JP6554432B2 - Shock absorber - Google Patents

Description

The present invention relates to a slow衝材.

Conventionally, fences are erected around sports stadiums such as baseball stadiums and athletic stadiums to prevent balls and other equipment from jumping out of the stadium.
As the fence, a shock absorbing fence is widely used to attach a shock absorbing structure unit to a fence main body to prevent injury when the player collides with excessive force (Patent Document 1).
As a buffer structure unit to be mounted on the fence body of the buffer fence, a shock absorber and a surface sheet covering the buffer material are known, and a sponge having a thickness of several tens of centimeters is used as the buffer material. The thing using the shape-like soft resin foam is known.
Such relatively large cushioning materials are used not only for sports purposes but also for conveying goods, etc., and are also used for protecting not only people but also devices and arts and crafts. Yes.

Japanese Patent Laid-Open No. 10-165557

The shape of the cushioning material varies widely depending on the object to be protected and the place of use.
As a resin foam used for such a buffer material, an extrusion foam molded body extruded in a board shape using a sizing die, a bead foam molded body produced by in-mold molding of foamable resin beads, etc. It has been known.
Among them, bead foam molded articles are suitable for use as cushioning materials in that they are easy to manufacture even if the product shape is relatively complicated.
However, in the case of bead foam molded articles, resin beads are likely to be compressed near the molding surface of the mold, and resin beads near the surface are likely to be crushed. It is hard to say that it is excellent.

From such a thing, it is possible to adhere a thing like a sponge sheet | seat to the surface of a bead foam molded body, to composite foam, and to improve buffer property.
However, such a composite foam may cause a sudden repulsive force when the compressive force of the object to be protected reaches the interface between the sponge sheet and the bead foam molded body, and has a large push-up feeling against impact. There is a risk of becoming a thing.
Then, this invention makes it a subject to provide the composite foam excellent in the buffering property, using a bead foam molded object, and also to provide the buffer material excellent in a buffer and easy to manufacture.

In order to solve the above-mentioned problems, the present invention is a cushioning material having a composite foam comprising two or more resin foams that are used in the impact absorption of an object to be protected and laminated in a direction to which the impact is applied. Of the two or more resin foams of the composite foam, the resin foam far from the protection target is a bead foam molded body made of a thermoplastic resin, and the resin foam near the protection target is It is a foamed sheet made of a thermoplastic resin, and the foamed sheet is composed of only a single foamed layer, or has a laminated complementary structure in which a polymer film is laminated on a sheet of a foamed layer single layer. And adhere to the surface of the bead foam to form the surface of the composite foam, and the foam layer is adhered to the bead foam , and the composite foam is the bead foam. The adhesive interface between the molded body and the foamed sheet is Has a melting Chakumen, the foam surface hardness of the sheet is lower than the surface hardness of the expanded bead molded article, the beads expanded molded, expanded beads constituting the adhesion interface protrudes,該Happo beads The present invention provides a cushioning material in which the foam sheet bites into the foam sheet to form asperities at the adhesive interface, and the average height of the projections of the asperities is 0.2 mm or more.

In the composite foam of the present invention, a foam sheet having a surface hardness lower than that of the bead foam is heat-fused to the surface of the bead foam.
Therefore, the composite foam can exhibit excellent cushioning properties by the foam sheet.
Further, in the composite foam of the present invention, the foam beads constituting the bonding interface between the bead foam molded body and the foam sheet are protruded to form an unevenness.
Therefore, according to the present invention, it is possible to reduce the rebound resilience on the surface of the bead foam molded body as compared with the case where the foam beads are crushed in the surface layer portion.
For example, in the composite foam of the present invention, when the compressive force of the object to be protected is applied to the interface between the foam sheet and the bead foam molded body, first, only the convex portion of the bead foam molded body is compressed, A compressive force may be applied to the entire bead foam molded body.
Therefore, the composite foam of the present invention can gradually improve the repulsive force when the compressive force of the protection object reaches the interface.
That is, according to the present invention, it is possible to suppress that the composite foam rapidly increases the repulsive force at the time of impact absorption by the unevenness of the surface of the bead foam molded body, and the composite foam suitable for use as a buffer material A body can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic perspective view which showed an example of the shock absorbing structure unit which concerns on one Embodiment. The schematic sectional drawing which showed the internal structure of the buffer structure unit. The expanded sectional view which expanded and showed a part of FIG. 2 typically. Schematic which showed the shaping | molding die used for manufacture of a composite foam. Schematic which showed the manufacture procedure of composite foam. The schematic perspective view which showed typically the method of evaluating the buffering property of a composite foam. The figure (graph) which shows the evaluation result of the buffer property of a composite foam.

