JP6026814B2 - Polyolefin resin expanded particles and molded articles thereof - Google Patents

Description

  The present invention relates to polyolefin resin foamed particles and molded articles thereof, and more particularly, to polyolefin resin foamed particles capable of in-mold molding having a multilayer structure to which the performance of a foam having an open cell structure is added, and molded articles thereof. .

  Since the polyolefin resin foamed particles maintain a high closed cell ratio, in the molding of the foamed particles, the expansion force of the foamed particles when heated (hereinafter referred to as secondary foaming force) and the foamed particles. Due to the melting of the surface, it has good in-mold moldability, can be molded into various shapes according to the application, and due to its excellent expanded particles, or characteristics and performance of expanded molded particles, Widely used in packaging materials, building materials, and vehicle shock absorbing materials.

  The lower the closed cell ratio of the polyolefin-based resin foam particles, the smaller the secondary foaming force at the time of in-mold molding, and the easier the fusibility between the foam particles becomes. In the case of expanded particles having an excessively low closed cell ratio, that is, expanded particles having an open cell structure, the fusion property is insufficient as described above, so that the in-mold molding heating temperature is increased to ensure the fusion property. However, molding shrinkage becomes large, and it becomes impossible to obtain a foamed particle molded body having good dimensional retention. On the other hand, foams having an open-cell structure obtained by an extrusion foaming method or the like are used for various applications that make use of performance such as flexibility, sound absorption, and adsorptivity. Under such circumstances, a foamed particle molded body that can be integrally molded with a three-dimensional shape by in-mold molding is also required to have an open-cell structure excellent in performance such as flexibility, sound absorption, and adsorptivity. However, even if the foamed particles having an open cell structure are employed to obtain a foamed particle molded body having an open cell structure, the foamed particle molded body having an open cell structure has the problem of moldability as described above. Was difficult.

  Conventionally, various studies have been made on foamed particle molded bodies having an open-cell structure.

  For example, Patent Document 1 discloses a foamed molded body in which a surface layer portion of a synthetic resin foam molded body is heated to form continuous cells to form an open cell layer on the surface layer portion, and a closed cell layer is formed on the inner layer portion, and its manufacture. A method is disclosed. According to this method, it is possible to obtain a foamed molded product having an open cell structure as the surface layer portion of the foamed molded product and a closed cell structure as the inner layer portion. However, when a foamed molded article having a closed cell structure is made into continuous cells by heating, there is a problem that the molded article shrinks due to the heating and inferior in dimension retention.

  In Patent Document 2, after the surface of the foamable thermoplastic resin particles is coated with a plasticizer, it is heated and foamed, and the surface is melted to form thermoplastic resin foam particles having depressions on the surface. It is disclosed to form a foamed molded article. In this method, it is difficult to obtain a product with excellent chemical resistance and oil resistance because the polystyrene resin expanded particles are made into open cells with a plasticizer, and it can be applied to polyolefin resin expanded particles. It was a difficult technology to do.

  Patent Document 3 discloses a polypropylene resin in-mold foam-molded article in which the closed cell ratio is adjusted to 50% or more and 70% or less. This polypropylene resin foam molded article is molded in-mold with polypropylene resin foam particles having a closed cell ratio adjusted to 50% or more and 70% or less mixed with a low-melting point polymer or an inorganic substance as a means for forming open cells. It is a method. In this method, if an expanded particle molded body having an open cell ratio exceeding 50% is to be obtained, the open cell ratio of the expanded particles must also be increased, resulting in poor in-mold moldability. Therefore, it is difficult for the foamed particle molded body obtained by this method to further increase the open cell ratio, and therefore the effect of improving the performance such as sound absorption and flexibility required for the open cell structure is small.

  Patent Document 4 discloses a polypropylene resin expanded particle having an open cell ratio of greater than 40% including a cell opener and a method for producing the same, but the polypropylene resin expanded particle is inferior in moldability as described above. It was a thing.

  Although any of the above-mentioned patent documents discloses a foamed molded article having open cells and means for forming open cells, the polyolefin resin foamed particles having an open cell structure and excellent in-mold moldability, and The molded body is not disclosed.

JP-A-7-290080 JP 2007-197471 A JP 2006-297807 A JP 2006-509051 A

  The present invention provides a polyolefin resin foamed particle having a special structure that can solve the problems of in-mold moldability and mold shape reproducibility that the conventional polyolefin resin foamed particles having an open cell structure have. In addition, the conventional polyolefin-based resin foam particle molded body had problems such as flexibility, recoverability, sound absorption, etc. that the performance improvement effect required for the foam having an open cell structure was insufficient. An object of the present invention is to provide a polyolefin resin foamed particle molded body having a special structure that can be improved.

The present inventor has intensively studied to solve the above problems, paying attention to the cellular structure constituting the polyolefin resin foamed particles, and forming a foamed layer having a relatively high closed cell ratio in the outer layer portion of the foamed particles, The present inventors have found expanded particles having a structure in which a portion having a low closed cell ratio is formed at the core of the expanded particle.
That is, the gist of the present invention is the following [1] to [7].

[1] Polyolefin-based resin foamed particles, the foamed particles being disposed inside the foamed particle on the center side of the foamed particle with respect to the outer layer part of the cell structure in which adjacent bubbles are partitioned by the cell membrane wall A hollow portion or cavity that is surrounded by an inner layer portion formed by melting the bubble membrane wall and / or a non-flat surface wall formed by melting and shrinking the bubble membrane wall has a Jo portion, the expanded beads inside the foamed beads center side than the outer layer portion, the bubble membrane wall is destroyed by melting, breakage, or that polyolefin-based resin foam, characterized in that the perforations particle.
[2] The polyolefin resin forming the outer layer part is a polypropylene resin, and the DSC curve obtained by the heat flux differential scanning calorimetry of the foam forming the outer layer part is unique to the polypropylene resin. The polyolefin resin expanded particles according to [1] above, wherein an endothermic peak having an endothermic amount of 5 to 30 (J / g) appears on the higher temperature side than the intrinsic endothermic peak together with the endothermic peak.
[3] The DSC curve obtained by heat flux differential scanning calorimetry of the foam forming the outer layer portion is a linear low-density polyethylene-based resin forming the outer layer portion. The endothermic peak having an endotherm of 10 to 40 (J / g) appears on the higher temperature side than the inherent endothermic peak together with the endothermic peak inherent to the linear low-density polyethylene resin, as described in [1] above Polyolefin resin foam particles.
[4] The polyolefin resin according to [1] above, wherein the polyolefin resin constituting the polyolefin resin expanded particles satisfies at least one of the following conditions (1) to (3): Resin foam particles.
(1) The DSC curve obtained by heat flux differential scanning calorimetry of the foam forming the outer layer part has one or more endotherms on the higher temperature side than the inherent endothermic peak together with the endothermic peak inherent to the polyolefin resin. A peak A appears, and one or more endothermic peaks B appear on the higher temperature side of the inherent endothermic peak together with the inherent endothermic peak of the polyolefin resin in the DSC curve obtained by heat flux differential scanning calorimetry of the entire expanded particle. The total endothermic amount of the endothermic peak B is 3 (J / g) or less smaller than the total endothermic amount of the endothermic peak A.
(2) The polyolefin layer in which the inner layer portion is formed inside the foamed particles closer to the center of the expanded particle than the outer layer portion, and the melting point of the polyolefin resin forming the outer layer portion forms the inner layer portion 3 to 25 ° C. higher than the melting point of the resin.
(3) The inner layer part is formed inside the foamed particles closer to the center of the foamed particle than the outer layer part, and the melt flow rate of the polyolefin resin forming the inner layer part forms the outer layer part. 10-50 (g / 10 min) higher than the melt flow rate of polyolefin resin.
[5] The inner layer part is formed inside the foamed particles closer to the center of the foamed particle than the outer layer part, and the weight ratio of the outer layer part to the inner layer part is 20:80 to 80:20. The polyolefin resin expanded particles according to any one of [1] to [4] above.
[6] The above-mentioned [1] to [1], wherein the resin layer is formed of a polymer having a melting point lower than that of the polyolefin resin forming the outer layer part or outside the outer layer part. [5] The polyolefin resin expanded particles according to any one of [5].
[7] A polyolefin-based resin foamed particle according to any one of the above [1] to [6] is molded in-mold, and a skeleton having a cell structure in which adjacent cells are separated by a cell membrane wall; A polyolefin having a density of 0.02 to 0.09 g / cm ³ and a closed cell ratio of 60% or less, which is present between the skeleton parts, and the bubble film wall has a broken, broken or perforated bubble broken part. -Based resin expanded particle molded body.

