JP2015199830A - Polyolefin resin foamed sheet and production method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyolefin resin foamed sheet excellent in acoustic absorption characteristics and its production method.SOLUTION: A polyolefin resin foamed sheet contains open cells of an open cell rate of 50% or higher and has an apparent density of 600 kg/mor lower, and at least one of its surfaces has an irregular structure including open parts of the open cells. A method of polyolefin resin foamed sheet comprises molding a resin composition containing a polyolefin resin by extrusion foaming to form an irregular structure on the surface and providing apertures in convex parts.

Description

  The present invention relates to a polyolefin resin foam sheet and a method for producing the same.

  Foam sheets are widely used as sound-absorbing materials in the automotive field such as vehicles. Examples of such foams include polyurethane resin foam sheets, synthetic rubber or natural rubber foam sheets, polyolefin resin foam sheets, polystyrene resin foam sheets, and the like. For example, in the automotive field, polyolefin resins such as polypropylene resin, low density polyethylene resin, high density polyethylene resin, and linear low density polyethylene resin are used as materials for forming foam sheets. As a material excellent in mechanical strength and moldability, it is frequently used.

  As such a polyolefin resin foam sheet, for example, Patent Document 1 describes “a polyolefin resin foam sheet characterized by having a portion in which the cell diameter changes along the thickness direction”.

  Patent Document 2 states that “a non-foamed layer is laminated and integrated on both surfaces of a heat-resistant polystyrene resin polyolefin resin foam sheet having an open cell ratio of 50% or more, and the heat-resistant foamed styrene is formed from one surface of the non-foamed layer. A foam sheet for interior material, characterized in that a non-through hole reaching the resin foam layer is formed is described.

JP 2013-82915 A JP 2007-45099 A

  In recent years, sound absorbing characteristics required for sound absorbing materials have been increased. In particular, for automobiles and the like, not only has a desired strength and weight reduction, but further improvement of sound absorbing characteristics against noise and the like has been desired.

  This invention makes it a subject to provide the polyolefin resin foam sheet excellent in the sound absorption characteristic, and its manufacturing method.

  The inventors of the present invention have studied the sound absorption characteristics of the polyolefin resin foam sheet. As a result, the surface on which the continuous bubbles are opened has a concavo-convex structure, and the continuous bubbles are opened on at least a part of the convex portions. It has been found that the polyolefin resin foam sheet exhibits excellent sound absorption characteristics by providing the opening. The present invention has been completed based on these findings.

(1) A polyolefin resin foam sheet having continuous cells with an open cell ratio of 50% or more, an apparent density of 600 kg / m ³ or less, and at least one surface of which is an opening of the continuous cells A polyolefin resin foamed sheet having a concavo-convex structure including a convex part having a surface.
(2) The polyolefin resin foam sheet according to (1), wherein all or part of the convex portions of the concave-convex structure are convex portions having openings of the continuous bubbles.
(3) The polyolefin resin foam sheet according to (1) or (2), wherein the one surface has a skin layer in which bubbles other than the opening are not exposed.
(4) A method for producing a polyolefin resin foam sheet in which a resin composition containing a polyolefin resin is extruded and foam-molded, an uneven structure is formed on the surface thereof, and an opening is provided in the protrusion.

  In the present invention, the sound absorption characteristic means a normal incidence sound absorption coefficient measured based on JIS A 1405.

  According to the present invention, it is possible to provide a polyolefin resin foam sheet having excellent sound absorption characteristics and a method for producing the same.

FIG. 1 is a schematic cross-sectional view showing a cross section of a preferred embodiment of the polyolefin resin foam sheet of the present invention. FIG. 2 is a graph showing the sound absorption characteristics of the polyolefin resin foam sheets produced in Examples and Comparative Examples.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings as appropriate, but the present invention is not limited thereto.

As shown in FIG. 1, a preferred polyolefin resin foam sheet (hereinafter sometimes referred to as a foam sheet) 1 of the present invention is preferably composed of a single layer made of the same material. As a result, the mass and cost of the sound-absorbing material can be reduced as compared with a laminated sheet or a thick sheet generally used as a sound-absorbing material having excellent sound-absorbing characteristics, and the moldability is also improved. improves.
Here, the same material refers to a material containing the same polyolefin resin, and includes materials having different types and compositions (contents) of additives.
A circle B in FIG. 1 is a schematic enlarged cross-sectional view showing a cross-sectional portion b of the foamed sheet 1 in an enlarged manner, but the cross-sectional portion b is also in the foamed state similarly shown in the circle B.

