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Reny

Basic Properties
  • Property
  • Fabrication
  • Product Design

Reny is a proprietary molding compound based on mainly polyamide MXD6 that has been reinforced with glass fiber, carbon fiber or special minerals. Reny generally has superior mechanical strength and modulus compared with other engineering plastics. Thus, Reny is suitable as a metal substitute in many applications, including automobiles, electronics, electrical appliances, machinery, and construction.

Special features:

  • Excellent mechanical strength and modulus over a wide range of temperatures
  • Superior to commodity polyamides in dimensional stability and mechanical strength due to low water absorption
  • Low thermal expansion coefficient, equivalent to that of metal alloys
  • Highly resistant to oils and organic solvents
  • Low mold shrinkage and low warpage
  • Good surface finish even in highly filled grades

Comparison with other PA resins

Our High-Performance Polyamide resin (Its brand name is “Reny”) is one of the polyamide (PA) resin materials. PA resin is a general term for macromolecular materials which have amide linkage (-CONH-) in the polymeric repeating unit (monomer unit), and in particular, the ones containing aliphatic backbone are called “Nylon” (The term “Nylon” was originally a brand name of DuPont in the United States but is currently common as a general term as described above). General-purpose PA resins which are produced in large volumes include Nylon 6 and Nylon 66, which are both utilized as crystalline resins.

PA resins have characteristics attributable to the hydrogen bond formation of the amide linkage that are superior chemical resistance, thermal distortion resistance, heat retention stability, hydrolysis resistance, toughness (difficulty in breaking) when absorbing water and gas barrier property. On the other hand, they are also characterized by yellowing due to ultraviolet light and heat, dimensional change (increase in dimension) and reduction in mechanical strength and rigidity attributable to water absorption.

Our High-Performance Polyamide resin (“Reny”) has the highest level of mechanical strength and rigidity as an engineering plastic material as well as lower water-absorbing property (i.e., little change in dimension and physical properties) than general-purpose PA resins. Therefore, this material is suitable for metal substitution applications. Such features of “Reny” come from a combination of high mechanical strength and rigidity unique to crystalline PA resins made of aromatic diamine (typically meta-xylylenediamine, abbreviated as MXD; the chemical structure of such a PA resin made of MXD and adipic acid is shown below),

and our compounding technique taking advantage of the basic mechanical properties of the crystalline PA resin with reinforcing materials (filler; such as glass fiber).

Mold temperature and drying conditions for molding “Reny”

When injection-molding our High-Performance Polyamide resin “Reny”, a relatively high mold temperature (mold surface 120 – 140℃) is preferred. If the mold temperature is approximately 80℃, an annealing process (for approximately one hour at 130℃) may be required, increasing the crystallinity of molded articles to secure the strength and rigidity. In addition, when moisture is absorbed, silver streaks can appear on the surface of molded articles, thus it is recommended to dry before molding in hot air stream (12 hours or longer at 80℃, or 4 hours or longer at 120℃).

[Explanation] About the characteristics of crystalline and amorphous resins

(1) Macromolecule crystallization

Crystallization of macromolecule (in this document, linear polymer molecule is set forth as a premise for explaining the principle) refers to a phenomenon in which parts of chainlike polymeric molecule gather together to make up flux which are partially arranged in one direction under certain given conditions, for example, under the cooling conditions in the molten state during injection molding or the concentrating conditions in the solution state (Refer to Figure 2), although it refers to a phenomenon in which small molecules and ions are arranged systematically to make up a crystal in the case of molecular crystals (Example: sugar) and ionic crystals (Example: salt) (Refer to Figure 1). In addition, when macromolecules crystalize, amorphous regions with varying molecular conformation other than such crystalline region normally exist together.


[Figure 1] A schematic diagram showing molecular and ionic crystals (simple cubic lattice, as an example);
blue represents molecules or ions and grey represents crystal lattices (hypothetical concept).
The same crystal lattices continue systematically in the directions of X, Y, and Z axes.

[Figure 2] A schematic diagram of a crystalline resin;
blue represents crystalline regions and grey represents amorphous regions. In the crystalline regions, macromolecular chains form fluxes in the same direction.
In the amorphous regions, macromolecular chains locate indeterminately.

The both crystallizations have a common feature that molecules, ions and polymeric repeating units (monomer units) seek to employ the most stable conformation thermodynamically, using intermolecular forces or ionic binding as driving forces. However, the macromolecule case is essentially different from the ones of low molecular or ionic crystals because of the less freedom of macromolecular mobility than monomers (low molecules) before polymerization; i.e., monomer units are bundled each other within a polymeric chain. This reduction of molecular mobility unique to macromolecules is the cause of remaining amorphous regions. Furthermore, the proportion of crystalline region (“crystallinity”) and the sizes of respective crystalline regions (“crystal size or crystallite size”) are largely dependent on the molding conditions.

Macromolecular chains are basically amorphous when in the molten or solution state, but they crystallize as cooled or concentrated because the effect of intermolecular force (attractive force) becomes evident. However, macromolecules have one more characteristic that their viscosity increases significantly as cooled or concentrated in the molten or solution states, respectively, compared to low molecule systems. Due to this viscosity increase effect, it actually happens that macromolecules become solidified before they crystallize well. Therefore, in general, the crystallinity can be increased by taking a longer time for macromolecular chains to relocate them through slow cooling or slow concentration. It can be understood that so-called amorphous resins such as polycarbonate resin (PC resin) and polyphenylene ether resin (PPE resin) tend to solidify in an amorphous state in the molding process, because they crystallize slowly.

