JP2000007810A - Polyolefin-based resin crosslinked foam and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an polyolefin-based resin crosslinked foam having a smooth skin surface and larger diameters of cells and therefore having an excellent compression characteristics, and to provide its method. SOLUTION: When including both (A) an exothermically decomposable chemical foaming agent and (B) an endothermically decomposable foaming agent in an polyolefin-based resin and then applying electron beam curing, the polyolefin-based resin crosslinked foam of this invention has 10-50 times expansion ratio, 15-50% crosslinking degree, 0.6-1.5 mm average bubble diameter and a compression strength (25%) larger than that of the polyolefin-based resin crosslinked foam obtained from the resin composition having the same composition as the above resin composition except for not containing the agent B by 1.2-2.0 times. The polyolefin-based resin crosslinked foam is obtained by the extrusion molding of a polyolefin-based resin composition added with an agent A having >=25 kcal/mol decomposition calorific value and an B agent, in which the decomposition temperature is lower than that of the agent A, at the temperature lower than that of the decomposition temperature of the agent A, by electron beam curing of the foamable molded product and then by thermal foaming at the temperature 10-50 deg.C higher than that of the decomposition temperature of the agent A.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crosslinked polyolefin resin foam and a method for producing the same, and more particularly, to a polyolefin having a smooth and clean skin surface and having excellent compression properties by containing a large cell diameter. The present invention relates to a crosslinked resin foam and a method for producing the same.

[0002]

2. Description of the Related Art Crosslinked polyolefin resin foams are excellent in heat resistance, light weight, heat insulation, cushioning, sound insulation and the like, and are easy to mold by various processing methods. It is used in a wide range of fields, such as pad materials for automobile interiors and heat insulating materials for architectural applications, packing, and carpet underlay applications.

In the method for producing a crosslinked polyolefin resin foam, in particular, as a method of crosslinking a polyethylene resin or a polypropylene resin, there are a chemical crosslinking method using a peroxide and a radiation crosslinking method by electron beam irradiation. The foam obtained from the former chemical crosslinking method has a coarse cell structure,
There is a problem that the skin surface becomes rough, but on the other hand, there is an advantage that compression properties are excellent due to large bubbles. On the other hand, the foam obtained by the radiation crosslinking method has an advantage that the skin surface is smooth and clean because the cells are fine, but there is a disadvantage that the compression characteristics are low because the cells are fine. .

[0004] In view of this situation, a cross-linked polyolefin resin foam having only the advantages of both cross-linking methods, that is, a smooth skin surface obtained from a radiation cross-linking method,
There is an urgent need to realize a crosslinked polyolefin resin foam having excellent compression properties due to coarsening of cells obtained by a chemical crosslinking method.

Conventionally, as an attempt to improve the compression characteristics by controlling the coarsening of bubbles in the radiation crosslinking method, a method of forming a film in the bubbles by adding an additive having a melting point near the heating and foaming temperature has been proposed. Had been. However, in this method, it is necessary to increase the size of the additive in order to increase the bubble diameter, and when the additive size is increased, the dispersion tends to be poor, so that the bubble diameter becomes uneven, so that it is not always satisfactory. It could not be said to be a method of controlling the bubble diameter.

Japanese Patent Application Laid-Open No. Hei 8-302051 discloses that a decomposable chemical blowing agent is mixed with a polyolefin resin, and a low-boiling gas or solvent is injected under pressure into the resin composition. A method has been proposed in which a foamed sheet is extruded at a temperature at which the chemical foaming agent does not decompose, and this is crosslinked and foamed with an electron beam to form a foam having a large and uniform cell diameter. However, this method requires an extra step of injecting a low-boiling gas or solvent at a stage prior to forming the molded body, so that the cost is increased and the compression characteristics of the obtained foam are not necessarily satisfied. There was a problem that did not become.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems and to provide a crosslinked polyolefin resin foam having a smooth skin surface, a large cell diameter and excellent compression properties. It is an object of the present invention to provide a body and a method for producing the same.

[0008]

The crosslinked polyolefin resin foam of the present invention, which achieves the above object, contains an exothermic decomposition type chemical blowing agent and an endothermic decomposition type foaming agent, and is crosslinked with an electron beam. Resin cross-linked foam,
The expansion ratio of the foam is 10 to 50 times, and the degree of crosslinking is 15 to 5
0%, the average bubble diameter is 0.6 to 1.5 mm, and 25
% Of the crosslinked polyolefin resin foam obtained with the same composition except that the endothermic decomposition type foaming agent was excluded.
% Compression hardness is 1.2 to 2.0 times.