Embodiments of the present invention will be described below.
In the following, the case where the composite foam is used as a cushioning material of the cushioning structure unit will be described as an example with reference to the drawings.
FIG. 1 is a schematic perspective view of a buffer structure unit in which the composite foam of the present embodiment is used, and FIGS. 2 and 3 are schematic cross-sectional views of the buffer structure unit.
As shown in these drawings, the buffer structure unit 1 has a rectangular plate shape, has a sheet-like surface material 10, and has a rectangular plate shape slightly smaller than the buffer structure unit 1 inside the surface material 10. A cushioning material 20 is included.

  As said surface material 10 in this embodiment, polymer sheets, such as fiber sheets, such as a fabric, a polyvinyl chloride sheet and a rubber sheet, etc. are mentioned, for example.

The cushioning material in the present embodiment has two types of foaming: a rectangular plate-shaped bead foam molded body 21 that is slightly thinner than the cushioning material, and a foam sheet 22 bonded to the entire surface of the bead foam molded body 21. It is a composite foam constituted by a body.
The bead foam molded body 21 and the foam sheet 22 in the present embodiment are both made of a thermoplastic resin.
The bead foam molded body 21 and the foam sheet 22 are bonded by heat fusion, and are bonded without using an adhesive.
That is, in the composite foam used as the cushioning material, the foam sheet 22 is bonded to the surface of the bead foam molded body 21, and the adhesive interface between the foam sheet 22 and the bead foam molded body 21 is thermally fused. It is the landing side.

In the present embodiment, it is important that the hardness of the surface 22 x of the foam sheet 22 is lower than the hardness of the surface 21 x of the bead foam molded body 21.
Therefore, the foam sheet 22 of the present embodiment is a foam sheet composed of only a single foam layer, but may be provided with a plurality of foam layers instead of this, and if necessary, the foam sheet. 22 may be a laminated foam sheet of a foam layer and a non-foam layer.
That is, the foamed sheet of the present embodiment may be, for example, a laminated foamed sheet obtained by laminating a soft polymer film imparted with designability by a design or the like and a foam layer single layer sheet.
The "surface hardness" of the foam sheet or bead foam molded body in the present specification means Asker C hardness described later.

In addition, it is important that in the bead foam molded body 21, the foam beads constituting the surface 21x are in a state of being individually projected on the surface.
That is, the bead foam molding 21 has irregularities formed on the surface 21x, and the irregularities of the irregularities bite into the foam layer 22a of the foam sheet 22 at the adhesive interface.
Moreover, as for the said bead foam molded body 21, the average height of the said convex part is 0.2 mm or more. The average height of the convex portions is preferably 1 mm or more.

The “average height of convex portions” referred to here is obtained as follows.
First, the bead foam molded body 21 is cut so that a cross section as schematically shown in FIG. 3 appears.
In addition, cutting of the bead foam molded body 21 is performed so as to be as perpendicular as possible to the bonding interface with the foam sheet, and care is taken so that the foam bead is not deformed as much as possible.
And one foam bead (for example, code | symbol B1 of FIG. 3) is chosen at random from the foam beads which form the adhesion interface with the foam sheet 22. FIG.
Next, one expanded bead B2 (hereinafter, “second bead B2”) of the two expanded beads forming an adhesive interface on both sides of the expanded bead B1 (hereinafter also referred to as “first bead B1”). And the other foam beads B3 (hereinafter, also referred to as "third beads B3") are observed.
Then, the point P1 closest to the foamed sheet (hereinafter also referred to as “first point P1”) is specified among the places where the first bead B1 and the second bead B2 are in contact with the cell membrane.
That is, the separation starting point of the bubble membrane of the first bead B1 and the second bead B2 on the surface 21x of the bead foam molded body 21 is specified.
Similarly, the point P2 closest to the foamed sheet (hereinafter also referred to as “second point P2”) is identified among the places where the first bead B1 and the third bead B3 are in contact with the cell membrane.
Then, the height H (vertical height with respect to the imaginary line L1) at which the first bead B1 protrudes is obtained from the imaginary line L1 connecting the second point P2 and the first point P1.
The operation for obtaining the protrusion height H is performed on approximately 100 foam beads, and the average height of the protrusions of the bead foam molded body 21 is obtained by arithmetically averaging all the obtained protrusion height values. .
In order to obtain the protrusion height H, the cross section of the bead foam molded body is photographed using a scanning electron microscope (SEM) or an optical microscope, and is enlarged approximately 25 times the actual size. This can be done based on the image.

The bead foam molded body 21 is advantageous in that a higher “average height of the convex portion” is exerted to exert a strong adhesive force with the foam sheet 22.
On the other hand, when the “average height of convex portions” of the bead foam molded body 21 is excessively high, the surface 22 bx of the resin film layer 22 b may be uneven and the appearance of the surface may be impaired.
Therefore, the average height of the convex portions is usually equal to or less than the average thickness of the foamed sheet 22.
In addition, when the expansion ratio of the foam sheet 22 is "e times", it is difficult to compress the foam sheet 22 to "1 / e" or less of the current thickness.
Therefore, when the thickness of the foam sheet 22 is “t (mm)”, it is difficult to compress the foam sheet 22 thinner than “t / e (mm)”.
In other words, it is difficult to reduce the thickness of the foam sheet 22 to “t−t / e (mm)” or more.
For this reason, the “average height of the protrusions” is preferably “t−t / e (mm)” or less.
Further, the “average height of the convex portion” is preferably 5% or more of the average cell diameter of the expanded beads.