(2) The properties of the crystalline region of macromolecules

Since the crystalline region has a dense structure based on strong intermolecular force, they generally show a higher thermal softening temperature and elastic modulus as well as lower coefficient of linear thermal expansion (CLTE) and water absorption rate (that is, a reduction in dimension change due to temperature and humidity) than those of the amorphous region. Of these, thermal softening temperature roughly corresponds to, in the amorphous region, the glass transition temperature (Tg) which correlates with the rigidity of monomer unit structure (the lowness of mobility or flexibility of molecular structure); but in the crystal region corresponds to the melting point (hereinafter quote as “Tm”) which is higher than Tg.

Therefore, in resin molded articles, the increase of the crystallinity moves above physical properties generally to the preferred direction. However, since the crystalline regions dispersed in the amorphous region function as a stress concentration point induced by external force due to a difference in elastic modulus, the toughness of resin molded articles generally decreases as the crystallinity increases and moves in the direction of embrittlement. If the crystallinity is the same, toughness can be improved by reducing the crystalline size.

(3) The properties of the amorphous regions of macromolecules

The amorphous region in resin molded articles functions as a matrix (continuous phase) containing the crystalline regions (hard and difficult to be thermally-softened) as “fillers” (reinforcing materials to be filled). Although the thermal properties of the amorphous region are dominated by the aforementioned Tg, for the mechanical properties it is important to understand mechanism of the amorphous region exhibiting toughness (durability).

At temperatures lower than Tg, the amorphous region subjected to external force (e.g., tensile, flexural, compressive and torsional stresses, as well as gravity force causing self-weight deformation) causes reversible (elastic) deformation first. This phenomenon is relatively small deformation which can be restored by eliminating the external force, and can also be observed in hard and brittle materials such as inorganic glass. However, the toughness of the amorphous region, in terms of a molecular discussion, depends on how far irreversible (plastic) deformation is allowed after the elastic deformation limit. The nature of the plastic deformation is a process of viscous flow, that is, a process in which macromolecular chains tangled with each other dissipate the energy of external force as heat by moving irreversibly to change their arrangement (conformation) gradually and the entire material deforms while bearing breakage.

A trigger which leads plastic deformation to breakage is occurrence of micro-crack (cleavage) and micro-void. Assuming an ideal amorphous region, that is a case where stress concentration factors such as foreign matter and inhomogeneous structure (e.g., crystalline regions, fluctuation of density in amorphous) do not exist, micro-cracks/voids are considered to be caused by (1) macromolecular chain ends, (2) unbinding of macromolecular chain entanglements, and (3) breakage of macromolecular chains, which could be the cause of very tiny voids in the molecular dimension can be generated in the macroscopic deformation. Among these three factors, (1) and (2) are reduced as the molecular weight increases, because the smaller the number of molecular ends per unit weight becomes and the more difficult the entangled chains become unbound, the larger (the longer) the molecular weight becomes (It can be estimated from an example that the longer the boiled noodles are, the more difficult to unbind the entanglements involved in the entire noodle). That is, larger molecular weight is better for toughness.

Concerning the above (3) Breakage of macromolecular chains which is also associated with the perspective of entanglement as described in the above (2), the hardness of the macromolecular chain (the rigidity of monomer unit structure) is one of the factors. That is, if macromolecular chains are flexible, they can follow the entire deformation without eliminating the molecular entanglements. However, if they are rigid, they cannot follow the deformation due to low mobility and stress is concentrated in the entangled points. As a result, it is considered that breakage of macromolecular chains tends to occur. It can be said that the rigidity of macromolecular chains is the cause of complicated behaviors which contradict each other in a practical way. That is, the higher rigidity increases the elastic modulus of amorphous regions and also increases the aforementioned Tg (increases the thermal softening temperature) but reduces melt flowability (increases the molten viscosity to deteriorate the moldability) as thermal properties. On the other hand, if the molecular weight is decreased to increase the melt flowability, the toughness is reduced as described above.

(4) Crystalline and amorphous resins

Basically, linear polymer molecules have the capability to crystallize under certain cooling or concentration conditions. However, “crystalline resins” generally refer to resins which undergo crystallization so that practically preferred physical property balance is shown under common injection or extrusion molding conditions. On the other hand, “amorphous resins” refer to resins which almost do not crystallize under such common molding conditions.

Engineering plastic materials as “crystalline resin” including Polyamide (PA) resin, Polyacetal (or Polyoxymethylene, POM) resin, Polybutylene terephthalate (PBT) resin, Polyethylene terephthalate (PET) resin, and Polyphenylenesulfide (PPS) resins, etc. are characterized by superior molten flowability and chemical resistance, as well as a profound reinforcing effect (an effect of improving elastic modulus, strength, and heat resistance) by compounding fillers such as glass fiber.

The ones as “amorphous resin” including Polycarbonate (PC) resin, modified Polyphenylene ether (m-PPE) resin, and Polyalylate (PAR) resin, etc. are characterized by transparency, anisotropy, and small molding shrinkage.

Product Info.

  • ポリカーボネート樹脂(PC樹脂)ユーピロンノバレックスザンター
  • ポリブチレン テレフタレート樹脂 (PBT樹脂) ノバデュラン
  • ポリアセタール樹脂(POM樹脂)ユピタール
  • 変性ポリフェニレン エーテル樹脂(m-PPE樹脂)ユピエースレマロイ
  • 高性能ポリアミド樹脂(PA樹脂)レニー
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