  The polyolefin resin foamed particles of the present invention have an outer layer part that forms a cell structure in which adjacent cells are separated by a cell wall. Can be made possible. In addition, the inside of the foamed particle closer to the center of the foamed particle than the outer layer part has a structure in which the cell membrane wall is broken, broken, or perforated. Therefore, the flexibility, recoverability, and sound absorption of the foam having an open cell structure are provided. The foamed particles and the molded body thereof can be provided with performance required for the foam having an open cell structure.

  The foamed particles of the present invention have in-mold molding properties such as in-mold moldability and mold shape reproducibility possessed by closed-cell structure foam particles, and flexibility, recoverability, and sound-absorbing properties of foams having an open-cell structure. It is an epoch-making expanded particle that can combine properties such as buffering properties, water absorption, water storage, and filter material selection.

  In addition, the polyolefin-based resin foamed particle molded body of the present invention obtained by molding the foamed particles in-mold also has flexibility, recoverability, sound absorption, buffering, water absorption, water storage, foam having an open cell structure, It can be provided with characteristics such as filter material selection, has a wide degree of freedom in shape selection by integral molding with three-dimensional in-mold molding, packaging material, cushioning material, building material, vehicle member, bedding core It is suitable as a material or the like.

It is a graph which shows the measurement result of the sound absorption rate of the foamed-particle molded object of Examples 1, 2, and 3. FIG. It is a graph which shows the measurement result of the sound absorptivity of the foaming particle molded object of Example 4, 5, 6, 7. It is a graph which shows the measurement result of the sound absorption coefficient of the foamed-particle molded object of a comparative example. It is a expanded particle cross section which shows an example of the cell structure of the expanded particle which concerns on this invention, (1)-(7) is an enlarged micrograph (magnification 30 time) of the expanded particle cross section obtained in Examples 1-7 in order. ). Compared with the structure of the outer layer part of the foamed particle, the inside of the foamed particle at the center of the foamed particle breaks, breaks or perforates the bubble membrane wall, and the structure is a continuous hole, fiber, hollow or hollow, or a combination of these It shows that it exhibits the structure. Fig. 4 (1) is a composite configuration of fibrous and hollow shapes, Figs. 4 (2), (3) and (7) are fibrous configurations, and Figs. 4 (4) and (5) are mostly hollow. Alternatively, a hollow configuration, FIG. 4 (6), shows a communication hole configuration. It is a expanded particle cross section which shows the bubble structure of the expanded particle which concerns on a comparative example, (1)-(4) is an enlarged micrograph ((1), (4) of the expanded particle cross section obtained in comparative examples 1-4 in order. 3), (4) magnification 30 times, and (2) magnification 20 times).

The foamed particle of the present invention comprises an outer layer part having a cell structure in which adjacent bubbles of polyolefin resin foamed particles are partitioned by a cell membrane wall, and the inside of the foamed particle closer to the center of the foamed particle than the outer layer part is a cell. The membrane wall breaks, breaks, or is perforated, and the structure is (1) a communicating hole, (2) a fiber, (3) a hollow or hollow shape, or an inner layer portion or cavity of a structure in which these are combined. Formed from.
That is, the expanded particles according to the present invention can be confirmed by an enlarged micrograph of the expanded particle cross section shown in FIG. A bubble structure partitioned by a bubble membrane wall is formed, and almost no holes or tears are observed on the bubble membrane wall. Due to the cell structure of the outer layer part, appropriate mechanical properties of the foamed particles, in-mold moldability such as foam particle shrinkage-inhibiting effect and expansion capacity maintaining performance when foamed particles are molded in-mold, shape retention of the foamed particle molded body Performance is expressed. In addition, as long as the performance of the foamed particles of the present invention is expressed, there may be a case where holes and tears are rarely observed on the bubble membrane wall of the outer layer portion.

  On the other hand, in the foamed particles of the present invention, the inside of the foamed particles closer to the center of the foamed particles than the outer layer part is formed by melting (1) part of the bubble film wall, and more than the bubble film wall of the outer layer part. The inner layer part of the communication hole-like structure composed of a bubble partition wall having a large number of communication holes perforated by the bubble film, and (2) the bubble film is melted and stretched to such an extent that it does not retain its shape as a bubble film wall. In addition, the inner layer portion of the fibrous structure made of countless thin fibrous resin bodies and (3) the bubble membrane wall is formed by melting and shrinking, thereby forming the membrane wall by melting and shrinking. A hollow portion or a hollow portion surrounded by a non-flat wall is formed, or an inner layer portion of the communication hole-like, fiber-like and hollow or hollow composite structure is formed.

  In the expanded particle according to the present invention, the outer layer portion of the expanded particle has a cell structure in which adjacent cell membranes are independent from each other, and the structure inside the expanded particle center side from the expanded particle outer layer portion, that is, the structure inside the expanded particle Is a special structure as described above, and can exhibit various characteristics as expanded particles. The foamed particles whose internal structure mainly has the above structure (1) are particularly excellent in recoverability and dimension retention during molding in the mold, and the foamed particles mainly having the structure (2) are particularly excellent in sound absorption, and mainly In addition to being particularly excellent in flexibility in the expanded particles having the structure of (3), the expanded particles of the present invention are excellent in flexibility, recoverability, sound absorption, buffering, water absorption, Performances such as water retention, water storage, filters, and carriers can be expressed.

Examples of the base resin constituting the polyolefin resin expanded particles in the present invention include polypropylene resins and polyethylene resins.
Examples of the polypropylene resin include a propylene homopolymer and a propylene copolymer. In addition, as said propylene-type copolymer, (alpha)-, such as propylene and ethylene or / and C1-C20 1-butene, 1-pentene, 1-hexene, 1-octene, 4-methyl-1-butene. Examples include random copolymers with olefins, block copolymers, and random block copolymers. Specifically, binary copolymers such as propylene-ethylene random copolymer, propylene-butene random copolymer, Preferable examples include terpolymers such as propylene-ethylene-butene random copolymers. Further, the proportion of the comonomer component other than propylene in the propylene-based copolymer is not particularly limited, but the structural unit derived from propylene in the copolymer is 50% by weight or more, further 70% by weight or more, In particular, it is preferable to contain 80 to 99.5% by weight.