The thickness of the foam sheet 22 can be determined as follows.
First, the composite foam is cut and the cross section is observed in the same manner as the above-mentioned “average height of convex portions”.
And one foam bead (for example, code | symbol B4 of FIG. 3) is chosen at random out of the foam beads which form the adhesion interface with the foam sheet 22. FIG.
Of the interfaces between the foam sheet and the foam beads B4 (hereinafter also referred to as “fourth beads B4”), the top position TL closest to the foam sheet surface 22x and the most distant from the foam sheet surface 22x. The bottom position BL is specified.
Then, a distance T1 from an imaginary line L2 passing through an intermediate point between the top position TL and the bottom position BL to the surface 22x of the foamed sheet can be obtained, and this distance can be set as the thickness of the foamed sheet 22 at the location. .
In addition, the average thickness of the foam sheet 22 is obtained by performing an operation for obtaining the thickness (T1) at a plurality of locations in the same manner as the above-mentioned “average height of the convex portion” and arithmetically averaging all the obtained values. Desired.

In addition, the average cell diameter of the foam beads is determined as an average value of the major axes of the foam beads forming the adhesive interface.
That is, the cross-section of the composite foam is observed in the same way as the “average height of the convex portion” and “thickness of the foam sheet”, and the longest line segment connecting two different points on the contour line of the foam bead. The lengths of the line segments (for example, the symbols R1 and R2 in FIG. 3) which become longer can be determined, and the lengths can be averaged to obtain an average bubble diameter.

In the composite foam of this embodiment, the expansion ratio of the bead foam molded body 21 is 30 times or more, and the average foam magnification of the bead foam molded body 21 and the foam sheet 22 is 10 times or more. It is preferable.
In the composite foam of the present embodiment, the Asker C hardness of the surface in contact with the surface material 10 is preferably 50 or less, and the Asker C hardness of the surface of the foam sheet 22 is preferably 50 or less.
The expansion ratio of the bead foam molding 21 or the foam sheet 22 and the average expansion ratio of the composite foam (average expansion ratio between the bead foam molding and the foam sheet) are usually obtained by dividing the true density by the apparent density. be able to.
For the true density, non-foamed test pieces produced by heat-pressing the bead foam molded body 21, the foam sheet 22, and the composite foam are subjected to “Method A (underwater substitution method) defined in JIS K7112: 1999. ) "Based on the measurement.
Further, the apparent density of the bead foam molded body 21, the foam sheet 22, and the composite foam can be measured based on JIS K7222: 2005.
Further, the Asker C hardness can be measured using a commercially available Asker C hardness meter, and the measurement is performed on the surface 22x of the foam sheet of the composite foam in a standard state (for example, 25 ° C., 50% RH). It can be obtained as an instantaneous value when performed.
In addition, “true density”, “apparent density”, and “Asker C hardness” are also obtained as an average value of measured values at a plurality of locations in the same manner as “average height of protrusions” and “average thickness”.

The apparent density of the bead foam molded body 21 is preferably in the range of 10 to 50 kg / m ³ from the viewpoint of strength, light weight, heat insulation, and the like of the bead foam molded body 21 and is preferably 15 to 40 kg / m. more preferably in the range of m ^3, and particularly preferably in the range of 25~35kg / ^{m 3.}

  The bead foam molding 21 may be formed of a polyolefin resin, a polystyrene resin, a polyester resin, a polycarbonate resin, or the like.

  Examples of the polyolefin resin include polyethylene resin, polypropylene resin, ethylene-α-olefin copolymer resin, and ethylene-vinyl acetate copolymer resin.

Examples of the polystyrene resin include homopolymers of styrene monomers (for example, GPPS (styrene homopolymer)) and copolymers. Examples of the styrene monomers include styrene, Examples include methyl styrene and ethyl styrene.
Examples of monomers other than the styrene monomer constituting the copolymer include methacrylic acid esters such as methyl methacrylate, acrylic acid esters, acrylic acid, methacrylic acid, acrylonitrile, maleic anhydride, and the like. .
The styrene resin may be high impact polystyrene (HIPS) containing a rubber component such as butadiene rubber.

Examples of the polyester resin include polyethylene terephthalate resin, polybutylene terephthalate resin, polyethylene naphthalate resin, and polylactic acid resin.
The polyester resin may be a modified product containing two or more kinds of diols or two or more dicarboxylic acids.

