JP4965136B2 - Method for producing polyolefin resin foam - Google Patents

Description

  The present invention relates to a method for producing a polyolefin-based resin foam that can be used as, for example, automobile parts, building materials, and the like, and can obtain a foam with a high expansion ratio without causing deformation after foaming.

Conventionally, in the production of polyolefin resin foam such as polyethylene resin foam, a pyrolytic foaming agent is used as a foaming agent, and a decomposition gas is generated by heating to a temperature at which the foaming agent is thermally decomposed. The polyolefin gas can be foamed by the decomposition gas. For example, there is known a method for producing a polyolefin foam by adding a foaming agent and a metal phthalocyanine compound containing azodicarbonamide and sodium bicarbonate as main components to a polyolefin resin such as polyethylene resin (for example, , See Patent Document 1). According to this method, it is presumed that the metal phthalocyanine compound can promote the decomposition of azodicarbonamide, suppress the formation of decomposition residues, and reduce cyanide ions.
JP-A-10-251430 (pages 2 and 3)

  However, in the conventional method for producing a polyolefin resin foam described in Patent Document 1, although harmful components such as cyanide ions can be reduced, since azodicarbonamide is used as a foaming agent, the decomposition product thereof is used. The generation of urea, which causes ammonia and fogging (glass fogging), which are odor components, cannot be completely eliminated. Therefore, it is conceivable to use only sodium bicarbonate without using azodicarbonamide as a foaming agent. However, in that case, if an attempt is made to produce a foam having a foaming ratio of 5 times or more, the resulting foam undergoes large deformation due to shrinkage within a few hours after foaming and cannot be used as a product. Therefore, there is a problem that it is only possible to obtain a foam having an extremely low expansion ratio of less than 5 times, and in order to obtain a foam having a higher expansion ratio than that, another foaming agent must be used in combination.

  Accordingly, an object of the present invention is to provide a method for producing a polyolefin resin foam that can easily produce a foam having a foaming ratio of 5 times or more without causing deformation after foaming. It is in.

In order to achieve the above object, a method for producing a polyolefin resin foam of the invention according to claim 1 includes a polyolefin resin, sodium hydrogen carbonate that decomposes when heated to generate carbon dioxide and water vapor, and an alkali. Carbon dioxide gas generated by decomposition of sodium hydrogen carbonate, which is made of a metal or alkaline earth metal oxide and heated after mixing raw materials having an oxide content of 5 to 100 parts by mass per 100 parts by mass of polyolefin resin A method for producing a polyolefin resin foam in which a polyolefin resin is foamed by heating, cooling after the heating, and then reheating at 50 to 120 ° C. for 3 to 24 hours .

A method for producing a polyolefin resin foam according to a second aspect of the present invention is the invention according to the first aspect, wherein the raw material contains a crosslinking agent .

According to the present invention, the following effects can be exhibited.
The method for producing a polyolefin resin foam of the invention according to claim 1 includes a polyolefin resin, sodium hydrogen carbonate that decomposes upon heating to generate carbon dioxide and water vapor, and an oxide of an alkali metal or an alkaline earth metal It is carried out by heating after mixing the raw material comprising. In the process, the polyolefin resin foams due to the carbon dioxide gas generated by the decomposition of sodium hydrogen carbonate, and at the same time, the water vapor generated by the decomposition of the sodium hydrogen carbonate reacts with the oxide of alkali metal or alkaline earth metal and is absorbed. The

At this time, since the content of the oxide is set to 5 to 100 parts by mass per 100 parts by mass of the polyolefin resin, water vapor can be sufficiently absorbed without hindering foaming of the raw material. For this reason, it is possible to prevent the foam from being deformed by reducing the volume due to the water vapor being cooled and reducing the volume, the pressure in the bubbles (cells) of the foam being lowered, and contracting. Therefore, a foam having a foaming ratio of 5 times or more can be easily produced without causing deformation after foaming. In addition, since cooling after the heating and then reheating at 50 to 120 ° C. for 3 to 24 hours, water vapor in the foam cell can be reliably removed, and the above effect can be improved. .

