【発明の詳細な説明】[Detailed description of the invention]
本発明は炭素繊維にポリアミド樹脂を被覆した
特定のかさ密度を有するポリアミド樹脂成形物強
化用チヨツプドストランドに関するものである。
炭素繊維はガラス繊維と比べて高弾性、耐摩耗
性、軽量性、静電気特性に優れ、樹脂、金属、セ
ラミツク等の強化材として使用されている。特に
ポリアミド樹脂に強化材として使用した場合に
は、弾性率、限界PV値、耐摩耗性、静電気特性
を向上させ、紡績機械部品等の優れた素材となり
得る。
しかしながら、炭素繊維と樹脂の接着性は良好
とは言い難く、単に炭素繊維と樹脂を混合したも
のは、炭素繊維の特性を有効に利用しているとは
言い難い。炭素繊維と樹脂の接着性を向上させる
ために、炭素繊維の表面処理が行われて来たが、
この処理方法は、本質的にエポキシ樹脂等の熱硬
化性樹脂に対して有効であり、ポリアミド樹脂等
の熱可塑性樹脂に対しては有効でない。
本発明者はポリアミド樹脂と炭素繊維の接着性
を改善するために、種々の検討を鋭意行つた結果
本発明に到達した。
即ち、本発明は、炭素繊維にポリアミド樹脂を
被覆してなり、かさ密度250g／以上のポリア
ミド樹脂成形物強化用チヨツプドストランドであ
る。
本発明によれば、炭素繊維とポリアミド樹脂の
接着性の改善だけでなく、押出機の供給口におけ
るくい込みがよいため一般に行われている押出機
によるペレツト化に先立つたヘンシエルミキサ
ー、Ｖ型ブレンダー等の炭素繊維とポリアミド樹
脂の予備混合工程を省略することができる。その
結果炭素繊維とポリアミド樹脂を直接押出機に投
入できるために炭素繊維の破断（短繊維化）も少
なくて済み、機械特性の向上は著しいものであつ
た。
本発明で使用される炭素繊維はアクリル系、レ
ーヨン系、リグニン系、ピツチ系等その種類は問
わない。また炭素繊維の表面処理の有無にはこだ
わらないが、表面酸化処理を行つた炭素繊維の方
が、酸化によつて生じる―COOH、―CO、―
OH基等の官能基とポリアミド樹脂のアミド基と
の反応が起こり、樹脂と繊維の接着の面からは好
ましい。この場合の表面酸化の方法は硝酸法、電
気分解法等一般に行われている処理方法で良い。
本発明で使用される被覆用ポリアミド樹脂はナ
イロン６、ナイロン66等の一般に市販されている
樹脂及びアルコール可溶性変性ナイロンであり、
その分子量は問わない。更に被覆樹脂用の溶剤と
してはフエノール類、塩化カルシウム、飽和メタ
ノール溶液、エタノール、メタノール等をあげる
ことができる。即ち上述のポリアミド樹脂の粉
末、ペレツトをこれらの溶剤に溶解した濃度0.5
〜20wt％に適宜調整した溶液に、炭素繊維のロ
ービングを連続的に浸漬しそして、脱溶剤して適
当な長さ、好ましくは１〜10mmに切断して炭素繊
維のチヨツプドストランドを製造する。
本発明において、ポリアミド樹脂の炭素繊維に
対する樹脂付着量は、炭素繊維のチヨツプドスト
ランドのかさ密度が250g／以上になる様に限
定する。
ここで言うかさ密度とは、次の様に定義する。
即ち100mlのメスシリンダーに炭素繊維のチヨツ
プドストランドを充填し、次いでメスシリンダー
の底部を机上等適当な場所で数回軽く打ち、100
mlの示線に丁度合う様に炭素繊維を取捨し、100
mlの重量を測定してかさ密度とする。かさ密度が
250g／未満であれば、そのチヨツプドストラ
ンドは、開繊され易い状態にあり押出機のホツパ
ー内で樹脂との摩擦によつて容易に開繊され、ブ
リツジ現象を生じ、定量供給が困難となり、前述
した樹脂被覆のメリツトの一つである押出機への
直接投入が不可能になり、前述の予備混合が必要
となるため、炭素繊維の切断、成形物の品質低下
などの原因となる（後記表１、表２参照）。
本発明の炭素繊維チヨツプドストランドは直
接、射出成形機で樹脂と共に溶融混練して成形可
能であるが、繊維の分散性及び取扱い易さから従
来行われている押出機等によるペレツト化が好ま
しい。この場合炭素繊維の添加量は特に限定しな
いが、補強効果、加工性等の面から５〜50wt％
が好ましい。
この様にして得られた炭素繊維強化ポリアミド
樹脂成形材料組成物は、射出成形、押出成形等一
般の成形法で成形可能であり、それらは優れた機
械特性を有している。
以下実施例によつて更に説明するが、本発明は
以下の実施例に限定されるものではない。
実施例 １
Ｎ―メトキシメチル化ナイロン６をメチルアル
コールに溶解し、濃度が0.2〜5.0wt％のに調整し
た溶液製、酸化処理を施した炭素繊維のロービン
グに60m／Hrの速度で連続的に浸漬しそして、
脱溶剤を行い更に６mmにカツトし、種々のかさ密
度のチヨツプドストランドを得た。
この種々のかさ密度のチヨツプドストランドを
ナイロン６ペレツトと共に、炭素繊維添加量が
20wt％になる様に定量供給し、40mmベント付押
出機で溶融混練し直径３mmのダイを通して押出し
た。この時押出機の供給口における樹脂とチヨツ
プドストランドのくい込み具合を観察し、また押
出物を供給後20分より３分おきに約１時間約1g
を採取し、硫酸分解法にて炭素繊維含有率を測定
し、その標準偏差を計算した。結果を表１に示
す。
The present invention relates to chopped strands for reinforcing polyamide resin molded products having a specific bulk density, which are carbon fibers coated with polyamide resin. Carbon fiber has superior elasticity, wear resistance, light weight, and electrostatic properties compared to glass fiber, and is used as a reinforcing material for resins, metals, ceramics, etc. In particular, when used as a reinforcing material in polyamide resin, it improves elastic modulus, critical PV value, abrasion resistance, and electrostatic properties, making it an excellent material for parts of spinning machines, etc. However, the adhesion between carbon fiber and resin cannot be said to be good, and it cannot be said that simply mixing carbon fiber and resin effectively utilizes the characteristics of carbon fiber. Carbon fiber surface treatment has been carried out to improve the adhesion between carbon fiber and resin.