  As the polycarbonate-based resin, those formed from carbonic acid and glycol or bisphenol can be employed. For example, 2,2-bis (4-oxyphenyl) propane (bisphenol A), 2,2-bis (4 -Oxyphenyl) butane, 1,1-bis (4-oxyphenyl) cyclohexane, 1,1-bis (4-oxyphenyl) isobutane, 1,1-bis (4-oxyphenyl) ethane, etc. Aromatic polycarbonate resins are mentioned.

The foam sheet 22 adhered to the bead foam molded body 21 formed of such a resin preferably has an apparent density in the range of 15 to 70 kg / m ³ .
(Equivalent to 15 to 70 times)
Apparent density of the foamed sheet 22 is more preferably in the range of 30~55kg / ^{m 3,} and particularly preferably in the range of 25~50kg / ^{m 3.}
(Equivalent to 20 to 40 times)
The thickness of the foam sheet 22 is preferably 1.0 mm or more, more preferably in the range of 1.5 to 7.0 mm, and particularly preferably in the range of 3.0 to 5.0 mm. .

In consideration of recycling and the like, it is preferable that the composite foam can be recycled without separating the foam sheet 22 and the bead foam molded body 21 from each other.
From such a meaning, it is preferable that the foamed sheet 22 contains the same kind of thermoplastic resin as the resin contained in the bead foam molded body 21.
Further, in view of the thermal fusion bondability between the foam sheet 22 and the bead foam molded body 21, the same kind of thermoplastic resin as the resin contained in the bead foam molded body 21 corresponds to the bead foam molded body 21. It is preferable that it is contained more in the part which forms the adhesion interface.
As resin which the said foam sheet 22 and the said bead foam molded body 21 contain in common, it is preferable that it is polyolefin resin.
That is, it is preferable that the composite foam of this embodiment is entirely formed of a polyolefin resin, and from the viewpoint of buffer property, the polyolefin resin is a crosslinked foam or an olefin thermoplastic elastomer-containing foam. It is more preferable.

As the bead foam molded body 21, for example, one produced by a general manufacturing method can be adopted, and one produced by in-mold molding of foamable resin beads can be adopted.
The expandable resin beads used for in-mold molding may be in a substantially non-foamed state containing a foaming agent, or may be a pre-expanded one of the non-foamed resin beads.

In addition, as the foam sheet 22, the resin exemplified for the bead foam molded body 21 is melt-kneaded by an extruder together with a foaming agent, and the obtained melt-kneaded product is extruded and foamed from a circular die or a flat die attached to the extruder. What is obtained is preferable.
When the foam sheet 22 has a multilayer structure, it can be produced by a coextrusion method, an extrusion lamination method, a thermal lamination method, or the like.

The foaming agent to be used for the foamable resin beads and the foaming agent for producing the foamed sheet are not particularly limited, and those conventionally used may be mentioned.
Specifically, examples of the blowing agent include aliphatic hydrocarbons such as propane, i-butane, n-butane, i-pentane, and n-pentane, N ₂ , CO ₂ , water, and alcohols.

  In addition, although detailed description regarding the formation material of a composite foam is not repeated any more here, various additives (being added to the general resin molded product (bead foam molded body 21 or foam sheet 22) ( Weathering agents, antibacterial agents, flame retardants, pigments, fillers, termiticides, fungicides and the like may be suitably contained.

The composite foam of this embodiment can be produced by, for example, the following methods (1) to (3).
(1) The foam sheet 22 and the foamable resin beads are accommodated in a mold for producing the bead foam molded body 21, and the foamable resin beads are heated to thermally fuse the foamable resin beads. The bead foam molded body 21 and the foamed sheet 22 are heat-sealed while forming the bead foam molded body 21.
(2) The foamed sheet 22 and the bead foam molded body 21 are separately prepared in advance, and then the bead foam molded body 21 and the foamed sheet are heated by heating at least one surface of the bead foam molded body 21 and the foamed sheet 22. A method of heat-sealing by bringing them into pressure contact with heat-sealable state after putting them into heat-sealable state.
(3) The melt-kneaded product is extruded and foamed to produce a foamed sheet, and the foamed sheet extruded from the extruder is covered with a prefabricated bead foam molded product before it is completely cooled. A method of heat-welding by pressure welding.

The composite foam of the present embodiment exhibits irregularities by forming irregularities on the surface of the bead foam molded body 21 and causing the convex portions of the irregularities to bite into the foam sheet 22, and exhibits excellent buffer property as well as the bead foam molded body 21. And strong adhesiveness between the foam sheet 22 and the foamed sheet 22.
Therefore, in the above methods (1) and (2), it is preferable to heat and soften the foam sheet prior to heat fusion with the bead foam molded body.
Moreover, in said (1), since the expansion force of an expandable resin bead can be utilized as a pressure for making a convex part bite into a foam sheet, as a method of producing the composite foam of this embodiment, The method shown in (1) is preferred.