Both surfaces of the surface layer of the foam sheet 1 are skin layers 2 in which bubbles are not exposed. Here, the bubble is not exposed means that the surface does not have a bubble opening, and the convex portion has a bubble opening other than the continuous bubble 5 described later on the surface. Means no. By using the skin layer 2 with no air bubbles exposed as the surface layer, the skin layer 2 is excellent in terms of strength, sound diffusion and blocking inside the material.
In the present invention, the skin layer 2 includes both the surface-side skin layer 2a having a concavo-convex structure and the surface-side skin layer 2b opposite to the skin layer 2a unless otherwise specified. The skin layers 2a and 2b are the same except that the shapes are different.
In addition, it is clear that the strength of the foam sheet 1 is excellent because the non-foamed skin layer 2 covers both surfaces of the foam sheet 1.

The foam sheet 1 has continuous bubbles 5 as indicated by a circle B in FIG.
In the present invention, the continuous bubble 5 refers to a bubble in which adjacent bubbles are continuous with each other at the joint. That is, each bubble in the foam sheet 1 does not exist as a closed cell, but is connected to an adjacent bubble to form a continuous bubble 5, thereby forming a long cavity like a maze. In the foam sheet 1 as a whole, the ratio of the continuous bubbles 5 to the total bubbles (open cell ratio) is 50% or more. The ratio of continuous bubbles 5 is preferably 50 to 90%, more preferably 60 to 80%. In the present invention, the open cell ratio is defined to be measured by the method described in Examples described later.
When the open cell ratio is 50% or more, the foam sheet 1 has a porous structure in which a long cavity is formed like a maze, and the maze degree of the propagation path of the solid propagation sound of the incident sound wave and the propagation path of the air propagation sound is increased. Characteristics can be improved. If the open cell ratio is too low, the sound absorption characteristics of the foamed sheet 1 may be reduced. In addition, when too high, there exists a possibility that the moldability and rigidity at the time of compression of the foam sheet 1 may fall.

Although the bubble diameter of the continuous bubble 5 is not specifically limited, Specifically, about 100-600 micrometers is preferable. In the present invention, the bubble diameter is calculated by the following formula using the bubble area average value S obtained by dividing the total bubble area by the number of bubbles in the observed cross section of the polyolefin resin foam sheet 1.
Bubble diameter = 2 × √ (S / π)

If the foamed sheet 1 has a concavo-convex structure on at least one surface, the sound absorption characteristics can be further enhanced as described later.
In the foam sheet 1, one surface (skin layer 2a side) has an uneven structure, and the other surface (skin layer 2b side) has a flat structure.

The concavo-convex structure 7 only needs to be composed of convex portions 7a and concave portions 7b. The concavo-convex pattern or the like of the concavo-convex structure is not particularly limited, but in the foamed sheet 1, it is preferable that the convex portions 7a and the concave portions 7b are alternately arranged in one direction, and the convex portions 7a in two directions orthogonal to each other. More preferably, the recesses 7b are arranged alternately and repeatedly. Examples of such a concavo-convex structure pattern include various repetitive patterns such as a wavy pattern and a lattice pattern (including a houndstooth pattern).
Moreover, the shape of each of the convex portion 7a and the concave portion 7b is not particularly limited. For example, the shape of the convex portion 7a when viewed in plan includes a polygon such as a quadrangle and a hexagon, a circle, an ellipse, and a line. Further, examples of the shape when the convex portion 7a is viewed from the side include a rectangle (columnar shape) such as a square and a rectangle, a cone shape, a frustum shape, and a semicircular shape.
Further, the interval (pitch) between the concave portion 7b and the convex portion 7a is not particularly limited. For example, 0.1-10 mm is preferable and, as for the space | interval of the convex part 7a adjacent to an arrangement direction, 0.5-5 mm is more preferable.

