JP2755988B2 - Injection molding method and molded article of thermoplastic resin composition containing long fibers - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a molding method for injection-molding a thermoplastic resin composition reinforced with long fibers, and a molded product obtained by the method. In particular, the present invention relates to an injection molding method and a molded product for obtaining a molded product excellent in strength, rigidity, impact resistance, dimensional accuracy, surface smoothness, etc. by utilizing the characteristics of a thermoplastic resin composition reinforced with long fibers. It is.

[Conventional technology and its problems]

A resin composition or molded article reinforced with long fibers obtained by a pultrusion molding method, a filament winding method and the like, and in which the fibers are aligned, makes full use of the properties of the long fibers, and provides strength, rigidity, and impact of the resin. It is preferable to improve characteristics and the like. Conventionally, most of such long-fiber reinforced resin compositions or molded articles have a thermosetting resin as a basic resin because of the easiness of impregnating fibers with the resin. In such a case, a step of reacting and curing the compound is required later, resulting in not only inferior molding processing efficiency (productivity) but also a limitation in the shape of the molded product. Was lacking. On the other hand, when a thermoplastic resin is used as the base resin, the resin is not sufficiently impregnated into the fibers due to the high viscosity of the resin, and as a result, the fibers and the resin are easily separated, impairing the moldability, or impairing the fibers. Has the disadvantage of not being able to obtain a sufficient reinforcing effect due to the lack of practicality, but with the recent advances in impregnation technology, especially with improvements in equipment, thermoplastic resins and base resins The production of a long-fiber reinforced resin composition having good impregnating properties has become possible, and it has come to attract attention.

However, such long-fiber-reinforced thermoplastic resin compositions, which potentially have extremely excellent properties, have not yet been established with a resin molding technique to take advantage of their characteristics, and impair the excellent properties during molding. There was a problem. That is, when such a long fiber reinforced thermoplastic resin composition is molded by a conventionally known injection molding technique, the fibers are broken at the time of molding, and as a result, the characteristics of long fiber reinforcement are lost, and the short fiber reinforced resin composition There is a problem that it will be almost the same as the physical properties of the molded article, taking advantage of the characteristics of the long fiber reinforced thermoplastic resin composition, strength, rigidity, impact properties, low deformability, molded article surface condition, etc. In order to obtain a more excellent molded product, improvement of molding technology is essential.

[Means for solving the problem]

The present inventors have solved this problem by taking full advantage of the excellent properties inherent in long fiber reinforced thermoplastic resin compositions, and forming moldings with even higher strength, rigidity, impact properties, low deformability, etc. As a result of intensive studies on a molding method for obtaining a product, the present invention has been reached.

That is, the present invention relates to a pellet-like thermoplastic resin composition having a length of 3 mm or more containing 10 to 80% by weight (in the composition) of fibers having substantially the same length as the pellet and arranged in the length direction of the pellet. In molding, the depth of the screw groove is substantially 5 mm or more over the entire length of the screw, and at least in the feed portion, the depth of the screw groove is 7 mm
The present invention relates to an injection molding method for a thermoplastic resin composition containing long fibers, characterized by using the injection molding machine described above, and a molded product obtained by the method.

First, the molding method used in the present invention will be described.

The molding method of the present invention takes advantage of the excellent properties inherent in the thermoplastic resin composition reinforced with long fibers, strength, rigidity, and the purpose of obtaining a molded product having high impact properties and the like, It has the following features.

First, in the molding method of the present invention, the depth of the groove of the screw is substantially 5 mm or more over the entire length of the screw,
At least in the feed section, it is essential to use an injection molding machine in which the depth of the screw groove is 7 mm or more. When using a molding machine with a screw groove depth of about 2 to 5 mm in the measuring section (usually the minimum section) and about 4 to 7 mm in the feed section as used in conventional general injection molding machines. In the plasticization, the fiber breaks at the screw part during kneading, the strength, rigidity, impact strength, etc., which fully take advantage of the excellent characteristics of the resin composition reinforced with long fibers, are low, and the deformation is low. It was found that a molded article in a good condition could not be obtained, and only a molded article having physical properties, deformation, and surface state low enough to be obtained by molding a conventionally known short fiber reinforced resin composition could be obtained. On the other hand, the upper limit of the groove depth of the screw can be made large as long as it is allowed in relation to the diameter or strength of the screw. More preferably, molding is performed using a molding machine in which the groove depth of the screw is substantially 6.5 mm or more over the entire length of the screw, and at least the feed portion is 8.5 mm or more. Further, the preferable depth of the screw groove is also related to the diameter of the cylinder, and the ratio of the groove depth of the screw / cylinder system is set to 0.1 or more over the entire length of the screw.
It is preferable to perform molding using the molding machine described above.

