JP3637188B2

JP3637188B2 - Method for producing foam

Info

Publication number: JP3637188B2
Application number: JP29049597A
Authority: JP
Inventors: 敏中野
Original assignee: Tokuyama Corp
Current assignee: Tokuyama Corp
Priority date: 1997-10-07
Filing date: 1997-10-07
Publication date: 2005-04-13
Anticipated expiration: 2017-10-07
Also published as: JPH11106538A

Description

【０００１】
【発明の属する技術分野】
本発明は、発泡体の製造方法に関し、被発泡物質がポリマー、無機酸化物若しくは炭素質物質又はこれらの混合物からなる発泡体を所望の発泡倍率に効率よく製造する方法を提供する。
【０００２】
【従来の技術】
一般に、ポリマー例えばポリ塩化ビニルなどを被発泡物質とする発泡体を得るには、従来、主として化学発泡剤が用いられている。化学発泡剤としては、酢酸アミル、酢酸ブチル、ジアゾアミノベンゼンなどの有機質発泡剤と炭酸水素ナトリウム、炭酸アンモニウムなどの無機質発泡剤があげられるが、無機質発泡剤を用いた場合、均一にコントロールされた発泡体を得ることは困難であるばかりでなく、発泡倍率も５〜６倍が限度であり、高発泡倍率の発泡体は得られない。一方、有機質発泡剤を用いた場合は比較的高発泡倍率の発泡体が得られるが、発泡倍率には、発泡剤の種類及びその配合割合、発泡剤の分解温度のコントロール、ポリマーの種類及び安定剤の種類等の各要素が複雑に関係し、所望の発泡倍率にコントロールした発泡体を得ることは容易でなく、試行錯誤的に予備試験を繰り返し行なう必要があるなど繁雑であるという欠点を有する。
【０００３】
【発明が解決しようとする課題】
上記の現状に鑑み、本発明は所望の発泡倍率にコントロールが容易なポリマー発泡体等の発泡材料の製造方法を提供することを課題とする。また発泡倍率のみならず得られる発泡体の硬質、軟質、弾性質などの特性のコントロールについてもその方法を開示する。さらにまた被発泡物質がポリマー以外の無機酸化物若しくは炭素質物質又はポリマーとこれらの混合物である場合にも適用できる発泡体の製造方法の提供を課題とする。
【０００４】
【課題を解決するための手段】
本発明者は、上記課題を達成すべく種々検討した結果、従来一般に用いられている化学発泡剤に代えて樹脂エマルジョンを用いるとともに、発泡倍率調節剤として脱水ゲル化促進剤を併せ用いることによって目的を達成し得ることを見いだした。
【０００５】
化学発泡剤を用いずに樹脂エマルジョン自体を発泡剤に用いること及び脱水ゲル化促進剤を発泡倍率調節剤に用いることは、いずれも従来見られない新しい知見である。すなわち本発明は粉末状のポリマー、無機酸化物若しくは炭素質物質又はこれらの混合物からなる被発泡物質に樹脂エマルジョン及び脱水ゲル化促進剤を配合し、混練した後に加熱発泡させることを特徴とする発泡体の製造方法である。
【０００６】
【発明の実施の形態】
本発明においてはまず被発泡物質が粉末状であることが必要である。粉末状にすることにより被発泡物質を樹脂エマルジョン及び脱水ゲル化促進剤と混練して得られるペースト状物質の粘度が向上し、加熱発泡時における発泡セルの崩壊が少なくガス圧を有効に利用して効率的な発泡がなされる。
【０００７】
粉末状の粒径範囲としては一般に直径１ｍｍ以下、好ましくは４０〜６０メッシュである。
【０００８】
被発泡物質としてのポリマーは合成樹脂の他、木粉等の天然ポリマーも用いられる。合成樹脂としては重合性不飽和結合を有する単量体の単独重合体又はその共重合体、及びジカルボン酸とジアルコールから、若しくは相当するラクトンから誘導されるポリエステルなどがあげられる。重合体又はその共重合体としては、例えば塩化ビニル樹脂、ポリプロピレン、ポリエチレン、酢酸ビニル樹脂、ポリスチレン、（メタ）アクリル樹脂、塩化ビニリデン樹脂、塩素化ポリエチレン、塩素化ポリプロピレン、ブタジエン樹脂、プロピオン酸ビニル樹脂、ポロビニルアルコール及びその誘導体、ＡＡＳ樹脂、ＡＥＳ樹脂、ＡＳ樹脂、ＡＢＳ樹脂及びＭＢＳ樹脂などが挙げられ、好ましくは塩化ビニル樹脂、ポリプロピレン、ポリエチレン、酢酸ビニル樹脂及びポリスチレンが用いられる。ジカルボン酸とジアルコールから若しくは相当するラクトンから誘導されるポリエルテルとしては、例えばポリエチレンテレフタレート、ポロビニレンテレフタレートなどが挙げられる。
【０００９】
これらのポリマーの１種又は２種以上の混合物を用いることができる。また、無機酸化物としては第IIＡ族、第IIIＡ族、第IVＡ族、第VIＡ族及び第VIII族の金属酸化物又はその塩であり、例えばアルミナ、酸化カルシウム、酸化マグネシウム、炭酸カルシウム、石膏、シリカ、酸化クロム及び酸化鉄などが挙げられる。さらに上記の金属酸化物若しくはその塩はカオリン、活性白土、ケイ砂、ケイ石、ケイソウ土、タルク、マイカ、パーライト、ベントナイト、ボーキサイ、ゼオライト、硝子粉、フェライトなどであってもよい。しかし好ましくは一般にシリカ、硝子粉、アルミナ、フェライト、酸化チタン、酸化クロム、酸化鉄、タルク及びゼオライトが用いられる。また炭素質物質としては、黒鉛及び無定形炭素が好ましく用いられる。