In the concavo-convex structure, the height of the convex portion 7a is not particularly limited, and is preferably 10 to 2000 μm and particularly preferably 200 to 1000 μm in terms of sound absorption characteristics.
When the foamed sheet 1 has the skin layer 2a, the concavo-convex structure 7 is preferably composed of a convex portion 7a and a concave portion 7b that have a height difference equal to or higher than the thickness of the skin layer 2a. In the concavo-convex structure 7, “a height difference equal to or greater than the thickness of the skin layer 2 a” means that the height of the convex portion 7 a when the surface of the concave portion 7 b is the reference plane is the same as the thickness of the skin layer 2 a It is higher than the thickness of 2a.

The height difference is not uniquely determined by the thickness of the skin layer 2a to be formed, but is preferably 10 μm or more, for example. More preferably, it is 10-2000 micrometers, Most preferably, it is 200-1000 micrometers.
This height difference can also be set as appropriate by means for forming the opening 5a of the continuous bubble 5. For example, when a needle roller is used, 500 to 2000 μm is preferable, and 500 to 1000 μm is particularly preferable.

In the foam sheet 1, the continuous bubbles 5 are opened in all or a part of the convex portions 7 a having a concavo-convex structure. This opening 5 a is normally formed in the skin layer 2.
The opening diameter of the continuous bubble 5 is not particularly limited, and can be selected according to the sound (frequency) incident on the continuous bubble 5 of the foam sheet 1. For example, 100-5000 micrometers is preferable and 500-2000 micrometers is more preferable. In this way, by adjusting the size of the opening diameter in accordance with the sound (frequency) to be absorbed, a more excellent sound absorption characteristic is obtained.

The convex part 7a in which the continuous bubbles 5 open may be a part of the convex part 7a forming the concave-convex structure (for example, 10% or more with respect to the total number of the convex parts 7a). It is preferable that it is the whole convex part 7a.
In addition, the number of openings 5a included in one convex portion 7a may be one or plural. Preferably one.
As described above, it is preferable that the foam sheet 1 has a concavo-convex structure in which at least one surface has the skin layer 2a. Moreover, it has the continuous bubble 5 inside, and this continuous bubble 5 is opening to the convex part 7a of the uneven structure. Due to this opening, the foam sheet 1 has a structure in which the internal continuous bubbles 5 and the external space of the foam sheet 1 have air permeability through the opening 5a.

  Thereby, for example, when the foam sheet 1 is used for an automobile part as described later, for example, noise generated from the engine or the like is drawn into the foam sheet 1 from the incident surface 1a, and the low frequency sound region is within the continuous bubble. 5 can be appropriately diffused. In addition, since the sound transmission path is long like a labyrinth from the incident surface 1a to the other surface (outgoing surface) 1b, the high frequency sound range is also efficiently diffused inside the sheet 1 Can be converted into energy. As a result, the sound absorption efficiency can be increased in a wide frequency range.

  In addition, when the opening 5a is provided in the convex portion 7a of the concavo-convex structure formed on the sound incident surface 1a, particularly good sound absorption characteristics are exhibited with respect to the sound entering from the sound incident surface. Although the details are not yet clear, if the surface of the foam sheet 1 has a concavo-convex structure, the structure of the continuous bubble 5 becomes more complicated, so the sound transmission path becomes a more complicated labyrinth structure. it is conceivable that. Moreover, since the load when forming the opening 5a can be reduced by forming the opening 5a intermittently rather than on the entire surface of the foam sheet 1, the labyrinth structure of the sound transmission path in the continuous bubble 5 can be reduced. This is thought to be because it becomes difficult to be destroyed by an excessive load.

  Thus, the foam sheet 1 can enhance the sound absorption characteristics (sound absorption efficiency) in a wide frequency range.

  In the present invention, the concavo-convex structure may be provided on at least one surface (incident surface 1a side) of the foam sheet 1, but does not require a sound blocking function, and the sound absorption characteristics of both surfaces of the polyolefin resin foam sheet are emphasized. In this case, it is possible to provide a concavo-convex structure on both surfaces of the polyolefin resin foam sheet (incident surface 1a side and outgoing surface 1b side). In this case, it is possible to provide an opening of continuous bubbles in at least a part of the convex portion.

The apparent density of the expanded sheet 1 is preferably in the 600 kg / ^{m 3} or less, 180~450kg / ^{m 3} and more preferably. If the apparent density is too high, the sound absorption characteristics may be deteriorated. On the other hand, if it is too low, the moldability may be reduced. By making the apparent density within the above range, it is possible to achieve both moldability and sound absorption characteristics at a higher level. The apparent density is a value measured according to JIS K 7222: 2005.

