JPH10235671A - Polyolefin resin multi-layer foam and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyolefin resin multi-layer foam that has a wide cushioning width and which can be used for cushion materials, wrapping and packaging materials, cases, mats or the like, various types of covers and footgears. SOLUTION: This foam comprises a foam layer B in which a mean value P of the degree of orientation of a cell for individual cells ranges 2.5 to 4.5, the individual cells being expressed by a cell diameter in a direction normal relative to upper and lower surface of the foam that are parallel to each other/a cell diameter in a direction normal to a thickness direction of the foam, and a foam layer A having a mean degree of orientation of a cell Q which is smaller than P in a range of 0.5 to 3.5. In this case, the foam layer A is laminated on one or both sides of the foam layer B so as to be integral therewith with no interface interposed between the foam layers A and B.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyolefin resin multilayer foam having a wide cushioning width and usable for cushioning materials, packaging materials, cases, mats, various covers, footwear and the like, and a method for producing the same. is there.

[0002]

2. Description of the Related Art It is known that characteristics of a foam such as strength, cushioning property, heat insulation and light weight are usually influenced by factors such as raw material, specific gravity, thickness and cell independence of the foam. It is common for the characteristics of the foam to be tailored to suit the intended use. by the way,
In order to combine the characteristics of such foams and expand the range of applications, a method of laminating and integrating foams having different characteristics has been generally and widely employed. As a feature of the above-mentioned multilayer foam, the bubble shape contained in each foamed layer is spherical, and the laminating method is as follows: lamination with an adhesive, heat fusion, or JP-A-6-344362. As can be seen, there is known a method in which a foamable raw material is supplied into a molding die in which a base material is previously set and foamed. Also, a method of obtaining a multi-layer foamed molded body by stacking foamable materials of the same type mixed with the same amount of a foaming agent in a mold, and then foaming any foamed material at a similar expansion coefficient, has been used. Better known.

[0003]

As described above, in the conventional multilayer foam, the bubbles contained in each foam layer are spherical, and there has been a limit in diversifying the characteristics of the foam. In addition, in the conventional laminating method, there is a problem that a lamination interface exists, and if the interfacial bonding strength is insufficient, there is a problem that the laminating interface is peeled off at the time of use. Therefore, a material is not selected in consideration of the interfacial bonding strength. Not be. Also, according to the conventional method, an extra lamination step is required,
Problems such as reduced productivity and increased processing costs occur.
Further, in the method of foaming the two types of foamable materials at the same expansion rate, the characteristic difference between the foamed layers of the obtained foam is poor, and in some cases, the foam may be rough at the joint interface. Also.

[0004]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the present inventor has found that by combining and laminating foam layers having a specific degree of cell orientation, the impact absorption range can be widened, Alternatively, the present inventors have found that diversification of foam characteristics such as a change in compression characteristics depending on the degree of distortion can be realized, and have completed the present invention.

[0005] That is, the present invention relates to "cell diameter in a direction orthogonal to the upper surface and lower surface of a foam parallel to each other (hereinafter referred to as the thickness direction of the foam) / cell diameter in a direction orthogonal to the thickness direction of the foam." The average value (hereinafter referred to as the average bubble orientation degree) P of the individual bubble orientation degrees of the individual bubbles represented by
Foamed layer (B) in the range of ~ 4.5, and 0.
A polyolefin resin multilayer foam comprising a foamed layer (A) having a small average cell orientation degree Q in the range of 5 to 3.5, and the foamed layer (A) is laminated on one side or both sides of the foamed layer (B) The present invention relates to a polyolefin resin multilayer foam which is integrated and has no bonding surface at the interface between the foam layer (A) and the foam layer (B), and a method for producing the same. As a method for producing the present foam, a sheet-like polyolefin resin containing a foaming gas in a pressure-sealed state in an opposing mold openable mold is foamed under reduced pressure by increasing the volume in the mold. In the method for producing a foam expanded only in the thickness direction,
When the foamed layer (A) is laminated and integrated on one side of the foamed layer (B), under the condition that the temperature of one side of the sheet is lower than the temperature of another side of the sheet, the foamed layer (A) is In the case where the sheet is laminated and integrated on both sides, the above-mentioned foaming is started under the condition that the sheet surface layer temperature is lower than the sheet inner layer temperature.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

