersion medium release foaming method, propane, isobutane, n-butane, isopentane, n-pentane, cyclopentane, n-hexane, cyclobutane, cyclohexane are generally exemplified. , Chlorofluoromethane, trifluoromethane, 1,1,1,2-tetrafluoroethane, 1-chloro-1,1-difluoroethane, 1,1-difluoroethane, 1-chloro-1, Organic physical blowing agents such as 2,2,2-tetrafluoroethane, hydrofluoroolefin, etc., or inorganic physical blowing agents such as nitrogen, carbon dioxide, argon, air, etc. Among these, non-ozone-depleting and cheap inorganic physical blowing agents are preferred, especially nitrogen, air, and carbon dioxide. In addition, these blowing agents may be used in combination of two or more.

The amount of foaming agent used is appropriately determined according to the relationship between the bulk density of the multilayer foamed particles to be obtained and the foaming temperature. Specifically, in the case of the aforementioned foaming agent excluding nitrogen and air, the usage-amount of the foaming agent is usually not less than 2 parts by weight and not more than 50 parts by weight per 100 parts by weight of resin particles. And in the case of nitrogen and air, the pressure in the airtight container is within the pressure range of 15MPa(G) to 5MPa(G), preferably 1.55MPa(G) to 3.5MPa(G) Use within the amount.

In a sealed container, water is preferred as the dispersion medium for dispersing the resin particles, but any one that does not dissolve the resin particles can be used. Examples of such dispersion medium include ethylene glycol, glycerin, methanol, ethanol, etc. .

The size of the average cell diameter is adjusted by the type and amount of foaming agent, foaming temperature and the amount of foam regulator added. Bulk density (expansion ratio) can be adjusted according to the amount of foaming agent added, the foaming temperature, and the pressure difference between the pressure inside the container and the atmospheric pressure when foaming. Within an appropriate range, generally, the more the amount of foaming agent added, the higher the foaming temperature, and the larger the differential pressure, the smaller the bulk density of the foamed particles obtained.

In a sealed container, when the resin particles are dispersed in the dispersion medium and heated to the foaming temperature, a dispersant can be used to prevent the multi-layered resin particles from being fused to each other. Both inorganic and organic dispersants can be used as long as they do not dissolve in water or the like and do not melt even when heated, but generally, inorganic ones are preferred.

As an inorganic dispersant, powders such as kaolin, talc, mica, alumina, titanium oxide, and aluminum hydroxide are preferred. The dispersing agent preferably has an average particle diameter of 0.001 μm to 100 μm, especially 0.001 μm to 30 μm. In addition, the amount of the dispersant to be added is usually preferably not less than 0.01 parts by weight and not more than 10 parts by weight relative to 100 parts by weight of the resin particles.

It is also preferable to use anionic surfactants such as sodium dodecylbenzenesulfonate and sodium oleate or aluminum sulfate as a dispersing aid. The dispersing aid is usually preferably added in a range of not less than 0.001 parts by weight and not more than 5 parts by weight per 100 parts by weight of resin particles.

When producing multi-layered expanded particles with low density, it is preferable to perform so-called two-stage foaming in which multi-layered expanded particles are produced by a dispersion medium releasing foaming method, and then the obtained multi-layered expanded particles are expanded. In two-stage foaming, the multilayer foamed particles are filled in a pressurizable airtight container, and the pressure treatment is carried out by a gas such as air to increase the internal pressure of the multilayered foamed particles to 0.6 or more than 0.01MPa(G). After the operation below MPa (G), take out the multilayer expanded particles from the airtight container and heat them with a heating medium such as steam, thereby easily obtaining multilayer expanded particles with low bulk density.

The expanded particle molded body can be obtained by filling the above-mentioned multi-layered expanded particles into a molding die, and then heat-molding it using a heating medium such as steam, using conventionally known methods. Specifically, after filling the multi-layered expanded particles into the forming mold, by introducing steam into the mold, the multi-layered expanded particles are heated and foamed to fuse with each other to obtain a molded body in the shape of the shaped space. Also, as a method of obtaining a molded article with a low molded article density, there is a pressure treatment to increase the pressure inside the multilayered expanded bead similar to the operation in the above-mentioned two-stage foaming, if necessary, and pressurize the inside of the multilayered expanded bead. The method of in-mold forming after adjusting the internal pressure to 0.01MPa(G) or more and 0.2MPa(G) or less.