A further preferred method for producing this composite foam will be described. The composite foam of this embodiment is, for example, a mold in which a foamable resin bead made of a thermoplastic resin is molded in a mold to produce a bead foam molded body It can implement using the shaping | molding apparatus provided with, and can implement and manufacture following process (a)-(c) in order using this shaping | molding apparatus.
(A) A housing step of housing the foamed sheet made of thermoplastic resin and the foamable resin beads in the mold and bringing the foamed sheet into contact with the molding surface of the mold.
(B) A preheating step of heating and softening the foamed sheet.
(C) A heating medium such as superheated steam is introduced into the mold to foam the expandable resin beads, and a bead foam molded body is formed by the foamable resin beads, and the bead foam molded body and the foam sheet are heated. A molding process for fusing.
In addition, the composite foam obtained by heat-sealing the bead foam molded article and the foam sheet in the molding step can be taken out of the mold, for example, by cooling the entire mold.

As the molding die, for example, one shown in FIG. 4 can be employed.
The mold 100 according to the present embodiment includes a male and female mold (female mold 110, male mold 120) configured in pairs in the top and bottom in FIG. 4 front view, and the foam in the molding space CV formed in the mold. And a filling machine 130 for filling the functional resin beads.
The male and female molds are configured to form a rectangular plate-shaped molding space CV corresponding to the shape of the composite foam inside.

In the present embodiment, the mold 100 has a female mold 110 at the upper side in FIG. 4 and a male mold 120 at the lower side, and the female mold 110 includes the composite foam. A rectangular plate formed integrally with the female top wall portion 111 so as to extend downward from the outer peripheral edge of the lower surface of the female top wall portion 111 and a plate shaped female top wall portion 111 which is also somewhat large. A frame-shaped female side wall portion 112 is provided.
The male mold 120 is provided with a male top wall portion 121 having a planar shape corresponding to an opening shape on the lower end side of the female side wall portion 112 of the female mold 110 on the upper surface side.
That is, the molding die 100 has a molding surface formed by the surfaces of the male top wall 121, the female top wall 111, and the female side wall 112, and the female mold 110 and the male mold 120 are closed. Sometimes these define the forming space CV.

Although not shown, in each of the female top wall portion 111 and the female side wall portion 112, a plurality of through holes having a shape preventing penetration of the foamable resin beads are provided as a plurality of steam flow holes. It is formed in the place.
On the other hand, no steam flow hole is formed in the male top wall portion 121, and the surface is flat.
The molding die 100 in this embodiment introduces superheated steam having a gauge pressure of about 0.05 MPa to 0.1 MPa into the molding space through the steam circulation holes, and directly contacts the superheated steam with the foamable resin beads. The foamable resin beads are formed so that they can be fused together.
Further, as described above, although the steam flow holes are not formed in the male top wall portion 121, the molding die 100 in the present embodiment introduces the superheated steam to the lower surface side of the male top wall portion 121 It forms so that the type | mold top wall part 121 can be heated.

  The filling machine 130 for introducing the expandable resin beads into the molding space includes a filling gun that penetrates the female top wall 111 so that the expandable resin beads can be supplied to the molding space CV from above. It has become.

The method for producing a composite foam using this mold will be described more specifically with reference to FIG. 5 as follows.
(A) Open the mold, place the foam sheet 22 ′ cut into the size of the male top wall 121 into contact with the upper surface of the male top wall 121, and close the mold.
(Ii) The expandable resin particles 21 'are supplied from the filling gun to the extra space on the foam sheet to fill the inside of the molding space with the expandable resin particles. At this time, the female mold 110 and the male mold 120 are not completely closed, and the capacity is 105% to 120% when the capacity of the molding space in the completely closed state is 100%. It is preferable that the foamed resin particles are filled with a little extra and then clamped to keep the foamed sheet 22 'pressed by the foamable resin particles 21' from the upper surface side. By doing this, it is possible to make the biting of the convex portion of the bead foam molded body into the foam sheet good.
(C) Next, the foam sheet 22 'is heated through the male top wall portion 121 to sufficiently soften the foam sheet 22', and then superheated steam is introduced into the forming space from the steam flow holes of the female die 110. The expandable resin particles 21 ′ are expanded in volume and the expandable resin particles 21 ′ are thermally fused to each other to form a bead foam, and the bead foam and the foam sheet are thermally fused. When the main component of the foamed sheet is a crystalline polymer having a melting point of “Tm (° C.)”, the foamed sheet is heated at a surface temperature of the foamed sheet of (Tm-50) ° C. or higher, (Tm-5) ° C. It is preferable to carry out the following. In the case where the main component of the foam sheet is an amorphous polymer having a glass transition point of “Tg (° C.)”, the foam sheet is heated so that the surface temperature of the foam sheet is (Tg−50) ° C. or more (Tg -5) It is preferable to carry out so that it will be below ℃. The melting point and the glass transition point can be determined by the DSC method (heating rate 10 ° C./min) according to JIS K 7121: 1987, and the glass transition point is determined as a midpoint glass transition temperature of the standard. Can do.