  In the method for producing a polyolefin resin foam of the invention according to claim 2, since the raw material contains a crosslinking agent, the mechanical properties of the foam are improved in addition to the effects of the invention according to claim 1. Can be made.

In the following, embodiments that are considered to be the best of the present invention will be described in detail.
The polyolefin-based resin foam (hereinafter also simply referred to as a foam) in the present embodiment is produced as follows. That is, a polyolefin resin, sodium bicarbonate that decomposes when heated as a foaming agent to generate carbon dioxide (carbon dioxide) and water vapor, and a raw material composed of an oxide of an alkali metal or alkaline earth metal as a water absorbing agent are mixed and heated. Then, the polyolefin resin is foamed with carbon dioxide gas generated by decomposition of sodium hydrogen carbonate. The content of the oxide is set to 5 to 100 parts by mass per 100 parts by mass of the polyolefin resin in order to sufficiently absorb water vapor generated by the decomposition of sodium hydrogen carbonate.

First, the raw material of a foam is demonstrated in order.
(Polyolefin resin)
The polyolefin resin foam is preferably flexible and low in hardness, and therefore preferably has a foaming ratio of 5 to 50 times. Here, the expansion ratio is 5 to 50 times means that the apparent density measured in accordance with JIS K 6767-1: 1995 Annex B is 20 to 200 kg / m ³ (reciprocal of expansion ratio). Means that. When the expansion ratio is less than 5 times, the foam becomes hard and lacks flexibility, which is not preferable when used as a cushioning material or the like. On the other hand, if it exceeds 50 times, the foam is too soft and the shape cannot be maintained, which is not preferable.

Examples of the polyolefin resin forming the polyolefin resin foam include a polyolefin copolymer resin which is a copolymer of an olefin and a monomer copolymerizable therewith in addition to the polyolefin resin. Examples of the polyolefin resin include polyethylene resin and polypropylene resin. Examples of polyolefin copolymer resins include ethylene-vinyl acetate copolymer resins, ethylene-propylene copolymer resins, ethylene-butene copolymer resins, ethylene-acrylic acid esters (methyl esters, ethyl esters, propyl esters, butyl esters, etc. Examples thereof include a copolymer resin, a chlorinated product thereof (chlorine content of 45 mol% or less), or a mixture with polypropylene (isotactic polypropylene or atactic polypropylene). One or more of these polyolefin resins are appropriately selected and used.
(Foaming agent)
Sodium hydrogen carbonate (sodium bicarbonate, NaHCO ₃ ) is used as the foaming agent, and the decomposition start temperature thereof is higher than the mixing (kneading) temperature (usually 90 to 130 ° C.) of the polyolefin resin foam raw material. Lower than temperature (usually 130-160 ° C). That is, sodium hydrogencarbonate is not decomposed when the raw materials are mixed, but is decomposed by heating at the time of foaming, and is converted into sodium carbonate based on the reaction formula shown below, and carbon dioxide gas and water vapor are generated.

2NaHCO ₃ → Na ₂ CO ₃ + CO ₂ + H ₂ O
It is preferable that content of a foaming agent is 5-50 mass parts per 100 mass parts of polyolefin resin. When the content of the foaming agent is less than 5 parts by mass, a sufficient carbon dioxide gas generation amount cannot be obtained, the foam becomes hard and lacks flexibility, which is not preferable. On the other hand, when the amount exceeds 50 parts by mass, the amount of carbon dioxide gas generated by the foaming agent becomes excessive, the foam becomes low density, and the shape retainability of the foam is deteriorated.
(Water absorbent)
Next, the alkali metal or alkaline earth metal oxide reacts with water vapor generated by the decomposition of sodium hydrogen carbonate to absorb moisture in the foam. As the oxide of the alkali metal, potassium oxide (K ₂ O), cesium oxide (Cs ₂ O), sodium oxide (Na ₂ O), or the like is used. As the alkaline earth metal oxide, calcium oxide (CaO), magnesium oxide (MgO), or the like is used.