Further, the method for producing a crosslinked polyolefin resin foam of the present invention is characterized in that an exothermic decomposition type chemical foaming agent having a decomposition calorific value of 25 Kcal / mol or more, An endothermic decomposition type foaming agent having a decomposition temperature lower than that of the chemical blowing agent is added, and the polyolefin resin composition is extruded at a temperature lower than the decomposition temperature of the exothermic decomposition type chemical blowing agent to form an expandable molded article. After that, the foamable molded article is irradiated with an electron beam to perform crosslinking, and then heated and foamed at a temperature higher by 10 to 50 ° C. than the decomposition temperature of the exothermic decomposition type chemical foaming agent.

According to the present invention, when a composition is used in which an endothermic decomposition type foaming agent having a decomposition temperature lower than that of an exothermic decomposition type chemical blowing agent is added to a polyolefin resin, the composition is extruded. It is possible to uniformly disperse and form spherical microbubbles in a molded article of the present invention, and to form a state in which a large cell diameter is uniformly distributed by subjecting this molded article to cross-linking by electron beam irradiation and heating and foaming. it can. As a result, while obtaining a smooth skin surface, 2
The compression characteristics represented by 5% compression hardness can be improved.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, examples of the polyolefin resin used for the crosslinked polyolefin resin foam include a polyethylene resin and a polypropylene resin. The polyethylene resin refers to an ethylene homopolymer (polyethylene) or a copolymer of ethylene and an α-olefin. The polyethylene resin has a MFR of 0.915 to 0.940 g / cm ³ , preferably 0.920 to 0.935 g / cm ^3.
Those having a (melt flow rate) in the range of 1.0 to 30 g / 10 min, preferably 2 to 8 g / 10 min are preferably used.

The type of α-olefin to be copolymerized with ethylene is not particularly limited, but is generally ethylene / α-olefin 2 using α-olefin having 4 to 8 carbon atoms.
The former copolymer is advantageous in terms of both price and physical properties. The density of the polyethylene resin is 0.915 g / cm ³
If less than, the flexibility of the resin is remarkable, stickiness occurs, and blocking occurs when the foam is used,
Mechanical strength tends to decrease. 0.940g
If it exceeds / cm ³ , it is preferable in terms of mechanical strength, but on the contrary, the elongation tends to decrease, and the compression recovery of the foam tends to decrease.

The MFR of the polyethylene resin is 1.0 g /
If it is less than 10 minutes, the melt viscosity of the resin increases,
During the production of the foaming sheet, the exothermic decomposition-type chemical foaming agent is decomposed by shearing heat and tends to generate undesired coarse bubbles. If it exceeds 15 g / 10 minutes, the melt viscosity is low, which is preferable in sheet production. However, on the other hand, the ability to retain the gas generated by the endothermic foaming agent is reduced, and as a result, the unevenness of the fine bubbles formed in the molded body is uneven. Is generated.

The crosslinked polyolefin resin foam of the present invention is prepared by mixing an ethylene homopolymer (specifically, a high-pressure low-density polyethylene resin) and a copolymer of ethylene and an α-olefin. Alternatively, a mixture of a linear low-density polyethylene resin and a high-density polyethylene resin may be used.

[0015] In the present invention, the polypropylene resin is a propylene homopolymer (polypropylene),
It is a random or block copolymer of propylene and ethylene or an α-olefin, and has a melting point of 125 to 1
55 ° C, preferably in the range of 130 to 145 ° C, MFR of 0.5 to 10 g / 10 min, preferably 1.5 to 4 g / 1
Those having a range of 0 minutes are preferably used.

The type of the α-olefin to be copolymerized with propylene is not particularly limited, but ethylene or an α-olefin having 4 to 8 carbon atoms is preferable. Specific examples of the α-olefin having 4 to 8 carbon atoms include: Examples thereof include butene, hexene, ethylene / butene, and ethylene / hexene. In order to maintain the mechanical strength of the foam, the foam preferably has as large a carbon number as possible and is a terpolymer.