  Examples of the polyethylene resin include high density polyethylene, medium density polyethylene, low density polyethylene, linear low density polyethylene, linear ultra-low density polyethylene, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, Examples thereof include ethylene-methacrylic acid copolymers. Further, the proportion of the comonomer component other than ethylene in the ethylene-based copolymer is not particularly limited, but the structural unit derived from ethylene in the copolymer is 50% by weight or more, further 70% by weight or more, In particular, it is preferable to contain 80 to 99.5% by weight.

  Further, among the polyolefin resins used in the present invention, in relation to the method for producing the expanded particles of the present invention described later, a polyolefin resin corresponding to the outer layer portion of the expanded particles and a polyolefin resin corresponding to the inside of the expanded particles It is preferable from the viewpoint of the adhesiveness between the outer layer part and the inside that at least one of these is a resin polymerized using a metallocene polymerization catalyst.

  Examples of the polyolefin resin used in the present invention include polystyrene resins such as polystyrene, styrene-maleic anhydride copolymer, styrene-acrylonitrile copolymer, ethylene-propylene rubber, ethylene-1- Heat of rubber such as butene rubber, propylene-1-butene rubber, ethylene-propylene-diene rubber, isoprene rubber, neoprene rubber, nitrile rubber, hydrogenated product of styrene-diene block copolymer or styrene-diene block copolymer A plastic elastomer or the like may be blended or copolymerized. These resins, rubbers, or elastomers may be used in combination of two or more.

  Further, the polyolefin-based resin constituting the expanded particles may be a non-crosslinked resin or a crosslinked crosslinked resin. However, in order to obtain the expanded particles of the present invention, at least the interior of the multilayer resin particles described later is included. The constituting polyolefin resin is preferably a non-crosslinked polyolefin resin.

  Foamed particles having a special structure of the present invention can be obtained by adjusting the layer structure of the multilayer resin particles before foaming to obtain the foamed particles. Specifically, the softening temperature, the melting temperature of the polyolefin resin constituting the outer layer portion of the resin particle corresponding to the outer layer portion of the expanded particle and the polyolefin resin constituting the inner layer portion of the resin particle corresponding to the inner portion of the expanded particle, Using the difference in thermal properties such as fluidity, the resin constituting the outer layer portion and the inner layer portion of the multilayer resin particles was selected and selected by at least one of the following methods (a) to (u): Using multi-layer resin particles composed of a combination of resins, known polyolefin resin particles are dispersed in a dispersion medium in a sealed container, heated in the presence of a physical foaming agent, pressurized, and a predetermined holding step is performed. Then, after impregnating the resin particles with the foaming agent, the resin particles containing the foaming agent and the dispersion medium from the sealed container at the foaming temperature are discharged from the sealed container to the low pressure region to obtain the foamed particles. Obtaining the expanded particles of the present invention Kill.

  (A) For resin particles consisting only of a resin capable of forming the outer layer portion of the multilayer resin particles, conventionally known polyolefin-based resin particles are dispersed in a dispersion medium in a sealed container, and the temperature is increased in the presence of a physical foaming agent. Pressurize and form a high-temperature endothermic peak that can be confirmed by DSC curve obtained by heat flux differential scanning calorimetry of foamed particles in the holding step described later, and then contain foaming agent from the sealed container at the foaming temperature The foaming particles at each foaming temperature are obtained by releasing the resin particles and the dispersion medium into the low pressure region to obtain foamed particles under the conditions where the foaming temperature is changed in increments of 1 ° C (same conditions other than the foaming temperature are the same). Get. Next, the endothermic amount of the high-temperature endothermic peak of each foamed particle obtained by heat flux differential scanning calorimetry is obtained, and the foaming temperature is increased with the horizontal axis representing the foaming temperature and the vertical axis representing the endothermic peak of the high-temperature endothermic peak. A graph A showing a relationship in which the endothermic amount a of the endothermic peak on the high temperature side decreases linearly is obtained.

  Similarly for resin particles consisting only of resin capable of forming the inside of the multilayer resin particles, the endothermic amount c of the endothermic peak on the high temperature side decreases linearly as the foaming temperature increases, or the foaming temperature increases. Irrespective of this, a graph C showing a constant value of the endothermic amount c of the endothermic peak on the high temperature side is obtained.

  Then, based on both graphs, the value of the endothermic amount a of the endothermic peak on the high temperature side that can be read from the graph A at the foaming temperature assumed to obtain the expanded particles of the target magnification from the multilayer resin particles is 5 J / g or more. The outer layer portion and the inner layer portion of the multilayer resin particles satisfying the condition of the endothermic amount c of the endothermic peak on the high temperature side that can be read from the graph C at the foaming temperature satisfy 0 to 27 J / g (including 0). Select resin. It should be noted that the endothermic amount a is compared with the endothermic amounts a and c of the high temperature side endothermic peaks that can be read from the graph A and the graph C at the foaming temperature assumed to obtain the expanded particles of the target magnification from the multilayer resin particles. It is preferable to select a resin that constitutes the outer layer portion and the inner layer portion satisfying the relationship that the endothermic value c is smaller by about 5 J / g or more, and more preferably by 10 J / g or more.

  (Ii) Compare the melting point of each polyolefin resin capable of forming the outer layer part and the inner layer part of the multilayer resin particle, and the resin that can form the outer layer part than the melting point of the resin that can form the inner layer part. The resin constituting the outer layer portion and the inner layer portion of the multilayer resin particles is selected so that the melting point is about 3 to 25 ° C higher, preferably 5 to 20 ° C higher. In addition, as for melting | fusing point of polyolefin resin which forms the outer layer part of the said multilayer resin particle, 120-160 degreeC is preferable. As the melting point, “when melting temperature is measured after performing a certain heat treatment” described in JIS K7121 (1987) is adopted (both the heating rate and the cooling rate in the condition adjustment of the test piece are 10 ° C./min. And a value obtained as the peak temperature of the endothermic peak accompanying melting of the resin on the DSC curve obtained by heating at a heating rate of 10 ° C./min by heat flux differential scanning calorimetry. When there are a plurality of endothermic peaks on the DSC curve, the vertex temperature of the endothermic peak having the largest area is defined as the melting point. As a measuring device, DSCQ1000 manufactured by TA Instruments Inc. can be used.

  (Iii) The melt flow rate of each polyolefin resin capable of forming the outer layer portion and the inner layer portion of the multilayer resin particle is compared, and the inner layer portion is formed more than the melt flow rate of the resin capable of forming the outer layer portion. The outer layer portion and the inner layer portion of the multi-layer resin particles are so arranged that the melt flow rate of the resin to satisfy the relationship is generally 10 to 50 (g / 10 minutes) higher, preferably 15 to 45 (g / 10 minutes) higher. Select the constituent resin. The melt flow rate of the polyolefin resin forming the inner layer portion of the multilayer resin particles is preferably 20 to 40 (g / 10 minutes). In the case of polypropylene resin, the melt flow rate is measured under conditions of 230 ° C. and a load of 21.17 N in accordance with JIS K7210 (1976), and in the case of polyethylene resin, 190 ° C. Measured under the condition of load 21.17N.

