JPH0462108A - Preparation of fiber-reinforced thermoplastic resin pellet - Google Patents

Abstract

PURPOSE:To prepare efficiently a fiber-reinforced thermoplastic resin pellet by a method wherein a reinforcing fiber and a thermoplastic fiber are combined; a composite fiber with a specified combining ratio is heated in the fiber direction to melt the thermoplastic fiber; the composite is cut at a specified length by applying a pressure by using a fitting roll. CONSTITUTION:A composite fiber wherein 25-70wt.% reinforcing fiber are incorporated and a combining ratio of the reinforcing fiber and a thermoplastic fiber is at least 10% is continuously heated in the fiber direction by means of radiation heating and convection heating to melt the thermoplastic fiber. A rod-like fiber-reinforced thermoplastic resin obtd. by applying continuously a pressure by using a male and a female fitting roll is cut into a length of 3-60mm to prepare a fiber-reinforced thermoplastic resin pellet. If the combining ratio is lower than 10%, a good pellet is hardly prepd. with respect to impregnating characteristics. In addition, if the content of the reinforcing fiber is less than 25wt.%, such physical properties as impact resistance and wear resistance decrease and if the content is more than 70wt.%, impregnation of the reinforcing fiber with a matrix resin is not enough and it is impossible to obtain a molded item with good mechanical characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to fiber-reinforced thermoplastic resin pellets that can be used for injection molding, extrusion molding, etc., and a method for producing the same.

(Conventional technology) Fiber-reinforced thermoplastic resin composites such as fiber-reinforced engineering plastics (hereinafter abbreviated as engineering plastics) are
The market has been steadily growing, centering on injection molding, and it has now become an extremely important industrial material. In general, the method for making pellets for these engineering plastics is to melt them using a kneader when using fibers as a reinforcing material, and cut the fibers that will become the reinforcing fibers into IJ Fuchs resin into 3-inch pieces. After mixing, extrusion, cooling and solidification 2~
It is manufactured by a method of forming pellets with a length of about 3 mm. In addition, as described in Japanese Patent Publication No. 83-37694, the reinforcing fibers that have been opened are passed through a melted thermoplastic resin bath to impregnate the reinforcing fibers with the thermoplastic resin, and then the length of the fibers is about 10 mm. A method has been developed to obtain long fiber-reinforced pellets by cutting the pellets into long fibers. In addition, after filling the reinforcing fibers with thermoplastic resin fine particles, the fibers are heated to melt the thermoplastic resin fine particles, and then male and female interlocking rolls are used to fill the thermoplastic resin between the reinforcing fibers. Impregnation methods have also been developed. Injection molded products using chips produced by these methods have longer reinforcing fibers in the molded product than before, and although the physical properties of the molded product have improved, it is still difficult to invent more efficient manufacturing methods. desired.

(Problems to be Solved by the Invention) In injection molded products produced using injection molding pellets produced by the conventional compounding method as described above, reinforcing fibers such as glass fibers have a length of several hundreds. As a result, the reinforcing effect of the fibers decreased and physical properties such as impact resistance and fatigue resistance were insufficient. In addition, in the method of impregnating thermoplastic resin in molten resin, and in the method of filling fine particles of thermoplastic resin into reinforcing fibers and then heating and melting them to obtain a long fiber reinforced thermoplastic resin, the fibers in the pellets are not wetted by the resin. Problems such as poor quality and limited manufacturing speed still remain. Therefore, the present invention relates to a method for solving such problems and producing fiber-reinforced thermoplastic resin pellets with better impregnation properties and higher efficiency.

(Means and effects for solving the problems) The present invention is intended to solve the problems as described above.
Using a conjugate fiber containing % wt% of reinforcing fibers and having a blending ratio of at least 10%, the conjugate fibers are subjected to radiation heating and convection heating in the fiber direction. After melting the thermoplastic fiber by continuously applying heat or a combination thereof, the composite fiber is obtained by continuously applying pressure to the composite fiber using one or more pairs of male and female interlocking rolls. The present invention provides a fiber-reinforced thermoplastic resin pellet obtained by cutting a rod-shaped fiber-reinforced thermoplastic resin into lengths of 3 to 601 mm, and a method for producing the same.