The copolymerization amount of ethylene or α-olefin having 4 to 8 carbon atoms copolymerized with propylene is 2 to 15
% By weight, preferably 3 to 8% by weight. When the copolymerization amount is less than 2% by weight, the crystallinity of the resin increases,
Also, since the melting point becomes higher, the obtained foam becomes harder,
The buffering property decreases. Further, the impact resistance at low temperatures is deteriorated, and even the exothermic decomposition type chemical foaming agent is decomposed due to shear heat generated during the production of the foaming sheet, and undesired large bubbles tend to be generated. When the copolymerization amount exceeds 15% by weight, although the buffering property and the impact resistance are preferable, the melting point is lowered, and the heat resistance of the obtained foam tends to be lowered.

If the melting point of the polypropylene-based resin is lower than 125 ° C., there is a greater tendency to be restricted in terms of application in terms of heat resistance. On the other hand, when the temperature exceeds 155 ° C., there is an advantage that the use is expanded. However, the exothermic decomposition type chemical foaming agent is decomposed due to shear heat generated during the production of the sheet for foaming, and undesired large bubbles are easily generated.

The MFR of the polypropylene resin is 0.5 g
If it is less than / 10 minutes, the melt viscosity of the resin increases, so that the heat-generating chemical foaming agent is easily decomposed due to shearing heat generated during the production of the foaming sheet, and coarse bubbles are easily generated. On the other hand, if it exceeds 5 g / 10 minutes, the melt viscosity is low, which is preferable from the viewpoint of sheet production. However, since the generated gas holding power by the endothermic foaming agent becomes weak, the size of the fine bubbles tends to become uneven. Alternatively, the elongation of the foam is reduced, or the shape holding force is degraded during heat forming such as vacuum forming, and it is difficult to obtain a good molded product.

The crosslinked polyolefin resin foam of the present invention may be used by mixing the above polypropylene resin and polyethylene resin. The mixing ratio of the polyethylene resin is 10 to 50% by weight, preferably 15% by weight.
The content of the polypropylene resin is 50 to 90% by weight, preferably 60 to 85% by weight. Foams obtained from a mixture of a polypropylene-based resin and a polyethylene-based resin are particularly suitable for fields in which properties such as heat resistance, low-temperature impact resistance and heat moldability are simultaneously required in addition to compression properties. .

When a polypropylene resin is used, it is necessary to impart electron beam crosslinkability. As an additive therefor, a reactive monomer containing two or more vinylic double bonds, specifically, 1.9 nonanediacrylate or p-divinylzene is used in an amount of 2 to 5 per 100 parts by weight of the polypropylene resin. It is desirable to add parts by weight. Also,
The polyolefin-based resin component may be mixed with a polyolefin-based resin other than the polypropylene-based resin and the polyethylene-based resin in an amount of 30% by weight or less.

These other polyolefin resins include low-density polyethylene, ethylene-propylene rubber (EPM), ethylene-propylene rubber-diene rubber (EPDM), high-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-acrylic acid. Copolymers, ethylene- (meth) alkyl acrylate copolymers, and terpolymers obtained by copolymerizing these copolymers with ethylene and maleic anhydride as a third component are exemplified.

Among them, ethylene-propylene rubber (EP
M), ethylene-propylene rubber-diene rubber (EPD)
M), an ethylene- (meth) alkyl acrylate copolymer, or a terpolymer obtained by copolymerizing maleic anhydride as a third component with a copolymer of these ethylene and ethylene. However, when the content of these other polyolefin-based resins exceeds 30% by weight, it is preferable in terms of the flexibility and cushioning property of the foam, but it is not preferable because heat resistance, mechanical strength, moldability and the like are reduced.

The foamable polyolefin resin component may further contain a heat stabilizer, a weathering agent, a flame retardant, a flame retardant aid, specifically, an antimony compound, a dispersant,
A crosslinking agent, a crosslinking assistant, and the like may be added. The polyolefin-based resin composition which can be crosslinked by electron beam irradiation according to the present invention has, as a foaming agent, an exothermic decomposition type chemical blowing agent having a heating value of decomposition of 25 Kcal / mol or more, and a decomposition temperature higher than the exothermic decomposition type chemical blowing agent. And a low endothermic decomposition type foaming agent.