In the heat fusion between the bead foam molded body and the foamed sheet, the foamed sheet on the surface of the bead foam molded body is unlikely to be crushed because the foamed sheet is sufficiently softened.
Therefore, the bead foam molded body after forming the composite foam with the foam sheet has a milder impact resilience than the bead foam molded body formed only by the foamable resin beads alone.
And the uneven | corrugated shape in the heat sealing | fusion with the bead foam molding and foam seat | sheet which are formed at this time is also effective in exhibiting the buffer property excellent in the composite foam.
In the present embodiment, since the male top wall portion 121 is flat, the surface of the composite foam is also smooth and beautiful.
Then, in order to further improve the appearance of the composite foam, for example, a metal plate which is mirror-finished and has a smoothness better than that of the male top wall portion is separately prepared, and the operation of (i) above Alternatively, a metal plate may be interposed between the male top wall portion and the foam sheet to form a male molding surface with the metal plate.

As described above, the composite foam of this embodiment is not only excellent in buffering properties by forming irregularities on the surface of the bead foam molded body 21 and biting the irregularities on the foam sheet 22. Thus, the bead foam molded body 21 and the foam sheet 22 exhibit strong adhesiveness.
Therefore, a recess may be formed in advance on one side of the foam sheet prior to heat fusion to the bead foam molded body.
That is, in the method for producing a composite foam according to the present embodiment, the foam sheet 22 before heat fusing at least one of the plurality of point-like pressing marks and the plurality of linear pressing marks to the bead foam molded body 21 is performed. A preforming step for forming on one side is further carried out, and in the molding step, the surface on which the foam sheet pressing marks are formed is heat-sealed to the bead foam molded body, thereby causing the protrusions to bite into the foam sheet. It is preferable to promote.
The pressing marks can be provided on the foam sheet by performing thermoforming to press the foam sheet in a dot shape or a linear shape.
When providing linear press marks, the press marks need not be aligned in one direction, and may be provided on the foam sheet in a lattice shape, for example.
Moreover, the linear press mark does not need to be linear, and may be curved.
Furthermore, there is no need to unify the size and shape of the point-like pressing roots and linear pressing marks formed in one foam sheet, and there are a plurality of types having different sizes and shapes, or a plurality of different thicknesses and lengths. It may be of a kind.

If the press mark provided on the foamed sheet is a dot, the size can usually be 3 to 5 mm.
Moreover, if a press mark is linear, the thickness can usually be 3-5 mm.
In addition, the size of a point-like pressing mark means the diameter of the circle which has the same area, and the thickness of a linear pressing mark means the value which remove | divided the area by the length.
When providing a press mark in a foam sheet, it is preferable that the area ratio shall be about 30% (for example, 20 to 40%).

The composite foam thus obtained is suitable as a component of the buffer structure unit 1 of the present embodiment because of its excellent buffer property.
The cushioning structure unit 1 can be manufactured by using the composite foam as it is or by processing it into a cushioning material and covering the cushioning material with the surface material 10.
In addition, in this embodiment, although the buffer structure unit of a specific shape is illustrated regarding the use of a composite foam, the use of the composite foam of this invention is not limited to such a thing.
The composite foam of the present invention can be used other than the buffer structure unit.
Furthermore, the composite foam of the present invention can be variously modified without being limited to the above examples.

  EXAMPLES Next, although an Example is given and this invention is demonstrated in more detail, this invention is not limited to these.

(Preparation of composite foam)
A composite foam was produced using a foam sheet and a bead foam as shown in Table 1.
In addition, the foam sheet used the foam layer independent thing and the thing provided with the foam layer and the resin film layer.
Here, except for Comparative Examples 2 and 4, the foam sheet and the bead foam molded body were integrated by a mold to make a composite foam, but in Comparative Example 2, the foam sheet and the bead foam molded body were simply attached It produced by putting together.
In Comparative Example 4, a bead foam molded body was used alone.
The thickness, expansion ratio and the like of the foam sheet and the bead foam molding are as shown in Table 1.
About the formation material of a foam sheet, it is as having shown the symbol in Table 1.
The meanings of the abbreviations are as follows.

PS: Styrene homopolymer (GPPS)
LDPE: low density polyethylene resin PP / TPO: composite resin obtained by melt-kneading polypropylene resin and olefinic thermoplastic elastomer

Further, the forming material of the bead foam molded body is as shown in Table 1 by abbreviations.
The meanings of the abbreviations are as follows.

