JP3819042B2 - Crystalline resin injection molding method - Google Patents
Crystalline resin injection molding method Download PDFInfo
- Publication number
- JP3819042B2 JP3819042B2 JP28946393A JP28946393A JP3819042B2 JP 3819042 B2 JP3819042 B2 JP 3819042B2 JP 28946393 A JP28946393 A JP 28946393A JP 28946393 A JP28946393 A JP 28946393A JP 3819042 B2 JP3819042 B2 JP 3819042B2
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- Prior art keywords
- crystalline resin
- temperature
- mold
- resin
- injection molding
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- Injection Moulding Of Plastics Or The Like (AREA)
Description
【０００１】
【産業上の利用分野】
本発明は、結晶性樹脂の成形方法に関するものである。
【０００２】
【従来の技術】
一般に結晶性樹脂は結晶化することにより密度、融点が高くなり、硬度や弾性率などが大きくなる。また異方性を示し、水分や染料、可塑化剤などが結晶組織へ入り込みにくいなどの特徴を有する。結晶性樹脂の中でも特にポリアセタール樹脂は、力学特性、熱的特性に加え、摺動特性、摩擦摩耗特性が非常に優れるため、歯車、軸受け、カムなどの機構部品に多く使われている。
【０００３】
しかし、一般にポリアセタール樹脂の射出成形においては、金型温度が熱変形温度以下の４０〜１２０℃の範囲で設定されることが多く、これらの条件では、溶融樹脂が金型キャビティ面で急激に冷却されるため、成形品表面にスキン層が形成され、これに成形品の残留応力が加わるため、表面外観が悪くなる。
また耐候性の面では、紫外線により分子鎖が切断され、これが残留応力によって分子量低下を引き起こし、成形品表面にひび割れを発生させるといった欠点を有している。
【０００４】
【発明が解決しようとする課題】
本発明の目的は、従来技術における上記したような課題を解決し、優れた特性を有する結晶性樹脂の射出成形方法を提供することにある。
【０００５】
【課題を解決するための手段】
本発明者らは、射出成形方法について鋭意研究を重ねた結果、結晶性樹脂の射出成形方法において、射出圧縮機能を有する成形機を用いて該結晶性樹脂の融点以上に加熱された金型内に溶融された結晶性樹脂を充填し、充填直後に金型キャビティ内の該結晶性樹脂を加圧圧縮しながら、金型温度を該結晶性樹脂の熱変形温度以下まで冷却させることにより、上記課題を解決できることを見いだし本発明を完成した。
【０００６】
すなわち、本発明は、結晶性樹脂の射出圧縮成形方法であって、射出圧縮機能を有する成形機を用いて該結晶性樹脂の融点以上に加熱された金型内に溶融さた結晶性樹脂を充填し、充填直後に金型キャビティ内の当該結晶性樹脂を加圧圧縮しながら、金型温度を結晶性樹脂の熱変形温度以下まで冷却させることを特徴とする結晶性樹脂の射出成形方法に関する発明である。
【０００７】
本発明において、熱可塑性樹脂材料の中の結晶性樹脂とは、適当な条件を与えることにより結晶化しうる樹脂である。例えばポリエチレン、ポリプロピレン、ポリアミド、ポリアセタール、ポリビニルアルコールなどが用いられる。
結晶性樹脂は一般に結晶領域と非晶領域が存在し、冷却速度の影響により結晶領域の割合が大きく変わってくる。つまり結晶性樹脂が溶融している状態から、金型内に射出されるため、樹脂が急激に冷却され、金型面に最も近い成形品表面部分にスキン層が形成される。このスキン層は非晶質、あるいは結晶化度の低い球晶が存在している。