For example, calcium oxide reacts with water vapor according to the following chemical formula, and changes to calcium hydroxide.
CaO + H ₂ O → Ca (OH) ₂
Content of this oxide is 5-100 mass parts per 100 mass parts of polyolefin resin, and it is preferable that it is 10-100 mass parts. When the content of the oxide is less than 5 parts by mass, the absorption of water vapor in the foam is insufficient, and the remaining water vapor is cooled to become water, resulting in volume reduction and deformation of the foam. On the other hand, when the content of the oxide exceeds 100 parts by mass, the content of the oxide is excessive, and the oxide that does not react with water vapor becomes a cause of hindering foaming of the raw material, making foaming difficult.
(Crosslinking agent)
Subsequently, in order to form a cross-linked structure in the polyolefin resin foam and maintain a predetermined hardness and strength, it is preferable to add a cross-linking agent to the raw material of the polyolefin resin foam. As such a cross-linking agent, an organic peroxide having a decomposition temperature equal to or higher than the flow starting temperature of the polyolefin resin and decomposed by heating to generate free radicals to cause cross-linking in the polyolefin resin is used. Specific examples of the organic peroxide include dicumyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, 4,4-di (t-butylperoxy) -n- Examples include butyl valerate, α, α′-di (t-butylperoxy-m-isopropyl) benzene, 1,3-bis-t-butylperoxyisopropylbenzene, and the like. Content of a crosslinking agent is 0.1-10 mass parts normally per 100 mass parts of polyolefin resin, Preferably it is 1-3 mass parts. When the content of the cross-linking agent is less than 0.1 parts by mass, a sufficient cross-linking structure cannot be formed in the foam. When the content exceeds 10 parts by mass, the cross-linking agent becomes excessive and the foam is cross-linked. The structure becomes too dense and the foam lacks flexibility.

In addition to the components described above, an inorganic filler, a foam stabilizer, a flame retardant, a stabilizer, a colorant, a plasticizer, and the like can be blended in the polyolefin resin foam raw material according to a conventional method. Among them, the inorganic filler will be described.
(Inorganic filler)
The inorganic filler is blended to make the foam a desired hardness and to make the size of the cells (cell diameter) in the foam finer based on the particle diameter of the inorganic filler. By blending this inorganic filler, an interface is formed between the polyolefin resin and the inorganic filler, an interfacial tension is generated there, and this portion becomes a cell nucleus. Therefore, the average particle size of the inorganic filler is preferably 100 to 200 μm. If the average particle size of the inorganic filler is less than 100 μm, the cells in the foam tend to be too fine and the foam tends to become hard, whereas if it exceeds 200 μm, the cells in the foam become rough, It shows a tendency for unevenness to increase. Although it does not specifically limit as an inorganic filler, A calcium carbonate, magnesium hydroxide, aluminum hydroxide, etc. are used. It is preferable that content of an inorganic filler is 5-100 mass parts per 100 mass parts of polyolefin resin. When the content of the inorganic filler is less than 5 parts by mass, the hardness of the foam cannot be made sufficiently hard, and the cells in the foam cannot be made sufficiently fine. Exceeding the mass part is not preferable because the foam becomes too hard and the cell diameter tends to be too large.

  Next, the polyolefin-based resin foam is manufactured by mixing the raw materials of the polyolefin-based resin foam described above, and then injecting it into, for example, a foaming mold and heating to foam. At that time, foaming is started by decomposition of sodium hydrogen carbonate immediately after heating and generation of carbon dioxide gas, and the viscosity gradually increases and foaming is continued to form a foam having a closed cell structure.