The foam sheet 1 preferably has a normal incidence sound absorption coefficient of 0.5 or more at a measurement frequency of 0.5 to 6.4 kHz, more preferably 0.6 or more, and further preferably 0.75 or more.
For example, an electric vehicle has a noise of a motor sound or an inverter sound in the vicinity of 6 kHz. If the foam sheet 1 is formed into a desired shape and applied to a dash insulator for an automobile, the sound absorbing material has high sound absorption characteristics and is rigid. be able to.
Here, the normal incident sound absorption coefficient is a numerical value measured based on JIS A 1405.

Although the thickness (total thickness) of the foam sheet 1 is not particularly limited, it is usually 1.0 mm or more, and preferably 2 to 5 mm.
Moreover, when it has the skin layer 2, the thickness of the skin layer 2 is although it does not specifically limit, Usually, it is 1 micrometer or more, Preferably it is 10-50 micrometers.

The foam sheet 1 is formed of a polyolefin resin.
The polyolefin resin is not particularly limited as long as it is a resin composed of an α-olefin homopolymer or copolymer. For example, low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, linear Ultra-low density polyethylene, ethylene-propylene block copolymer, ethylene-propylene random copolymer, ethylene-butene block copolymer, ethylene-butene random copolymer, ethylene-vinyl acetate copolymer, ethylene-methyl methacrylate Copolymer, ethylene-methacrylic acid copolymer ionomer-based resin crosslinked with metal ions, propylene homopolymer, propylene-ethylene random copolymer, propylene-butene random copolymer, propylene-ethylene block copolymer Polymer, propylene Butene block copolymer, polybutene, polypentene, propylene - ethylene - butene terpolymer, a propylene - acrylic acid copolymer, propylene - co-maleic anhydride polymers, and the like. Moreover, these can be used alone or in combination of two or more.

Among these, polypropylene resins are preferably used from the viewpoints of recyclability, moldability, heat resistance, actual performance, etc.
From the viewpoint of obtaining good cold shock resistance, it is preferable to include high-density polyethylene. In the case where the foamed sheet 1 contains high-density polyethylene, the content is preferably 50 to 99.9% by mass, and more preferably 95 to 99% by mass.

Moreover, it is preferable that the foam sheet 1 contains a propylene-ethylene block copolymer. As a result, the foamability of the resulting foamed sheet is improved, and the melting temperature at the time of extrusion becomes relatively low. Thus, viscoelasticity suitable for foaming is developed over a wide temperature range, and as a result, a good foamed structure can be easily formed. Can be formed.
This block copolymer preferably has a melt index of 1.9 or less.
In the foam sheet 1, the content of the block copolymer is preferably 15 to 70% by mass.

Moreover, when using the foam sheet 1 in low temperature environments, such as -30 degreeC, it is preferable that a high density polyethylene is included as a main component. The impact resistance in the low temperature environment of the foam sheet 1 obtained by including a high density polyethylene as a main component can be improved.
Here, containing as a main component means that the content is 50-99.9 mass%.

The foamed sheet 1 may contain a polyolefin resin and a thermoplastic resin other than the thermoplastic elastomer described later as long as the effects of the present invention are not impaired.
As used herein, “other thermoplastic resin” means a resin that does not contain halogen, such as polystyrene, polymethyl methacrylate, acrylic resin such as styrene-acrylic acid copolymer, styrene-butadiene copolymer, polyvinyl acetate, polyvinyl Alcohol, polyvinyl acetal, polyvinyl pyrrolidone, petroleum resin, cellulose, cellulose acetate, cellulose nitrate, methyl cellulose, hydroxymethyl cellulose, hydroxymethyl cellulose, hydroxypropyl cellulose, and other cellulose derivatives, saturated alkyl polyester resins, polyethylene terephthalate, polybutylene terephthalate, polyarytate Group polyester resin, polyamide resin, polyacetal resin, polycarbonate resin, polyester sulfone resin, poly E double sulfide resin, polyether ketone resin, and a copolymer having a vinyl polymerizable monomer and nitrogen-containing vinyl monomers.
One type of thermoplastic resin other than these polyolefin resins may be contained, or a plurality of types may be contained. The type and content are selected according to the desired physical properties.