The foam of the present invention comprises a foam layer (A) and a foam layer (B), and the degree of orientation of the bubbles contained in the foam layer (A) is lower than that of the foam layer (B). It is characterized by the following. The average cell orientation degree P contained in the foamed layer (B) is in the range of 2.5 to 4.5, and when it is less than 2.5, not only the effect of the cell orientation to exhibit characteristics is poor, but also the foamed layer (A) ) Is not easy, and if it exceeds 4.5, the cell wall separating the cells has an extremely elongated and unstable structure, so that the strength of the foam is insufficient and the foam layer has Recoverability is significantly reduced. Further, the average cell orientation degree Q of the foamed layer (A) is smaller than the average cell orientation degree P of the foamed layer (B) in the range of 0.5 to 3.5, and (P−Q) <0.5. In this case, differentiation from the foamed layer (B) is not easy, and the meaning of multilayering is poor. When (P−Q)> 3.5, Q
Since <1, the cells in the foamed layer (A) have a vertically elongated shape in a direction perpendicular to the thickness direction of the foam. However, such bubbles are used in the present invention to foam the resin only in the thickness direction. It cannot be obtained depending on the manufacturing method.

The thickness of the foamed layer (A) and the foamed layer (B) occupied in the multilayer foam in the present invention is not particularly limited, but the characteristics of each foamed layer are well balanced with the foam. In order to reflect, the thickness of the foamed layer (A) is X,
When the thickness of the polyolefin resin multilayer foam is Z,
It is preferable that the following relationship be satisfied.

X = R × Z (R: 0.05-0.4) When P is less than 0.05 in the above formula, the thickness of the foamed layer (A) becomes poor, and the function manifesting effect by multi-layering becomes poor. When it is difficult to obtain and exceeds 0.4, the characteristics of the foamed layer (A) dominate the function of the foam.

The polyolefin resin used in the present invention includes, for example, propylene homopolymer, ethylene-propylene random copolymer, ethylene-propylene block copolymer, propylene-α-olefin copolymer, low-density polyethylene, High density polyethylene,
Examples thereof include polybutene, ethylene-α-olefin copolymer, ethylene-vinyl acetate copolymer, and a mixture obtained by mixing a rubber or a thermoplastic elastomer which can be mixed with these polymers. Examples of the α-olefin include 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, and the like. Examples of the mixable rubber include natural rubber, polybutadiene rubber, and polyisoprene. Rubber, styrene-butadiene copolymer rubber, nitrile rubber, chloroprene rubber, ethylene-
Propylene copolymer rubber and the like can be mentioned, and as the above-mentioned thermoplastic elastomer, generally available ones can be used, and particularly, styrene-based thermoplastic elastomers and polyolefin-based thermoplastic elastomers are preferably used.

A filler may be mixed with the polyolefin resin as long as the object of the present invention is not impaired. The filler may be talc, silica, carbon black, metal powder, glass fiber, carbon fiber, water, or the like. Magnesium oxide, antimony trioxide, zinc borate, bromine compounds, ceramics, zeolites and the like can be used.

In the method for producing a polyolefin resin multilayer foam of the present invention, a pair of concave and convex molds, a flat / concave mold, and the like can be cited as the molds that can be opened facing each other. In these molding dies, the inner surface is parallel to the resin expansion direction, that is, the direction in which the thickness of the foam increases, and the resin containing the foaming gas can expand in the thickness direction along the inner surface of the molding die. A device devised as described above is preferably used. As a method for performing the pressure sealing and depressurization, using a pair of molds provided with a sealing packing or the like on the contact surface, the mold is slid to perform pressure sealing by performing mold clamping, Also, a method of reducing the pressure by opening the mold, a method of performing pressure sealing and decompression by sliding the piston in a pair of molding dies that are closed by contact, or a method of sealing in advance A method of supplying a resin containing a foaming gas into a molding die at a high pressure by a method such as an injection molding method to seal the resin under pressure, and reducing the pressure by opening the mold, and further, foaming in an unsealed molding die A method in which a resin containing gas is filled at a high pressure and the resin is sealed using packing or gas injection, or the like can be used.