【００１０】
本発明の最大の特徴は前記の被発泡物質に発泡剤として樹脂エマルジョン、発泡倍率調節剤として脱水ゲル化促進剤を配合し、混練した後に加熱発泡させることである。
【００１１】
樹脂エマルジョンと脱水ゲル化促進剤を併用することによって所望とする任意の発泡倍率の発泡体を得ることができる。
【００１２】
これら両者を併せ用いることによって良好な発泡体が得られる作用機構は、明らかではないが本発明者は次のように推測している。即ち本発明における発泡の作用機構は、樹脂エマルジョン中の分散質である樹脂表面の付着水が加熱時に蒸気化するエネルギーと脱水ゲル化促進剤の作用によるゲル化時の良好な粘度上昇の相方の条件が相俟って良好な製泡がなされるものと推測される。尚、本明細書においてゲル化とは非ゾルの状態を指称する。
【００１３】
本発明に用いられる樹脂エマルジョンは一般に市販されている各種の樹脂エマルジョンを用いることができる。例えば酢酸ビニル樹脂エマルジョン、酢酸ビニル−アクリロニトリル共重合体エマルジョン、酢酸ビニル−エチレン共重合体エマルジョン、酢酸ビニル−エチレン−塩化ビニル共重合体エマルジョン、アクリル共重合体エマルジョン、アクリル−スチレン共重合体エマルジョン、合成ゴムエマルジョン若しくは天然ゴムエマルジョンなどが挙げられる。エマルジョンにするため水に分散させるには適宜の乳化剤を用いることができ、一般には界面活性剤が用いられ、例えばノニオン界面活性剤及びアニオン界面活性剤を用いることができる。
【００１４】
樹脂エマルジョン中の樹脂の分子量は特に制限はないが、一般に１０，０００〜１００，０００、好ましくは３０，０００〜６０，０００が望ましい。また樹脂エマルジョンの濃度は樹脂分が２０〜７０重量部、好ましくは３０〜６５重量部のものが用いられる。
【００１５】
樹脂エマルジョンの配合割合は、通常被発泡物質１００重量部に対して樹脂エマルジョン２４〜３５０重量部が用いられ、樹脂エマルジョンの樹脂濃度も考慮してこれらの範囲内で適宜決定すればよい。また脱水ゲル化促進剤としては、硼酸若しくはその塩類、電解質例えば食塩、塩化カルシウム、硫酸ナトリウム等の水溶性塩類、各種イオン界面活性剤が挙げられるが、特に硼酸、食塩、塩化カルシウムが好ましく用いられる。
【００１６】
脱水ゲル化促進剤の配合割合は一般に樹脂エマルジョン中の水分１００重量部に対して脱水ゲル化促進剤０．１〜２０重量部、好ましくは１〜５重量部が用いられる。
【００１７】
本発明において脱水ゲル化促進剤は前記のように良好な発泡体を得るために必要であり、また発泡倍率の調節剤として作用する。一般に、被発泡物質に対する樹脂エマルジョンの配合割合が増せば発泡倍率は高くなるが、被発泡物質と樹脂エマルジョンの具体的な各種組み合わせにおいて両者の配合割合の自由度はあまり大きいものではない。従ってこれら両者の配合割合のみで発泡倍率をコントロールするには限度がある。しかるに本発明においては脱水ゲル化促進剤を用いて発泡倍率を良好にコントロールすることができる。即ち、脱水ゲル化促進剤の配合割合の増減によって、低発泡から高発泡までの所望の発泡倍率の発泡体を得ることができる。また、本発明においては、発泡倍率のみならず得られる発泡体の硬質、軟質、弾性質などの特性コントロールも比較的容易に行なうことができる。即ち、硬質の発泡体を得るには、例えば樹脂エマルジョンとして塩化ビニル樹脂エマルジョン、アクリル樹脂エマルジョンを用い、被発泡物質のポリマーとして塩化ビニル樹脂、ポリプロピレン及び無機酸化物としてシリカ、アルミナを用いればよい。軟質の発泡体を得るには例えば樹脂エマルジョンとして酢酸ビニル樹脂及びゴムエマルジョンを用い、被発泡物質として塩化ビニル樹脂を用いればよい。また弾性質の発泡体を得るには、例えば樹脂エマルジョンとしてゴムエマルジョンを用い、被発泡物質としてポリプロピレン、ポリエチレン、ポリ塩化ビニルを用いることにより目的が達成される。
【００１８】
さらに一般に比較的に大きな独立セルの多い発泡体を得るには得られる発泡体の厚さを８ｍｍ程度未満にして、且つ樹脂エマルジョンにゴムエマルジョンを用いるとよい。
【００１９】
また比較的小さな連続セルの多い全体的に均一な発泡体を得るには、得られる発泡体の厚さを８ｍｍ程度以上にして、且つ樹脂エマルジョンとして塩化ビニル樹脂エマルジョン、酢酸ビニルエマルジョンを用いればよい。
【００２０】
本発明の発泡体を得るには、前記の粉末状の被発泡物質、樹脂エマルジョン及び脱水ゲル化促進剤を配合する第１工程に続いて第２工程としてこれら３者の配合物を十分に混練することが必要である。
【００２１】
この混練工程は続く加熱発泡工程においてガス圧を利用して効率よく発泡セルを形成する生地を作る上で重要である。例えばヘンシエルミキサー、リボンブレンダー、Ｖ型ブレンダーなどを用いて均一に十分に混練することが望まれる。