【０００８】
これらのスキン層が存在すると、機械的物性が低下したり、残留応力によりスキン層が破壊されるため表面外観が悪くなるといった問題がある。これらは結晶性樹脂が急冷されるために発生するものである。従って成形時の金型温度を結晶性樹脂の融点よりも高い温度に保持することで、結晶性樹脂が流動抵抗の少ない状態で流れることが可能になる。この際に金型温度を高温にする方法として、水蒸気を用いる。通常の成形では金型温度をコントロールする媒体として水や油が用いられる。しかし結晶性樹脂の融点まで昇温させるためにはかなりの時間がかかってしまう。そこで金型を昇温させる媒体として水蒸気を用いることにより、短時間で結晶性樹脂の融点まで昇温することが可能となる。
【０００９】
蒸気を発生させる方法としては電気ボイラーを用いる。また冷却には水蒸気、水、エアを任意に組合せ、冷却速度をコントロールするものである。また該結晶性樹脂の熱変形温度以下まで冷却させるまでの間、成形品に任意の圧力をかけ続けることにより、後収縮が少なく、寸法精度の優れた製品を得ることができる。冷却は金型温度が該結晶性樹脂の熱変形温度以下に下がるまで続ける。
金型温度が熱変形温度以上では、成形品の取り出しの際に離型不良や変形がおきてしまう。このため成形品の取り出し温度は該結晶性樹脂の熱変形温度以下で行う必要がある。好ましくは成形品の取り出し温度は熱変形温度の１０℃以下がよい。
【００１０】
【作用】
即ち、本発明は、結晶性樹脂を成形する際に、金型温度を該結晶性樹脂の融点以上に昇温することにより、結晶性樹脂が流動抵抗の少ない状態で流れることが可能となり、残留応力を低減させることができる。また成形直後は、結晶性樹脂と金型の温度差が少ないため、結晶性樹脂の冷却速度が遅くなり、徐冷されることにより成形品表面のスキン層が形成されず、耐候性が向上し、表面外観も著しく改善されるものである。
【００１１】
【実施例】
以下、実施例により本発明の詳細を説明する。
金型として、直径が１００ｍｍφ、厚みが１０〜２０ｍｍの成形品を得るための蓋型の金型を使用した。キャビティは圧縮量を０〜５ｍｍ可変させることが可能である。成形機は射出圧縮機能を有する縦型の成形機（アイダエンジニアリング（株）製、商品名：ＭＡＸ１００）を用い、成形材料はポリアセタール樹脂（三菱ガス化学（株）製、商品名：ユピタール Ｆ２０−０２）を用いた。金型を昇温させる水蒸気を発生させる装置として小型電気ボイラー（日本電熱（株）、商品名：ＥＢ２０）を用いた。
【００１２】
実施例１
金型を完全に閉じ、ポリアセタール樹脂を樹脂温度２００℃、金型初期温度１７０℃の条件で射出注入後、３０〜１００ｂａｒの加圧力で圧縮をかけながら、金型内の冷却溝に水蒸気、水、エアを流し、冷却を行う。金型温度が該結晶性樹脂の熱変形温度以下（１３６℃）になるまで冷却を行う。
冷却後得られた成形品はスキン層は認められず、表面外観が良く、耐候性の優れた特性を有していた。
【００１３】
比較例１
金型を完全に閉じ、ポリアセタール樹脂を樹脂温度２００℃、金型初期温度８０℃の条件で射出注入後、３０〜１００ｂａｒの加圧力で圧縮をかけながら、金型内の冷却口に冷却水を流して冷却を行う。これにより得られた成形品はスキン層が形成されており、シワやアバタが発生し表面外観が悪く、耐候性が劣っていた。
【００１４】
比較例２
金型を完全に閉じ、ポリアセタール樹脂を樹脂温度２００℃、金型初期温度１２０℃の条件で射出注入後、３０〜１００ｂａｒの加圧力で圧縮をかけながら、金型内の冷却口に冷却水を流して冷却を行う。これにより得られた成形品はわずかに薄いスキン層が形成されており、アバタが発生していた。耐候性も劣っていた。
【００１５】
【発明の効果】
本発明の成形方法によれば、結晶性樹脂の成形において、表面外観の良好な成形品を得ることができる。また耐候性を向上させることができる。[0001]
[Industrial application fields]
The present invention relates to a method for molding a crystalline resin.