This treatment method is essentially effective for thermosetting resins such as epoxy resins, but not for thermoplastic resins such as polyamide resins. The inventors of the present invention have conducted various studies in order to improve the adhesiveness between polyamide resin and carbon fiber, and as a result, they have arrived at the present invention. That is, the present invention is a chopped strand for reinforcing a polyamide resin molded product, which is made by coating carbon fiber with a polyamide resin and has a bulk density of 250 g/or more. According to the present invention, not only the adhesion between carbon fiber and polyamide resin is improved, but also the penetration at the feed port of the extruder is good. The premixing step of carbon fiber and polyamide resin can be omitted. As a result, the carbon fibers and polyamide resin could be directly fed into the extruder, so there was less breakage of the carbon fibers (shortening of the fibers), and the mechanical properties were significantly improved. The carbon fibers used in the present invention may be of any type, including acrylic, rayon, lignin, and pitch fibers. Also, it does not matter whether the carbon fiber has been surface-treated or not, but carbon fibers that have undergone surface oxidation treatment are more likely to produce -COOH, -CO, - produced by oxidation.
Reaction between functional groups such as OH groups and amide groups of the polyamide resin occurs, which is preferable from the viewpoint of adhesion between the resin and fibers. In this case, the surface oxidation method may be a commonly used treatment method such as a nitric acid method or an electrolysis method. The coating polyamide resin used in the present invention is commonly commercially available resins such as nylon 6 and nylon 66, and alcohol-soluble modified nylon.
The molecular weight does not matter. Furthermore, examples of the solvent for the coating resin include phenols, calcium chloride, saturated methanol solution, ethanol, methanol and the like. That is, the above-mentioned polyamide resin powder or pellets are dissolved in these solvents at a concentration of 0.5.
Carbon fiber rovings are continuously immersed in a solution appropriately adjusted to ~20wt%, then the solvent is removed and cut into appropriate lengths, preferably 1 to 10 mm, to produce chopped carbon fiber strands. do. In the present invention, the amount of polyamide resin attached to the carbon fibers is limited so that the bulk density of the chopped strands of the carbon fibers is 250 g/or more. The bulk density mentioned here is defined as follows.
That is, fill a 100 ml graduated cylinder with chopped carbon fiber strands, then tap the bottom of the graduated cylinder several times on a desk or other suitable location to
Remove the carbon fiber to exactly match the ml marking line, and add 100
Measure the weight in ml to find the bulk density. The bulk density
If it is less than 250g, the chopped strands are in a state where they are easily opened due to friction with the resin in the hopper of the extruder, causing a bridging phenomenon and making it difficult to supply a fixed amount. This makes it impossible to directly feed the resin into the extruder, which is one of the advantages of resin coating mentioned above, and the premixing described above is required, which can lead to cutting of carbon fibers and deterioration of the quality of molded products. (See Tables 1 and 2 below). The chopped carbon fiber strands of the present invention can be directly molded by melt-kneading them with a resin in an injection molding machine, but due to the dispersibility of the fibers and ease of handling, it is not possible to pelletize them using a conventional extruder or the like. preferable. In this case, the amount of carbon fiber added is not particularly limited, but from the viewpoint of reinforcing effect, workability, etc., it is 5 to 50 wt%.