In the present invention, in addition to the requirement for the groove depth of the screw, it is more effective to use a molding machine in which the ratio of the length (L) / diameter (D) of the screw is 7 to 15. It was recognized that. Screw length (L) /
In the molding using a molding machine having a diameter (D) ratio of less than 7, the plasticizing and kneading ability is reduced, which is disadvantageous in terms of moldability, particularly in terms of the molding cycle. Conversely, screw length (L) /
The ratio of the diameter (D) exceeds 15, and at about 15 to 25 used in conventional general injection molding machines, fiber breakage due to kneading is recognized, and the excellent properties of the long fiber reinforced composition are impaired. become. More preferably, screw length (L) /
That is, a molding machine having a diameter (D) ratio of 9 to 13 is used.

It is also preferable to use a screw having a compression ratio smaller than 1.8.

In the present invention, in molding the long fiber reinforced thermoplastic resin composition, if molded using a molding machine to which the improvement has been added as described above, fiber breakage during molding is reduced,
Although a molded product excellent in strength, rigidity, impact characteristics, and the like can be obtained by itself, it is preferable to further employ the following molding conditions in order to obtain a molded product having further higher characteristics.

First, one of the preferable molding conditions is that when the resin composition is measured and plasticized, the screw rotation speed is 20 to 50 rp.
m, back pressure 0 to 50 kg / cm ² . If the screw rotation speed is less than 20 rpm, it takes time to measure and plasticize the resin, and the moldability, especially in terms of the molding cycle, is inferior.
Conversely, at a high rotation speed of 50 to 200 rpm as used in normal molding, the effect on the physical properties due to fiber breakage cannot be ignored. Also, as for the back pressure, 50 to 50 commonly used
At 100 kg / cm ² , it is inevitable that the physical properties are somewhat impaired due to fiber breakage. More preferable back pressure is 0-30kg / c
a m ^2.

Another preferable molding condition is that molding is performed at an injection speed (screw advance speed) of 0.2 to 1.0 m / min. If the injection speed is extremely low, the molding cycle, poor filling, etc., will result in inferior moldability. Conversely, if it is 1 to 10 m / min, which is usually used, the effect on the physical properties due to fiber breakage is inevitable. It will be.

Further, it is preferable that the resin temperature in the injection molding be a temperature somewhat higher than the resin temperature generally used for molding the fiber-reinforced resin composition.

The structure, molding conditions, and the like of other molding machines not mentioned in the above description are not particularly limited, and may be appropriately selected from known structures of molding machines, molding conditions, and the like.

Next, the thermoplastic resin composition containing long fibers used for molding in the present invention will be described.

The long fiber-containing thermoplastic resin composition used in the present invention has a length of 3 mm containing 10 to 80% by weight (in the composition) of fibers having substantially the same length as the pellets and arranged in the length direction of the pellets. The above pellet-shaped composition is obtained by, for example, a production method after pultrusion molding. In particular, it is preferable to use a pellet composition having a length of 5 mm or more.

Here, the thermoplastic resin serving as the base is not particularly limited, and any known thermoplastic resin can be used. For example, olefin polymers (polyethylene, polypropylene, etc.), acrylate or methacrylate polymers (polymethyl methacrylate, etc.), polystyrene, AS resin, ABS resin, polyacetal, polyamide (nylon
6,66), polyesters (polyethylene terephthalate, polybutylene terephthalate, etc.), polycarbonate, polyphenylene sulfide, polyurethane and the like. These resins may be modified by known methods such as grafting and crosslinking. It is also possible to use two or more of these resins in combination.