That is, reinforcing fibers and thermoplastic fibers are mixed by a known method to obtain composite fibers. For example, the method of pulling bicontinuous fibers together and electrostatically opening them and mixing them in the state of both fibers, or the method of pulling bicontinuous fibers together and passing them through a turbulent flow of air to mix them, can increase the cross-mixing rate. A conjugate fiber having a diameter of at least 109A is obtained.

The fiber mixing ratio here is expressed by the following formula.

Here, N indicates the total number of reinforcing fibers, NcX indicates the number of groups when the reinforcing fibers are divided into several groups, and X indicates one specific group within the group. It shows the number of filaments within. In the above formula, 100X(N-X)/N-1 means a mixed fiber state, and the smaller X is, the better the mixed fiber state is. Also, Nc
X/N/X is the weight. If the fiber blend ratio is lower than 10%, it is difficult to produce pellets with good impregnation properties in the subsequent pelletizing step, which is not preferred. Also,
The reason why the reinforcing fiber content is set from 25 wt% to 70 wt% is because if the reinforcing fiber content is less than 25 wt%, physical properties such as impact resistance and fatigue resistance will be relatively low.
If the amount is more than 0 wt%, the reinforcing fibers will not be impregnated with the IJ Fuchs fat and a molded article with good mechanical properties cannot be obtained, so the effects of the present invention will not be fully exhibited, which is not preferable. Moreover, the reason why composite fibers are used here is that the content of reinforcing fibers can be increased.

Next, the composite fiber is continuously heated at a temperature equal to or higher than the melting point of the thermoplastic fiber by using either radiation or forced convection or a combination of both heating methods to melt the thermoplastic fiber. As a heating method using radiation, far-infrared rays, near-infrared rays, or both irradiation can be used. It is especially preferable to use both far-infrared rays and near-infrared radiant heating in combination. In that case, far-infrared rays are first used. After semi-melting the thermoplastic resin fibers, the thermoplastic resin is completely melted using near infrared rays, thereby melting the thermoplastic resin without thermally deteriorating it. Further, as a method of forced convection heating, a method of heating and injecting air or nitrogen gas can be used.

Injecting such heated gas to the composite fiber is an efficient method for heating air that is difficult to heat. Further, in order to prevent oxidative deterioration of the thermoplastic resin, it is desirable to use nitrogen, which is an inert gas.

A rod-shaped fiber-reinforced thermoplastic resin is produced by continuously applying pressure to the composite fiber obtained by melting the thermoplastic fibers using a pair or multiple pairs of male and female mating rolls. The roll can be made of metal or ceramic, and metal is more preferable. The groove width of the male and female mating rolls used for applying pressure is as follows.

b = a ~10 That is, two or more pairs of male and female mating rolls, usually one
Although up to 0 pairs can be used, if a large number of pairs are used, the groove widths may all be the same or may be gradually narrowed. Gradually narrowing the groove width (in cases where the groove width is gradually narrowed, voids in the molten composite fibers are removed, the moldability of the rod-shaped fiber-reinforced thermoplastic resin is improved, and the impregnability is improved). Pellets with good moldability can be produced.The width of the pellets is 2 to 101@, more preferably 2 to 5.0.If the width is 10s1 or more, the pellets will not easily dig into the mold during injection molding.

Also, the width is 2.0. - In the following cases, the pellets will be damaged during injection molding and the reinforcing fibers will be seriously damaged, which is not preferable. The linear pressure applied to the composite fibers by the metal interlocking rolls is 5 x 10-'kg/ell m den ~
It is preferable that it is 1,5 x 10-3 kg/cs/den. If the linear pressure is less than 5 x 10-41 < g/c, it is undesirable because many voids will occur in the pellet, and if the linear pressure is 1.5 x 10-3 kg/c, it is not preferable.
m·den or more is not preferable because the reinforcing fibers in the pellet will break.

It is preferable that the surface humidity of the roll is 5 to 220°C. If the surface temperature of the roll is lower than 5° C., the molten thermoplastic resin of the molten composite fiber will be rapidly cooled and solidification will begin rapidly, making it difficult to shape into pellets and to remove voids, which is not preferable. Furthermore, if the temperature is higher than 220° C., problems such as the molten composite fibers winding around the roll and thermal deterioration of the resin occur, making it impossible to obtain good pellets. Furthermore, the operability in pellet production is also poor, which is not preferable. In addition, with respect to the arrangement of the male and female mating rolls, only the female roll may be located on the lower side, or the female rolls and male rolls may be located alternately on the lower side.