【００２２】
一般に望ましいペースト状の粘度は被発泡物質の種類によって異なり、例えば塩化ビニル樹脂の場合は高い発泡倍率の発泡体を得るためには低粘度が好ましく、一方アルミナの場合は、高粘度でも高い発泡倍率の発泡体が得られる。混練工程に続いて、第３工程として加熱発泡を行なう。
【００２３】
一般に加熱発泡はロール成形機、押出し成形機又は金型成形機等を用いてバルク、シート、フィルム等の成形物又は任意の形状の成形物として、好ましくは非酸化的雰囲気下で加熱して行なわれる。加熱方法は、好ましくは主としてゲル化促進を目的とする予備加熱と、主として発泡を目的とする発泡加熱の二段加熱が望ましい。
【００２４】
これらの両加熱は被発泡体の種類、樹脂エマルジョンの種類及び所望とする発泡体の特性によって異なるが、通常予備加熱は１００℃以下で１〜５分程度、また発泡加熱は１００〜２１０℃程度で押出し成形、ロール成形などの連続成形の場合１〜５分程度、金型成形などの静置成形の場合８〜１０分程度が好ましい。
【００２５】
【実施例１】
塩化ビニル樹脂粉末３６ｇに酢酸ビニル樹脂エマルジョン（樹脂分濃度５０％）２９ｇ及びシリカ粉末２．１ｇを配合し充分混練し、これに硼酸カルシウム０．３ｇを添加し、更に混練して後に密閉金型に入れ、常温から１００℃まで５分間、次いで１９０℃までを１０分間かけて昇温せしめ、その後、自然冷却して比重０．３２、発泡倍率４．３の発泡体５０ｇを得た。発泡体の表皮は可塑剤２０重量％添加の軟質塩化ビニル樹脂相当の硬さを有し弾性質であった。
【００２６】
【実施例２】
塩化ビニル樹脂粉末１３ｇに酢酸ビニル樹脂エマルジョン（樹脂分濃度５０％）１９．６ｇ、シリカ粉末１．４ｇ及び食塩０．２ｇを配合し充分混練して密閉金型に入れ、実施例１と同じ条件で加熱冷却して、比重０．２５、発泡倍率５．６の発泡体２１．７ｇを得た。発泡体の表皮は可塑剤２０重量％添加の軟質塩化ビニル樹脂相当の硬さを有し弾性質であった。
【００２７】
【実施例３】
塩化ビニル樹脂粉末３６ｇにスチレン−ブタジエン系ゴムラテックス（固形分４９％、日本ゼオン社商品名ＮＩＰＯＬ−ＬＸ４３）２３ｇ、シリカ粉末２．１ｇ及び硼酸カルシウム０．６９ｇを配合し充分混練して密閉金型に入れ、実施例１と同じ条件で加熱冷却して、比重０．６、発泡倍率２．３の極めてゴム状弾性質に富んだ発泡体５０ｇを得た。
【００２８】
【実施例４】
シリカ粉末２０ｇ及び酸化クロム粉末０．１ｇに酢酸ビニル樹脂エマルジョン（樹脂分濃度５０％）１８．５ｇ及び硼酸カルシウム０．２ｇを配合し充分混練して密閉金型に入れ、常温から１００℃まで５分間、次いで２００℃までを１０分間かけて昇温せしめ、その後、自然冷却して厚さ０．２５ｃｍの１０ｃｍ平方のシート状発泡体１５．８ｇを得た。発泡体は比重０．５７、発泡倍率３．４でその表皮は比較的硬く極めて高い弾性質を有していた。
【００２９】
【実施例５】
シリカ粉末９０ｇに実施例３で用いたスチレン−ブタジエン系ゴムラテックス５０ｇ及び硼酸カルシウム０．０３ｇを配合し充分混練して密閉金型に入れ、常温から１００℃まで５分間、次いで１８０℃までを８分間かけて昇温せしめ、その後、自然冷却して比重０．７６、発泡倍率１．８６の発泡体１２０ｇを得た。発泡体は極めて屈曲性に富み、弾性質であった。
【００３０】
【実施例６】
フロート硝子粉末２０ｇに酢酸ビニル樹脂エマルジョン（樹脂分濃度５０％）１６．２ｇ及び食塩０．１５ｇを配合し充分混練して密閉金型に入れ、実施例４と同じ条件で加熱冷却し、比重０．３９、発泡倍率４．７の発泡体１３０ｇを得た。
【００３１】
【実施例７】
ポリプロピレン粉末３６ｇに酢酸ビニル樹脂エマルジョン（樹脂分濃度５０％）２９ｇ、シリカ粉末２．１ｇ及び硼酸カルシウム０．０２ｇを配合し充分混練して密閉金型に入れ、実施例４と同じ条件で加熱冷却して、比重０．３、発泡倍率３．７の発泡体４７ｇを得た。
【００３２】
【実施例８】
アルミナ粉末４０ｇに酢酸ビニル樹脂エマルジョン（樹脂分濃度５０％）３５．２ｇ、食塩０．３ｇ及び硼酸カルシウム０．２ｇを配合し充分混練して密閉金型に入れ、常温から１００℃まで５分間、次いで１８０℃までを１０分間かけて昇温せしめ、その後、自然冷却して比重０．３８、発泡倍率８．４の発泡体５３．７ｇを得た。発泡体の表皮は、可塑剤１５重量％添加の軟質塩化ビニル樹脂相当の硬さを有し弾性質であった。
【００３３】
【実施例９】
黒鉛粉末４２ｇに酢酸ビニル樹脂エマルジョン（樹脂分濃度５０％）４１．９ｇ、シリカ粉末２．１ｇ及び硼酸カルシウム０．８ｇを配合し充分混練して密閉金型に入れ、常温から１００℃まで５分間、次いで２１０℃までを１０分間かけて昇温せしめ、その後、自然冷却して比重０．４１、発泡倍率４．７の発泡体６１．５ｇを得た。
【００３４】
【実施例１０】
塩化ビニル樹脂粉末１３ｇに酢酸ビニル樹脂エマルジョン（樹脂分濃度５０％）１９．５ｇ及びシリカ粉末１．０ｇを配合し充分混練し、これに脱水ゲル化促進剤を添加し、更に混練して後に密閉金型に入れ、実施例１と同じ条件で加熱冷却して発泡体を得た。用いた脱水ゲル化促進剤の添加量と得られた発泡体の発泡倍率は表１に示す通りであった。
【００３５】
【表１】