  The selection of the resin constituting the outer layer portion and the inner layer portion of the multilayer resin particles is not necessarily made up of the outer layer portion and the inner layer portion as long as the conditions in at least one of the above methods (a) to (u) can be satisfied. The resin to be used may not be a different raw material.

  The multilayer resin particles composed of the outer layer portion and the inner layer portion are, for example, Japanese Patent Publication No. 41-16125, Japanese Patent Publication No. 43-23858, Japanese Patent Publication No. 44-29522, Japanese Patent Publication No. 60-185816. It can be produced by a coextrusion method described in a publication or the like. Generally, an outer layer part forming extruder and an inner layer part forming extruder for multilayer resin particles are used and connected to a coextrusion die. Melting and kneading required resin components and additives as needed in the outer layer forming extruder, and melt kneading required resin components and additives as required in the inner layer forming extruder To do. Each melt-kneaded product is joined in the die to form a multilayer structure comprising a cylindrical inner layer portion and an outer layer portion covering the outer surface of the inner layer portion, and a die attached to the die outlet at the tip of the extruder. Multi-layer resin particles are produced by extruding into a strand shape from the pores, and cutting the pellets so that the weight of the resin particles becomes a predetermined weight after cooling or before cooling.

  Examples of the shape of the multilayer resin particles used in the present invention include a columnar shape, a rugby ball shape, and a spherical shape. Foamed particles obtained by foaming such multilayer resin particles have a columnar shape, a rugby ball shape, or a spherical shape according to the shape of the resin particles before foaming.

  The average weight of the foamed particles can be adjusted by adjusting the average weight per resin particle for obtaining the foamed particles to the average weight per foamed particle. If the average weight per one of the expanded particles is too small, the foaming efficiency is deteriorated, and if it is too large, the filling property in the mold at the time of molding is inferior. It is preferably 01 to 10.0 mg, particularly 0.1 to 5.0 mg.

  In the multilayer resin particles forming the expanded particles of the present invention, the resin forming the inside of the expanded particles and the resin forming the outer layer portion are preferably in a weight ratio of 20:80 to 80:20, more preferably Is 25:75 to 75:25. If the weight ratio of the resin forming the outer layer portion of the multilayer resin particles is too small, the proportion of the outer layer portion of the closed cell structure of the foam particles made of the multilayer resin particles is relatively small, and at the time of in-mold molding There is a possibility that the shrinkage of the molded body increases and the dimensional retention is inferior. On the other hand, if the weight ratio of the resin forming the outer layer portion is too large, the foamed particles obtained are formed by breaking, breaking, or perforating the bubble membrane wall formed inside the foamed particles. There is a possibility that the performance exhibited by the specific structure described, that is, the fiber shape, the communication hole shape, the hollow shape or the hollow shape, and the internal structure having these composite structures may not be sufficiently exhibited. The above weight ratio corresponds to the weight ratio between the weight of the outer layer portion of the polyolefin resin foamed particle of the present invention and the weight obtained by subtracting the weight of the outer layer portion from the weight of the foamed particle (inner weight). is there.

  The polyolefin resin foamed particles of the present invention having the above-described special structure are obtained from normal temperature by differential heat calorimetry using a polyolefin resin foam forming the outer layer portion of the polyolefin resin foamed particles as a sample. A DSC curve obtained when heated to 220 ° C. at a heating rate of 10 ° C./min has one endothermic peak inherent to the polyolefin resin (hereinafter also referred to as an intrinsic peak) and one higher temperature than the intrinsic peak. The above endothermic peak (hereinafter, also referred to as a high temperature peak) is the point of view such as the fusibility between the foam particles related to the moldability of the foam particles and the dimensional stability of the resulting foam particle molding. To preferred.

  Specifically, when the polyolefin resin forming the outer layer portion of the polyolefin resin foamed particle of the present invention is a polypropylene resin, the heat flux differential scanning calorimetry of the foam forming the outer layer portion is used. It is preferable to select a DSC curve having a high temperature peak with an endotherm of 5 to 30 J / g and further 8 to 25 J / g together with the intrinsic peak of the polypropylene resin. In addition, when two or more high temperature peaks appear, it is preferable that the total endothermic quantity of those high temperature peaks is in the above range.

  Further, when the polyolefin resin forming the outer layer part in the polyolefin resin expanded particle of the present invention is a linear low density polyethylene resin, the heat flux differential scanning calorific value of the foam forming the outer layer part It is preferable to select a DSC curve obtained by the measurement, in which an endothermic amount of 10 to 40 J / g and a high temperature peak of 15 to 35 J / g appear together with the intrinsic peak of the linear low density polyethylene resin. In addition, when two or more high temperature peaks appear, it is preferable that the total endothermic quantity of those high temperature peaks is in the above range.

  The total endothermic amount of the DSC curve, that is, the total endothermic amount of the intrinsic peak and the high temperature peak is 50 to 50 when the polyolefin resin forming the outer layer portion is a polypropylene resin. 120 (J / g), more preferably 60 to 100 (J / g). When the polyolefin resin forming the outer layer portion is a linear low-density polyethylene resin, 80 to 150 (J / g) J / g), more preferably 100 to 130 (J / g).

  The total endothermic amount of the DSC curve of the resin forming the outer layer portion of the expanded particles and the endothermic amount of the high temperature peak are measured by the measuring method based on JIS K7122 (1987) as follows. First, a sample of 2 to 8 mg is collected from the outer layer part of the expanded particles, and the sample is heated from a normal temperature (approximately 25 ° C.) to 220 ° C. at a rate of 10 ° C./min with a heat flux differential scanning calorimeter. The sample may be collected from the outer layer portion by slicing the outer layer portion of the foamed particles using a cutter knife, a microtome, etc., and collecting a predetermined amount of the outer layer portion for use in measurement. When the outer layer portion obtained from one expanded particle is less than 2 to 4 mg, the above procedure is repeated using a plurality of expanded particles to collect a required amount of sample. In addition, the total endothermic amount of the DSC curve of the expanded particles and the measurement of the endothermic amount of the high temperature peak are as follows. It can be measured in the same manner as the measurement of the endothermic amount of the high temperature peak.

  In the DSC curve obtained by the above measurement, an intrinsic peak derived from the polyolefin resin and one or more high temperature peaks appear on the higher temperature side than the intrinsic peak, and the endothermic amount of the high temperature peak corresponds to the peak area. Specifically, it can be obtained as follows.

  First, a straight line (α−β) connecting a point α corresponding to 80 ° C. on the DSC curve and a point β on the DSC curve corresponding to the melting end temperature (T) of the expanded particles is drawn. The melting end temperature (T) is a temperature corresponding to the intersection of the DSC curve and the baseline on the high temperature side of the high temperature peak on the highest temperature side.

  Next, a straight line parallel to the vertical axis of the graph is drawn from the point γ on the DSC curve corresponding to the valley between the intrinsic peak and the high temperature peak, and the point intersecting with the straight line (α−β) is defined as δ. The area of the high temperature peak is the area surrounded by the curve of the high temperature peak portion of the DSC curve, the line segment (α-β), and the line segment (γ-δ), which corresponds to the endothermic amount of the high temperature peak. To do. Further, the total endothermic amount of the DSC curve in this specification is represented by the area of the portion surrounded by the DSC curve and the straight line (α-β), which corresponds to the total endothermic amount of the endothermic curve peak.