As the exothermic decomposition type chemical foaming agent, azo chemical foaming agents, specifically, azodicarbonamide, metal salt of azodicarboxylic acid, N.I. N'-dinitrosopentamethylenetetramine; Examples include P'-oxybenzenesulfonyl hydrazide and tetrazole chemical blowing agent systems, specifically 5-phenyltetrazole and the like. Also,
The type of the endothermic decomposition type foaming agent is extremely limited, but specifically, fine powder of ammonium bicarbonate, preferably fine powder of ammonium bicarbonate having an average particle diameter of 20 μm or less is preferably used.

The crosslinked polyolefin resin foam of the present invention is characterized in that it is in the form of a closed cell crosslinked foam.
Moreover, the crosslinked polyolefin resin foam has an expansion ratio of 10 to 50 times, a degree of crosslinking of 15 to 50%, and an average cell diameter of 0.6 to 1.5 mm. And as the compression characteristics,
The 25% compression hardness is 1.2% of the 25% compression hardness of a crosslinked polyolefin resin foam obtained with the same composition except that the endothermic decomposition type foaming agent is excluded from the above two types as the foaming agent. ~ 2.0 times.

In other words, the 25% compression hardness of the polyolefin resin crosslinked foam of the present invention is the same composition except that only the exothermic decomposition type chemical blowing agent is used as a blowing agent, and the electron beam crosslinked polyolefin resin is used. It has 1.2 to 2.0 times the 25% compression hardness of the crosslinked foam.

In the polyolefin resin crosslinked foam of the present invention, when the expansion ratio is less than 10 times, when the foam sheet is irradiated with radiation to crosslink, the foam due to radiation energy depth which is a drawback of radiation crosslinking is obtained. In addition to causing problems with the thickness limitation of the sheet for use and ultimately the arbitrariness of the product thickness, since the sheet contains fine bubbles, radiation scattering due to fine bubbles is expected when irradiated, Therefore, the thickness of the foam sheet is limited.
Further, if the expansion ratio exceeds 50 times, no matter how large the cell diameter is, the compression recovery property and the buffering property are undesirably reduced.

If the degree of cross-linking is less than 15%, the ability to retain the foaming gas when the foam is formed is insufficient, and the foam may be broken and the gas may escape, so that the desired foaming ratio may not be achieved. If the degree of crosslinking exceeds 50%, it is preferable in terms of the ability to retain the foaming gas, but some of the bubbles are broken due to insufficient elongation in the foaming process by the exothermic decomposition type chemical foaming agent, and as a result, The distribution becomes worse.

The crosslinked polyolefin resin foam of the present invention has a large average cell diameter of 0.6 to 1.5 mm within the above-mentioned expansion ratio and degree of crosslinking, and has a 25% compression hardness as a representative value of the compression characteristics. As described above, the crosslinked polyolefin-based resin foam obtained by making the same composition except that the endothermic decomposition type foaming agent is removed from the above two types of foaming agents has a 25% compression hardness of 1.2 to 1.2. It can be 2.0 times.

Generally, the average cell diameter of a crosslinked polyolefin resin foam obtained by a conventional radiation crosslinking method is in the range of the above-mentioned expansion ratio and degree of crosslinking because only an exothermic decomposition type chemical blowing agent is used as a blowing agent. 0.
It is about 2 to 0.5 mm, and up to 0.6 mm at most. Therefore, the 25% compression hardness as compression characteristics was only about 0.3 to 1.5 kg / cm ² .

The crosslinked polyolefin resin foam of the present invention, which is obtained by the radiation crosslinking method, is controlled so that the average cell diameter becomes 0.6 to 1.5 mm.
Accordingly, the 25% compression hardness is 1.2 to 2.0 times the 25% compression hardness of the conventional polyolefin resin crosslinked foam using only the exothermic decomposition type chemical foaming agent, and excellent compression characteristics are obtained. Have.

When the average bubble diameter is smaller than 0.6 mm,
If the multiple of the% compression hardness is less than 1.2 times, the compression properties cannot be improved to a satisfactory level as compared with conventional foams. On the other hand, the average bubble diameter is larger than 1.5 mm,
When the multiple of the 25% compression hardness exceeds 2.0 times, the bubble diameter becomes too large and the unevenness of the skin becomes large, so that not only is the quality inferior, but also the production becomes difficult.