The foaming gas in the present invention is a known chemical blowing agent which can be decomposed by heating, for example, azodicarbonamide, N, N'-dinitrosopentamethylenetetramine, 4,4'-oxysbis (benzenesulfonylhydrazide), Gases such as carbon dioxide, nitrogen, carbon monoxide, ammonia, and water vapor generated by decomposing sodium hydrogen carbonate and the like by heating can be given.

Further, in the method for producing a polyolefin resin multilayer foam according to the present invention, it is necessary to make the viscoelasticity of the resin at the time of foaming suitable for the orientation of bubbles, and for that purpose, a known chemical crosslinking agent is used. Preferably, the resin is cross-linked to impart good elongation of bubbles at the time of foaming and elasticity sufficient to suppress foam breakage. Examples of such a chemical crosslinking agent include benzoyl peroxide, 2,5-dimethyl-2,5-di-t-butylperoxyhexane, and 2,5-dimethyl-2,5-di-t-butylperoxyhexane. Organic peroxides such as toxin-3, dicumyl peroxide and t-butylhydroxy peroxide, azide compounds such as 1,9-nonanebissulfonazide, and silane compounds such as vinyltriethoxysilane can be used. . In this case, as a crosslinking aid for promoting crosslinking, for example, triallyl cyanurate, triallyl isocyanurate, trimethylolpropane trimethacrylate, 1,2-polybutadiene, divinylbenzene and the like can be used in combination. Further, in addition to the method using the chemical crosslinking agent, α ray, β ray,
γ-rays, neutron rays, electron beams, a method of irradiating a polyolefin resin with ionizing radiation such as X-rays to perform crosslinking can also be used, and in this case, a crosslinking aid that promotes the crosslinking may be used in combination. preferable.

In the manufacturing method according to the present invention, the sheet-like thermoplastic resin containing the foaming gas is foamed by reducing the pressure by increasing the volume in the mold. Is lower than the inner layer temperature of the sheet, or the above-mentioned foaming is started under the condition that the temperature of one side of the sheet is lower than the temperature of another side of the sheet, whereby a foamed layer having a different degree of cell orientation is formed. .
The multilayer foam according to the present invention has a foam layer having a low degree of cell orientation laminated and integrated on one or both sides of a foam layer having a high degree of cell orientation. In order to obtain a foam laminated on one side of the layer 2, a method is used in which foaming is started under the condition that the temperature of one side of the sheet is lower than the temperature of the other side, and a foamed layer as shown in FIG. In order to obtain a foam in which 1 is laminated on both sides of the foam layer 2, a method is used in which foaming is started under the condition that the sheet surface layer temperature is lower than the sheet inner layer temperature.

A sheet-like molten resin containing a foaming gas in a pressure-sealed state is usually in contact with a molding die or a piston, and a temperature difference is generated between both surfaces of the molding die or the piston in contact with the molten resin. If so, a temperature difference occurs between the two surfaces of the sheet immediately before foaming. The temperature difference causes a viscosity difference in the sheet. By the way, it is known that bubbles expand while expanding the resin in the growth process, and the growth of the bubbles in the thickness direction of the resin layer having a higher viscosity is hindered as compared with the resin layer having a lower viscosity. The foamed layer of the high-viscosity resin layer suppresses the degree of orientation of the bubbles to be lower than that of the foamed layer of the low-viscosity resin layer. As a result, the foam shown in FIG. 1 is obtained.