When using the multi-layer expanded particles of the present invention for in-mold forming, the forming steam pressure is preferably not less than 0.05MPa(G) and not more than 0.46MPa(G), more preferably not less than 0.07MPa(G) and not more than 0.35MPa(G). Preferably, it is not less than 0.09 MPa (G) and not more than 0.32 MPa (G).

In the present invention, after filling the multi-layer expanded particles with a compression ratio in the forming mold of 4% to 25% by volume, preferably 5% to 20% by volume, steam is used to carry out The method of in-mold molding can obtain the desired expanded particle molded body.

The adjustment of the compressibility is carried out by cracking and filling the amount of the multi-layered expanded particles exceeding the volume of the cavity when the expanded particles are filled into the forming mold (cavity). Crack filling is to discharge the air in the forming mold from the mold when filling the multilayer expanded particles into the forming mold, and efficiently fill the multilayer expanded particles into the forming mold. A filling method that does not completely close the forming mold. Also, the so-called cracking refers to the opening part of the molding die, which is cracked after the multi-layer expanded particles are filled in the molding die, and finally closed when steam is introduced, resulting in compression of the filled multi-layer expanded particles. [Example]

Hereinafter, the present invention will be described in more detail with reference to examples. But the present invention is not limited by these examples.

Table 1 shows the types and physical properties of the ethylene-propylene random copolymer (A) used as a raw material in Examples and Comparative Examples.

The types and physical properties of the ethylene-propylene random copolymer of the polyolefin resin (B) used as a raw material in Examples and Comparative Examples are as follows. Polyolefin-based resin (B): ethylene-propylene random copolymer, ethylene content (3.0% by mass), melting point 134°C, flexural modulus 770MPa, MFR 7g/10min (230°C/2.16kg load).

Zinc borate is used as the air bubble regulator.

Carbon dioxide is used as physical blowing agent.

In Table 1, melting point (Tm), crystallization temperature (Tc), MFR, molecular weight (Mn), molecular weight (Mw), molecular weight (Mz), and flexural modulus were measured by the following methods.

[Measurement of melting point, heat of fusion, crystallization temperature] The melting point and crystallization temperature of the copolymer (A) and the resin (B) were determined in accordance with JIS K7121:1987. Specifically, 2 mg of a granular sample was made into a test piece, and based on the heat flux differential scanning calorimetry method described in JIS K7121:1987, the temperature was raised from 30°C to 200°C at a heating rate of 10°C/min, and then the test piece was heated at 10°C. Cool down to 30°C at a cooling rate of °C/min, and then heat up from 30°C to 200°C at a heating rate of 10°C/min. The peak temperature of the endothermic peak determined by the DSC curve is set as the melting point. And, the calorific value of the endothermic peak obtained from the DSC curve was set as the heat of fusion. In addition, the crystallization temperature is the value measured according to JIS K7121 (1987). When the sample is heated from 30°C to 200°C at a heating rate of 10°C/min and melted, the temperature is lowered to 30°C at a cooling rate of 10°C/min. The peak temperature of the heat of crystallization peak of the obtained DSC curve was defined as the crystallization temperature (° C.). In addition, a heat flux differential scanning calorimeter (DSC.Q1000 manufactured by T.A Instruments Co., Ltd.) was used as a measuring device.

(MFR(melt flow rate)) The MFR of the ethylene-propylene random copolymer (A) and the polyolefin resin (B) was measured in accordance with the test condition M (230° C./2.16 kg load) of JIS K7210:1999.

[Molecular weight determination method and measurement conditions] Pretreatment of the sample: put 30 mg of the sample into 20 mL of o-dichlorobenzene, shake it at 145°C to dissolve, then heat filter the solution with a sintered filter with a pore size of 1.0 μm as the analysis sample, and measure it under the following conditions. Measuring device: HLC-8321GPC/HT high temperature gel permeation chromatography (manufactured by TOSOH Co., Ltd.) Analysis device: data processing software Empower3 (manufactured by Japan WATERS Co., Ltd.) String: 2 pieces of TSKgel GMH6-HT, 2 pieces of TSKgel GMH6-HTL (inner diameter 7.5mm×length 300mm, manufactured by TOSOH Co., Ltd.) Mobile phase : o-dichlorobenzene (containing 0.025% BHT) Column temperature : 140°C Detector : Differential Refractometer (RI) Flow rate : 1.0mL/min Sample concentration : 0.15%(W/V)-o-dichlorobenzene Injection volume : 400μL Sampling interval: 1 second Column calibration: monodisperse polystyrene (manufactured by TOSOH Co., Ltd.) Molecular weight conversion: Polypropylene (PP) conversion/universal calibration method Also in Table 1, the molecular weights of raw materials before producing expanded particles were measured. In the step of producing expanded particles, since the molecular weight is not expected to fluctuate greatly, it is considered that the molecular weight can still be measured by taking out the expanded core layer and performing the above operation.

