JPH0325450B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Objective) The present invention relates to a polyamide resin foam molded article with improved warpage. (Prior art) Polyamide resin is widely used in internal combustion engine parts, mainly automobile parts, due to its excellent heat resistance and oil resistance, and is used in parts used in the engine room, such as cylinder head covers and transmission covers. Active efforts are being made to apply this technology to large parts that require good sealing, such as intake manifolds. Since these products are large parts, the amount per piece is large, and the environment in which they are used is harsh, a foam reinforced with glass fiber is considered optimal. However, when injection molding such large items from polyamide resin pellets filled with conventional chopped strand or roving type glass fibers (hereinafter referred to as conventional glass fibers), warpage generally occurs due to the orientation of the glass fibers. This was considered to be a drawback. Regarding warpage, the situation is the same with foams, and depending on the molded product design, there are many cases in which warpage cannot be eliminated, and improvements in this problem are required. By the way, as a means to improve the warpage of polyamide resin injection molded products reinforced with various fillers from a material standpoint, in the case of non-foamed molded products, it is possible to fill them with granular or minerals with a small L/D, or to fill them with ordinary glass fiber. It is common practice to use these minerals in combination. However, upon investigation by the present inventor, it was found that these methods cannot be applied to foams. In other words, threads using granular minerals or minerals with a small L/D do improve warpage, but cannot obtain a uniform foamed state, and threads that use granular minerals or minerals with a small L/D in combination with ordinary glass fibers The resulting yarn was found to be insufficient in terms of both warping and uniform foaming. In view of these circumstances, the present inventor has conducted extensive studies with the aim of obtaining a foam molded product that has a uniform foaming state and is free from warping and can be used for large parts in the engine room of an automobile, and has developed the present invention. reached. (Structure and Effect of the Invention) That is, the present inventor uses glass fibers whose L/D is within a specific range of 4 or more and 15 or less, by weight of 13% or more and 50% or more.
By foam injection molding polyamide resin containing less than The present invention was achieved by discovering that it is possible to obtain usable heat resistance by contacting a high-temperature part. The present invention will be explained in detail below. The glass fiber with an L/D of 4 or more and 15 or less as used in the present invention is commonly referred to as milled fiber in the glass fiber industry association, and is made by pulverizing long glass fibers to a specific length. As expected.
The value of L/D is the value in the state of kneading and pelletizing with an extruder, and the meaning of L/D of 4 or more and 15 or more is that the ratio of fibers existing in this range is the weight fraction.
Refers to the presence of 80% or more. If L/D deviates above this range, the anisotropy of shrinkage during molding becomes noticeable and warping is likely to occur, which is undesirable.
If L/D deviates below this range, it is not preferable because a uniform foamed state cannot be obtained. The polyamide resin referred to in the present invention is not particularly limited for the purpose of obtaining a uniformly foamed foam with little warpage, and includes nylon 46, nylon 66, nylon 612, etc. obtained by condensation polymerization of diamine and dicarboxylic acid. , nylon 6, nylon 11, nylon 12, etc. obtained by polymerization of lactam, or copolymers, blends, etc. of these can be used. For applications requiring heat resistance, nylon 46 or nylon 66, which have a high melting point, are most preferred. Further, these polyamide resins may contain antioxidants, dyes and pigments, weatherproofing agents, lubricants, plasticizers, etc. in their compositions. The foam referred to in the present invention is produced by plasticizing and melting resin pellets containing a chemical blowing agent in an injection molding machine, which is usually referred to as the shot shot method by the injection molding industry, and is made by plasticizing and melting the resin pellets in a mold so as not to completely fill the mold. The foam can be obtained most simply by filling the cavity at high speed and using the pressure of foaming gas to obtain a foam, but is not limited to this method, and can be obtained by any known foam injection molding method. I can do it. In addition, the degree of foaming is determined depending on the purpose of use and is not particularly limited, but it is usually 15% or more.