  In addition, although the said high temperature peak is recognized by the 1st DSC curve obtained by heating up to 220 degreeC at 10 degree-C / min as mentioned above, after the 1st DSC curve was obtained, Subsequently, the temperature is lowered from 220 ° C. to 40 ° C. at 10 ° C./min, and again raised to 220 ° C. at 10 ° C./min, which is not recognized in the second DSC curve obtained.

  The high temperature peak of the foamed particles is a known foaming method, that is, when the resin particles are dispersed in a dispersion medium in a closed container and heated, without raising the temperature above the melting end temperature (Te) of the resin particles, Hold for a sufficient time at an arbitrary temperature (Ta) within a range of 15 ° C. lower than the melting point (Tm) of the resin particles and lower than the melting end temperature (Te), preferably about 10 to 60 minutes. Resin melting point (Tm) −10 ° C. to melting end temperature (Te) + 5 ° C. is adjusted to an arbitrary temperature, and at that temperature, that is, foaming temperature (Tb), resin particles are discharged from the container to the low pressure region. Can be obtained by a foaming method. The retention of the resin particles within the temperature range of the above-mentioned resin particles for forming a high temperature peak can be set in multiple stages within the temperature range, and sufficient time is taken within the temperature range. It is also possible to form the high temperature peak by slowly raising the temperature.

  The formation of the high temperature peak in the expanded particles and the magnitude of the high temperature peak heat amount depend on the selection of the resin constituting the expanded particles, the temperature Ta, the holding time at the temperature, the temperature Tb, and the like. For example, the amount of heat at the high temperature peak of the expanded particles tends to increase as the holding time at the temperature Ta increases. On the other hand, the higher the temperature Tb, the smaller the tendency. By taking these points into consideration and repeating the preliminary test several times, it is possible to know the production conditions for the expanded particles exhibiting the desired high-temperature peak heat quantity. In addition, the temperature range which concerns on formation of the high temperature peak mentioned above is a suitable temperature range at the time of using an inorganic type physical foaming agent as a foaming agent. Therefore, when the foaming agent is changed to an organic physical foaming agent, the appropriate temperature range shifts by about 0 to 30 ° C. to the lower temperature side than the above temperature range depending on the type and amount of use.

  The polyolefin resin foamed particles of the present invention can be produced as follows using multilayer resin particles that satisfy at least one of the above conditions (A) to (U).

  Using the extruder for forming the outer layer portion of the polyolefin-based resin particles and the extruder for forming the inner layer portion in the present invention, if necessary, using an extruder for forming the resin layer described later on the outside of the outer layer portion, these extrusions A die for forming a multilayer strand is attached to the outlet of the machine, and an inner layer part forming extruder, an outer layer part forming extruder, and a resin layer forming extruder are provided with a polyolefin resin for forming the inner layer part and the outer layer part. The polyolefin resin to be formed and the resin for forming the resin layer are supplied to the respective extrusions at a predetermined ratio, melted and kneaded under heating, and the melt-kneaded product is introduced into the multilayer strand forming die and joined in the die. Extruded as a multi-layer strand from a small hole in the die attached to the tip of the exit of the extruder, the extruded strand was water-cooled, and the weight of the resin particles was approximately 1.3 mg to 1.5 mg with a pelletizer. Obtain a predetermined multilayer resin particles was dried and cut to a size that.

  For the production of the foamed particles of the present invention, polyolefin resin particles obtained by granulation by the above-described method and the like and a foaming agent are dispersed in a dispersion medium such as water in a closed container, and heated under stirring to form a resin. After the particles are softened and the resin particles are impregnated with a foaming agent, the resin particles are discharged and foamed at a temperature equal to or higher than the softening temperature of the resin particles under a low pressure (usually atmospheric pressure) in the container. Known foaming methods described in Japanese Patent No. 2183, Japanese Patent Publication No. 56-1344, Japanese Patent Publication No. 62-61227, and the like can be applied. In addition, when the contents in the sealed container are released from the sealed container to a low pressure region in order to obtain expanded particles, back pressure is applied to the sealed container with the used foaming agent or an inorganic gas such as nitrogen or air. It is preferable to discharge the contents so that the pressure in the container does not drop rapidly. The dispersion medium for dispersing the resin particles in the production of the expanded particles is not limited to the above-described water, and any solvent that does not dissolve the resin particles can be used. Examples of the dispersion medium other than water include ethylene glycol, glycerin, methanol, ethanol and the like, but usually water is used.

  In the above method, in the dispersion medium, if necessary, poorly water-soluble such as aluminum oxide, tricalcium phosphate, magnesium pyrophosphate, zinc oxide, and kaolin so that the resin particles are uniformly dispersed in the dispersion medium. It is preferable to disperse a dispersing agent such as a dispersing agent such as an inorganic substance and an anionic surfactant such as sodium dodecylbenzenesulfonate and sodium alkanesulfonate. The amount of the dispersant added to the dispersion medium when producing the foamed particles is such that the ratio of the weight of the resin particles to the weight of the dispersant (the weight of the resin particles / the weight of the dispersant) is 20 to 2000, and further 30. It is preferable to set it to -1000. Further, the ratio of the weight of the dispersing agent to the weight of the dispersing aid (the weight of the dispersing agent / the weight of the dispersing aid) is preferably 1 to 500, more preferably 5 to 100.

  As the foaming agent used in the method for producing foamed particles, an organic physical foaming agent, an inorganic physical foaming agent, or a mixture thereof can be used. Examples of organic physical blowing agents include aliphatic hydrocarbons such as propane, butane, hexane, pentane and heptane, alicyclic hydrocarbons such as cyclobutane and cyclohexane, chlorofluoromethane, trifluoromethane, 1,1-difluoroethane, Examples include 1,1,1,2-tetrafluoroethane, halogenated hydrocarbons such as methyl chloride, ethyl chloride, and methylene chloride; and dialkyl ethers such as dimethyl ether, diethyl ether, and methyl ethyl ether. It can be used by mixing. Moreover, as an inorganic type physical foaming agent, nitrogen, carbon dioxide, argon, air, water, etc. are mentioned, These can be used in mixture of 2 or more types. When mixing and using an organic physical foaming agent and an inorganic physical foaming agent, what was arbitrarily selected from the above-mentioned organic physical foaming agent and an inorganic physical foaming agent can be used in combination. In addition, when using together an inorganic type physical foaming agent and an organic type physical foaming agent, it is preferable that an inorganic type physical foaming agent contains at least 30 weight% or more.

  Among the above foaming agents, an inorganic physical foaming agent is particularly preferable from the viewpoint of environmental friendliness, and nitrogen, air, carbon dioxide, and water are particularly preferable. In addition, when water is used as a dispersion medium together with resin particles in a sealed container when obtaining expanded particles, water that is a dispersion medium is obtained by using a mixture of the resin particles with a water absorbent resin or the like. It can be used efficiently as a foaming agent.

  The amount of the foaming agent used is determined in consideration of the apparent density of the target foamed particles, the type of base resin, or the type of foaming agent. Usually, the organic physical foaming agent is used per 100 parts by weight of the resin particles. On the other hand, it is preferable to use 0.5 to 30 parts by weight for the inorganic physical foaming agent.

