JPH052695B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a foamed resin molded product having excellent isotropic mechanical properties. Aromatic condensation polymers that exhibit anisotropy when melted (hereinafter referred to as liquid crystal polymers) have excellent mechanical properties due to the parallel arrangement of molecules, and are mainly used for making fibers, films, etc. It is used in many applications in the field of uniaxially oriented products. However, molded products made of liquid crystalline polymers that have a three-dimensional expanse have a high degree of anisotropy due to their orientation characteristics, and their mechanical properties, especially in the direction perpendicular to the flow direction of the resin, are extremely poor. There is. Therefore, the present inventors investigated with the aim of obtaining a liquid crystalline polymer molded product that is isotropically excellent in mechanical properties, and found that by imparting a foamed structure to the liquid crystalline polymer molded product, the polymer molecular chains were foamed. It was discovered that the material has a structure that is highly oriented along the plane, exhibits a three-dimensional orientation effect, and can obtain excellent mechanical properties in isodirection. That is, the present invention provides an aromatic system which exhibits optical anisotropy when melted and is made by copolymerizing polyethylene terephthalate or polyethylene-1,2-diphenoxyethane-4,4'-dicarboxylate with p-acetoxybenzoic acid. The present invention provides a foamed resin molded product having a cell content of 5 to 50% by volume, which is formed by foam-molding a condensation polymer. Conventional foamed resin molded products have various characteristics such as porous morphology and light weight, and are used for many applications, but their mechanical properties depend on the volume fraction occupied by the resin in the molded product. The level was almost proportional to that of the previous year. In other words, if E is the value representing the mechanical properties of a foamed resin molded product and ρ is the density, then E/ρ is almost constant, and a small ρ satisfies the lightweight requirement, but E also has a certain value. It was a small value. However, the present invention focused on the flow of resin during the foaming process in the production of foamed resin molded products, and found that the E/ρ value could be increased by strengthening the orientation of the resin due to the flow. It has been discovered that when a polyester polymer is used, the E/ρ value of the foam can be specifically increased,
It can be called truly revolutionary in the sense that it effectively combines so-called foaming technology and the excellent alignment properties of liquid crystalline polymers. The liquid crystalline polymer used in the present invention exhibits optical anisotropy in a molten state and is a so-called thermotropic liquid crystal. This optical anisotropy can be confirmed by observing the molten polymer using, for example, an optical system equipped with orthogonal polarizers, which transmits polarized light and produces a strong birefringence. The liquid crystalline polymer used in the present invention is polyethylene terephthalate or polyethylene-1,2
- An aromatic copolyester made by reacting p-acetoxybenzoic acid with diphenoxyethane-4,4'-dicarboxylate and polycondensing it, and copolymerizing a small amount of an aromatic dihydroxy compound or dicarboxylic acid. Good too. Among these liquid crystalline polymers, when the polymer is spun under optimal conditions, the initial elastic modulus of the spun yarn is 200 g/d.
The above are preferably used. A requirement for constituting the foamed resin molded product of the present invention is that the liquid crystalline polymer has a foamed structure, that is, the molded product has a three-dimensional curved surface. If you try to make it larger, the bubble structure will inevitably become larger,
On the other hand, there is a relationship between increased non-uniformity of the molded product and uneven stress distribution during loading, which requires optimization depending on the desired mechanical properties. The more desirable mechanical properties can be obtained. In addition, the foaming rate of the molded product is preferably in the range of 5 to 50% by volume, especially 10 to 50% by volume.If it is less than 5% by volume, the effect of increasing the E/ρ value will be small, and if it exceeds 50% by volume. This is not preferable because shape retention is impaired and mechanical properties are generally deteriorated. There are no particular restrictions on the foaming method in the present invention,
Commonly used blowing agents include solvent-type blowing agents such as cyclic hydrocarbons and halogenated hydrocarbons, carbonates such as calcium carbonate and sodium carbonate, and decomposition-type blowing agents such as azo compounds, nitroso compounds, and sulfonyl compounds. Any foaming agent can be used, and can be appropriately selected depending on the type of liquid crystal polymer and the desired foamed structure. Also,
Depending on the desired foamed structure, it is also possible to introduce a crosslinked structure into the liquid crystalline polymer, and a crosslinking agent such as an epoxy compound can also be added. Regarding the molding method, any method can be used as long as a molded product having a foamed structure can be obtained, and examples include commonly used extrusion molding, injection molding, press molding, and blow molding. It is not limited to this. During molding, additives such as reinforcing agents, fillers, nucleating agents, pigments, antioxidants, stabilizers, plasticizers, lubricants, and mold release agents are added to the liquid crystal polymer along with foaming agents to form molded products. can be imparted with desired properties. The foamed resin molded article of the present invention thus obtained has excellent isotropic mechanical properties and is useful for various uses. The present invention will be further explained below with reference to Examples. In addition, the bending elastic modulus in the examples is ASTM
Measured according to D790. Example 1 Polyethylene terephthalate with an intrinsic viscosity of 0.88
5.2Kg (27mol) and p-acetoxybenzoic acid 4.9
Kg (27 mol) was charged into a reactor equipped with a stirrer, a distillation column and a nitrogen gas inlet, and under a nitrogen gas atmosphere,
The mixture was stirred at about 280°C for about 60 minutes, and most of the acetic acid was distilled off. Next, while keeping the reaction system at 280℃,
When the mixture was brought to a vacuum of mHg and stirring was continued for an additional 3 hours, about 6.8 kg of pale yellow polymer was obtained.
This polymer had an intrinsic viscosity of 0.68, a melting point of 228°C, and exhibited good optical anisotropy in the molten state. Potassium carbonate was added as a blowing agent to 100 parts by weight of the liquid crystalline polyester obtained above in the proportions shown in Table 1, and the mixture was melt-mixed at 250° C. in a 65 mmφ extruder, extruded into guts, and pelletized. Each pellet was placed in a 5 oz screw in-line injection molding machine set at 250°C and the mold temperature
A square plate with a thickness of 3 mm x 80 mm x 80 mm was molded at 60°C. This square plate was cut into a width of 12 mm in both the flow direction and the vertical direction, and the flexural modulus of the obtained test piece was measured. This result and the density of the specimen (ρ),
The evaluation results of bubble magnification and E/ρ are also shown in Table 1.

