JP2771457B2 - Injection molding method of phenolic resin molding material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for injection molding a phenolic resin molding material having excellent heat stability and curability.
The present invention relates to an injection molding method capable of performing low-pressure molding and obtaining a molded article with less generation of burrs.

[0002]

2. Description of the Related Art Phenolic resin molding materials are well-balanced in heat resistance, electrical properties, mechanical properties, dimensional stability and the like, and are used in a wide range of fields including electric parts. Generally, these are molded by injection molding,
In a molten state plasticized at 90 to 120 ° C. in a cylinder of an injection molding machine, the resin has a property of increasing viscosity and losing fluidity due to progress of a curing reaction of a resin. Since the thermal stability of the molten resin is low, it is necessary to minimize the heat generation of the resin in the cylinder of the injection molding machine. An injection molding machine for plasticizing a thermoplastic resin having a large ratio of screw length to diameter (L / D ratio) in order to plasticize and melt the phenolic resin molding material (generally L / D = 18 to 20)
When the resin is used, a large amount of heat is generated, a curing reaction of the resin proceeds, and the resin is cured in the injection cylinder and cannot be injected.

[0003] For this reason, in order to mold a phenolic resin molding material, heat is generally generated during plasticization by using a full flight screw having no compression ratio, no backflow prevention ring, and providing a water-cooled jacket in an injection cylinder. It is necessary to use an injection molding machine equipped with a mechanism for minimizing this. In addition, a general phenolic resin molding material has a relatively high viscosity even in a state where it is plasticized to 90 to 120 ° C. in a cylinder. Is rapidly increased, and the time during which the fluidity is maintained is extremely short. Therefore, in order to obtain a good molded product, injection must be performed at a high pressure in a short period of time and injected into a mold. As a result, the injection amount tends to vary due to the backflow of the molten resin in the cylinder, and In addition, the molded product is easily distorted due to generation of burrs and internal stress.

[0004]

The present invention has been made as a result of various studies to solve these problems. The purpose of the present invention is to provide a plasticized molten state in a cylinder during injection molding. An injection molding machine having a plasticizing mechanism generally used for molding a thermoplastic resin molding material by using a phenol resin molding material having extremely excellent thermal stability and extremely low melt viscosity in a plasticized state. In this method, a phenolic resin molding material is injection-molded, and an object of the invention is to obtain a molded product with less occurrence of burrs.

[0005]

According to the present invention, there is provided an injection molding method for a phenolic resin molding material, wherein a melt viscosity at 100 ° C. is determined by an injection molding machine having a plasticizing mechanism provided with a backflow prevention ring at a screw tip. 10 ⁴ Pa · s or less,
Preferably, the present invention relates to an injection molding method characterized by injection-molding a phenolic resin molding material of preferably 10 ³ Pa · s or less.

In the present invention, a phenolic resin molding material having a melt viscosity at 100 ° C. of 10 ⁴ Pa · s or less is obtained by mixing a normal phenolic resin with a crystalline phenolic compound having a low viscosity at the time of melting. Although a molding material is preferable, as a compounding example, a resin component consisting of a binuclear or higher crystalline phenol compound and a phenol resin,
Hexamethylenetetramine and a filler are blended as essential components, and this blend is kneaded with a low-viscosity phenolic resin molding material. Further, the above blend is blended with a compound containing two hydroxyl groups on a benzene ring. Low-viscosity phenolic resin molding material.

In the present invention, the crystalline phenol compound having two or more nuclei includes bisphenol compounds such as bisphenol A, bisphenol F, bisphenol AD, bisphenol Z, bisphenol S and derivatives thereof, biphenol and its derivatives, and trinuclear phenol compounds. Alternatively, there are tetranuclear phenol compounds and the like, and one or more of these can be used. Such a binuclear or higher crystalline phenol compound is used to impart the property that the phenolic resin molding material is solid at room temperature, melts more quickly by plasticization during injection molding to have a low viscosity, and can be molded under low pressure. Can be In addition, as the phenol resin, a normal novolak-type phenol resin obtained by a reaction between a phenol and formaldehyde can be used.

The compound having two or more hydroxyl groups on the benzene ring is used for imparting the property of improving the curing rate while maintaining a low viscosity without impairing the above properties of the binuclear or higher crystalline phenol compound. Can be As such a compound, one or more of resorcin, hydroquinone, catechol, phloroglucinol, pyrogallol, and derivatives thereof can be used, but resorcin is particularly preferred for accelerating curing.

In the present invention, as described above, the melt viscosity at 100 ° C. of the phenolic resin molding material is 10 ⁴
Pa · s or less, and preferably 10 ³ Pa · s or less. Therefore, in the present invention, as an example of the phenol resin, a compound of a crystalline phenol compound (A) having two or more nuclei and a phenol resin (B) can be mentioned, and the compounding ratio thereof can be arbitrarily selected. However, A / B is preferably 80/20 to 30/70. If the amount of component A is small, the above-mentioned characteristics of crystallinity cannot be sufficiently exhibited, and if it is large, curing is slow. Further, as the blending ratio of the component B increases, the viscosity of the molten resin increases and the curability improves, so that it can be appropriately blended within the above range according to the purpose. Further, the compound (C) having two or more hydroxyl groups on the benzene ring is used for accelerating the curing, and the preferable compounding ratio is the total amount of the above components A and B / C component = 97/3 to 90/10. If the amount of the component C is less than this range, the effect of accelerating the curing becomes small, and if the amount is too large, the curability decreases. Even if the phenolic resin used in the present invention is other than the above, the melt viscosity of the molding material is 10 ⁴
Basically, any material can be used as long as it satisfies Pa · s or less, preferably 10 ³ Pa · s or less.