【００３６】
【実施例１１】
シリカ粉末８０ｇにアクリル−スチレン共重合体エマルジョン（樹脂分濃度４７％ヘキスト社商品名モビニール７５２）２４ｇ及び脱水ゲル化促進剤として食塩を配合し充分混練して後に密閉金型に入れ、実施例８と同じ条件で加熱冷却して表皮が硬く極めて高い剛性を有し、可塑剤無添加の硬質塩化ビニル樹脂に酷似した発泡体を得た。用いた食塩の添加量と得られた発泡体の発泡倍率は表２に示す通りであった。
【００３７】
【表２】

【００３８】
【発明の効果】
従来の化学発泡剤を用いた発泡体の製造方法では、発泡剤の種類及びその配合割合、発泡剤の分解温度のコントロール、ポリマーの種類及び安定剤の種類等の各要素が発泡倍率に複雑に関係し、所望の発泡倍率にコントロールした発泡体を得るのが容易でなかったのに対し、本発明では発泡倍率を主として脱水ゲル化促進剤で行なうことができ、発泡倍率のコントロールが容易であり、発泡倍率が１〜１０倍の広範囲に亘って所望とする発泡体を得ることができる。このため例えば高発泡体として各種断熱材、低発泡体として車輌のシートのクッション材や断熱内装材などの用途に必要に応じて対応することができる。
【００３９】
また発泡体の硬質、軟質、弾性質などの特性のコントロールも比較的容易である。従って例えば使用する面が平面の場合はいずれでもよいが、局面に対しては軟質発泡体、クッション性を要する場合は弾性発泡体など必要に応じて使い分けをすることができる。さらに被発泡物質としてフェライト又は黒鉛を用いた場合、電波吸収体としても有用な発泡体を得ることができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a foam, and provides a method for efficiently producing a foam having a foamed material composed of a polymer, an inorganic oxide, a carbonaceous material, or a mixture thereof at a desired expansion ratio.
[0002]
[Prior art]
In general, a chemical foaming agent has been mainly used in the past to obtain a foam having a foamed material such as a polymer such as polyvinyl chloride. Chemical foaming agents include organic foaming agents such as amyl acetate, butyl acetate, and diazoaminobenzene, and inorganic foaming agents such as sodium bicarbonate and ammonium carbonate. When inorganic foaming agents are used, they are uniformly controlled. Not only is it difficult to obtain a foam, but also the expansion ratio is limited to 5 to 6 times, and a foam with a high expansion ratio cannot be obtained. On the other hand, when an organic foaming agent is used, a foam with a relatively high foaming ratio can be obtained. However, the foaming ratio includes the type of foaming agent and its blending ratio, the control of the decomposition temperature of the foaming agent, the type of polymer and its stability. Each element such as the type of agent is complicatedly related, and it is not easy to obtain a foam controlled to a desired foaming ratio, and there is a disadvantage that it is complicated such that it is necessary to repeat a preliminary test by trial and error. .
[0003]
[Problems to be solved by the invention]
In view of the above-mentioned present situation, an object of the present invention is to provide a method for producing a foam material such as a polymer foam that can be easily controlled to a desired foaming ratio. Also disclosed is a method for controlling not only the expansion ratio but also the properties of the resulting foam, such as hard, soft, and elastic. It is another object of the present invention to provide a method for producing a foam which can be applied even when the foamed material is an inorganic oxide other than a polymer, a carbonaceous material, or a polymer and a mixture thereof.
[0004]
[Means for Solving the Problems]
As a result of various studies to achieve the above-mentioned problems, the inventor of the present invention uses a resin emulsion in place of a conventionally used chemical foaming agent, and also uses a dehydration gelation accelerator as a foaming ratio regulator. I found that I could achieve.
[0005]
The use of the resin emulsion itself as a foaming agent without using a chemical foaming agent and the use of a dehydration gelation accelerator as a foaming ratio adjusting agent are both new findings that have not been seen in the past. That is, the present invention is a foam characterized by blending a resin emulsion and a dehydrating gelation accelerator into a foamed material composed of a powdered polymer, an inorganic oxide, a carbonaceous material, or a mixture thereof, kneading and then foaming by heating. It is a manufacturing method of a body.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, it is first necessary that the foamed material is in a powder form. By making powder, the viscosity of the paste-like substance obtained by kneading the foamed substance with the resin emulsion and the dehydration gelation accelerator is improved, and the foamed cells are less collapsed during heating and foaming, and the gas pressure is effectively used. Efficient foaming.
[0007]
The powdery particle size range is generally 1 mm or less in diameter, preferably 40 to 60 mesh.
[0008]
As a polymer to be foamed, a natural polymer such as wood powder is used in addition to a synthetic resin. Examples of the synthetic resin include a homopolymer of a monomer having a polymerizable unsaturated bond or a copolymer thereof, and a polyester derived from a dicarboxylic acid and a dialcohol or a corresponding lactone. Examples of the polymer or copolymer thereof include vinyl chloride resin, polypropylene, polyethylene, vinyl acetate resin, polystyrene, (meth) acrylic resin, vinylidene chloride resin, chlorinated polyethylene, chlorinated polypropylene, butadiene resin, and vinyl propionate resin. Polo vinyl alcohol and derivatives thereof, AAS resin, AES resin, AS resin, ABS resin and MBS resin, and the like, preferably vinyl chloride resin, polypropylene, polyethylene, vinyl acetate resin and polystyrene. Polyethers derived from dicarboxylic acids and dialcohols or corresponding lactones include, for example, polyethylene terephthalate and porovinylene terephthalate.
[0009]
One or a mixture of two or more of these polymers can be used. Examples of the inorganic oxide include Group IIA, Group IIIA, Group IVA, Group VIA and Group VIII metal oxides or salts thereof, such as alumina, calcium oxide, magnesium oxide, calcium carbonate, gypsum, Examples thereof include silica, chromium oxide and iron oxide. Further, the metal oxide or salt thereof may be kaolin, activated clay, silica sand, silica stone, diatomaceous earth, talc, mica, perlite, bentonite, bauxite, zeolite, glass powder, ferrite, and the like. However, preferably silica, glass powder, alumina, ferrite, titanium oxide, chromium oxide, iron oxide, talc and zeolite are generally used. As the carbonaceous material, graphite and amorphous carbon are preferably used.