The foam sheet 1 may contain a cell nucleating agent for refining the cells as necessary. As the cell nucleating agent, inorganic fine particles such as talc, calcium carbonate, titanium oxide, and barium sulfate, heat-decomposable organic cell nucleating agent, thermoplastic elastomer, and melt-type crystallization nucleating agent can be used. It is not limited to.
The content of the cell nucleating agent in the foamed sheet 1 is preferably 0.1 to 30 parts by mass with respect to 100 parts by mass of the polyolefin resin.

  In addition to the cell nucleating agent, the foam sheet 1 can be used within the range that does not impair the spirit of the present invention, and, if necessary, a crystallization accelerator, an antioxidant, an antistatic agent, an ultraviolet ray inhibitor, a light stabilizer, a fluorescent agent. Brighteners, pigments, dyes, compatibilizers, lubricants, reinforcing agents, flame retardants, crosslinking aids, plasticizers, thickeners, thickeners, thermal stabilizers, processing aids, impact modifiers, fillers You may have various additives, such as.

The foam sheet 1 preferably includes a fibrous material. By containing a fibrous material, weight reduction and cold impact resistance can be improved. Moreover, the fibrous material does not affect the foamability.
Examples of fibrous materials include polyamide fibers, polyvinyl alcohol fibers, cellulosic semi-synthetic fibers, cellulosic recycled fibers, acrylic fibers, polyester fibers, polyurethane fibers, polyvinyl chloride fibers, polyvinylidene chloride fibers, aramid fibers, polyarylate. Fiber, polyimide fiber, polyparaphenylene benzobisoxazole fiber, polyphenylene sulfide fiber, polyethylene fiber, polypropylene fiber, fluorine fiber, carbon fiber, polycarbonate fiber, glass fiber, epoxy fiber, phenol fiber and melamine fiber, etc. These 1 type (s) or 2 or more types can be used.
Among these, glass fiber is particularly preferable because it can maintain a high foaming rate and high rigidity.
Although the content rate of the fibrous material in the foamed sheet 1 is not specifically limited, It is preferable to set it as 15 mass% or less at the point which can maintain a higher foaming rate, and it may be 1-14.9 mass%. More preferably, it is more preferably 5 to 14.8% by mass, and still more preferably 10 to 14.5% by mass.

The material for forming the foamed sheet 1 may contain a foaming agent for forming bubbles in addition to the above components.
The foaming agent is classified into a solid compound that decomposes to generate a gas, a liquid that vaporizes when heated, an inert gas that can be dissolved in a resin under pressure, and any of these can be used.
Among these, as solid compounds, for example, azodicarbonamide, dinitrosopentamethylenetetramine, hydrazole dicarbonamide, sodium bicarbonate, p, p′-oxybisbenzenesulfonylhydrazide (OBSH), N, N′-dinitrosopentamethylene Examples thereof include tetramine (DPT), p-toluenesulfonyl hydrazide, benzenesulfonyl hydrazide, diazoaminobenzene, N, N′-dimethyl-N, N′-dinitroterephthalamide, and azobisisobutyronitrile.
Examples of the liquid to be vaporized include saturated aliphatic hydrocarbons such as propane, n-butane, isobutane, n-pentane, isopentane, and hexane, aromatic hydrocarbons such as benzene, xylene, and toluene, methyl chloride, and chlorofluorocarbon. And halogenated hydrocarbons such as dimethyl ether and ether compounds such as methyl tert-butyl ether.
Examples of the inert gas include an inert gas such as carbon dioxide, nitrogen, helium, and argon, and alternative chlorofluorocarbon.
Among these, carbon dioxide (carbon dioxide) is preferable in consideration of solubility in polyolefin resin and ease of microbubble formation.

Next, the manufacturing method of the foam sheet 1 is demonstrated.
Although the foaming method is not particularly limited, an extrusion foam molding method in which a resin composition containing a polyolefin resin and, if desired, the above-described various additives and a foaming agent is subjected to extrusion foam molding is preferable.
In the extrusion foam molding method, for example, a sheet extruded through a die lip attached to an extruder is immediately and smoothly formed without being crushed by a molding roll die, and then expanded and then the extruded product is cooled by a cooling roll. And the method of setting it as the polyolefin resin foam sheet precursor is mentioned.
In the extrusion foam molding method, the skin layer 2 is formed on both surfaces by a molding roll die and a cooling roll.
The polyolefin resin foamed sheet precursor may be produced by preparing an extruded sheet in advance and simultaneously performing a crosslinking reaction and foaming on the sheet.