A foam with good cells can be obtained at a cell ratio of 40% (volume ratio of spaces within the foam). (Example) The present invention will be described below using examples. [Example 1] Relative viscosity ηrel = 3.0 from 1,4-diaminobutane and adipic acid (25°C, 1% by weight solution in 95.5% sulfuric acid)
Nylon 46 (Polytetramethylene adipamide)
was polymerized. Polymerization begins with 1,4-diaminobutane.
1,4-diaminobutane and adipic acid were reacted in excess of 6 mol% at a temperature of 200°C to 220°C for 3 hours to obtain a brittle solid prepolymer, and then this prepolymer was subjected to nitrogen gas blowing at normal pressure. Solid phase polymerization was carried out at 260°C for 3 hours to form the final polymer. Milled fiber (diameter
13μm) 33% by weight was added, and the melt resin temperature was 310℃.
It was pelletized through an extruder under the following conditions. After dissolving the obtained pellets in sulfuric acid, the glass fiber length was measured, and the number average fiber length was 70 μm, and the weight ratio of pellets with L/D of 4 to 15 was 95%. 0.3% 5-phenyltetrasol was dry-blended on the surface of the pellet as a foaming agent, and the average thickness was 4 mm, length was 330 mm, width was 110 mm, and height was 60 mm.
A box-shaped molded product having a diameter of 1.5 mm was foam injection molded from both ends of the bottom using a two-point pin gate method at a molten resin temperature of 310° C. so that the average bubble ratio was 25%. The obtained box-shaped molded product was placed on a surface plate with the bottom facing up, and the maximum value of the rise of the side wall flange portion from the surface of the surface plate was measured using a dial gauge. Next, in order to observe the cell state of the molded product, a 500W photography light was used to shine light from the back of the molded product.
The presence of bubbles visible to the naked eye and the state of cells in the cross section of the molded product were observed using a scanning electron microscope. Furthermore, the molded product was left in a gear oven at 200°C for 10 hours, and the heat resistance was visually evaluated, focusing on changes in shape. [Example 2] In Example 1, nylon 66 with a relative viscosity ηrel = 2.8 was used instead of nylon 46, and the extrusion pelletizing and injection molding conditions were set to a molten resin temperature of 290°C.
It was carried out in the same manner as in Example 1 except that. The number average length of glass fibers in the pellets obtained by extrusion was 80 μm, and the weight ratio of glass fibers with L/D of 4 to 15 was 95%. [Comparative Example 1] The same procedure as in Example 2 was carried out except that the amount of milled fiber used was 10% by weight. [Comparative Example 2] Example 2 was carried out in the same manner as in Example 2, except that glass fibers were added in an amount of 33% by weight of chopped strands with a diameter of 13 μm and a length of 3 mm. The number average length of glass fibers in the pellets obtained by extrusion is approximately
Weight ratio of 250μm and L/D of 15 or more is 80%
It was hot. [Comparative Example 3] The same procedure as in Example 2 was carried out except that the filler added was 33% by weight of calcium silicate powder. [Comparative Example 4] In Comparative Example 2, the polymer used was nylon 6 (ηrel=2.8), and the molten resin temperature during extrusion pelletizing and injection molding was 260°C.
It was carried out in the same manner as Comparative Example 2. The number average length of glass fibers in the pellets obtained by extrusion is 300 μm.
The weight ratio of those with L/D of 15 or more was 90%. Table 1 shows the results of the above examples and comparative examples. As shown in this table, glass fiber reinforced yarns with specific L/D showed very satisfactory effects. 【table】

Claims (1)

[Claims] 1. The ratio L/D of fiber length (L) to fiber diameter (D) is 4 or more15
A molded article made by foam injection molding using a polyamide resin filled with the following glass fibers in an amount of 13% to 50% by weight. 2. The molded article according to claim 1, which is formed by foam injection molding, and the polyamide resin is nylon 46 or nylon 66. 3. The molded article according to claim 1 or 2, wherein the molded article is a cylinder head cover or intake manifold for an internal combustion engine.