In Table 1, the ethylene content (wt%) of the copolymer (A) and the copolymer (B) was measured by the above-mentioned method. Specifically, it measures as follows.

但，式(5)~(7)中，K’a：各波數中所見之吸光係數(K’a=A/ρt)，K’c：修正後之吸光係數，A：吸光度，ρ：樹脂之密度(單位：g/cm ³)，t：薄膜狀之試驗片的厚度(單位：cm)。 (Ethylene Component Content) The ethylene component content of the polypropylene-based resin was determined by a known method determined using IR spectroscopy. Specifically, the Handbook of Polymer Analysis (edited by the Symposium on Polymer Analysis of the Japanese Society of Analytical Chemistry, date of publication: January 1995, publisher: Kinokuniya Shoten, page number and project name: 615~616 "II.2.3 2.3 .4 Propylene/ethylene copolymer", measured by the method described in 618~619 "II.2.3 2.3.5 Propylene/butylene copolymer"). First, the polypropylene resin was thermocompressed into a film at 180°C to produce a plurality of test pieces with different thicknesses. Next, by measuring the IR spectrum of each test piece, the absorbance (A722, A733) at 722 cm ^-1 and 733 cm ^-1 derived from ethylene was read. Next, for each test piece, the content of the ethylene component in the polypropylene-based resin was calculated using the following formulas (5) to (7). The arithmetic mean value of the ethylene content obtained for each test piece was set as the ethylene content (unit: mass %) in the polypropylene-based resin.

However, in formulas (5)~(7), K'a: the absorption coefficient seen in each wave number (K'a=A/ρt), K'c: the corrected absorption coefficient, A: absorbance, ρ: Density of resin (unit: g/cm ³ ), t: thickness of film-like test piece (unit: cm).

The flexural elastic modulus of the resin was measured in accordance with JIS K 7171 (2008). In addition, as a measuring device, Tensilon universal tester RTF-1350 manufactured by A&D Co., Ltd. was used.

Embodiment 1~4, comparative example 1~3 [Manufacturing of multilayer resin particles] It is used in the exit side of the resin particle core layer extruder with an inner diameter of 50mm and the resin particle coating extruder with an inner diameter of 30mm. The type and amount of ethylene-propylene random copolymer (A) and cell regulator masterbatch (1 part by weight relative to 100 parts by weight of copolymer (A)) were supplied to resin particles with an inner diameter of 50 mm as shown in Table 2. The extruder for the core layer simultaneously supplies the type and amount of propylene-based resin (B) as the polyolefin-based resin shown in Table 2 to the extruder for the resin particle coating layer with an inner diameter of 30 mm, respectively at a set temperature of 200 After heating, melting and kneading in the range of ℃ to 220℃, it is supplied to the die nozzle and merged in the die nozzle to form a sheath core (the mass ratio of the resin particle core layer to the resin particle coating layer is 95:5), self-installation The thin hole of the metal cover at the front end of the extruder is co-extruded with the multi-layer strands covered with the coating layer on the side of the core layer, and the co-extruded strands are put into water for water cooling, and cut by a pelletizer ( 1.2 mg, L/D=2.9), and obtained cylindrical multilayered resin particles having a two-layer structure (sheath-core structure) (with respect to the core of the cylinder, a coating layer is formed on the peripheral surface of the cylinder). In addition, the weight and L/D of the multilayered resin particles are arithmetic mean values obtained from 100 multilayered resin particles randomly selected from the group of multilayered resin particles.

[Manufacture of multi-layer expanded particles] Feed 20 kg of the obtained multilayer resin particles into a 100 L autoclave together with 60 L of water in the dispersion medium, and add 15 g of kaolin as a dispersant, 12 g of sodium alkylbenzenesulfonate and aluminum sulfate as a dispersant in the dispersion medium 3g, press carbon dioxide as a foaming agent into the airtight container to make the container pressure 2.2MPa(G), heat it up to the foaming temperature of 150°C under stirring, and keep it at the same temperature for 15 minutes, after adjusting the peak heat of high temperature , the contents of the autoclave were released to atmospheric pressure together with water to obtain multilayer expanded particles.