[0010]
The greatest feature of the present invention is that a resin emulsion as a foaming agent and a dehydration gelation accelerator as a foaming ratio adjusting agent are blended in the foamed material, kneaded and then heated and foamed.
[0011]
A foam having any desired expansion ratio can be obtained by using a resin emulsion and a dehydration gelation accelerator in combination.
[0012]
Although the mechanism of action by which a good foam can be obtained by using both of these is not clear, the present inventor presumes as follows. That is, the action mechanism of foaming in the present invention is that the water adhering to the resin surface, which is a dispersoid in the resin emulsion, vaporizes when heated and the viscosity rises favorably during gelation due to the action of the dehydrating gelation accelerator. It is presumed that good foaming is achieved in combination with the conditions. In this specification, gelation refers to a non-sol state.
[0013]
As the resin emulsion used in the present invention, various commercially available resin emulsions can be used. For example, vinyl acetate resin emulsion, vinyl acetate-acrylonitrile copolymer emulsion, vinyl acetate-ethylene copolymer emulsion, vinyl acetate-ethylene-vinyl chloride copolymer emulsion, acrylic copolymer emulsion, acrylic-styrene copolymer emulsion, Synthetic rubber emulsion or natural rubber emulsion can be used. An appropriate emulsifier can be used for dispersing in water to form an emulsion, and generally a surfactant is used. For example, a nonionic surfactant and an anionic surfactant can be used.
[0014]
The molecular weight of the resin in the resin emulsion is not particularly limited, but is generally 10,000 to 100,000, preferably 30,000 to 60,000. The concentration of the resin emulsion is such that the resin content is 20 to 70 parts by weight, preferably 30 to 65 parts by weight.
[0015]
The blending ratio of the resin emulsion is usually 24 to 350 parts by weight of the resin emulsion with respect to 100 parts by weight of the foamed substance, and may be appropriately determined within these ranges in consideration of the resin concentration of the resin emulsion. Examples of the dehydration gelation accelerator include boric acid or salts thereof, electrolytes such as water-soluble salts such as sodium chloride, calcium chloride, and sodium sulfate, and various ionic surfactants. Boric acid, sodium chloride, and calcium chloride are particularly preferably used. .
[0016]
The mixing ratio of the dehydration gelation accelerator is generally 0.1 to 20 parts by weight, preferably 1 to 5 parts by weight, based on 100 parts by weight of water in the resin emulsion.
[0017]
In the present invention, the dehydration gelation accelerator is necessary for obtaining a good foam as described above, and also acts as a regulator for the expansion ratio. In general, as the blending ratio of the resin emulsion to the foamed material increases, the foaming ratio increases. However, in various specific combinations of the foamed material and the resin emulsion, the degree of freedom of the blending ratio of both is not so great. Therefore, there is a limit in controlling the foaming ratio only by the blending ratio of these two. However, in the present invention, the expansion ratio can be well controlled using a dehydrating gelation accelerator. That is, a foam having a desired expansion ratio from low foaming to high foaming can be obtained by increasing or decreasing the blending ratio of the dehydrating gelation accelerator. In the present invention, not only the expansion ratio but also the properties of the obtained foam such as hard, soft and elastic can be controlled relatively easily. That is, in order to obtain a hard foam, for example, a vinyl chloride resin emulsion or an acrylic resin emulsion may be used as the resin emulsion, and a vinyl chloride resin, polypropylene, and silica or alumina may be used as the polymer of the foamed material. In order to obtain a soft foam, for example, a vinyl acetate resin and a rubber emulsion may be used as the resin emulsion, and a vinyl chloride resin may be used as the foamed material. In order to obtain an elastic foam, the object is achieved, for example, by using a rubber emulsion as the resin emulsion and using polypropylene, polyethylene, or polyvinyl chloride as the foamed material.
[0018]
Furthermore, in general, in order to obtain a foam having a relatively large number of independent cells, the thickness of the obtained foam should be less than about 8 mm, and a rubber emulsion should be used as the resin emulsion.
[0019]
Further, in order to obtain an overall uniform foam having a relatively small number of continuous cells, the thickness of the obtained foam should be about 8 mm or more, and a vinyl chloride resin emulsion or a vinyl acetate emulsion may be used as the resin emulsion. .
[0020]
In order to obtain the foam of the present invention, these three blends are sufficiently kneaded as the second step following the first step of blending the above-mentioned powdery substance to be foamed, the resin emulsion and the dehydration gelation accelerator. It is necessary to.
[0021]
This kneading step is important in making a dough that efficiently forms foam cells using gas pressure in the subsequent heating and foaming step. For example, it is desirable to uniformly and sufficiently knead using a Henschel mixer, a ribbon blender, a V-type blender, or the like.
[0022]
Generally, the desired pasty viscosity varies depending on the type of foamed material. For example, in the case of a vinyl chloride resin, a low viscosity is preferable in order to obtain a foam having a high expansion ratio, whereas in the case of alumina, a high expansion ratio is obtained even at a high viscosity. Foam is obtained. Subsequent to the kneading step, heat foaming is performed as a third step.
