帯電防止剤の表面濃度は、０．１〜３．０μｇ／ｃｍ２に限定される。ポリオレフィン系樹脂押出発泡体の帯電防止剤は、ほぼ気泡膜表面にブリードアウトすることから、帯電防止剤の表面濃度は、帯電防止剤添加量、発泡体密度、発泡体のセルサイズより以下の近似式で計算される。したがって下記近似式より算出した帯電防止剤の表面濃度が０．１〜３．０μｇ／ｃｍ２を満たす範囲内で、帯電防止剤添加量、発泡体密度、発泡体のセルサイズがそれぞれの好ましい範囲から選択される。帯電防止剤の表面濃度が０．１〜２．０μｇ／ｃｍ２であると吸水率が低くなるので好ましい。帯電防止剤の表面濃度が０．１〜１．０μｇ／ｃｍ２であると吸水率が更に低くなるのでより好ましい。
帯電防止剤表面濃度（μｇ／ｃｍ２）
＝（（樹脂１００質量部に対する帯電防止剤添加量（質量部）／１００）／気泡膜表面積）×１００００００
気泡膜表面積（ｃｍ２／ｇ発泡体）
＝３．２９×（１−発泡体密度／樹脂密度）／（セルサイズ／２×発泡体密度）
ここで、各物性値の単位は、
発泡体密度：ｇ／ｃｍ３ 樹脂密度：ｇ／ｃｍ３ セルサイズ：ｃｍ
The surface concentration of the antistatic agent is limited to 0.1 to 3.0 μg / cm 2 . Since the antistatic agent of polyolefin resin extruded foam almost bleeds out to the cell membrane surface, the surface concentration of the antistatic agent is less than the amount of antistatic agent added, the foam density, and the cell size of the foam. Calculated by the formula. Therefore, within the range where the surface concentration of the antistatic agent calculated from the following approximate expression satisfies 0.1 to 3.0 μg / cm 2 , the preferable amount of the antistatic agent added amount, the foam density, and the cell size of the foam are respectively preferable ranges. Selected from. When the surface concentration of the antistatic agent is 0.1 to 2.0 μg / cm 2 , the water absorption rate is lowered, which is preferable. When the surface concentration of the antistatic agent is 0.1 to 1.0 μg / cm 2 , the water absorption is further reduced, which is more preferable.
Antistatic agent surface concentration (μg / cm 2 )
= ((Antistatic agent added amount with respect to 100 parts by mass of resin (parts by mass) / 100) / Bubble membrane surface area) × 1000000
Bubble membrane surface area (cm 2 / g foam)
= 3.29 x (1-foam density / resin density) / (cell size / 2 x foam density)
Here, the unit of each physical property value is
Foam density: g / cm 3 Resin density: g / cm 3 Cell size: cm
[実施例２]
１５０ｍｍのバレル内径を有するスクリュー型押出機の供給領域に９００ｋｇ／時間の速度で、低密度ポリエチレン（密度０．９２１ｇ／ｃｍ３、ＭＩ＝２．９ｇ／１０分）を、樹脂１００質量部に対し、気泡調整剤としてタルク１．５質量部と帯電防止剤としてパルミチン酸モノグリセライド６０質量％とアルキル基が１０から２０（炭素数の平均値＝１５）であるアルキルスルホン酸ナトリウム４０質量％の混合物０．５質量部ともに供給した。押出機のバレル温度を１９０℃〜２１０℃に調整し、押出機の先端に取り付けた発泡剤注入口から発泡剤としてノルマルブタン（燃焼範囲下限値：１．８ｖｏｌ％）をこの樹脂１００質量部に対し１３質量部を圧入し、当該溶融樹脂組成物と混合して発泡性溶融混合物とした。この発泡性溶融混合物を押出機の出口に取り付けた冷却装置で１０８℃まで冷却した後、約３．４ｍｍの平均厚みと約２１５ｍｍ幅の開口部形状を有するオリフィスプレートより、常温、大気圧下の雰囲気中に連続的に押し出して発泡させ、樹脂発泡体の引き取り速度を調整しながら成形して、厚み６２ｍｍ、幅６００ｍｍ、長さ１０００ｍｍ、セルサイズ０．０８ｃｍ、密度０．０２２ｇ／ｃｍ３、独立気泡率９５％、帯電防止剤の表面濃度約１．４μｇ／ｃｍ２の板状樹脂発泡体を得た。得られた発泡体について発泡後３０分に帯電圧の測定を行い、この発泡体を発泡１時間後から４０℃で１０日間その後室温で３日間保存した後、吸水率の評価を行なった。その結果を表１に示す。
[Example 2]
Low-density polyethylene (density 0.921 g / cm 3 , MI = 2.9 g / 10 min) is supplied to a supply area of a screw-type extruder having a barrel inner diameter of 150 mm at a speed of 900 kg / hour with respect to 100 parts by mass of the resin. , A mixture of 1.5 parts by mass of talc as a foam regulator, 60% by mass of monoglyceride palmitate as an antistatic agent, and 40% by mass of sodium alkylsulfonate having an alkyl group of 10 to 20 (average carbon number = 15) Both 5 parts by mass were supplied. The barrel temperature of the extruder was adjusted to 190 ° C. to 210 ° C., and normal butane (combustion range lower limit: 1.8 vol%) was added to 100 parts by mass of the resin as a blowing agent from a blowing agent inlet attached to the tip of the extruder. On the other hand, 13 parts by mass was press-fitted and mixed with the molten resin composition to obtain a foamable molten mixture. After cooling this foamable molten mixture to 108 ° C. with a cooling device attached to the exit of the extruder, it was cooled at room temperature and atmospheric pressure from an orifice plate having an average thickness of about 3.4 mm and an opening shape of about 215 mm wide. foamed continuously extruded into the atmosphere, and molded while adjusting the drawing speed of the resin foam, thickness 62 mm, width 600 mm, length 1000 mm, cell size 0.08 cm, density of 0.022 g / cm 3, independently Bubble ratio 95%, antistatic agent surface concentration about 1. A 4 μg / cm 2 plate-like resin foam was obtained. The obtained foam was measured for 30 minutes after foaming, and after 1 hour from foaming, the foam was stored at 40 ° C. for 10 days and then at room temperature for 3 days, and then the water absorption was evaluated. The results are shown in Table 1.