The multilayer expanded particles thus obtained have a core foam layer made of a polypropylene resin and a coating layer made of a polyolefin resin covering the core foam layer.

In Table 2, the bulk density, average cell diameter, and independent cell ratio of the multilayer expanded particles were measured by the aforementioned method.

In Table 2, the high temperature peak heat and the total melting peak heat were determined by the aforementioned method.

[Manufacture of expanded particle molded body] As the forming die, a large die having a rectangular parallelepiped forming cavity with internal dimensions of 600 mm in length x 1250 mm in width x 50 mm in thickness direction was used. From the fully closed state of the mold to the state of opening 5mm (at this time, the dimension in the thickness direction of the molding cavity is 55mm), the multilayer expanded particles are filled in the molding cavity. After the filling is completed, the mold is completely closed (cracking amount 5mm, 10%). Subsequently, steam is supplied into the molding cavity to heat the multi-layered expanded particles, and the expanded particles are secondarily expanded and melted to obtain a molded body of expanded particles. The heating method is to supply steam for 5 seconds in the state of opening the discharge valve of the two-sided mold for preheating (exhaust step), then heat one side at a pressure 0.08MPa(G) lower than the forming steam pressure described in Table 2, and then After heating one side from the opposite direction at a pressure 0.04MPa(G) lower than the forming steam pressure shown in Table 2, heat both sides at the forming steam pressure shown in Table 2 (main heating). After the heating is completed, the pressure is released, and the mold is water-cooled until the surface pressure of the expanded particle molded body in the mold is 0.04 MPa (G), then the mold is opened, and the expanded particle molded body is taken out from the mold. The obtained expanded particle molded body was cured for 12 hours under an environment of atmospheric pressure and a temperature of 80°C. In addition, the water cooling time refers to the time for water cooling until the surface pressure of the expanded particle molded body in the mold becomes 0.04 MPa (G) after the heating is completed. Table 2 shows the physical properties of the obtained expanded particle molded body. In addition, the molding steam pressure shown in Table 2 represents the lowest molding steam pressure in the molding at which a molded product with a good appearance can be obtained. Also, the criteria for a molded article with good appearance is that the fusion rate of the molded article is 80% or more, and a molded article with a good appearance can hardly see gaps or depressions on the surface of the molded article.

In Table 2, the molded body density, shrinkage rate, deviation rate from reference dimensions, and compressive stress at 50% deformation were measured as follows.

[Molded product density of expanded bead molded product] The value obtained by dividing the weight of the expanded bead molded product by the volume obtained from the external dimension of the expanded bead molded product, and the unit is converted into [kg/m ³ ].

[Fusion rate] The fusion rate was measured by the following method. Randomly cut out a test piece with a length of 150 mm, a width of 75 mm, and a thickness of 20 mm (leave at least one surface of the skin) from the expanded particle molded body. For this cuboid-shaped molded body sample, a notch with a depth of 5 mm was cut on one surface (leaving at least the skin without notch) at the central part in the longitudinal direction, so as to cut across the entire width, and this was used as a test piece. Next, place the test piece on the side where the cutout is set on two support plates made of rigid bodies with a height of 100 mm, a width of more than 80 mm, and a thickness of 10 mm, which are erected in parallel with a center-to-center distance of 70 mm and whose upper ends are rounded to a radius of 5 mm. Facing the lower side, and the length direction of the test piece is perpendicular to the support plate, and the preparation is equally straddled. Next, use a pressing plate made of a rigid body with a height of 60mm, a width of 80mm, and a thickness of 10mm after the front end is rounded to a radius of 5mm. On the opposite side, set the pressing speed of the pressing plate to 200mm/min to perform a 3-point flexure test, and press until the test piece breaks, or until the test piece breaks away from the support plate and completely enters between the support plates. Next, the cross-section of the test piece was observed, and the numbers of the expanded particles broken inside and the expanded particles peeled off at the interface were respectively measured by visual observation. Next, the ratio of internally broken expanded particles to the total number of internally broken expanded particles and expanded particles separated at the interface was calculated, and expressed as a percentage as a fusion rate (%). Also, the expanded particles existing on the initial 5 mm cut are not included in the calculation. And, when focusing on one expanded particle on the fractured surface of the test piece, considering the area including both the damaged part and the part peeled between the expanded particles, the area of the broken part is When it was 50% or more, it was counted as the number of broken parts, and when the area of the damaged part was less than 50%, it was counted as the number of peeling between expanded particles. Moreover, in the test results, when the test piece is not completely broken, the non-broken part is considered to be completely destroyed, and the non-broken part is cut vertically (in the thickness direction of the test piece) with a knife, and counted on the cut surface. The number of expanded particles was taken as the number of internally destroyed expanded particles, and the fusion rate (%) was determined as described above. The fusing rate of the obtained expanded particle molded body was all above 90%.