On the other hand, in order to obtain the foam shown in FIG. 2, as a method for generating a temperature difference in the sheet immediately before foaming as described above, a foaming gas which is usually under a temperature condition higher than the foaming temperature is used. A method in which the molten resin is rapidly cooled to a foaming temperature or lower suitable for orienting the bubbles is used. If both the surface of the molding die and the piston in contact with the molten resin are rapidly cooled, the vicinity of the surface of the sheet-shaped molten resin that comes into contact with the molding die or the piston is cooled accordingly. However, a resin having a lower thermal conductivity than a metal or the like results in the cooling following layer 3 and the cooling non-following layer 4 in FIG. 3 due to the rapid cooling, and as a result, the more cooled resin layer 3 becomes a resin layer. As compared with No. 4, the viscosity is increased.

In the resin layer 3 cooled to a temperature below the foaming temperature suitable for the orientation of the bubbles, the bubbles cannot be oriented and grown sufficiently, while the resin layer 4 is not sufficiently cooled. For this reason, foaming can be performed under a temperature condition suitable for orienting the bubbles.

The temperature difference between the surface temperatures of the mold and the like in contact with the molten resin depends on the thickness of the sheet-like polyolefin resin in the mold, the type of the polyolefin resin, and the average cell orientation of the intended foam. Although it is selected depending on the degree and the like, usually the range of 6 to 15 ° C. is preferable. When the temperature is less than 6 ° C, the average cell orientation difference between the foamed layers is small, and the effect of multilayering is not sufficiently obtained. The viscosity of the contacting resin may be out of the temperature range suitable for foaming, resulting in a foamed layer having poor foamability.

Although the temperature difference existing between the resin layers immediately before foaming as described above cannot be measured exactly, it is probably 5 ° C. to 1 ° C.
It is assumed that the temperature is in the range of about 0 ° C.

(Function) The cell structure contained in the foam layer constituting the polyolefin resin multilayer foam in the present invention forms a structure similar to a honeycomb structure. As described in JP-A-68679, a honeycomb structure has a structure in which cells have a vertically long structure in a thickness direction, and is known to exhibit excellent characteristics in strength, absorption of a large impact, and the like. . On the other hand, it is known that a structure having spherical or nearly spherical cells exhibits excellent properties such as flexibility, recoverability, and relaxation of small impact.
The multilayer foam in the present invention can be compared to a foam in which these two types of structures are combined and laminated and integrated, and can have the functions of the above two types of structures.

As a specific case where the multilayer foam of the present invention works effectively, for example, a foam layer having a small degree of cell orientation is used as a surface layer, and a foam layer having a large degree of cell orientation is used as a buffer material having an inner layer. And that it can respond to a wide range of impacts. The conventional soft foam containing spherical cells elastically deforms and absorbs relatively small impacts, but has a problem that it easily exceeds the deformation limit for large impacts and does not exhibit buffering performance. . In addition, the honeycomb structure effectively absorbs a large impact due to plastic deformation after buckling, but has a problem that it is difficult to exhibit a buffering performance against a small impact and has poor recovery after deformation. . However, in the case using the foam of the present invention, the surface layer effectively buffers small impact, and the inner honeycomb foam layer effectively absorbs a large impact exceeding the deformation limit of the surface layer. is there.
In addition, the surface layer is excellent in recoverability, so that it can be used repeatedly, and since it is flexible, the surface layer has an excellent touch feeling.
Further, by using the honeycomb foam layer as the inner layer, the strength per weight of the foam is improved, and the specific gravity and the thickness of the foam can be reduced.

Further, according to the method for producing a multilayer foam of the present invention, it is not necessary to use different raw materials for forming a multilayer, and it is possible to omit steps such as lamination after molding or heat fusion. The absence of an adhesive interface eliminates the need for consideration of the adhesive strength of the interface and eliminates the problem of peeling.

[0024]

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

The average values P and Q of the degree of bubble orientation of each bubble, which is represented by “the bubble diameter in the thickness direction / the bubble diameter in the direction perpendicular to the thickness direction”, were determined by the following method.