As the fiber, any known fiber such as glass fiber, carbon fiber, silica fiber, silica / alumina fiber, boron fiber, boron nitride fiber, potassium titanate, metal fiber, and heat-resistant polymer fiber can be used. Although it is possible to use more than one kind in combination, glass fibers, carbon fibers and heat-resistant polymer fibers are particularly preferred. The content of such fibers is from 10 to 80% by weight in the composition. If the fiber content is less than 10% by weight, sufficient improvement in strength, rigidity, impact strength, etc. cannot be obtained, and if it exceeds 80% by weight, molding becomes extremely difficult. In particular, when the molding method of the present invention is applied to a resin composition containing a high-concentration long fiber of 30 to 70% by weight, the effect is remarkable, and fiber breakage, which is a disadvantage of the conventional molding method, is reduced. Prevention makes it possible to remarkably improve strength, rigidity, impact strength, and the like, and is extremely preferable because there is no problem such as molding failure.

Further, the long fiber reinforced resin composition used in the present invention,
Known substances generally added to thermoplastic resins, for example, stabilizers such as antioxidants and ultraviolet absorbers, antistatic agents, flame retardants, coloring agents such as dyes and pigments, lubricants, crystallization accelerators, crystal nuclei Agent, carbon black, glass beads, glass powder,
It may contain a powdery or plate-like inorganic filler such as glass flake, silica, mica and the like.

〔Example〕

Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited thereto.

Examples 1 to 8 and Comparative Examples 1 to 7 Thermoplastic resin compositions reinforced with long fibers as shown in Tables 1 to 3 (all of 12 mm long pellets obtained by a pultrusion molding method) The fiber length was substantially the same as that of the pellets) was injection-molded by a molding method having the requirements specified in the present invention as shown in the same table. Tables 1 to 3 show the evaluation results of physical properties and the like.

For comparison, the same resin composition used in the examples was molded and evaluated by a conventionally known molding method, and a thermoplastic resin reinforced with a conventionally known short fiber was used. The compositions were molded by a molding method having the requirements specified in the present invention and evaluated, and the results are also shown in Tables 1 to 3.

In addition, the measuring methods of the evaluated physical properties etc. are as follows.

Tensile strength and elongation: Conforms to ASTM D-638 Flexural modulus: Conforms to ASTM D-790 Impact strength: Conforms to ASTM D-256 Dispersion fiber length: Decomposes and removes resin using molded pieces for tensile test After that, the remaining fiber was measured by using a universal projector, and the warpage of the molded product: a flat plate of 120 mm square and 2 mm thick was formed.
Surface condition (roughness): The above molded piece (flat plate) was observed with the naked eye, and the surface smoothness (roughness) was relatively evaluated. It can be seen that the molding method exhibits a special effect in molding a thermoplastic resin composition reinforced with long fibers.

[Effects of the Invention] As is clear from the above description and Examples, according to the injection molding method of the present invention, fiber breakage during molding is remarkably improved, and a thermoplastic resin composition containing long fibers is originally used. It is a very useful thing that can obtain molded products with excellent properties such as strength, rigidity, impact resistance, dimensional accuracy, surface smoothness etc.
Thereby, the use of the thermoplastic resin composition containing long fibers can be dramatically expanded.

Claims (6)

(57) [Claims] 1. A pellet-shaped thermoplastic resin composition having a length of 3 mm or more and containing 10 to 80% by weight (in the composition) of fibers substantially the same length as the pellets and arranged in the longitudinal direction of the pellets. In forming a long fiber, the depth of the groove of the screw is substantially 5 mm or more over the entire length of the screw, and at least in the feed part, the depth of the groove of the screw is 7 mm or more. Injection molding of a thermoplastic resin composition containing: 2. The injection molding method of a thermoplastic resin composition containing long fibers according to claim 1, wherein an injection molding machine having a ratio of length (L) / diameter (D) of the screw of 7 to 15 is used. 3. The method of injection molding a thermoplastic resin composition containing long fibers according to claim 1, wherein an injection molding machine having a screw compression ratio of less than 1.8 is used. 4. Screw rotation speed 20-50rpm, back pressure 0-50k
4. Injection molding under the condition of g / cm < ² >.
Injection molding of the thermoplastic resin composition containing long fibers according to the above item. 5. An injection speed (screw advance speed) of 0.2 to 1.0.
The injection molding method for a thermoplastic resin composition containing long fibers according to any one of claims 1 to 4, wherein the thermoplastic resin composition is molded at m / min. 6. A thermoplastic resin molded product obtained by injection molding the thermoplastic resin composition containing long fibers according to any one of claims 1 to 5.