PS: Styrene homopolymer (GPPS)
· EVA / PS: composite resin obtained by polymerizing styrene monomer after absorbing styrene monomer to ethylene-vinyl acetate copolymer resin (EVA) particles · PP / PS: modification by grafting styrene monomer Polypropylene resin

The conditions for producing a composite foam from this foam sheet and bead foam are also as shown in Table 1.
In addition, using a mold as shown in FIG. 4 and FIG. 5, a flat composite foam having a size of 300 mm long, 400 mm wide and a total thickness of 30 mm was produced.
At the time of molding, the foam sheet and the foamable resin beads accommodated in the mold were divided into three stages and heated, and then, as shown in Table 1, a cooling time of 90 seconds to 240 seconds was provided.
The abbreviations for the first to third three-stage heating methods shown in Table 1 have the following meanings.

A: Heating from the foam sheet side (the lower side in the example of FIG. 5). However, the mold itself was heated because there was no steam flow hole in the mold.
B: Heating from the opposite side to the above A (upper side in the example of FIG. 5). Superheated steam was introduced into the mold through the steam flow hole.
AB: Both heating by A and heating by B are performed.
A: Heating from the same direction as A above. However, using a mold having a vapor circulation hole, superheated steam was introduced through the vapor circulation hole into the mold containing only the expandable resin beads not containing the foam sheet.
B: Heating from the opposite direction to a. However, superheated steam was introduced into the mold through the steam flow hole.
Ab: Both the heating by a and the heating by b are performed.

  Here, as shown in Table 1, the superheated steam used for in-mold molding had a vapor pressure (gauge pressure) of 0.07 MPa (about 115 ° C.) to 0.27 MPa (about 140 ° C.).

With respect to the prepared composite foam, the buffer property was measured by the Asker C hardness on the front surface (foamed sheet front surface) and the back surface (bead foam molded body rear surface), and the spot compression test shown in FIG.
Moreover, cross-sectional observation was implemented with respect to the composite foam, and the average height of the convex part of the unevenness | corrugation in the adhesion interface of a bead foam molding and a foam sheet was calculated | required.

The buffer property of the composite foam was measured as follows.
First, a measurement sample S having a flat rectangular plate shape having a thickness of 60 mm in length and width and the total thickness of the composite foam (“30 mm” in Example 1) was cut out from the obtained composite foam.
A jig PB having a cylindrical protrusion P1 with a diameter of 30 mm is attached to a crosshead (not shown) of the Tentilon universal testing machine via a load cell (not shown), and approximately horizontal below the jig PB. A support base FB having a top surface was set.
The jig PB was mounted below the crosshead so that the protruding direction of the protrusion P1 was downward.
The measurement sample S was mounted on the support base FB such that the surface S1 on the foam sheet side was on the top side.
The support base FB on which the measurement sample S is mounted is positioned such that the protrusion P1 abuts on the center position of the measurement sample S when the crosshead is lowered.
The cross head was lowered, and the jig FB set above the measurement sample S was lowered at a speed of 1 mm / min.
The crosshead was lowered at the same speed even after the protrusion P1 contacted the upper surface of the measurement sample S, and the repulsive stress applied from the measurement sample S to the jig FB was measured with a load cell.

Test equipment: Tensilon universal testing machine UCT-10T (made by ORIENTEC Co., Ltd.)
Sample: 60 (width) x 60 (length) x 30 (total thickness) (unit: mm)
Pressurized surface size: Center location of sample Diameter 30mm
Test direction: Pressurization from the surface of the foam sheet of the composite foam Test speed: 1 mm / min
Test piece condition adjustment / test environment: 23 ± 2 ° C, RH50 ± 5%, more than 24 hours

The following items were evaluated regarding the cushioning properties of the composite foam.
In addition, about the evaluation result, it determined on the basis as shown below.

<Evaluation criteria for buffer property>
Evaluation was carried out using Example 1 and Comparative Examples 2 to 4.

<Stress-displacement curve>
A comparative plot of stress versus compressive displacement of the sample was made (see FIG. 7).

<Stress reduction>
From the stress-displacement curve, the following evaluation was made. ◎: Initial stress rise (elastic modulus) is low, and a decrease in stress due to the formation of irregularities on the adhesive interface is observed. ○: Initial stress rise (elastic modulus) is low. ×: Initial stress rise (elastic modulus) is high

<Restorability>
○: In the compression displacement corresponding to the thickness of the foam sheet, almost no surface unevenness after the compression release occurs. Δ: Some surface unevenness after the compression release occurs slightly. ×: The surface unevenness after the compression release is remarkable.

<Peeling resistance>
○: Interfacial peeling from the non-compressed part did not occur during the compression test ×: Interfacial peeling from the non-compressed part occurred during the compression test

  Further, the appearance and heat sealability of the composite foam were evaluated by the following methods, and were determined as follows.

<Appearance criteria>
The appearance of the surface formed by the foam sheet of the obtained flat plate-like composite foam was visually observed.
The result of visual observation was determined based on the following evaluation.

Evaluation A: “Yes” or “No” irregularities caused by the foam foam
Evaluation B: Heat scorch (wrinkles, dents) of the foam sheet by steam “Available”, “None”

○: A and B were both absent Δ: A was not present but B was present ×: A was present The results are shown in Table 1.
In addition, since it is only a bead foam about the comparative example 4, evaluation is excluded.