Any part of the cross section of the foam cut in the thickness direction of the foam and a direction orthogonal to the thickness direction is magnified 10 times by an optical microscope (manufactured by Nikon Corporation, product name: SMZ-2T) to obtain an optical image. A photograph is taken by a photographing device connected to the microscope. Then, for all the cells observed in this photograph, the above cell orientation degree is calculated from the numerical values obtained by measuring the cell diameter in the thickness direction of the foam and the cell diameter in the direction perpendicular to the thickness direction of the foam for all the cells observed in this photograph. Then, P and Q were determined by averaging these bubble orientation degrees.

R in Table 1 was determined by dividing the thickness of the foamed layer (A) by the thickness of the foam.

Example 1 Azodicarbonamide (manufactured by Eiwa Kasei Kogyo Co., Ltd., trade name: Vinylol AC) was used as a foaming agent with respect to 100 parts by weight of an ethylene-vinyl acetate copolymer (trade name: Ultracene 540, manufactured by Tosoh Corporation). ^# 1C) 5 parts by weight, 0.35 parts by weight of 2,5-dimethyl-2,5-di-t-butylperoxyhexine-3 (manufactured by NOF CORPORATION, trade name Perhexine 25B-40) as a crosslinking agent Was prepared. The mixture was melt-kneaded with a 50 mmφ extruder and extruded as an unfoamed sheet through a T-die.

Next, the unfoamed sheet was inserted into a mold capable of opening the opposing mold, which was designed so that the contact portion could be sealed with silicone rubber packing, and sealed. Then, the piston was slid in the molding die, and the unfoamed sheet was pressurized at a pressure of 20 kgf / cm ² between the molding die and the piston. Then, the contact surfaces of the molding die and the piston with the unfoamed sheet were maintained at 200 ° C. to decompose the foaming agent and generate gas in the molten resin. Subsequently, the mold surface and the piston surface in contact with the molten resin were cooled, and when the mold surface reached 90 ° C. and the piston surface reached 100 ° C., the piston was opened and the thickness was 25 mm, the expansion ratio was 10 times,
A foam including two types of foam layers without a joint interface was obtained. In these foams, the degree of orientation of the bubbles in the foam layer on the side in contact with the mold surface was smaller than the degree of orientation of the bubbles in contact with the piston face, and the average degree of orientation of these bubbles was determined. The results are shown in Table 1.

In order to know the cushioning effect of the foam obtained as described above, the shock absorption characteristics were examined using a measuring method as shown in FIG.

In FIG. 4, a 50 mm thick steel plate 5
A 50 × 50 × 25 mm foamed test piece 6 is placed on the top, a 480 g cylindrical body 7 is dropped from above, and the vibration acceleration generated on the lower surface of the steel plate 5 after the collision is measured via the charge amplifier 8. FFT (Fast Fourier T
(transformer) analyzer 9. Reference numeral 10 denotes a vibration pickup provided on the lower surface of the steel plate, which plays a role in sensing vibration of the steel plate at the time of a collision with a cylinder. The height at which the columnar body 7 was dropped was 5 to 70 cm above the upper surface of the steel plate.

FIG. 5 shows the relationship between the drop height of the column to be dropped and the vibration acceleration. The vibration acceleration shown here is a value obtained by measuring the acceleration of the vibration generated on the lower surface of the steel plate generated at the time of the collision with the cylinder and taking the maximum value until the vibration is completed. It can be determined that the impact absorbing effect of the plate is high. When an object having a mass m is at a height h, the object is mgh (g is gravitational acceleration).
Therefore, the drop height in the above measurement can be regarded as an index of the magnitude of the impact energy. As a result of the above test, the impact absorption of the foam obtained in Example 1 was good in the range of low impact to high impact.

In order to examine the compression characteristics of the foam, a compression test was performed under the following conditions in accordance with JIS K 6767 (1976), and a stress-strain curve was obtained.

(Test Conditions) Specimen size: 50 mm in length, 50 mm in width, 25 mm in thickness Compression speed: 10 mm / min As a result of the above test, the foam obtained in Example 1 is flexible in an area with little distortion. Show a tendency to elastically deform,
The tendency of plastic deformation was shown by the increase of strain. FIG. 8 shows the results of these compression tests.