  In addition, the polyolefin resin foam particles obtained by being discharged from the closed container to the low-pressure region by the above-described method are subjected to a curing step under atmospheric pressure that is normally performed after the release, and are then put into a sealed container for pressurization. The pressure inside the foamed particles is adjusted to 0.01 to 0.6 MPa (G) by pressurizing with a pressurized gas such as air, and then the foamed particles are taken out from the container and steam or hot air is discharged. By using and heating, it is possible to obtain expanded particles having a lower apparent density (hereinafter also referred to as two-stage expansion).

  The expanded particles of the present invention obtained by the above method have the cross-sectional structure unique to the present invention described above.

In the polyolefin resin expanded particles of the present invention, the polyolefin resin constituting the expanded particles preferably satisfies at least one of the following conditions (1) to (3).
(1) The DSC curve obtained by heat flux differential scanning calorimetry of the foam forming the outer layer part has one or more endotherms on the higher temperature side than the inherent endothermic peak together with the endothermic peak inherent to the polyolefin resin. Peak A appears, and one or more endothermic peaks B appear on the DSC curve obtained by differential scanning calorimetry of the entire expanded particles, together with the endothermic peak inherent to the polyolefin resin, on the higher temperature side than the inherent endothermic peak. The total endotherm of the endothermic peak B is 3 (J / g) or less than the total endothermic amount of the endothermic peak A.
(2) The polyolefin layer in which the inner layer portion is formed inside the foamed particles closer to the center of the expanded particle than the outer layer portion, and the melting point of the polyolefin resin forming the outer layer portion forms the inner layer portion 3 to 25 ° C. higher than the melting point of the resin.
(3) The inner layer part is formed inside the foamed particles closer to the center of the foamed particle than the outer layer part, and the melt flow rate of the polyolefin resin forming the inner layer part forms the outer layer part. 10-50 (g / 10 min) higher than the melt flow rate of polyolefin resin.

  The expanded particles satisfying the above conditions (1) to (3) have configurations corresponding respectively to the conditions (a) to (u) of the method for producing expanded particles of the present invention using the multilayer resin particles described above. ) From the viewpoint of particularly excellent sound absorption, and from the viewpoint of particularly excellent flexibility, the expanded particles satisfying condition (3). Are preferable from the viewpoint of being particularly excellent in recoverability and dimensional retention during molding. The total endothermic amount, melting point, and melt flow rate of the endothermic peak in the above conditions (1) to (3) are the same as the endothermic amount, melting point, and melt flow rate of the endothermic peak in the conditions (a) to (u). This is the value obtained by In the case where the inner layer portion of the expanded particle is formed with a structure including the hollow or hollow portion shown in (4) of FIG. 4, the bubble membrane wall is formed by melting and shrinking, Measurement is performed by cutting out a sample for measuring the melting point and melt flow rate of the inner layer portion from the wall of the non-flat surface surrounding the hollow portion formed by melting and shrinking of the membrane wall.

  From the above viewpoint, the total endothermic amount of the endothermic peak B in the condition (1) is more preferably 4 to 15 (J / g) or less than the total endothermic amount of the endothermic peak A, and the outer layer portion is formed in the condition (2). It is more preferable that the melting point of the polyolefin-based resin is 5 to 20 ° C. higher than the melting point of the polyolefin-based resin forming the inner layer part, and the polyolefin-based resin forming the inner layer part in the condition (3) More preferably, the melt flow rate is 20 to 40 (g / 10 minutes) higher than the melt flow rate of the polyolefin resin forming the outer layer portion.

  On the outside of the outer layer part constituting the expanded particle of the present invention, the melting point is lower than the melting point of the polyolefin resin forming the outer layer part or lower than the melting point forming the outer layer part, or the thickness of the polymer not showing the melting point A thin resin layer can be formed. By forming the expanded particles having such a resin layer as the outermost layer, the moldability is improved, and a molded product having excellent fusion properties between the expanded particles can be obtained by being molded at a low temperature. When the thickness of the resin layer is too thick, the foamed molded body may be heavy. The thickness of the resin layer is preferably 0.1 to 30 μm, more preferably 1 to 20 μm.

  The foamed particles of the present invention may contain various additives. Examples of the additive include a bubble adjusting agent, an antistatic agent, a conductivity imparting agent, a lubricant, an antioxidant, an ultraviolet absorber, a flame retardant, a metal deactivator, a pigment, a dye, a crystal nucleating agent, or an inorganic filler. And various additives such as these can be included in the polyolefin-based resin constituting the foamed particles as desired. Moreover, a functional additive can express a sufficient function by the use of a small amount rather than adding it to the whole foamed particle by adding only a large amount to the said resin layer or the said resin layer.

  In addition to inorganic substances such as talc, calcium carbonate, silica, titanium oxide, gypsum, zeolite, borax, aluminum hydroxide, carbon, etc., the above-mentioned bubble regulators include phosphate nucleating agents, phenolic nucleating agents, amine-based nuclei. An organic nucleating agent such as an agent. It is preferable that the cell regulator is blended in an amount of 100 ppm by weight or more in each of the outer layer portion forming resin and the inner layer portion forming resin. Moreover, although the compounding quantity of said various additives changes with the addition objective, Preferably it is 0.03-10 weight part with respect to 100 weight part of base resin, More preferably, 0.05-5 weight part is mix | blended.

  In the expanded particles of the present invention, the area ratio between the outer layer portion and the inner portion is preferably 10:90 to 80:20, more preferably 20:80 to 60:40, in the outer layer portion and the inner portion. If the ratio of the outer layer portion becomes too large, the mechanical strength of the foamed molded product will be good, but the effects expected for a foam having an open cell structure such as sound absorption performance will be reduced.

  The area ratio between the outer layer portion and the inside is arbitrarily selected from the foamed resin particle group, and the foamed particle cross section obtained by cutting the foamed particle into approximately two equal parts is enlarged and projected with a microscope. In this enlarged projection view, it is obtained by calculating the area ratio between the area of the outer layer part and the area of the part obtained by subtracting the outer layer part from the cross section of the expanded particle (inner area) by image analysis.

  The expanded particles of the present invention usually have an apparent density of 10 to 500 g / L. The upper limit of the apparent density of the expanded particles of the present invention is preferably 300 g / L, more preferably 100 g / L, from the viewpoint of improving basic properties such as lightness and cushioning as a foam. On the other hand, the lower limit of the apparent density is preferably 15 g / L, and more preferably 30 g / L.

  The apparent density of the expanded particles in the present invention is obtained by submerging the expanded particle group having a weight of W (g) in a graduated cylinder containing water by using a wire mesh or the like, and obtained from the rise in the water level. Volume: V (L) is obtained, and the weight is determined by dividing the weight of the expanded particle group by the volume of the expanded particle group (W / V).