[Shrinkage] The shrinkage rate [%] of the expanded particle molded body is to substitute the measured value of the length of the long side of the molded body into (the length of the long side of the mold for molding [mm] - the length of the long side of the molded body [mm]) / the length of the mold for the mold Long side dimension [mm] x 100 was calculated|required. In addition, the so-called "length of the long side [mm] of the molded body" means that the expanded particle molded bodies obtained in the examples and the comparative examples were kept in an environment of 80°C for 12 hours, then cooled slowly, and then placed in an environment of 23°C. The measured value of the length of the long side of the expanded particle molded body after 6 hours of curing (n=10).

[Deviation rate from standard size] In the actual molded body, the shrinkage of the molded body is not caused uniformly in each part of the molded body. Therefore, the shape and size of the mold are not completely reproduced, but a dimensional difference occurs between each part of the molded body and the corresponding parts of the mold, and deformation occurs in the resulting molded body. The deviation rate is also a measured value showing the degree of deformation relative to the deformation of the standard mold cavity size. For a molded body obtained by molding using a cuboid-shaped molding cavity having a longitudinal dimension of 600 mm x a lateral dimension of 1250 mm x a thickness direction dimension of 50 mm, four reference points are set at each vertex of the cuboid as follows, Measure the deviation rate. Specifically, assuming a shape with the size of the aforementioned mold cavity, in the hypothetical shape, a plane (such as the left side) determined by the longitudinal direction and the thickness direction is selected as the reference of two parts facing the oblique direction Point (a1, b1). Next, assuming a state where the obtained expanded particle molded body and the virtual shape are overlapped so that the deviation between them is the smallest (or a state where the overlap is estimated to be the largest), measure the aforementioned reference points (a1, b1) and The dimension difference in the longitudinal direction of the portion (a2, b2) corresponding to the aforementioned reference point of the expanded particle molded body. Let these measured values be a and b. Furthermore, select two corners opposite to the oblique direction of another plane (such as the right side) determined by the longitudinal direction and the thickness direction as the reference point (c1, d1), and measure the aforementioned reference point (c1, d1) and The size difference in the longitudinal direction of the part (c2, d2) corresponding to the above-mentioned reference point of the foam particle molded body. Let the measured values be c and d. Next, divide the dimensional differences (a, b, c, d) in the longitudinal direction of the obtained four parts by the length of the expanded particle molded body and take the average value as the deviation rate from the reference size.

[Compressive stress at 50% deformation] Cut out a test piece of length 50mm×width 50mm×thickness 25mm except for the skin, and conduct a compression test at a compression speed of 10mm/min based on JIS K6767-1999 to determine the compression of the expanded particle molded body to 50% of the initial thickness compressive stress at . The test was carried out on 10 test pieces, and the average value of the obtained values was set as the compressive stress at 50% deformation.

Examples 1 to 4 are examples of producing multilayer expanded particles using ethylene-propylene random copolymers satisfying the constitution of the present invention. In-mold molding can be performed at low steam pressure, and the water cooling time in the cooling step is shorter than that of the comparative example, and the effect of shortening the water cooling time can be seen. In addition, the shrinkage rate and the deviation rate from the reference size were smaller than those of the comparative example.

Reference Example 1 and Reference Example 2 are examples of single-layer expanded particles without a coating layer. By comparing Reference Example 1 and Reference Example 2 with Examples and Comparative Examples, the effect of shortening the cooling time of the present invention can be understood, Even if the cooling time is shortened, the effect of small variation in dimensional changes due to shrinkage after molding, etc., is significantly exhibited by providing a coating layer.