Comparative Example 1 In Example 1, molding was performed in the same manner as in Example 1 except that the piston was opened when the mold surface in contact with the resin reached 97 ° C. and the piston surface reached 100 ° C. Thickness 25
mm, a foaming ratio of 10 times, and a foam including two types of foamed layers having no joint interface were obtained. In these foams, the degree of cell orientation of the foam layer on the side in contact with the mold surface was smaller than the degree of cell orientation of the foam layer in contact with the piston face. It is larger than the degree of cell orientation of the foamed layer on the mold side of the obtained foam. Table 1 shows the results of determining the average degree of orientation of these cells.

As a result of examining the impact absorption characteristics in the same manner as in Example 1, the absorption in the low impact region was insufficient. FIG. 5 shows the results of the shock absorption test.

Further, the compression characteristics of the obtained foam were examined by the same measuring method as in Example 1.
The foam obtained by the method showed plastic deformation even in a region with little distortion in which the foam showed elastic deformation tendency.
FIG. 8 shows the results of these compression tests.

Comparative Example 2 Example 7 was repeated except that 7 parts by weight of azodicarbonamide was added as a foaming agent and the piston was opened when the mold surface in contact with the resin reached 90 ° C. and the piston surface reached 105 ° C. Molding is performed in the same manner as in Example 1, and the thickness is 25 m
m, a foaming ratio of 12 times, and a foam containing two types of foamed layers having no joint interface were obtained. In these foams, the degree of cell orientation of the foam layer in contact with the piston face was larger than the degree of cell orientation of the foam layer in contact with the mold side,
Compared to the bubble orientation of the foam layer on the piston side of the foam obtained in Example 1, it is large, and the results of determining the average orientation of these bubbles are shown in Table 1.

As a result of examining the impact absorption characteristics in the same manner as in Example 1, the absorption in the high impact region was insufficient. FIG. 5 shows the results of the shock absorption test.

The compression properties of the obtained foam were examined by the same measuring method as in Example 1.
The foam obtained by the method showed plastic deformation even in a region with little distortion in which the foam showed elastic deformation tendency.
FIG. 8 shows the results of these compression tests.

Comparative Example 3 In Example 1, the mold surface in contact with the resin was 100 ° C.
Molding was performed in the same manner as in Example 1 except that the piston was opened when the piston surface reached 100 ° C., and the thickness was 25 m.
m, a single-layer foam having an expansion ratio of 10 times was obtained. Table 1 shows the average cell orientation degree of the obtained foam.

As a result of examining the impact absorption characteristics in the same manner as in Example 1, the absorption in the low impact region was insufficient. FIG. 5 shows the results of the shock absorption test.

The compression properties of the obtained foam were examined by the same measuring method as in Example 1.
The foam obtained by the method showed plastic deformation even in a region with little distortion in which the foam showed elastic deformation tendency.
FIG. 8 shows the results of these compression tests.

Comparative Example 4 A molding was performed in the same manner as in Example 1 except that the piston was opened when the molding surface in contact with the resin reached 80 ° C. and the piston side reached 85 ° C.
m, a foaming ratio of 6 times, and a foam including two types of foamed layers having no joint interface were obtained. In these foams, the degree of cell orientation of the foam layer in contact with the piston surface was larger than the degree of cell orientation of the foam layer in contact with the mold, but was obtained in Example 1. It is smaller than the degree of cell orientation of the foam layer on the piston side of the foam. Table 1 shows the results of determining the average degree of orientation of these cells.

As a result of examining the impact absorption characteristics in the same manner as in Example 1, the absorption in the low to high impact region was insufficient. FIG. 5 shows the results of the shock absorption test.