  When foaming the raw material of the polyolefin resin foam, both the one-stage foaming method and the two-stage foaming method are adopted. In the one-stage foaming method, the raw material of the polyolefin resin foam is filled into a foaming mold, heated and pressurized to decompose the foaming agent and, if necessary, the crosslinking agent, and then decompressed to expand to the desired apparent density at once. It is a method to make it. The two-stage foaming method is a method in which an intermediate foam obtained by the one-stage foaming method is heated at normal pressure and foamed in two stages to obtain a final foam having a desired apparent density. In the one-stage foaming method, the apparatus is simple and the operation procedure is easy. However, since the obtained foam has a relatively high hardness, it tends to break due to physical deformation and tends to break during foaming. On the other hand, in the two-stage foaming method, the apparatus is complicated and the operation procedure is likely to be difficult. However, since the foaming is performed in two stages sequentially, cracks and formation of cavities tend not to occur during foaming. Which foaming method is adopted is appropriately determined depending on the foaming ratio, the quality of the foam, the application, and the like.

  The water vapor generated in the heating process reacts with the alkali metal or alkaline earth metal oxides and is absorbed, but if the absorption is not sufficiently performed, the water vapor condenses after cooling to become water and the volume is reduced. Only the foam shrinks. Therefore, it is desirable to reheat the foam after cooling to reliably remove moisture. The reheating conditions are preferably 50 to 120 ° C. and 3 to 24 hours, and more preferably 70 to 120 ° C. and 5 to 24 hours. When the reheating temperature is less than 50 ° C. or the reheating time is less than 3 hours, water vapor is not sufficiently removed by reheating, and the effect of reheating cannot be obtained. On the other hand, when the reheating temperature exceeds 120 ° C. or when the reheating time exceeds 24 hours, the foam is softened due to excessive heating and changes in shape and changes in size, which is not preferable.

  Now, the operation of this embodiment will be described. A polyolefin resin foam is prepared by mixing a polyolefin resin, sodium hydrogen carbonate as a foaming agent, and a raw material composed of an oxide of an alkali metal or an alkaline earth metal as a water absorbing agent, and then heating. Then, it is performed by foaming a polyolefin resin. At that time, sodium hydrogen carbonate is thermally decomposed to generate carbon dioxide gas, and the polyolefin-based resin is foamed by the generated carbon dioxide gas, so that many fine cells are formed in the foamed body. At the same time, water vapor is generated by the thermal decomposition of sodium bicarbonate and is present in the cell. The generated water vapor is absorbed by reacting with an oxide of an alkali metal or alkaline earth metal, for example, calcium oxide, dispersed in the foam in the cell.

  At this time, if the content of the oxide is small, water vapor is not sufficiently absorbed, and if it is large, the oxide not involved in the absorption of water vapor impedes foaming, but the content of the oxide is 100 parts by mass of polyolefin resin. Since it is set to 5 to 100 parts by mass, the foaming can proceed smoothly and the water vapor generated as the foaming proceeds can be sufficiently absorbed. For this reason, the pressure in the cell of a foam can be maintained and a deformation | transformation of a foam is avoided.

The effects exhibited by the above embodiment will be described collectively below.
In the method for producing a polyolefin resin foam in the present embodiment, the polyolefin resin foams with carbon dioxide gas generated by decomposition of sodium hydrogen carbonate, and at the same time, water vapor generated by decomposition of sodium hydrogen carbonate is alkali metal or alkaline earth It reacts with and is absorbed by metal oxides. Furthermore, since the content of the oxide is set to 5 to 100 parts by mass per 100 parts by mass of the polyolefin-based resin, it is possible to absorb water vapor without hindering foaming of the raw material. Therefore, the volume of water vapor is reduced by cooling the water vapor to water, and the foam can be prevented from shrinking and deforming due to a decrease in pressure in the cell. Therefore, a foam having a foaming ratio of 5 times or more can be easily produced without causing deformation of the foam after foaming.

-By containing a crosslinking agent in the foam material, mechanical properties such as hardness and strength of the foam can be improved.
-The foam raw material is heated and then cooled, and then reheated at 50 to 120 ° C for 3 to 24 hours, whereby water vapor remaining in the cells of the foam can be more reliably removed.

  ・ By using only sodium hydrogen carbonate, which is an inorganic foaming agent, as a foaming agent, the content of volatile components in the foam is reduced compared to organic foaming agents such as azodicarbonamide, which have been used in the past. The odor of the body can be suppressed.