The rod-shaped fiber-reinforced thermoplastic resin obtained as described above is cut into lengths of 3 to 6011 mm using a pelletizer to obtain pellets. The length of the pellet needs to be 311 or more in order to increase the length of the reinforcing fiber in the injection molded product and improve the mechanical properties.In addition, from the point of view of feeding the pellet to the screw during molding, It must be 60m5 or less.

The reinforcing fibers that can be used in the present invention include continuous fibers such as glass fibers, carbon fibers, and aramid fibers, but are not limited to these fibers.

Further, thermoplastic fibers that can be used in the present invention include, for example, polypropylene, nylon 6, nylon 66, polybutylene terephthalate, polyethylene terephthalate, polyphenylene sulfide, polycarbonate,
Examples include polyetheretherketone, but are not limited to these thermoplastic fibers.

(Example) Examples of the present invention will be described below.

Composite fibers for obtaining fiber-reinforced thermoplastic resin pellets were produced using E-glass fibers and nylon 6 fibers having the following characteristics.

E Glass fiber total fineness: 67.5 tex (JIS R3420) Number of filaments: 400 (same t) Nylon 6 fiber total fineness: 150 denier (JIS L 1013)
Number of filaments = 30 (same as above) The basic method for producing composite fibers using these glass fibers and nylon 6 fibers is to feed the nylon 6 fibers to the E glass fibers in an overfeed state of +0.3% and use the rath run method. (Processing speed: 100 m/5 inch) to obtain composite fibers. Furthermore, the basic method for producing fiber-reinforced thermoplastic resin pellets is to heat the 15 composite fibers continuously to 230°C in heated air at a speed of 15m/1n, then use a far-infrared heater and a near-infrared heater. The composite fibers were heated to 300°C while flowing heated nitrogen gas at 1.5 Nm/h in a heating zone equipped with both heaters to melt the nylon 6 fibers. Female mating roll (groove width: 4.5゜4.0, 3.5, 3
．． A rod with a width of 3 mm and a thickness of about 1 mm was formed by applying pressure using rolls whose widths were gradually narrowed in the order of 0, 3.0, and 3.0 m. , to obtain fiber-reinforced thermoplastic resin pellets.

The pellets obtained as described above were molded using an injection molding machine, and the mechanical properties of the molded product were examined. The molding machine and molding conditions were as follows.

Injection molding machine: Toshiba Machine Co., Ltd. l5-100 EN injection molding conditions Molding temperature = 285°C Injection speed: 4 m/Nn Mold temperature 280°C The evaluation of the fiber-reinforced thermoplastic resin opening/socket article described below is as follows: The void ratio was calculated and evaluated as follows.

Td: Theoretical density of fiber-reinforced thermoplastic resin mouth/socket material d: Actual density In addition, the evaluation of injection molded products is based on the bending test (ASTMD79).
0), tensile test (ASTII! D 738)
(based on ASTM 025B) and Izod impact test (based on ASTM 025B).

(Examples 1 to 3) In the production of the above composite fiber, the glass fiber content was 30 (
Example 1), 50 (Example 2), 60 wt% (Example 3)
) was produced to obtain a fiber-reinforced thermoplastic resin rod-shaped article, and then pellets were produced by the above pellet and throat production method and injection molded.

Table 1 lists the mechanical properties of the rod-shaped article and injection molded article obtained.

(Comparative Examples 1 and 2) In the production of the above composite fiber, the glass fiber content was 10 (
Comparative Example 1) Composite fibers of 75 vt% (Comparative Example 2) were produced, and pellets were produced and injection molded under the same conditions as Examples 1 to 3. Table 1 lists the mechanical properties of the molded product obtained. Comparison with Examples 1 to 3 shows that in Comparative Example 1, the mechanical properties of the molded product are poor and are not of practical use. Furthermore, in Comparative Example 2, mechanical properties equivalent to the glass fiber content were not obtained.