The foamed particle molded body of the present invention can be produced by a known in-mold molding method.
For example, using a pair of conventional molds that mold the foamed particles in the mold, the foamed particles are filled into the mold cavity under atmospheric pressure or reduced pressure, and preferably the mold cavity volume is closed by closing the mold. A method using a reduced pressure molding method (for example, Japanese Patent Publication No. 46-38359) in which compression is performed so as to reduce by 70%, and then a heating medium such as steam is supplied into the mold and heated, and the foamed particles are heated and fused. Further, the foamed particles were pre-pressurized with a pressurized gas such as air as necessary to increase the pressure inside the foamed particles, and the pressure inside the foamed particles was adjusted to 0.01 to 0.2 MPa (G). Thereafter, the foamed particles are filled into the mold cavity under atmospheric pressure or reduced pressure, the mold is closed, and then a heating medium such as steam is supplied into the mold to heat-fuse the foamed particles (for example, (Japanese Patent Publication No. 51-22951) and the like. In addition, after filling foamed particles pressurized above the pressure into a cavity pressurized above the atmospheric pressure with compressed gas, a heating medium such as steam is supplied into the cavity to heat-fuse the foamed particles. It can also be molded by a filling molding method (for example, Japanese Patent Publication No. 4-46217). In addition, after filling the expanded particles into a pair of mold cavities under atmospheric pressure or reduced pressure, a heating medium such as steam is then supplied and heated to heat-fuse the expanded particles. (For example, Japanese Patent Publication No. 6-49795) or a method combining the above methods (for example, Japanese Patent Publication No. 6-22919) can be used.

  In the in-mold molding of the foamed particles, the foamed particle compact of the present invention supplies water vapor with a saturated vapor pressure of 0.05 to 0.45 MPa (G), preferably 0.10 to 0.40 MPa (G). Then, the foamed particles can be heated in a mold so that the foamed particles are fused to each other, and then the obtained foamed particle molded body is cooled and taken out from the cavity. As the steam heating method in the above molding method, a method of heating the expanded particles in the order of one-side heating, reverse one-side heating, and main heating is employed. In particular, a method of heating the expanded particles in the order of preliminary heating, one-side heating, reverse one-side heating, and main heating is preferable.

  The foamed particle molded body of the present invention is formed by a foamed particle supply device (hopper), a passage having a heating region and a cooling region, and an endless belt continuously moving in the passage. It can also be produced continuously by a continuous molding machine equipped with

The foamed particle molded body of the present invention is formed by the outer layer part of the foamed particle of the present invention, and the skeleton part of the cell structure in which adjacent bubbles are partitioned by the cell membrane wall, and the foamed particle of the present invention The outer layer portion is formed due to the structure inside the foamed particles on the center side of the foamed particles, and is present between the skeletal portions, and the bubble membrane wall is broken, fractured, or compared with the bubble membrane wall of the skeleton portion. A large number of perforated bubble breaking portions. In addition, it is preferable from a viewpoint of the fusion | bonding property of foamed particles, etc. that many bubble destruction parts are interspersed between this frame | skeleton part in the cross section of a foamed particle molded object. The foamed particle molded body of the present invention has a density of 0.02 to 0.09 g / cm ³ , preferably 0.025 to 0.06 g / cm ³ , and a closed cell ratio of 60% or less, preferably 5 to 50. % Polyolefin resin expanded particle molded body.

  The foamed particle molded body of the present invention has the structure composed of the skeleton part and the bubble destruction part, and the above-mentioned density and closed cell ratio, so that the foam having an open-cell structure has flexibility, recoverability, It can be provided with characteristics such as sound absorption, buffering, water absorption, water storage, filter, etc., and is suitable for packaging materials, cushioning materials, building materials, vehicle members, bedding core materials, etc. is there.

The density of the foamed particle molded body of the present invention is calculated by dividing the weight (g) of the test piece cut out from the molded body by the volume (L) obtained from the outer dimension of the test piece. In addition, the closed cell ratio of the foamed particle molded body of the present invention is determined by cutting a 25 × 25 × 30 mm sample from the center of the foamed particle molded body to obtain a measurement sample (all skin is cut off), and then ASTM-D2856- In accordance with the procedure C described in No. 70, using the value Vx of the true volume of the foam measured by the air comparison type hydrometer 930 manufactured by Toshiba Beckman Co., Ltd., the closed cell ratio S is calculated by the following formula: It calculated | required by the average value of N = 5.
(Equation 1)
S (%) = (Vx−W / ρ) × 100 / (Va−W / ρ) (1)
S: Closed cell ratio (%)
Vx: the true volume of the measurement sample measured by the above method = the sum of the volume of the resin constituting the foam and the total volume of bubbles in the closed cell portion in the foam (cm ³ )
Va: Apparent foam volume (cm ³ ) calculated from the outer dimensions of the measurement sample
W: Weight of measurement sample (g)
ρ: Density of resin constituting the measurement sample (g / cm ³ )

  Next, examples and comparative examples of the present invention will be described in detail.

The polyolefin resins used in Examples and Comparative Examples are shown below.

[Production of resin particles]
Examples 1-6, Comparative Examples 1-4
An extruder having a multilayer strand forming die attached to the outlet side of an inner layer portion forming extruder having an inner diameter of 50 mm and an outer layer portion forming extruder having an inner diameter of 65 mm was used. The polypropylene resin for forming the inner layer part shown in Table 1, Table 2 and Table 3 and the polypropylene resin for forming the outer layer part are supplied to each extruder by the inner layer part forming extruder and the outer layer part forming extruder. The melt-kneaded mixture is heated, and the respective melt-kneaded materials are introduced into the multilayer strand forming die, and the two melts are merged in the die to form two layers from the small holes in the die attached to the tip of the extruder. Extruded as a formed strand, the extruded strand was water-cooled, cut with a pelletizer to a weight of approximately 1.5 mg, and dried to obtain cylindrical multilayer resin particles.

Example 7
In addition to using the same inner layer forming extruder and outer layer forming extrusion as in Example 1, a resin layer forming extruder for forming a resin layer outside the outer layer was also provided. Inner layer forming resin and outer layer forming resin shown in Example 7 in Table 2 with a die for forming a multilayer strand attached to the outlet side of the inner layer forming extruder, the outer layer forming extruder and the resin layer forming extruder Resin and resin layer forming resin are supplied to the respective extruders at the ratios shown in Table 2, and melted and kneaded, and the melt is introduced into the multilayer strand forming die and merged in the die to reach the tip of the extruder. Strands formed in three layers having a resin layer were extruded from the small holes of the attached base, and multilayer resin particles having a resin layer formed on the outermost layer were obtained in the same manner as described above.

  The outer layer portion forming resin and the inner layer portion forming resin were added in the prepared master batch so that the content of zinc borate as a bubble adjusting agent was 1000 ppm by weight.

[Production of expanded particles]
1000 g of polyolefin resin particles obtained as described above, 3000 ml of water as a dispersion medium, 3 g of kaolin as a dispersion agent, 0.04 g of sodium dodecylbenzenesulfonate and 0.01 g of aluminum sulfate as a dispersion aid were equipped with a stirrer. Carbon dioxide (dry ice) was charged as a foaming agent so as to have an equilibrium vapor pressure shown in the foaming conditions in Tables 2 and 3 in a 5 L autoclave. Under stirring, the temperature was raised to a temperature 5 ° C. lower than the foaming temperature shown in the foaming conditions in Tables 2 and 3, and held at that temperature for 15 minutes, then raised to the foaming temperature and held at that temperature for another 15 minutes, The contents in the autoclave were released together with the dispersion medium under atmospheric pressure to obtain polyolefin resin expanded particles. Tables 2 and 3 show various physical properties of the obtained expanded particles such as the properties of the expanded particles.