The compression property of the obtained foam was examined by the same measuring method as in Example 1, and as a result, the foam was poor in flexibility. FIG. 8 shows the results of these compression tests. Example 2 5 parts by weight of azodicarbonamide (manufactured by Eiwa Kasei Kogyo Co., Ltd., trade name: Vinylol AC ^# 1C) as a foaming agent, based on 100 parts by weight of high-density polyethylene (manufactured by Tosoh Corporation, trade name: Nipolon Hard 4010), crosslinked A mixture comprising 0.4 parts by weight of 2,5-dimethyl-2,5-di-t-butylperoxyhexine-3 (manufactured by NOF CORPORATION, trade name: Perhexine 25B-40) as an agent was prepared, It was extruded as an unfoamed sheet through a T-die as in Example 1.

Next, the unfoamed sheet was inserted into a mold capable of opening the opposing mold, which was designed so that the contact portion could be sealed with silicone rubber packing, and sealed. Then, the piston is slid in the mold, and the unfoamed sheet is pressurized at a pressure of 20 kgf / cm ² between the mold and the piston. The contact surface was maintained at 200 ° C. to decompose the foaming agent and generate gas in the molten resin. Subsequently, the mold surface and the piston surface in contact with the molten resin are cooled at a rate of 30 ° C./min.
When the temperature reaches ℃, the piston is released and the thickness is 25m
m, a foam having an expansion ratio of 10 times was obtained. The obtained foam has a sandwich structure in which two types of foam layers having no bonding interface are formed, and the degree of orientation of the bubbles contained in the foam layer on the surface layer which was in contact with the mold surface and the piston surface is reduced to the foam layer located in the inner layer. It is smaller than the degree of orientation of the contained bubbles, and Table 1 shows the results of determining the average degree of orientation of these bubbles.

As a result of examining the compression characteristics of the obtained foam by the same measuring method as in Example 1, the foam showed a tendency to deform flexibly and elastically in a region with little distortion, and a tendency to plastically deform due to an increase in distortion. showed that. FIG. 6 shows the results of these compression tests.

Further, as a result of examining the impact absorption characteristics in the same manner as in Example 1, the impact absorption of the foam was good in the range of low impact to high impact. FIG. 7 shows the results of the shock absorption test.

Comparative Example 5 In Example 2, the mold surface and the piston surface in contact with the molten resin were cooled at a rate of 30 ° C./min, and after the mold surface and the piston surface in contact with the resin reached 120 ° C. Molding was carried out under the same conditions as in Example 2 except that the piston was opened after holding the temperature for one minute, and the thickness was 25 mm and the expansion ratio was 1
A 0-fold foam was obtained. The obtained foam was a single-layer foam, and the average degree of orientation of the cells is shown in Table 2.

As a result of examining the compression characteristics of the obtained foam by the same measuring method as in Example 1, the foam obtained in Example 2 showed a plastic deformation even in a region where elastic deformation was observed and the strain was small. It showed a typical deformation. FIG. 6 shows the results of these compression tests.

Further, as a result of examining the impact absorption characteristics in the same manner as in Example 1, the absorption in the low impact region was insufficient. FIG. 7 shows the results of the shock absorption test.

COMPARATIVE EXAMPLE 6 In Example 2, the mold surface and the piston surface in contact with the molten resin were cooled at a rate of 5 ° C./min. Molding was performed under the same conditions as in Example 2 except that
A foam having a thickness of 25 mm and an expansion ratio of 10 was obtained. The obtained foam has a sandwich structure in which two types of foam layers having no bonding interface have a sandwich structure, and the degree of orientation of bubbles contained in the foam layer on the surface layer which has been in contact with the mold surface and the piston surface is the foam layer located in the inner layer. Although it was smaller than the degree of orientation of the bubbles contained in, the degree of orientation of the bubbles on the surface layer is greater than the degree of orientation of the bubbles on the surface layer in Example 2, and the average degree of orientation of these bubbles was Table 1 shows the obtained results.

The compression properties and shock absorption properties of the obtained foam were examined by the same measuring method as in Example 1. As a result, the foam was similar to the single-layer foam obtained in Comparative Example 5. FIG. 6 shows the results of the compression test, and FIG. 7 shows the results of the shock absorption test.