[0002]
[Prior art]
In general, when a crystalline resin is crystallized, the density and melting point increase, and the hardness, elastic modulus, and the like increase. Also shows the anisotropy, moisture and dyes, etc. plasticizing agent has characteristics such as hardly enter into the crystal structure. Among the crystalline resins, polyacetal resin, in particular, is widely used for mechanical parts such as gears, bearings, and cams because it has excellent sliding characteristics and frictional wear characteristics in addition to mechanical characteristics and thermal characteristics.
[0003]
However, in general, in the injection molding of polyacetal resin, the mold temperature is often set in the range of 40 to 120 ° C. below the heat distortion temperature, and under these conditions, the molten resin is rapidly cooled on the mold cavity surface. Therefore, a skin layer is formed on the surface of the molded product, and the residual stress of the molded product is added to the skin layer.
In terms of weather resistance, the molecular chain is broken by ultraviolet rays, and this has the disadvantage that the molecular weight is lowered by residual stress, and cracks are generated on the surface of the molded product.
[0004]
[Problems to be solved by the invention]
An object of the present invention is to solve the above-described problems in the prior art and to provide an injection molding method of a crystalline resin having excellent characteristics.
[0005]
[Means for Solving the Problems]
As a result of intensive research on the injection molding method, the inventors of the present invention have found that in the injection molding method of the crystalline resin, the inside of the mold heated above the melting point of the crystalline resin using a molding machine having an injection compression function . By filling the crystalline resin melted in the mold cavity and immediately compressing and compressing the crystalline resin in the mold cavity , the mold temperature is cooled to a temperature equal to or lower than the thermal deformation temperature of the crystalline resin. The present invention has been completed by finding out that the problems can be solved.
[0006]
That is, the present invention is a method for injection compression molding of a crystalline resin, in which a crystalline resin melted in a mold heated to a temperature higher than the melting point of the crystalline resin using a molding machine having an injection compression function. The present invention relates to an injection molding method for a crystalline resin, wherein the mold temperature is cooled to a temperature equal to or lower than a thermal deformation temperature of the crystalline resin while filling and compressing the crystalline resin in the mold cavity immediately after filling. It is an invention.
[0007]
In the present invention, the crystalline resin in the thermoplastic resin material is a resin that can be crystallized by giving appropriate conditions. Such as polyethylene, polypropylene, polyamide, polyacetal, polyvinyl alcohol is used.
A crystalline resin generally has a crystalline region and an amorphous region, and the ratio of the crystalline region varies greatly due to the influence of the cooling rate. That is, since the crystalline resin is injected into the mold from the melted state, the resin is rapidly cooled, and a skin layer is formed on the surface of the molded product closest to the mold surface. This skin layer has amorphous or spherulites with low crystallinity.
[0008]
When these skin layers are present, there are problems that mechanical properties are deteriorated and the surface appearance is deteriorated because the skin layers are destroyed by residual stress. These occur because the crystalline resin is rapidly cooled. Therefore, by maintaining the mold temperature at the time of molding at a temperature higher than the melting point of the crystalline resin, the crystalline resin can flow with a low flow resistance. At this time, water vapor is used as a method for increasing the mold temperature. In normal molding, water or oil is used as a medium for controlling the mold temperature. However, it takes a considerable amount of time to raise the temperature to the melting point of the crystalline resin. Therefore, by using water vapor as a medium for raising the temperature of the mold, it is possible to raise the temperature to the melting point of the crystalline resin in a short time.
[0009]
An electric boiler is used as a method for generating steam. For cooling, water vapor, water, and air are arbitrarily combined to control the cooling rate. Further, by continuing to apply an arbitrary pressure to the molded product until the crystalline resin is cooled to a temperature equal to or lower than the heat distortion temperature, a product with less post-shrinkage and excellent dimensional accuracy can be obtained. Cooling is continued until the mold temperature falls below the thermal deformation temperature of the crystalline resin.