Reference Example 1 is an example in which single-layer expanded particles were produced in the same manner as in Example 1, using the same ethylene-propylene random copolymer as in Example 1, except that no coating layer was provided. The forming steam pressure of Example 1 is lower than that of Reference Example 1, and it is confirmed that the expanded particles having a coating layer satisfying the structure of the present invention have the effect of shortening the cooling time. In addition, in Example 1, both the shrinkage rate and the overall deviation rate were lower than those in Reference Example 1, and it was confirmed that even if the cooling time was shortened, the variation in dimensional change was still small. Reference example 2 is an example in which single-layer expanded particles were produced in the same manner as in comparative example 1, using the same ethylene-propylene random copolymer as in comparative example 1, except that no coating layer was provided. Also, Example 1 and Comparative Example 1 are examples in which the ethylene-propylene random copolymers constituting the foam core layer are different, and reference example 1 and reference example 2 are also different in that the ethylene-propylene random copolymers constituting the foam core layer are different. example. It can be seen that the effect of reducing the water cooling time of Example 1 relative to Comparative Example 1 is much greater than that of Reference Example 1 relative to Reference Example 2. In addition, it can also be seen that the multilayered expanded particles provided with a coating layer are superior in the overall deviation rate from the reference size. These effects are considered to be effects specific to multilayer expanded particles.

a: Intrinsic peak b: High temperature peak α: Point on the DSC line equivalent to 80°C T _E : Melting end temperature β: Point on the DSC curve equivalent to melting end temperature T _E γ: Between the inherent peak a and the high temperature peak b Point δ at the bottom of the valley: the point where a line parallel to the vertical axis of the chart from point γ intersects with the line (α-β)

[ Fig. 1 ] is a graph showing an example of the DSC curve of the first heating measured by heat flux differential scanning calorimetry.

Claims (12)

A multi-layer expanded particle, which is a multi-layer expanded particle with a foam core layer and a coating layer covering the foam core layer, characterized in that The foam core layer is composed of ethylene-propylene random copolymer (A) with an ethylene content of 2.5% by mass to 3.5% by mass, The covering layer is made of polyolefin resin (B), The DSC curve of the polyolefin resin (B) measured by differential scanning calorimetry (DSC) has more than one melting peak, and the melting peak temperature of at least one of the melting peaks is higher than that of the ethylene-propylene random The melting point (Tm) of the copolymer (A) is low, The weight average molecular weight (Mw) of the ethylene-propylene random copolymer (A) is not less than 200,000 and not more than 300,000, and the weight average molecular weight (Mw) of the ethylene-propylene random copolymer (A) is relative to the number average molecular weight The ratio (Mw/Mn) of (Mn) is 3.5 or more and 5 or less. The multilayer expanded particle as claimed in item 1, wherein the Z average molecular weight (Mz) of the aforementioned ethylene-propylene random copolymer (A) is relative to the number average molecular weight (Mn) of the ethylene-propylene random copolymer (A) The ratio (Mz/Mn) is 9.5 or more and less than 13. The multilayer expanded particle according to claim 1 or 2, wherein the melting point (Tm) of the aforementioned ethylene-propylene random copolymer (A) is 130°C or higher and 150°C or lower. Multi-layer expanded particles as any one of claims 1 to 3, wherein the crystallization temperature (Tc) of the aforementioned ethylene-propylene random copolymer (A) is related to the melting point (Tc) of the ethylene-propylene random copolymer (A) ( Tm) satisfies the following formula (1):

(However, the units of Tmc and Tc in the formula are both °C). The multilayer expanded particle according to any one of claims 1 to 4, wherein the Z-average molecular weight (Mz) of the ethylene-propylene random copolymer (A) is not less than 500,000 and not more than 1 million. The multi-layer expanded particle as claimed in item 5, wherein the Z-average molecular weight (Mw) of the aforementioned ethylene-propylene random copolymer (A) is relative to the number-average molecular weight (Mz) of the ethylene-propylene random copolymer (A). The ratio (Mz/Mw) is 2 or more and 5 or less. The multilayer expanded particle according to any one of claims 1 to 6, wherein the flexural modulus of elasticity of the aforementioned ethylene-propylene random copolymer (A) is 750 MPa or more. The multilayer expanded particle according to any one of claims 1 to 7, wherein the melt flow rate of the aforementioned ethylene-propylene random copolymer (A) is not less than 1 g/10 minutes and not more than 20 g/10 minutes. The multilayer expanded bead according to any one of claims 1 to 8, wherein the bulk density of the aforesaid multilayer expanded bead is not less than 10 kg/m ³ and not more than 300 kg/m ³ . The multilayer expanded particle according to any one of claims 1 to 9, wherein the average cell diameter of the foam core layer constituting the multilayer expanded particle is not less than 20 μm and not more than 400 μm. A molded expanded particle, which is obtained by in-mold forming the multi-layered expanded particle according to any one of claims 1 to 10. The expanded bead molded body according to claim 11, wherein the compressive stress at 50% deformation of the expanded bead molded body is not less than 100 kPa and not more than 500 kPa.

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