In the present invention, it is not clear why the average bubble diameter is controlled to increase as described above, and the 25% compression hardness (compression characteristics) can be increased. According to the experience of the present inventors, when the manufacturing conditions are inappropriate, there may be cases where bubbles containing bubbles are generated in the molded sheet due to partial decomposition of the exothermic decomposition type chemical foaming agent. Although the diameter was large, it was far from the controlled one, and it was judged that it was inferior in commercial value, but the bubbles generated by the partial decomposition of the exothermic decomposition type chemical blowing agent have a higher foaming temperature than the resin part Therefore, it has been considered that the viscosity of the resin decreases due to a partial rise in the temperature of the resin, and the bubbles are associated with each other. Also, once the decomposition of the exothermic decomposition type chemical foaming agent starts, there is no control method other than lowering the temperature, so it was generally considered that the bubbles could not be increased by radiation crosslinking.

However, as in the present invention, the exothermic decomposition type chemical foaming agent and the endothermic decomposition type foaming agent having a lower decomposition temperature than the exothermic decomposition type chemical foaming agent are used in combination, whereby the endothermic decomposition type foaming agent is actively used. When it is decomposed, the gas generated at this time lowers the ambient temperature, so that the resin viscosity increases. Therefore, it is considered that the effect of the present invention is exerted because the generation of bubbles caused by the exothermic decomposition type chemical foaming agent is small, and the bubbles are uniformly dispersed in a controlled state as independent bubbles.

The crosslinked polyolefin-based resin foam of the present invention is formed into a polyolefin-based resin crosslinkable by electron beam irradiation into an exothermic decomposition-type chemical foaming agent having a decomposition heating value of 25 Kcal / mol or more; And an endothermic decomposition type foaming agent having a lower decomposition temperature than that of the exothermic decomposition type chemical foaming agent. After being molded as a body, the foamable molded body is irradiated with an electron beam to perform crosslinking, and then heated and foamed by a foaming device set at a temperature 10 to 50 ° C. higher than the decomposition temperature of the exothermic decomposition type chemical foaming agent. Can be manufactured.

As the electron beam irradiation, any conventionally known radiation crosslinking method of irradiating ionizing radiation can be applied. Further, as the heating foaming method, any known method can be applied, specifically, a vertical hot air foaming method,
It is preferable to apply a method capable of processing in a continuous sheet, such as a horizontal hot air foaming method and a horizontal chemical solution foaming method.

The crosslinked polyolefin resin foam of the present invention has a smooth skin surface despite its large average cell diameter, and has a high 25% compression hardness and excellent compression characteristics. It can be applied to the field of building materials that are folded and processed, and the field of cushioning material when transporting glass sheets or steel sheets. Furthermore, taking advantage of its extremely high skin strength, it has scratch resistance like a car trunk mat. It can be widely applied to various industrial uses such as a required coating field and a molded article field such as a thermoformed mechanical part case.

[0039]

EXAMPLES In the following examples, measuring methods and evaluation criteria for each characteristic are as follows. [Cross-linking degree] The foam was cut into small pieces and 0.2 g of the foam was precisely weighed.
This sample was immersed in tetralin at 130 ° C. and heated for 3 hours with stirring to dissolve the dissolved portion. The insoluble portion was taken out and washed with acetone to remove tetralin, and further washed with pure water. Acetone is removed, moisture is removed with a hot air dryer at 120 ° C., and the mixture is naturally cooled to room temperature. The weight W ₁ (g) of this sample is measured, and the degree of crosslinking is determined from the following equation. Degree of crosslinking = (0.2−W ₁ /0.2)×100(%)

[Expansion Ratio] A sample of 10 cm × 10 cm was cut out from the foam, and its thickness t ₁ (cm) and weight W ₂ (g) were cut out.
And the expansion ratio is calculated from the following equation. Expansion ratio (g / cm ³ ) = W ₂ / (10 × 10 × t ₁ ) [Average cell diameter] Length (MD) direction and width (TD) of foam
The cross section cut out in each direction was observed at a magnification of 20 times.
Measure the minor axis (a) and major axis (b) of the bubbles existing in the long,
The value calculated by the following equation is defined as the average bubble diameter. Average bubble diameter (mm) = Σ [(a + b) / 2] / n

[Compression Characteristics] According to JIS K 6767, the foam of the present invention has a 25% compression hardness (c) and the foam prepared by removing the endothermic decomposition type foaming agent has a 25% compression hardness (d). Is measured, and the compression characteristic is calculated by the following equation. Compression characteristics = c / d

[Surface smoothness] Magic ink diluted 5 times with toluene was applied to the surface of the foam, and the coated surface was quickly wiped off with gauze. After wiping, observation was made. Those having no magic ink root were judged to be acceptable, and those having the magic ink root were judged to be unacceptable.