Hereinafter, the embodiment will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples.
(Examples 1-5 and Comparative Examples 1-3)
First, the raw material of the low density polyethylene resin foam used in each Example and Comparative Example is shown below.

Low-density polyethylene resin (LDPE): MFR (melt flow rate) 3 g / 10 min, density 0.923 g / cm ³ , manufactured by Asahi Kasei Corporation, Suntec F2225.4.
Sodium bicarbonate: sodium bicarbonate [NaHCO ₃ ], manufactured by Eiwa Kasei Kogyo Co., Ltd., Cellbon FE-507.

Crosslinking agent 1: Dicumyl peroxide, Kayaku Mill D-40C, manufactured by Kayaku Akzo Corporation.
Calcium oxide: Paste, manufactured by Omi Chemical Co., Ltd., C.I. M.M. L. No. 21.
And the raw material of the low density polyethylene resin foam used for each Example and each comparative example with the content shown in Table 1 was prepared. The content (blending amount) of each component in Table 1 represents parts by mass. Here, Comparative Example 1 shows an example not containing calcium oxide as a water-absorbing agent, Comparative Example 2 shows an example in which the content of calcium oxide is excessive, and Comparative Example 3 shows an example in which the content of calcium oxide is excessive. Show.

  These raw materials for the low-density polyethylene resin foam were kneaded in a 1 L volume kneader, and then kneaded for 5 minutes with a mixing roll heated to 100 ° C. Next, about 1 kg of the kneaded kneaded dough is put into a mold having a length of 160 mm, a width of 160 mm and a depth of 33 mm, and heated and pressurized at 155 ° C. for 60 minutes to foam and low-density polyethylene resin foam raw material Was obtained (one-stage foaming method). The pressure in the mold was set so as to resist the foaming pressure at the time of foaming and to form a foam having a foaming ratio of 10 times. And after leaving the raw material of the obtained low density polyethylene resin foam and its raw material sliced to thickness 10mm for 24 hours, the deformation | transformation state was observed visually. The results are shown in Table 1.

表１に示したように、実施例１〜５においては、原反の変形は見られなかった。また、実施例２〜５においては、スライスしたものについて変形は小さい結果であったが、実施例１では酸化カルシウムの含有量が実施例２〜５に比べて少量であったため、水分の吸収が若干少なく、変形が見られた。

As shown in Table 1, in Examples 1 to 5, no deformation of the original fabric was observed. Moreover, in Examples 2-5, although the deformation | transformation was a small result about what was sliced, in Example 1, since the content of calcium oxide was small compared with Examples 2-5, absorption of a water | moisture content was carried out. Slightly less deformation was observed.

  On the other hand, in Comparative Example 1 that did not contain calcium oxide and Comparative Example 2 in which the content of calcium oxide was too low, depression occurred in the original fabric. Further, in Comparative Example 3 in which the content of calcium oxide was excessive, excessive calcium oxide inhibited foaming, and foaming was difficult.

  Next, the raw fabric of the low density polyethylene resin foam obtained in Example 1 was reheated at the heating temperature and heating time as shown in Table 2, and then cooled at room temperature for 24 hours. Then, the reheated raw fabric was sliced to a thickness of 10 mm, the deformation and the dimensional shrinkage (%) were measured, and the results are shown in Table 2. Dimensional shrinkage (%) represents the percentage of shrinkage relative to the original dimension.

表２に示したように、実施例１−２〜１−７及び実施例１−１０では、再加熱後にスライスしたものについて変形がないか又は変形が少ない結果が得られ、さらに実施例１−５〜１−７では寸法収縮率も１５％以下に抑えることができた。一方、再加熱温度が４０℃の実施例１−１では反りに基づく変形が見られ、再加熱温度が１３０℃の実施例１−８では反りによる変形は見られなかったものの、寸法収縮率が３０％に達した。また、再加熱時間が２時間の実施例１−９では、再加熱時間が短いため、反りによる変形が認められた。従って、再加熱温度は５０〜１２０℃及び再加熱時間は３〜２４時間が好ましいことが明らかになった。
（実施例６〜１４）
実施例６では、実施例２において、低密度ポリエチレン樹脂に代えて下記に示すエチレン−酢酸ビニル共重合樹脂を用い、その他は実施例２と同様に実施した。実施例７では、実施例２において、架橋剤１のジクミルパーオキサイドを下記に示す架橋剤２に代えると共に、その含有量を表３に示すように変更した他は実施例２と同様に実施した。実施例８では、実施例２において、架橋剤１のジクミルパーオキサイドを下記に示す架橋剤３に代え、その他は実施例２と同様に実施した。実施例９では、実施例２において、架橋剤１のジクミルパーオキサイドを下記に示す架橋剤４に代え、その他は実施例２と同様に実施した。