[Manufacture of molded products]
The expanded particles were filled in a split plate molding mold having a length of 250 mm × 200 mm × thickness 50 mm, and heated at the vapor pressure shown in Tables 2 and 3. After completion of heating, after releasing and cooling, the molded product was taken out of the mold to obtain a plate-like foam molded product. The obtained foamed molded article was cured in an oven at 80 ° C. for 12 hours. The physical properties of the foamed molded products were evaluated for the obtained foamed materials, and the results are shown in Table 2 for Examples and Table 3 for Comparative Examples.

  The physical properties of the foamed molded product were evaluated as follows.

[Moldability (Dimension retention)]
Measure the dimensions of the foamed molded product against the mold dimensions during in-mold molding,
(Double-circle): The shrinkage | contraction rate of a molded object is less than 3%.
(Circle): The shrinkage rate of a molded object is 3 to 6%.
X: The shrinkage ratio of the molded body exceeds 6%.

[Compressive strength (50% strain compressive strength)]
A test piece of 50 × 50 × 25 mm was cut out from the foamed molded article and measured at a test speed of 10 mm / min according to JIS K6767.

[Sound absorption rate]
A test piece having a diameter of 90 mm and a thickness of 50 mm was cut out from the foamed molded article, and the sound absorption coefficient was measured according to JIS A1405 (standing wave ratio method) using a normal incidence sound absorption coefficient measuring device (TYPE10041A manufactured by Sotec Corporation). did.
1 and 2 show the sound absorption coefficient of the foam molded article according to the embodiment of the present invention, and FIG. 3 shows the sound absorption coefficient of the foam molded article of the comparative example.

  In Examples 1 to 3, the resin forming the outer layer portion of the multilayer resin particle and the resin forming the inner layer portion are resins having the same melting point and MFR, and the outer layer portion and the inner layer portion of the multilayer resin particle The weight ratio of was changed. Example 4 is contrasted with Example 3, and a resin having a lower melting point than that of Example 3 was used for the resin forming the inner layer portion. In Example 5, a resin in which the melting point of the resin forming the outer layer portion is lower than that in Example 4 was used. In Example 6, 0.075% by weight of organic peroxide (manufactured by NOF Corporation, trade name: Perhexa 25B) was added to the resin forming the outer layer as the resin forming the inner layer, and the MFR was greatly adjusted. The resin used was used. In Example 7, a resin layer was formed outside the outer layer portion.

  The inner layer portion of the foamed particles of Example 1 shows a composite structure of a fiber and a hollow, Examples 2, 3 and 7 show a fiber structure, and Example 6 shows a composite structure of a communication hole and a fiber. Was shown. The foamed particles obtained in Examples 1 to 7 were excellent in in-mold moldability, and the obtained molded article was good with the performance of a foam having an open cell structure such as sound absorption performance and flexibility. .

  Comparative Example 1 is a case where the outer layer portion and the inner layer portion have the same resin, and the foamed particle inner layer portion has no open cell structure and good moldability, but the performance of the foam having an open cell structure such as sound absorption performance cannot be obtained. Met. Comparative Example 2 was obtained by changing the production conditions of the expanded particles using resin particles having the same structure as Comparative Example 1, and both the outer layer portion and the inner layer portion are expanded cell foam cells. No good molded product could be obtained by in-mold molding. In Comparative Example 3, the difference in high-temperature peak heat quantity between the outer layer part and the inner layer part is small, and both the outer layer part and the inner layer part are foamed particles having a closed cell structure, so that the moldability is good, but the performance of a foam having an open cell structure is obtained. It was not possible. In Comparative Example 4, the MFR of the resin forming the outer layer portion is larger than the MFR of the resin forming the inner layer portion, the outer layer portion is a foamed particle having an open cell structure, and the inner layer portion is a closed cell structure, and sound absorption performance The performance of the foam having an open cell structure such as the above was not obtained, large shrinkage was observed, and the in-mold moldability was insufficient.

1. ・ Expanded particle outer layer part 2. ・ Inside expanded particle

Claims (7)

A foamed polyolefin-based resin, the foamed particle having an air bubble film in an outer layer part of a cell structure in which adjacent cells are separated by a cell wall, and inside the foamed particle closer to the center of the foam particle than the outer layer part A hollow portion or hollow portion surrounded by an inner layer portion formed by melting a wall and / or a non-flat surface wall formed by melting and shrinking a bubble membrane wall; the a, the expanded beads inside the foamed beads center side than the outer layer portion, the bubble membrane wall is destroyed by melting, breaking, or polyolefin resin expanded particles, characterized in that it is perforated.   The polyolefin resin forming the outer layer part is a polypropylene resin, and the DSC curve obtained by heat flux differential scanning calorimetry of the foam forming the outer layer part has an endothermic peak specific to the polypropylene resin. 2. The polyolefin-based resin expanded particles according to claim 1, wherein an endothermic peak having an endothermic amount of 5 to 30 (J / g) appears on a higher temperature side than the intrinsic endothermic peak.   The polyolefin resin forming the outer layer part is a linear low density polyethylene resin, and the DSC curve obtained by the heat flux differential scanning calorimetry of the foam forming the outer layer part is linear. 2. The polyolefin resin according to claim 1, wherein an endothermic peak having an endotherm of 10 to 40 (J / g) appears at a higher temperature than the inherent endothermic peak together with the endothermic peak inherent to the low density polyethylene resin. Expanded particles. 2. The polyolefin resin foamed particles according to claim 1, wherein the polyolefin resin constituting the polyolefin resin foamed particles satisfies at least one of the following conditions (1) to (3).
(1) The DSC curve obtained by heat flux differential scanning calorimetry of the foam forming the outer layer part has one or more endotherms on the higher temperature side than the inherent endothermic peak together with the endothermic peak inherent to the polyolefin resin. A peak A appears, and one or more endothermic peaks B appear on the higher temperature side of the inherent endothermic peak together with the inherent endothermic peak of the polyolefin resin in the DSC curve obtained by heat flux differential scanning calorimetry of the entire expanded particle. The total endothermic amount of the endothermic peak B is 3 (J / g) or less smaller than the total endothermic amount of the endothermic peak A.
(2) The polyolefin layer in which the inner layer portion is formed inside the foamed particles closer to the center of the expanded particle than the outer layer portion, and the melting point of the polyolefin resin forming the outer layer portion forms the inner layer portion 3 to 25 ° C. higher than the melting point of the resin.
(3) The inner layer part is formed inside the foamed particles closer to the center of the foamed particle than the outer layer part, and the melt flow rate of the polyolefin resin forming the inner layer part forms the outer layer part. 10-50 (g / 10 min) higher than the melt flow rate of polyolefin resin.   The inner layer portion is formed inside the expanded particle closer to the center of the expanded particle than the outer layer portion, and the weight ratio of the outer layer portion to the inner layer portion is 20:80 to 80:20. The polyolefin resin expanded particles according to any one of 1 to 4.   6. The resin layer according to claim 1, further comprising a polymer layer having a melting point lower than that of the polyolefin-based resin forming the outer layer part or outside the outer layer part. The polyolefin-based resin expanded particles described in 1. The polyolefin-based resin foamed particles according to any one of claims 1 to 6 are molded in-mold, and adjacent to each other, a bubble-structured skeleton part separated by a bubble membrane wall exists between the skeleton parts. And foamed polyolefin resin foamed particles having a bubble membrane wall having a broken, fractured or perforated bubble breakage part, a density of 0.02 to 0.09 g / cm ³ , and a closed cell ratio of 60% or less. body.