[0023]
In general, heat foaming is carried out by heating in a non-oxidizing atmosphere, using a roll molding machine, an extrusion molding machine, a mold molding machine, etc., as a molded product such as a bulk, a sheet, or a film, or a molded product of any shape. It is. The heating method is preferably two-stage heating, which is preheating mainly for the purpose of promoting gelation and foaming heating mainly for the purpose of foaming.
[0024]
Both of these heatings vary depending on the type of foam to be foamed, the type of resin emulsion, and the desired properties of the foam. Usually, preheating is 100 ° C. or less for about 1 to 5 minutes, and foaming heating is about 100 to 210 ° C. In the case of continuous molding such as extrusion molding and roll molding, it is preferably about 1 to 5 minutes, and in the case of stationary molding such as mold molding, it is preferably about 8 to 10 minutes.
[0025]
[Example 1]
29 g of vinyl acetate resin emulsion (resin concentration: 50%) and 2.1 g of silica powder are blended in 36 g of vinyl chloride resin powder and kneaded thoroughly, and 0.3 g of calcium borate is added thereto, and further kneaded and then sealed mold The mixture was heated from room temperature to 100 ° C. for 5 minutes and then to 190 ° C. over 10 minutes, and then naturally cooled to obtain 50 g of a foam having a specific gravity of 0.32 and an expansion ratio of 4.3. The foam skin had a hardness equivalent to a soft vinyl chloride resin added with 20% by weight of a plasticizer and was elastic.
[0026]
[Example 2]
A mixture of 19.6 g of vinyl acetate resin emulsion (resin concentration: 50%), 1.4 g of silica powder and 0.2 g of sodium chloride in 13 g of vinyl chloride resin powder, kneaded thoroughly and placed in a closed mold, the same conditions as in Example 1 Then, 21.7 g of a foam having a specific gravity of 0.25 and an expansion ratio of 5.6 was obtained. The foam skin had a hardness equivalent to a soft vinyl chloride resin added with 20% by weight of a plasticizer and was elastic.
[0027]
[Example 3]
36 g of vinyl chloride resin powder is blended with 23 g of styrene-butadiene rubber latex (solid content 49%, trade name NIPOL-LX43, Nippon Zeon Co., Ltd.), 2.1 g of silica powder and 0.69 g of calcium borate, and kneaded thoroughly and sealed mold And heated and cooled under the same conditions as in Example 1 to obtain 50 g of an extremely rich rubber-like elastic material having a specific gravity of 0.6 and an expansion ratio of 2.3.
[0028]
[Example 4]
20 g of silica powder and 0.1 g of chromium oxide powder were mixed with 18.5 g of vinyl acetate resin emulsion (resin concentration: 50%) and 0.2 g of calcium borate, kneaded thoroughly, and placed in a closed mold. Then, the temperature was raised to 200 ° C. over 10 minutes, and then naturally cooled to obtain 15.8 g of a 10 cm square sheet-like foam having a thickness of 0.25 cm. The foam had a specific gravity of 0.57 and a foaming ratio of 3.4, and its skin was relatively hard and very elastic.
[0029]
[Example 5]
90 g of silica powder was blended with 50 g of the styrene-butadiene rubber latex used in Example 3 and 0.03 g of calcium borate, kneaded thoroughly, and placed in a closed mold. The temperature was raised over a period of time, followed by natural cooling to obtain 120 g of a foam having a specific gravity of 0.76 and an expansion ratio of 1.86. The foam was extremely flexible and elastic.
[0030]
[Example 6]
20 g of float glass powder was mixed with 16.2 g of vinyl acetate resin emulsion (resin concentration 50%) and 0.15 g of sodium chloride, kneaded thoroughly and placed in a closed mold, heated and cooled under the same conditions as in Example 4, with a specific gravity of 0 And 39 g of a foam with an expansion ratio of 4.7 were obtained.
[0031]
[Example 7]
36 g of polypropylene powder was mixed with 29 g of vinyl acetate resin emulsion (resin concentration 50%), 2.1 g of silica powder and 0.02 g of calcium borate, kneaded thoroughly and placed in a closed mold, and heated and cooled under the same conditions as in Example 4. As a result, 47 g of a foam having a specific gravity of 0.3 and an expansion ratio of 3.7 was obtained.
[0032]
[Example 8]
40 g of alumina powder was blended with 35.2 g of vinyl acetate resin emulsion (resin concentration 50%), 0.3 g of sodium chloride and 0.2 g of calcium borate, kneaded thoroughly, and placed in a closed mold, from room temperature to 100 ° C. for 5 minutes. Next, the temperature was raised to 180 ° C. over 10 minutes, and then naturally cooled to obtain 53.7 g of a foam having a specific gravity of 0.38 and a foaming ratio of 8.4. The foam skin had a hardness equivalent to a soft vinyl chloride resin added with 15% by weight of a plasticizer and was elastic.
[0033]
[Example 9]
42 g of graphite powder is mixed with 41.9 g of vinyl acetate resin emulsion (resin concentration: 50%), 2.1 g of silica powder and 0.8 g of calcium borate, kneaded thoroughly and placed in a closed mold, and from room temperature to 100 ° C. for 5 minutes. Then, the temperature was raised to 210 ° C. over 10 minutes, and then naturally cooled to obtain 61.5 g of a foam having a specific gravity of 0.41 and an expansion ratio of 4.7.
[0034]
[Example 10]
19.5 g of vinyl acetate resin emulsion (resin concentration: 50%) and 1.0 g of silica powder are blended in 13 g of vinyl chloride resin powder and kneaded thoroughly, and a dehydration gelation accelerator is added thereto, and further kneaded and sealed. It put into the metal mold | die, and it heated and cooled on the same conditions as Example 1, and obtained the foam. The amount of the dehydration gelation accelerator used and the foaming ratio of the obtained foam were as shown in Table 1.
[0035]
[Table 1]