As shown in Table 2, in Examples 1-2 to 1-7 and Example 1-10, the results obtained by slicing after reheating were obtained with little or no deformation. In 5-1-7, the dimensional shrinkage rate could be suppressed to 15% or less. On the other hand, in Example 1-1 in which the reheating temperature was 40 ° C., deformation due to warping was observed, and in Example 1-8 in which the reheating temperature was 130 ° C., deformation due to warping was not observed, but the dimensional shrinkage ratio was It reached 30%. Further, in Example 1-9 in which the reheating time was 2 hours, deformation due to warping was recognized because the reheating time was short. Therefore, it was revealed that the reheating temperature is preferably 50 to 120 ° C. and the reheating time is 3 to 24 hours.
(Examples 6 to 14)
In Example 6, the same ethylene-vinyl acetate copolymer resin as shown below was used instead of the low-density polyethylene resin in Example 2, and the others were carried out in the same manner as in Example 2. In Example 7, the same procedure as in Example 2 was performed except that the dicumyl peroxide of the crosslinking agent 1 was replaced with the crosslinking agent 2 shown below and the content was changed as shown in Table 3. did. In Example 8, in Example 2, the dicumyl peroxide of the crosslinking agent 1 was replaced with the crosslinking agent 3 shown below, and the others were carried out in the same manner as in Example 2. In Example 9, the dicumyl peroxide of the crosslinking agent 1 in Example 2 was replaced with the crosslinking agent 4 shown below, and the others were carried out in the same manner as in Example 2.

  In Example 10, it carried out similarly to Example 2 except having changed the content of sodium hydrogen carbonate and calcium oxide into about half (7 parts by mass) (expanding ratio 7 times). In Example 11, Example 2 was carried out in the same manner as Example 2 except that cesium oxide was used instead of calcium oxide and the content thereof was changed to 10 parts by mass. In Example 12, Example 2 was carried out in the same manner as Example 2 except that potassium oxide was used instead of calcium oxide and the content thereof was changed to 10 parts by mass.

  In Examples 13 and 14, polyolefin foams were produced by a two-stage foaming method. Regarding the raw material of the foam, in Example 13, the content of sodium hydrogen carbonate was increased to 45 parts by mass in Example 2, and the content of calcium oxide was increased to 60 parts by mass (expanding ratio 40 times). In Example 14, the content of sodium hydrogen carbonate was increased to 50 parts by mass in Example 2, and the content of calcium oxide was increased to 70 parts by mass (foaming ratio 45 times).

  In the first stage of foaming, the foam material was kneaded with a kneader and a roll and then heated at 155 ° C. for 40 minutes for foaming to obtain a primary foam. Since the heating time is shorter than 60 minutes of the one-stage foaming method of Example 2, the decomposition of sodium hydrogen carbonate is in progress. In the second stage foaming, the primary foam was heated at 160 ° C. for 40 minutes for further foaming to obtain a secondary foam.

And about each Example, the deformation | transformation state was observed visually about the raw material of a foam, and what sliced the raw material, and those results were shown in Table 3.
Ethylene-vinyl acetate copolymer resin (EVA): vinyl acetate content 10 mass%, MFR (melt flow rate) 3 g / 10 min, density 0.929 g / cm ³ , manufactured by Tosoh Corporation, Ultrasen 540.