Next, the concavo-convex structure 7 is formed on at least one surface of the prepared polyolefin resin foam sheet precursor, and the opening 5a is provided in the convex portion 7a.
The uneven structure 7 can be formed by an embossing roll. Furthermore, when the embossing roll is used as a forming roll immediately after the extrusion die, the transferability of the embossing pattern is further improved.

  In order to provide the opening 5a in the convex portion 7a, for example, a method of piercing the needle of a needle roll into the convex portion 7a of the concave-convex structure 7 transferred to one surface of the polyolefin resin foamed sheet precursor using an embossing roll can be mentioned. . Thereby, the foam sheet 1 can be manufactured.

When using an embossing roll and a needle roll, the position of the convex part 7a of the concavo-convex structure 7 transferred by the embossing roll and the position of the needle erected on the needle roll are appropriately synchronized with each other. Are preferably overlapped (matched).
In the present invention, the opening 5a is not necessarily provided only in the convex portion 7a. For example, a needle roll may be manufactured so that a plurality of, for example, three openings 5a are formed for one convex portion a. For example, even when the rotation of the embossing roll and the needle roll is out of synchronization, the opening 5a is easily formed in the convex portion 7a.
The needle roll may be a hot needle roll that applies heat to the tip of the needle.

  The polyolefin resin foam sheet precursor has a concavo-convex structure on the surface where the needle pierces, and pierces the protrusion 7a. At this time, if the surface has a concavo-convex structure, the load when piercing the convex portion 7a can be reduced as compared with the case where the surface is flat. In particular, when piercing the concave portion 7b, only the concave portion 7b is pierced after the convex portion 7a is pierced, so that the load can be made smaller than when the convex portion 7a and the concave portion 7b are pierced simultaneously. Thereby, the continuous bubble 5 becomes difficult to be destroyed by an excessive load, and the sound absorption characteristic is improved.

  In the method for forming a concavo-convex structure, an embossing roll formed by forming an embossing pattern on a forming roll die can be used.

  The uneven structure can also be formed using an extrusion die in which a plurality of groove structures are formed. The concavo-convex structure formed by the extrusion die formed with a plurality of groove structures is formed into a structure having concavo-convex in a direction perpendicular to the extrusion direction, which is composed of a plurality of groove shapes formed in parallel to the extrusion direction. After forming the concavo-convex structure thus formed, the foamed sheet 1 can be manufactured by providing the opening 5a in the convex portion as described above.

The foam sheet 1 is used without any particular limitation as long as it is used for sound absorption characteristics.
The foam sheet 1 is excellent in sound absorption characteristics, preferably lightweight and high in strength, and is preferably formed into a desired shape and applied to a sound absorbing material for automobiles. Examples of sound absorbing materials include engine undercovers, floor undercovers, dash outer insulators, dash insulators, dash panels, bonnet insulators, roof insulators, floor insulators, rear wheel house insulators, rear tray insulators, high damping mel seats, mel sheet sandwich panels, etc. Is mentioned. More specifically, the foam sheet 1 is attached to the automobile body so that the incident surface 1a faces the noise source side such as the engine.
In particular, the present invention is preferably applied to a sound absorbing material of an electric vehicle, for example, a dash insulator used by being attached to a dash panel. Thereby, it can suppress that the noise of an engine room propagates to a driver's cab.

  Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

(Example 1)
The foam sheet 1 shown in FIG. 1 was prepared as follows.
Pellets of polypropylene resin (Nippon Polypro, Novatec PP FY6H (trade name), melt index 1.9) are supplied to the hopper, a 1360 mm wide sheet die is used, and a 40 mm outer diameter forming roll die is attached to the tip of the lip. The distance between the roll and the line where the roll contacts the sheet was 6.0 mm, and extrusion foam molding was performed to obtain a polyolefin resin foam sheet precursor having a thickness of 3 mm and a width of 1375 mm. The resulting polyolefin resin foam sheet precursor had an expansion ratio of 4 times.
This polyolefin resin foamed sheet precursor had skin layers 2 (thickness 15 μm) having no air bubbles formed on both surfaces thereof. The bubble diameter was 380 μm.