When the mold temperature is equal to or higher than the thermal deformation temperature, mold release defects and deformation occur when the molded product is taken out. For this reason, it is necessary to perform the taking-out temperature of the molded product below the thermal deformation temperature of the crystalline resin. Preferably, the temperature at which the molded product is taken out is 10 ° C. or less of the heat distortion temperature.
[0010]
[Action]
That is, in the present invention, when the crystalline resin is molded, by raising the mold temperature to the melting point of the crystalline resin or higher, the crystalline resin can flow with a low flow resistance. Stress can be reduced. Immediately after molding, since the temperature difference between the crystalline resin and the mold is small, the cooling rate of the crystalline resin is slowed down, and by gradually cooling, the skin layer on the surface of the molded product is not formed, and the weather resistance is improved. The surface appearance is also remarkably improved.
[0011]
【Example】
Hereinafter, details of the present invention will be described by way of examples.
As the mold, a lid mold for obtaining a molded product having a diameter of 100 mmφ and a thickness of 10 to 20 mm was used. The compression amount of the cavity can be varied from 0 to 5 mm. As the molding machine, a vertical molding machine having an injection compression function (manufactured by Aida Engineering Co., Ltd., trade name: MAX100) was used. ) Was used. A small electric boiler (Nippon Electric Heat Co., Ltd., trade name: EB20) was used as an apparatus for generating water vapor for raising the temperature of the mold.
[0012]
Example 1
After the mold is completely closed, polyacetal resin is injected and injected under conditions of a resin temperature of 200 ° C. and a mold initial temperature of 170 ° C., and then compressed with a pressure of 30 to 100 bar, steam and water are put into the cooling groove in the mold. Cool down with air. Cooling is performed until the mold temperature is equal to or lower than the thermal deformation temperature of the crystalline resin (136 ° C.).
The molded product obtained after cooling had no skin layer, good surface appearance, and excellent weather resistance.
[0013]
Comparative Example 1
After the mold is completely closed and polyacetal resin is injected and injected under the conditions of a resin temperature of 200 ° C. and a mold initial temperature of 80 ° C., cooling water is applied to the cooling port in the mold while being compressed with a pressure of 30 to 100 bar. Run to cool. The molded product thus obtained had a skin layer, wrinkles and avatars were generated, the surface appearance was poor, and the weather resistance was poor.
[0014]
Comparative Example 2
After the mold is completely closed and polyacetal resin is injected and injected under the conditions of a resin temperature of 200 ° C. and a mold initial temperature of 120 ° C., cooling water is supplied to the cooling port in the mold while being compressed with a pressure of 30 to 100 bar. Run to cool. The molded product thus obtained had a slightly thin skin layer, and avatars were generated. The weather resistance was also poor.
[0015]
【The invention's effect】
According to the molding method of the present invention, a molded product having a good surface appearance can be obtained in the molding of a crystalline resin. In addition, weather resistance can be improved.
Claims (3)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP28946393A JP3819042B2 (en) | 1993-11-18 | 1993-11-18 | Crystalline resin injection molding method |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP28946393A JP3819042B2 (en) | 1993-11-18 | 1993-11-18 | Crystalline resin injection molding method |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH07137073A JPH07137073A (en) | 1995-05-30 |
| JP3819042B2 true JP3819042B2 (en) | 2006-09-06 |
Family
ID=17743599
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP28946393A Expired - Fee Related JP3819042B2 (en) | 1993-11-18 | 1993-11-18 | Crystalline resin injection molding method |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP3819042B2 (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2001141005A (en) * | 1999-11-10 | 2001-05-25 | Tsubakimoto Chain Co | Shoe for tensioner device and chain guide |
| JP4079362B2 (en) * | 2003-03-13 | 2008-04-23 | 株式会社山武 | Molding method of resin molding |
| JP2005169925A (en) * | 2003-12-12 | 2005-06-30 | Ono Sangyo Kk | Method and apparatus for injection molding |
-
1993
- 1993-11-18 JP JP28946393A patent/JP3819042B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPH07137073A (en) | 1995-05-30 |
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