[0055]

[Table 1]

[0056]

The polyolefin resin multilayer foam of the present invention is constituted by two types of foam layers having different degrees of cell orientation. The effects thereof are to broaden the shock absorption range and to reduce the compressive strength. The compounding of different foamed layers can be mentioned, and it can be effectively used for the above-mentioned cushioning materials, packaging materials, cases, mats, various covers, footwear and the like. Further, according to the production method of the present invention, the procurement of different kinds of raw materials for the purpose of multi-layering, or the steps involved in laminating and bonding, and the productivity and production cost caused by the introduction of a special multi-layer molding die, etc. The problem is solved. Further, since the bonding interface does not exist in the multilayered foam of the present invention, there is no occurrence of a product defect due to roughening of bubbles at the bonding interface or peeling due to insufficient bonding strength.

[Brief description of the drawings]

FIG. 1 is a schematic view of a laminated foam according to the invention.

FIG. 2 is a schematic view of a laminated foam according to the present invention.

FIG. 3 is an explanatory view of a cross section of a sheet immediately before foaming in the method for producing a laminated foam according to the present invention.

FIG. 4 is a schematic diagram of a shock absorption characteristic measuring device.

FIG. 5 is a diagram illustrating a relationship between a falling height of a cylindrical body and a vibration acceleration.

FIG. 6 is a diagram showing the relationship between compressive stress and strain.

FIG. 7 is a diagram showing a relationship between a falling height of a cylindrical body and a vibration acceleration.

FIG. 8 is a diagram showing the relationship between compressive stress and strain.

[Explanation of symbols]

 1: foam layer with a small degree of cell orientation 2: foam layer with a large degree of cell orientation 3: cooling-following layer 4: cooling-following layer 5: steel plate 6: foam test piece 7: cylindrical body 8: charge amplifier 9: FFT Analyzer 10: Vibration pickup

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI B29K 105: 04 B29L 9:00

Claims (4)

[Claims] 1. A cell diameter in a direction orthogonal to an upper surface and a lower surface of a foam parallel to each other (hereinafter referred to as a thickness direction of a foam) / a cell diameter in a direction orthogonal to a thickness direction of a foam. The average value of the degree of bubble orientation of each individual bubble (hereinafter, referred to as
A foamed layer (B) in which P has an average cell orientation of 2.5 to 4.5 and a foamed layer having an average cell orientation Q smaller than P in a range of 0.5 to 3.5 (P). A) a polyolefin resin multilayer foam comprising:
The foam layer (A) is laminated and integrated on one side of the foam layer (B),
Furthermore, a polyolefin resin multilayer foam characterized in that there is no bonding surface at the interface between the foam layer (A) and the foam layer (B). 2. A foamed layer (B) having an average cell orientation P in the range of 2.5 to 4.5, and a smaller average cell orientation Q in the range of 0.5 to 3.5 than P. A polyolefin resin multilayer foam comprising a foamed layer (A), the foamed layer (A) is laminated and integrated on both sides of the foamed layer (B), and an interface between the foamed layer (A) and the foamed layer (B) Polyolefin resin multilayer foam characterized by having no joint surface. 3. A sheet-like polyolefin resin containing a foaming gas in a pressure-sealed state in an opposing mold openable mold is expanded only in the thickness direction while foaming under reduced pressure by increasing the volume in the mold. The method for producing a polyolefin resin multilayer foam according to claim 1, wherein in the method for producing a foam to be foamed, foaming is started under the condition that the temperature of one surface of a sheet is lower than the temperature of another surface of another sheet. 4. A sheet-like polyolefin resin containing a foaming gas in a pressure-sealed state in an opposing mold openable mold is decompressed and foamed only in the thickness direction while expanding under reduced pressure by increasing the volume in the mold. The method for producing a polyolefin resin multilayer foam according to claim 2, wherein in the method for producing a foam to be foamed, foaming is started under conditions in which the sheet surface layer temperature is lower than the sheet inner layer temperature.