Example 1 High-pressure low-density polyethylene (density: 0.923 g / c)
m ³ , melting point: 112 ° C., MFR: 4.8 g / 10 min) 1
00 kg, Irganox 1010 as a heat stabilizer at 0.1 g.
3 kg, azodicarbonamide as an exothermic decomposition type chemical blowing agent (decomposition temperature: 197 ° C, calorific value of decomposition: 24 Kcal / mol)
6.5 kg, sodium bicarbonate having an average particle diameter of 8 μm as an endothermic decomposition type foaming agent (decomposition temperature: 160 ° C., decomposition heat value: -20
1 kg of Kcal / mol) was charged into a Henschel mixer having an internal volume of 450 liters, and subjected to primary mixing to obtain a foamable resin composition.

This foamable resin composition is supplied to a vented extruder heated to a temperature at which the pyrolytic foaming agent does not decompose, that is, heated to 140 to 160 ° C., extruded into a sheet, and then extruded at a roll temperature of 75 ° C. The sheet was wound as a continuous sheet having a thickness of 3.0 mm and a width of 500 mm without air bubbles by a polishing type sheet forming machine.

Next, this sheet is irradiated with an electron beam to give a crosslink so that the degree of crosslinking becomes 32%, and the sheet is raised by 20 ° C. higher than the decomposition temperature of the exothermic decomposition type chemical foaming agent. The mixture was continuously supplied onto a heating medium bath heated to a temperature and foamed by heating. The foam sheet thus obtained is
6.1mm thick, 1300mm wide, 25x expansion ratio,
Average bubble diameter is 0.93mm, 25% compression hardness is 0.86kg
/ Cm ² , and the smoothness of the skin surface was acceptable. On the other hand, the 25% compression hardness of the foamed sheet produced under the same conditions except that the addition of the endothermic decomposition type foaming agent (sodium bicarbonate) among the two foaming agents was 0.61 kg / cm ² . Therefore, the compression characteristics of the polyethylene resin crosslinked foam of the present invention corresponded to 1.4 times.

Example 2 High-pressure low-density polyethylene (density: 0.923 g / c)
m ³ , Melting point: 108 ° C., MFR: 3.7 g / 10 min) Powder: 100 kg, MarkAO30 as heat stabilizer:
0.5 kg, DSTDP: 1.0 kg, azodicarbonamide as an exothermic decomposition type chemical blowing agent (decomposition temperature: 197 ° C.,
Calorific value of decomposition: 24 Kcal / mol): 8 kg, sodium bicarbonate having an average particle diameter of 12 μm as an endothermic decomposition type foaming agent (decomposition temperature:
160 ° C, heat of decomposition: -20 Kcal / mol): 0.5 kg
Was charged into a Henschel mixer having an internal volume of 450 liters, and subjected to primary mixing to obtain a foamable resin composition.

Next, this foamable resin composition was introduced into a vented extruder heated to 140 to 160 ° C. which does not decompose azodicarbonamide, and was extruded from a T-die to have a thickness of 2.0 mm and a width of 2.0 mm. It was wound up as a continuous sheet of 500 mm. Next, 7 Mrad is applied to this sheet.
Irradiation of electron beam to crosslink,
It was supplied to a silicone chemical solution foaming apparatus heated in the order of 5 ° C. and 225 ° C. to foam by heating, and then wound up as a continuous sheet foam.

The results of evaluation of the properties of the obtained sheet foam are as shown in Table 1. The 25% compression hardness of the sheet foam was 0.68 kg / cm ² , and the sheet was obtained under the same conditions except that the addition of the endothermic decomposition type foaming agent (sodium bicarbonate) was omitted. The 25% compression hardness of the foam was 0.43 kg / cm ² .