is preferred. The carbon fiber-reinforced polyamide resin molding material composition thus obtained can be molded by general molding methods such as injection molding and extrusion molding, and they have excellent mechanical properties. The present invention will be further explained below with reference to Examples, but the present invention is not limited to the following Examples. Example 1 A solution prepared by dissolving N-methoxymethylated nylon 6 in methyl alcohol and adjusting the concentration to 0.2 to 5.0 wt% was continuously applied to an oxidized carbon fiber roving at a speed of 60 m/Hr. Soak and
The solvent was removed and the strands were further cut into 6 mm pieces to obtain chopped strands with various bulk densities. These chopped strands with various bulk densities are combined with nylon 6 pellets, and the amount of carbon fiber added is
The mixture was supplied in a constant amount to 20 wt%, melted and kneaded using a 40 mm vented extruder, and extruded through a die with a diameter of 3 mm. At this time, observe the degree of penetration of the resin and chopped strands at the supply port of the extruder, and also feed approximately 1 g of extrudate every 3 minutes for approximately 1 hour from 20 minutes after feeding.
The carbon fiber content was measured using the sulfuric acid decomposition method, and its standard deviation was calculated. The results are shown in Table 1.
【表】
ものは強制的に押し込んだ。
表１に示される如く、かさ密度が250g／以
上のチヨツプドストランドの供給はスムーズであ
り、繊維含有率も均一になることがわかる。
実施例 ２
実施例１のかさ密度280g／のチヨツプドス
トランドとナイロン６との混合押出物を６mmにカ
ツトしてペレツトを作成した。このペレツトを金
型を用いて250〜260℃、50Kg／cm2で圧縮成形して
160×160×３mmの成形板を作成した。この成形物
より試験片を切り出して機械特性を測定して表２
に見られる如き値を得た。曲げ破断面を走査型電
子顕微鏡で観察したところ樹脂の繊維に対する接
着性は良好であつた。
実施例 ３
実施例１と同様にナイロン６のフエノール溶液
を用いてナイロン６の被覆を行い、かさ密度
280g／、６mmのチヨツプドストランドとし
た。これを用いて実施例２と同様にペレツトを作
成し圧縮成形を行い、その機械特性を測定した。
結果を表２に示す。
実施例 ４
酸化処理していない炭素繊維のロービングを用
いて実施例１と同様にＮ―メトキシメチル化ナイ
ロン６で被覆し、かさ密度280g／、６mmのチ
ヨツプドストランドを得た。次いで実施例２と同
様にペレツトを作成し圧縮成形を行い、その機械
特性を測定した。結果を表２に示す。
実施例 ５
実施例２で得たペレツトを再度押出機にて溶融
混練押出を行つてペレツト化し、実施例２と同様
に機械特性を測定して表２に見られる如き値を得
た。
本実施例は溶融混練し押出機を２回通すことに
よる繊維長の減少と、これに伴う機械特性の効果
を示したものである。
比較例
酸化処理を施した６mm長、かさ密度60g／の
炭素繊維を添加量が20wt％になる様にナイロン
６ペレツトとヘンシエルミキサーで充分混合した
ものを、実施例１と同様の操作で押出機にて押出
しペレツトを作製した。次いで実施例２と同様に
圧縮成形した。その成形物の機械特性を測定した
結果を表２に示す。[Table] Things were forced into the room.
As shown in Table 1, it can be seen that the chopped strands having a bulk density of 250 g/min or more are fed smoothly and the fiber content is uniform. Example 2 The mixed extrudate of Example 1 of the chopped strands with a bulk density of 280 g/nylon 6 and nylon 6 was cut into 6 mm pieces to make pellets. This pellet was compression molded using a mold at 250-260℃ and 50Kg/ cm2.
A molded plate of 160 x 160 x 3 mm was created. A test piece was cut out from this molded product and its mechanical properties were measured. Table 2
We obtained the values shown in . When the bent and fractured surface was observed using a scanning electron microscope, the adhesion of the resin to the fibers was found to be good. Example 3 Nylon 6 was coated using a phenol solution of nylon 6 in the same manner as in Example 1, and the bulk density was
280g/6mm chopped strand. Using this, pellets were prepared and compression molded in the same manner as in Example 2, and the mechanical properties of the pellets were measured.
The results are shown in Table 2. Example 4 Using non-oxidized carbon fiber roving, it was coated with N-methoxymethylated nylon 6 in the same manner as in Example 1 to obtain chopped strands with a bulk density of 280 g/6 mm. Next, pellets were prepared and compression molded in the same manner as in Example 2, and their mechanical properties were measured. The results are shown in Table 2. Example 5 The pellets obtained in Example 2 were again melt-kneaded and extruded using an extruder to form pellets, and the mechanical properties were measured in the same manner as in Example 2 to obtain the values shown in Table 2. This example shows the reduction in fiber length by melt-kneading and passing through an extruder twice, and the resulting effect on mechanical properties. Comparative Example Oxidized carbon fibers with a length of 6 mm and a bulk density of 60 g/ were thoroughly mixed with nylon 6 pellets in a Henschel mixer so that the amount added was 20 wt%, and extruded in the same manner as in Example 1. Extrusion pellets were produced using a machine. Next, compression molding was performed in the same manner as in Example 2. Table 2 shows the results of measuring the mechanical properties of the molded product.
【表】【table】