<Heat fusion test criteria>
A cut line was made on the surface of the obtained flat composite foam.
The score line was formed so as to cross the longitudinal center of the composite foam.
That is, a cut line was made along a straight line connecting the centers of a pair of long sides.
The score line was formed to a depth of about 5 mm using a cutter knife.
Then, the composite foam in which this score line was formed was folded by hand and divided into two.
Then, a range in which the number of foam beads is 100 to 150 is randomly selected in the fracture surface of the bead foam molded body portion of the composite foam divided into two, and the foam beads themselves are fractured within the range The number (a) and the number (b) broken at the interface between the foam beads were counted.
The internal fusion rate was calculated based on the following formula from the numbers of (a) and (b).

Internal fusion rate (%) = (a) / [(a) + (b)] × 100 (%)

Based on the internal fusion rate calculated as described above, evaluation was performed according to the following criteria.
○: Fusion rate 80% or more Δ: Fusion rate 50% or more and less than 80% ×: Fusion rate less than 50%

In addition, a cutting line with a depth of about 5 mm was inserted into the bisected composite foam along the interface between the foam sheet and the bead foam molded article with a cutter knife.
Thereafter, the foamed sheet was peeled from the composite foam along the score line.
The foam sheet was peeled off by hand.
Then, a range in which the number of foamed beads is 100 to 150 is randomly selected on the surface (peeling surface) of the bead foam molded article after the foamed sheet is peeled off, and the foamed beads themselves are broken in the range The number (c1) and the number (c2) in which a part of the foamed layer of the foamed sheet adhered to the surface of the foamed beads were counted, and the total value (c) (= c1 + c2) was obtained.
Moreover, in the said range, the number (d) of foam beads which are not fractured and the adhesion of a foam sheet is not observed (number of foam beads exposed on the peeled surface) was counted.
The interface fusion rate was calculated based on the following formula from the numbers of (c) and (d).

Interfacial fusion rate (%) = (c) / [(c) + (d)] × 100 (%)

Based on the interfacial fusion rate calculated as described above, the following criteria were used for evaluation.
○: Fusion rate 70% or more Δ: Fusion rate 40% or more and less than 70% ×: Fusion rate less than 40%

And heat fusion property of a composite foam was judged on the basis of the following standards based on each evaluation of an internal fusion rate and an interface fusion rate.
◎: Internal fusion rate ○ and interfacial fusion rate ○
○: Internal fusion rate ○ and interfacial fusion rate Δ
Δ: Internal adhesion ratio Δ, and interface adhesion ratio Δ to ○
X: Internal fusion rate x or interface fusion rate x

The results are shown in Table 1.
Comparative Example 2 was prepared by simply bonding a foam sheet and a bead foam molded body. Since Comparative Example 4 is only a bead foam, the table shows the internal fusion rate of the bead foam. Only in parentheses.
The results are shown in Table 1.
Moreover, the stress-displacement curve of the spot compression test is shown in FIG.

  From the above evaluation results, it can be seen that according to the present invention, a cushioning material having excellent cushioning properties can be obtained.

DESCRIPTION OF SYMBOLS 1 Buffer structure unit 10 Surface material 20 Buffer material 21 Bead foam molding 22 Foam sheet

Claims (4)

A cushioning material comprising a composite foam comprising two or more resin foams used for impact absorption of an object to be protected and laminated in a direction in which the impact is applied,
Among the two or more resin foams of the composite foam, the resin foam far from the object to be protected is a bead foam molded article made of thermoplastic resin, and the resin foam on the side near the object to be protected is thermoplastic It is a foam sheet made of resin,
The foam sheet is bonded to the surface of the bead foam as either a single foam layer only or has a laminated structure in which a polymer film is laminated on a foam layer single layer sheet. Forming a surface of the composite foam, and the foam layer is adhered to the bead foam molded body ,
The composite foam, the adhesive interface of expanded bead molded article and said foam sheet has a heat Chakumen, surface hardness of the foam sheet is lower than the surface hardness of the expanded bead molded article,
The beads expanded molded article, the average height of the expanded beads constituting the adhesion interface protrudes, and irregularities are formed in the bonding interface bites該Happo beads to the foam sheet, the convex portion of the concavo-convex The shock absorbing material is 0.2 mm or more. The foam expansion ratio of the bead foam molding is 30 times or more, the average foaming ratio between the bead foam molding and the foam sheet is 10 times or more, and the Asker C hardness of the surface of the foam sheet is 50 or less. The shock absorbing material according to item 1. The buffer material according to claim 1 or 2, wherein the foamed sheet contains a thermoplastic resin of the same type as the resin contained in the bead foam molded body. The buffer material according to claim 3, wherein the thermoplastic resin contained in both of the bead foam and the foam sheet is a polyolefin resin.