Comparative Example 1 In Example 2, the addition of an endothermic decomposition type blowing agent (sodium bicarbonate) as a blowing agent was omitted, and azodicarbonamide (decomposition temperature: 197 ° C., decomposition heat value: 24 Kcal / mol), a foamable resin composition into which 0.1 kg of liquefied butane was injected as an endothermic decomposition type foaming agent, and an electron beam irradiation amount of 1 kg.
The thickness was 3.5 under the same conditions except that 2 Mrad was used.
A foam sheet having a thickness of 0 mm and a width of 550 mm was obtained.

Table 1 shows the results of evaluating the properties of the foamed sheet. In addition, the 25% compression hardness of the above-mentioned sheet-like foam is 0.1.
60 kg / cm ^2, which 25% compressive hardness of the sheet-like foam except for omitting the addition of obtained in the same conditions endothermic decomposition type foaming agent (liquefied butane) with respect to 0.62 kg / cm ²
Met.

[0051]

[Table 1]

As is evident from the results in Table 1, the crosslinked polyolefin resin foam of the present invention has a skin whose surface smoothness can be obtained by the electron beam crosslinking method despite the large cell shape (average cell diameter). It has a surface level,
Moreover, the compression properties are superior to those of the conventional foam sheet using only the exothermic decomposition type chemical foaming agent.

On the other hand, in the crosslinked polyolefin resin foam of Comparative Example 1, since the endothermic decomposition type foaming agent did not satisfy the conditions of the present invention, the cell shape was uneven or the cell diameter was small, and the electron beam crosslinking method was used. And the compression characteristics are inferior.

[0054]

As described above, according to the crosslinked polyolefin resin foam and the production method of the present invention, a controlled average cell diameter of a large size can be obtained. The skin surface can be smooth and have excellent compression properties.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4F070 AA13 AA15 AA16 AC16 AC47 AE12 AE23 BA02 GA04 GC02 HA04 HB05 4F073 AA05 BA07 BA08 BA09 BA51 BB01 CA42 HA05 4F074 AA16 AA17 AA24 AA25 BA01 BA03 BA03 BA04 BB25 DA29 CC DA08

Claims (6)

[Claims] 1. A crosslinked polyolefin resin foam which contains an exothermic decomposition type chemical foaming agent and an endothermic decomposition type foaming agent and is crosslinked by electron beam, and has a foaming ratio of 10
~ 50 times, degree of crosslinking is 15 ~ 50%, average cell diameter is 0.6
1.5 to 1.5 mm and a 25% compression hardness of 1.2 to 2.25% of a 25% compression hardness of a polyolefin resin crosslinked foam obtained with the same composition except that the endothermic decomposition type foaming agent is excluded.
A crosslinked polyolefin-based resin foam having 0 times. 2. The polyolefin resin is polyethylene, polypropylene, a copolymer of propylene and ethylene, a copolymer of ethylene and an α-olefin having 4 to 12 carbon atoms, propylene and ethylene or 4 to 8 carbon atoms. 2. The copolymer of claim 1, which is a copolymer with an α-olefin.
The crosslinked foam of a polyolefin resin described in the above. 3. The crosslinked polyolefin resin foam according to claim 1, wherein the exothermic decomposition type chemical blowing agent is azodicarbonamide, and the endothermic decomposition type blowing agent is sodium bicarbonate. 4. An exothermic decomposition type foaming agent having an exothermic decomposition calorific value of 25 Kcal / mol or more and an endothermic decomposition type foaming agent having a lower decomposition temperature than the exothermic decomposition type chemical foaming agent. And then extruding the polyolefin-based resin composition at a temperature lower than the decomposition temperature of the exothermic decomposition type chemical foaming agent to form a foamable molded product, and then irradiating the foamable molded product with an electron beam. A method for producing a crosslinked polyolefin resin foam which is subjected to crosslinking and then heated and foamed at a temperature 10 to 50 ° C. higher than the decomposition temperature of the exothermic decomposition type chemical foaming agent. 5. The polyolefin-based resin is polyethylene, polypropylene, a copolymer of propylene and ethylene, a copolymer of ethylene and an α-olefin having 4 to 12 carbon atoms, propylene and ethylene or 4 to 8 carbon atoms. 5. A copolymer of any one of the above with an α-olefin.
3. The method for producing a crosslinked polyolefin resin foam according to item 1. 6. The method for producing a crosslinked polyolefin resin foam according to claim 4, wherein the exothermic decomposition type blowing agent is azodicarbonamide, and the endothermic decomposition type blowing agent is sodium bicarbonate.