[0036]
Example 11
Example 8 A mixture of 80 g of silica powder and 24 g of acryl-styrene copolymer emulsion (resin concentration: 47%, Hoechst's trade name: Movinyl 752) and sodium chloride as a dehydrating gelation accelerator, kneaded thoroughly, and then placed in a closed mold. Heated and cooled under the same conditions as above, a foam having a hard skin and extremely high rigidity, which was very similar to a hard vinyl chloride resin with no plasticizer added, was obtained. The amount of sodium chloride used and the expansion ratio of the obtained foam were as shown in Table 2.
[0037]
[Table 2]

[0038]
【The invention's effect】
In conventional foam production methods using chemical foaming agents, the factors such as the type of foaming agent and its proportion, the control of the decomposition temperature of the foaming agent, the type of polymer and the type of stabilizer are complicated in terms of foaming ratio. In relation to this, it was not easy to obtain a foam controlled to a desired foaming ratio, whereas in the present invention, the foaming ratio can be mainly controlled by a dehydrating gelation accelerator, and the foaming ratio can be easily controlled. The desired foam can be obtained over a wide range of expansion ratios of 1 to 10 times. For this reason, for example, various heat insulating materials can be used as high foams, and cushions for vehicle seats and heat insulating interior materials can be used as low foams as needed.
[0039]
Also, it is relatively easy to control the properties of the foam, such as hard, soft and elastic. Therefore, for example, the surface to be used may be any plane, but a soft foam may be used for the aspect, and an elastic foam may be used as necessary when cushioning is required. Further, when ferrite or graphite is used as the foamed material, a foam useful as a radio wave absorber can be obtained.