The foamed sheet 1 was manufactured by transferring the concavo-convex structure 7 to one surface of the polyolefin resin foamed sheet precursor using an embossing roll and providing the opening 5a in the convex part 7a of the concavo-convex structure 7 using a needle roll. .
Specifically, a 3.5 mm pitch lattice pattern was transferred to one surface of the polyolefin resin foam sheet precursor using an embossing roll having a 3.5 mm pitch lattice pattern. In the polyolefin resin foam sheet precursor, the height difference of the concavo-convex structure 7 was 0.5 mm. Next, using a needle roll (not heated) in which needles are implanted in a lattice pattern with a pitch of 3.5 mm, the needle is pierced until the skin layer 2a penetrates the convex portion 7b, and the opening 5a (opening diameter 1.. 2 mm).

(Comparative Example 1)
In Example 1, a polyolefin resin foam sheet was manufactured by forming openings on the flat surface of the polyolefin resin foam sheet precursor with a needle roll without forming the uneven structure 7. The opening pattern was the same as in Example 1.

  About the polyolefin resin foam sheet manufactured in Example 1 and Comparative Example 1, physical properties were evaluated by the following methods.

(Apparent density)
The apparent density was measured according to JIS K 7222: 2005.
The polyolefin resin foam sheet of Example 1 had an apparent density of 230 kg / m ³ .
The polyolefin resin foam sheet of Comparative Example 1 also had an apparent density of 230 kg / m ³ .

(Open cell ratio)
The open cell rate (communication rate) was specified by the following formula using a value measured using an air-comparing hydrometer 1000 type (manufactured by Tokyo Science) according to the method described in ASTM D-2856-87.
Open cell ratio (%) = (apparent volume−volume measured with an air-based hydrometer) / apparent volume × 100
The apparent volume was calculated from the outer dimensions of the polyolefin resin foam sheet.
The polyolefin resin foam sheet of Example 1 had a communication rate of 63%.
The polyolefin resin foam sheet of Comparative Example 1 had a communication rate of 63%.

(Normal incidence sound absorption coefficient)
The normal incident sound absorption coefficient was measured at a normal incident sound absorption coefficient based on JIS A 1405. Sound absorption characteristics were obtained by making a cylindrical sample with a diameter of 29 mm punched from each polyolefin resin foam sheet by a dumbbell punching machine, and using a multi-channel analysis system SR-4100 manufactured by Ono Sokki Co., Ltd. (analysis was DS-2100). ) Using the B tube, the sound absorption coefficient at 500 Hz to 6.4 kHz was measured for each sample by the 2-microphone method.
A graph of the obtained sound absorption coefficient is shown in FIG. In FIG. 2, the sound absorption coefficient of the polyolefin resin foam sheet produced in Example 1 is indicated by a solid line, and the sound absorption coefficient of the polyolefin resin foam sheet produced in Comparative Example 1 is indicated by a broken line.
As shown in FIG. 2, the polyolefin resin foam sheet of Example 1 exhibited a characteristic that the sound absorption coefficient exceeded 0.8 particularly in a high sound range including 5 to 7 kHz. On the other hand, the polyolefin resin foam sheet of Comparative Example 1 exhibited a characteristic that the sound absorption coefficient was less than 0.7 particularly in a high sound range including 5 to 7 kHz.

DESCRIPTION OF SYMBOLS 1 Foam sheet 1a Incident surface 1b Outgoing surface 2, 2a, 2b Skin layer 5 Continuous bubble 5a Opening part 7 Uneven structure 7a Convex part 7b Concave part

Claims (4)

A polyolefin resin foam sheet having open cells with an open cell ratio of 50% or more, an apparent density of 600 kg / m ³ or less,
A polyolefin resin foam sheet having a concavo-convex structure in which at least one surface includes a bulge having an opening of the continuous cell.   2. The polyolefin resin foam sheet according to claim 1, wherein all or a part of the convex portions of the concave-convex structure are convex portions having openings of the continuous bubbles.   The polyolefin resin foam sheet according to claim 1 or 2, wherein the one surface has a skin layer in which bubbles are not exposed except for the opening. A method for producing a polyolefin resin foam sheet, comprising subjecting a resin composition containing a polyolefin resin to extrusion foam molding, forming a concavo-convex structure on a surface thereof, and providing an opening in a convex portion.

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