(Comparative Example 3) A tank in which nylon 6 was heated and melted was provided, and Example 2 was poured into the tank.
After glass fibers were immersed under the same conditions as above, the amount of resin attached was controlled to 50 wt% using a die. The rod-shaped product thus obtained was cut into pieces of 10 Wit, and then injection molded under the same conditions as in Example 2, and the mechanical properties of the molded product were examined. The mechanical properties are listed in Table 1. From Table 1, it can be seen that in Comparative Example 3, there are more voids than in Example 2, and the mechanical properties of the injection molded product are lower.

(Comparative Examples 4 to 5) Using the same composite fiber as in Example 2, the pressure applied by the forming roll when producing a fiber-reinforced thermoplastic resin rod was 3×1.
0-'kg/cs-den (Comparative Example 4), 2,
The fabrication was performed under a linear pressure of OX 10-3 kg/cm·den (Comparative Example 5). 2. OXIO-3kg/cm・
Table 1 lists the mechanical properties of the rods and injection molded products manufactured at den. Also, 3 x to -4kg
/ It was not possible to obtain a rod worthy of evaluation in C/den. As can be seen from the comparison with Example 2, the linear pressure during molding was 2. At OX 10-3 kg/cm·den, the linear pressure was too high, causing damage to the glass fibers during pellet production, making it impossible to obtain a molded product with good mechanical properties. Also, 3 X 10-'kg/
It can be seen that at cs·den or higher, impregnation into resin glass fibers is poor and it is impossible to obtain rods and pellets worthy of evaluation.

(Comparative Examples 6 to 7) The humidity of the roll when producing a fiber-reinforced thermoplastic resin rod-shaped article using the same composite fiber as in Example 2 was 0°C (Comparative Example 8);
Production was performed at 240°C (Comparative Example 7). At 240° C., the molten conjugate fibers were wrapped around the rolls, making it impossible to obtain a rod worthy of evaluation. In addition, Table 1 shows the mechanical properties of injection molded rods and pellets obtained at 0°C.
It was listed on. It can be seen that at 0°C, there were many voids in the pellets and the physical properties of the injection molded product were not as good as in Example 2.

(Comparative Example 8) Using conjugate fibers having the same structure as in Example 2, conjugate fibers with a mixed fiber ratio of 5% were produced, and fiber-reinforced thermoplastic resin rods and pellets thereof were produced and injection molded. Table 1 lists the mechanical properties of the rod-shaped product and the mechanical properties of the injection molded product.

It can be seen that there are more voids than in Example 2 and the mechanical properties of the injection molded product are also poor.

(Effects of the present invention) From the results of the aforementioned Examples and Comparative Examples, injection molded products with excellent mechanical properties can be obtained by using pellets obtained by the method for producing fiber-reinforced thermoplastic resin pellets according to the present invention. Ta.

(Effects) By using the pellets produced by the method described above, a molded product with long reinforcing fibers and excellent mechanical properties can be obtained.

Furthermore, the pellets according to the present invention can be applied to other methods such as general injection molding as well as extrusion compression molding.

[Brief explanation of the drawing]

Figure 1 is an overall view of an apparatus for manufacturing a thermoplastic composite material having a constant cross-sectional shape according to the present invention. In the figure, ■: Mixed yarn ■: Supply roll ■: First heating zone ■: Second heating zone ■ : Yarns with melted thermoplastic fiber components ■, ■′, ■
, ■': Male and female interlocking roll ■: Taking-off belt ■: Yarn cooling section [phase] Dual-purpose object (thermoplastic composite material with a constant cross section) FIG. 3 is a front view and a side view of the male and female mating roll portions shown.

Claims (1)

[Claims] (1) Containing 25 to 70 wt% of reinforcing fibers and mixing the reinforcing fibers with thermoplastic fibers, the blending ratio is at least 1.
After melting the thermoplastic fiber by continuously applying heat to the composite fiber in the fiber direction by one or both of radiant heating and convection heating, a pair of male and female fibers are added to the composite fiber. Alternatively, a method for producing fiber-reinforced thermoplastic resin pellets by cutting a rod-shaped fiber-reinforced thermoplastic resin obtained by continuously applying pressure using a plurality of pairs of interlocking rolls into lengths of 3 to 60 mm.