Claims

A method for producing a foam, comprising mixing a resin emulsion and a dehydrating gelation accelerator in a foamed material comprising a powdered polymer, an inorganic oxide, a carbonaceous material, or a mixture thereof, kneading and then foaming by heating. .

The method for producing a foam according to claim 1, wherein the polymer is vinyl chloride resin, polypropylene, polyethylene, vinyl acetate resin, or polystyrene.

The method for producing a foam according to claim 1, wherein the inorganic oxide is silica, glass powder, alumina, ferrite, titanium oxide, chromium oxide, iron oxide, talc, or zeolite.

The method for producing a foam according to claim 1, wherein the carbonaceous material is graphite or amorphous carbon.

Resin emulsion is vinyl acetate resin emulsion, vinyl acetate-acrylonitrile copolymer emulsion, vinyl acetate-ethylene copolymer emulsion, vinyl acetate-ethylene-vinyl chloride copolymer emulsion, acrylic copolymer emulsion, acrylic-styrene copolymer The method for producing a foam according to claim 1, which is an emulsion, a synthetic rubber emulsion or a natural rubber emulsion.

The method for producing a foam according to claim 1, wherein the dehydrating gelation accelerator is boric acid or a salt thereof, an electrolyte or an ionic surfactant.

The method according to claim 1, wherein the blending ratio is 24 to 350 parts by weight of the resin emulsion with respect to 100 parts by weight of the foamed substance, and 0.1 to 20 parts by weight of the dehydrating gelation accelerator with respect to 100 parts by weight of water in the resin emulsion. The manufacturing method of the foam of description.