[Table] As is clear from Table 1, the foamed resin molded products of the present invention (Nos. 1 to 3) are unfoamed products (No. 4), and molded products with a bubble fraction of less than 5% by volume (No. 5). ), the isotropy of the flexural modulus is significantly improved. In addition, the molded product (No. 6) with a cell content exceeding 50% by volume has a significant decrease in flexural modulus. Example 2 Polyethylene 1,2-diphenoxyethane-4, having an intrinsic viscosity of 1.23, was prepared using the same formulation as in Example 1.
After adding 1 part by weight of lithium carbonate to 100 parts by weight of liquid crystalline polyester (melting point 230°C) prepared by copolymerizing 40 moles of 4'-dicarboxylate with 60 moles of ρ-acetoxybenzoic acid, the mixture was extruded in the same manner as in Example 1. When molded, the density (ρ) is 0.67 g/cm ³ , the bubble fraction is 50%, the bending elastic modulus in the flow direction is 8×10 ⁴ Kg/cm ² , the bending elastic modulus in the vertical direction is 6×10 ⁴ Kg/cm ² , etc. A foamed molded article with good orientation was obtained. Furthermore, when the same polyester was molded under the same conditions without adding a foaming agent, the bending elastic modulus in the flow direction was 14×10 ⁴ Kgf/cm ² and the bending elastic modulus in the vertical direction was 3×10 ⁴ Kgf/cm ^{2 .} It was hot. From this result, the foamed molded product of the present invention has a smaller ratio of the bending elastic modulus in the flow direction and the direction perpendicular to the flow direction than the unfoamed molded product,
It was found that the isotropy was improved.

Claims (1)

[Claims] 1. An aromatic condensation polymer that exhibits optical anisotropy when melted by copolymerizing p-acetoxybenzoic acid with polyethylene terephthalate or polyethylene-1,2-diphenoxyethane-4,4'-dicarboxylate. Made by foam molding, the bubble fraction is 5.
~50% by volume foamed resin molded product.