Crosslinking agent 2: 4,4-di (t-butylperoxy) -n-butyl valerate, manufactured by Kayaku Akzo Co., Ltd., Trigonoccus 17-40.
Crosslinking agent 3: 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, Kayaku Akzo Co., Ltd., Kayahexa AD-40C.

  Cross-linking agent 4: α, α′-di (t-butylperoxy-m-isopropyl) benzene, manufactured by Kayaku Akzo Co., Ltd., Parkadox 14-40C.

表３に示したように、エチレン−酢酸ビニル共重合樹脂を用いた実施例６においては、原反の変形はなく、スライスしたものについも変形は小さい結果が得られた。また、架橋剤の種類を変えた実施例７〜９においても、原反の変形はなく、スライスしたものについも変形が小さい結果が得られた。酸化カルシウムの含有量を約半分に減少させた実施例１０においても、原反の変形はなく、スライスしたものについも変形が小さい結果が得られた。酸化カルシウムに代えて酸化セシウム又は酸化カリウムを使用した実施例１１又は１２においても、原反の変形はなく、スライスしたものについも変形が小さい結果であった。

As shown in Table 3, in Example 6 using the ethylene-vinyl acetate copolymer resin, there was no deformation of the original fabric, and the result of small deformation was obtained even for the sliced one. Also, in Examples 7 to 9 in which the type of the crosslinking agent was changed, there was no deformation of the original fabric, and a result of small deformation was obtained even for the sliced one. Even in Example 10 in which the content of calcium oxide was reduced to about half, there was no deformation of the original fabric, and a result of small deformation was obtained even for the sliced one. In Example 11 or 12 using cesium oxide or potassium oxide instead of calcium oxide, there was no deformation of the original fabric, and the result of the deformation was small even for the sliced one.

  Further, in Examples 13 and 14 in which the foam produced by the two-stage foaming method was used to increase the sodium bicarbonate content to increase the foaming ratio and the calcium oxide content was increased, the deformation of the original fabric There was no change in the sliced material.

In addition, the said embodiment can also be changed and actualized as follows.
-As a water absorbing agent, the absorption of water vapor in the foam can be adjusted by using a plurality of types of alkali metal or alkaline earth metal oxides.

-Using multiple types of polyolefin resin, the physical properties of the foam can be adjusted.
Further, the technical idea that can be grasped from the embodiment will be described below .

  4. The polyolefin resin foam according to claim 1, wherein the alkali metal or alkaline earth metal oxide is calcium oxide, cesium oxide, or potassium oxide. 5. Production method. According to this manufacturing method, the effect of the invention according to any one of claims 1 to 3 can be sufficiently exhibited.

· The reheating process for producing a polyolefin resin foam of claim 1, characterized in that it is carried out for 5 to 24 hours at 70 to 120 ° C.. According to this manufacturing method, the effect of the invention according to claim 1 can be improved.

  Polyolefin resin, consisting of sodium hydrogen carbonate that decomposes when heated to generate carbon dioxide and water vapor, and an oxide of an alkali metal or alkaline earth metal, and the oxide content is 5 per 100 parts by mass of the polyolefin resin. A polyolefin resin foam obtained by mixing and heating a raw material of ˜100 parts by mass and foaming a polyolefin resin with carbon dioxide gas generated by decomposition of sodium hydrogen carbonate. In this case, the polyolefin resin foam is not deformed and has a foaming ratio of 5 times or more.

Claims (2)

It consists of a polyolefin resin, sodium hydrogen carbonate that decomposes when heated to generate carbon dioxide and water vapor, and an oxide of an alkali metal or alkaline earth metal, and the content of the oxide is 5 per 100 parts by mass of the polyolefin resin. A method for producing a polyolefin resin foam in which a raw material of ˜100 parts by mass is mixed and then heated, and the polyolefin resin is foamed with carbon dioxide gas generated by decomposition of sodium hydrogencarbonate, cooled after the heating, and then 50 A method for producing a polyolefin resin foam, characterized by reheating at ~ 120 ° C for 3 to 24 hours. The method for producing a polyolefin resin foam according to claim 1, wherein the raw material contains a crosslinking agent .