The fillers used in the phenolic resin molding material of the present invention include organic materials such as wood powder, pulp powder, various crushed fabrics, phenolic resin laminates and crushed molded products, silica, alumina, water and the like. One or more of inorganic powders such as aluminum oxide, glass, talc, clay, mica, calcium carbonate, and carbon, and inorganic fibers such as glass fiber and carbon fiber can be used. The mixing ratio in the phenolic resin molding material of the present invention is such that the resin component containing hexamethylenetetramine is 20 to
70% by weight and 80 to 30% by weight of filler. Also,
Various additives such as a lubricant, a coloring agent, a curing accelerator, and a flame retardant can be appropriately added to the phenolic resin molding material of the present invention.

The phenolic resin molding material of the present invention is obtained by mixing a resin component with hexamethylenetetramine, a filler, and other additives, and kneading the mixture with a roll mill, a twin-screw kneader or the like.
It can be manufactured by grinding. In addition, 2
When a compound having two or more hydroxyl groups is blended, the compound may be melt-mixed with the resin component and hexamethylenetetramine in advance, or may be kneaded with a filler or the like in the next step. The compounding of such a compound is preferable in order to maintain good fast curability and low pressure molding.

[0012]

The phenolic resin molding material of the present invention has, for example, a remarkably low viscosity in a molten state at 90 to 120 ° C., excellent thermal stability, and excellent curability at about 160 to 200 ° C. The reason for this is not clear enough, but 9
At 0 to 120 ° C., the binuclear or higher crystalline phenol compound having a relatively small molecular weight melts quickly and extremely low in viscosity, and the heat generated by shearing by the screw is small. The decomposition of methylenetetramine proceeds, and a hydroxyl group is added to the benzene ring.
It is considered that the presence of a compound having more than one compound further promotes the decomposition, thereby acting on the reaction between the crystalline phenol compound and the phenol resin, thereby promoting the curing reaction.

Therefore, the phenolic resin molding material of the present invention has low viscosity and excellent thermal stability, so that the acceleration of the curing reaction in the cylinder of the injection molding machine is suppressed, and the heat generated by the backflow prevention ring is not large. In addition, stable plasticization can be achieved, while rapid curing can be achieved in a high-temperature mold.

[0014]

EXAMPLES The present invention will be described below with reference to examples. In the formulations, "parts" are parts by weight. The phenolic resin molding material was obtained by kneading the resin and the compound shown in Table 1 with a heating roll. Using these, melt viscosity was measured and injection molding was performed, and the results of evaluating the in-cylinder stability and continuous moldability are also shown in Table 1.

(Measurement method) Melt viscosity: Shimadzu flow tester (CFT, Shimadzu Corporation)
-500C). 2. In-cylinder stability: After tens of shots of a phenol resin molding material are continuously molded, the phenol resin molding material is left in a weighed state and then injected after a certain period of time. When molding was performed by changing the standing time, the longest standing time at which the molten material could flow and sufficiently fill the mold was determined. 3. Continuous moldability: Injection molding of a test piece of 60φ × 8mm at a predetermined injection pressure (injection temperature 90 ° C, mold temperature 1)
80 ° C.) to determine the quality of the continuous formability. 4. Burr generation: Burrs generated in the molded product were judged by silent observation.

[0016]

[Table 1]

In the above Examples and Comparative Examples, an injection molding machine having a screw with a compression ratio of 2.0 and provided with a backflow prevention ring is generally used for molding a thermoplastic resin molding material. Compression ratio of 1.0
An injection molding machine having a screw without a backflow prevention ring is used for molding a thermosetting resin molding material such as a phenol resin.

[0018]

By using a phenolic resin molding material having a low viscosity at the time of melting, continuous injection molding can be performed with an injection molding machine having a high compression ratio and a plasticizing mechanism provided with a backflow prevention ring, which is used for a thermoplastic resin. It is possible. Also,
Since injection molding can be performed at a relatively low pressure, generation of burrs can be suppressed.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B29C 45/00-45/60 C08L 61/06

Claims (2)

(57) [Claims] In a method of injection molding a phenolic resin molding material, a melt viscosity at 100 ° C. is 10 ⁴ Pa · s or less by an injection molding machine having a plasticizing mechanism provided with a backflow prevention ring at a tip of a screw. An injection molding method characterized by injection molding a phenolic resin molding material. 2. The injection molding method according to claim 1, wherein the phenol resin molding material has a melt viscosity at 100 ° C. of 10 ³ Pa · s or less.