JP3377010B2 - Manufacturing method of thin molded products - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin molded article having a small warpage, excellent adhesiveness between a plurality of laminated different thermoplastic resin layers, and excellent surface appearance. The present invention relates to a method for efficiently manufacturing in a short time. [0002] Conventionally, in order to manufacture a molded article in which two kinds of thermoplastic resins are laminated, an injection molding machine equipped with two sets of injection devices is used, and one thermoplastic resin is molded into a mold. After injection, the mold was inverted and the next thermoplastic resin was injected from the mold surface opposite to the mold surface from which one thermoplastic resin was injected, or one thermoplastic resin was injected into the mold Then, a core is moved, the gap corresponding to the thickness of the thermoplastic resin to be injected next is provided in the mold, and a core back method of injecting the next thermoplastic resin into the gap is used. However, in the above method, when a thin and large molded product is molded, there is a problem that the molded product is warped and the two-layer adhesiveness is poor. In Japanese Patent Application Laid-Open No. 3-247423, there are disclosed two compression molding machines and a compression molding machine having a fixed lower mold and an upper mold movable up and down by a press mechanism. A method for producing a two-layer molded article is described. According to this method, although a relatively thin two-layer molded product can be obtained, a lump of thermoplastic resin is injected between the upper and lower molds having a wide gap, the control valve is closed, and then compression is performed. Because of the press method, the surface appearance of the molded product is inferior and burrs are likely to occur. In addition, there is a disadvantage that the surface temperature of the thermoplastic resin molded first and further the thermoplastic resin injected next decreases, and the adhesiveness between the laminated thermoplastic resin layers is poor. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to efficiently produce a thin molded article having less warpage, excellent adhesion between a plurality of different thermoplastic resin layers, and a good surface appearance. The idea is to propose a way to do that. The present inventors have conducted intensive studies on the above-mentioned problems, and as a result, have found a method of manufacturing a thin-walled molded product that solves the above-mentioned problems, and have completed the present invention. . That is, the present invention uses an injection compression molding apparatus in which a plurality of different thermoplastic resins and a plurality of injection devices for injecting each thermoplastic resin into a mold are connected to the mold. One thermoplastic resin is injected into the mold to perform molding, then the mold is opened, and between the molded thermoplastic resin and the mold, the next thermoplastic resin to be subjected to injection compression molding A gap having a thickness of 1.05 to 3.00 times the thickness is formed, the next thermoplastic resin is injected into the gap, and the injection amount becomes 60 to 90 wt% of the total injection amount of the thermoplastic resin. From the injection compression molding to obtain a thin molded product obtained by laminating a plurality of different thermoplastic resins. In the present invention, a plurality of different thermoplastic resins are used in combination. The type of the thermoplastic resin is not particularly limited, and a known thermoplastic resin can be used as long as it is suitable for a thin-walled molded product. For example, thermoplastic resins such as polyolefin, polyamide, polyimide, polyester, and polycarbonate can be used. [0008] The thermoplastic resins used in combination may be any combination as long as they are not the same thermoplastic resin. For example, it may be a combination of different types of thermoplastic resins such as polyolefin and polyamide, or between polyolefins, and even the same type of thermoplastic resin such as polypropylenes as long as the composition is different. Further, even thermoplastic resins of the same type and the same composition, or a combination of thermoplastic resins having different melt flow rates and types and amounts of fillers and additives contained therein may be used. Specific examples of suitable thermoplastic resins used in combination in the present invention include, for example, a combination of a highly rigid polypropylene filled with talc or glass fiber and a thermoplastic elastomer so that the surface is soft and rigid. High molded product can be obtained. In addition, a molded article that is lightweight and has excellent surface appearance can be obtained by a combination of expanded polypropylene and general polypropylene. In addition, a recycled molded article having excellent surface appearance can be produced by a combination of polypropylene that has been used once and then recycled and general polypropylene. Further, by combining maleic anhydride-modified polypropylene and polyamide, a molded article having excellent gasoline resistance can be obtained. In the present invention, not only a two-layer molded product,
Depending on the purpose, three or more layers may be used. [0010] The injection compression molding apparatus used in the present invention comprises:
A plurality of injection devices for injecting different thermoplastic resins into a mold are connected to the mold. The injection device may be of any type capable of melting thermoplastic resin and injecting it into a mold, such as a plunger type, plunger pre-plasticizer type, screw pre-plasticizer type, in-line screw type, and shear plasticizing. Formulas, high-pressure plasticizing formulas, and the like can be used. Also, as the injection compression method of the injection compression molding machine, known methods can be used without limitation,
For example, a method by two-stage mold clamping in a toggle mold-clamping injection compression molding machine, a method of switching the mold clamping force in a direct pressure mold-clamping injection compression molding machine, a core compression method by a mold structure, and the like can be mentioned. FIGS. 1 and 2 show examples of a mold structure suitably used in the present invention. As shown in FIG. 1, since the mold is subjected to injection compression molding, it is preferable that the fixed mold 1 and the movable mold 2 slide to seal the mold cavity. Further, it is preferable that the injection molding machine include hot runners 4 and 5 connected to the nozzles 6 and 7 and have a structure in which a plurality of thermoplastic resins are not mixed when a plurality of thermoplastic resins are sequentially injected into a mold. . In addition, gate 8,
9 may be in two places as shown in FIG.
As shown in (1), a switching valve 10 may be provided at the junction of a plurality of thermoplastic resins, and may be provided at one location. 1 and 2 show the mold structure in the case where there are two types of thermoplastic resin. However, when there are three or more types of thermoplastic resin, the same number of injection devices as the number of types of thermoplastic resin are used. , A nozzle, and a hot runner can achieve the method of the present invention. A method for producing a thin-walled molded product according to the present invention will be described with reference to FIG. First, one thermoplastic resin melted by the injection device is injected into the hot runner 4 through the nozzle 6 (or 7).
Through (or 5), injection molding is performed in the mold cavity 3. The molding method at this time may be ordinary injection molding, but when a thin molded product is injected, the flow length of the thermoplastic resin is improved, and furthermore, the occurrence of warpage and sink is reduced. It is preferable to employ injection compression molding. In the present invention, the method of molding the next thermoplastic resin differs from the pressing method in that the gap between the molds is narrowed while the next thermoplastic resin is injected into the mold, and the compression of the thermoplastic resin is performed. Is injection compression molding. That is, after injecting a predetermined amount of one thermoplastic resin into the mold, the movable mold 2 is moved, the mold is opened, and then injection compression molding should be performed between the injected thermoplastic resin and the mold. 1.05 to 3.00 times the thickness of the thermoplastic resin, and more preferably 1.10 to 2.00
A gap twice as thick is formed. If the gap is less than 1.05 times, the flow length of the thermoplastic resin does not increase, the warpage of the final molded article increases due to the orientation of the thermoplastic resin, and the adhesion between the laminated thermoplastic resins is poor. On the other hand, if the gap exceeds 3.00 times, the surface appearance of the molded article is impaired, and the problem that the next thermoplastic resin does not reach the end of the molded article is likely to occur, which is not preferable. [0014] The next injection of the thermoplastic resin into the mold is preferably performed before the surface of the molded article of one thermoplastic resin is cooled, and the mold is opened simultaneously with injection molding of one thermoplastic resin. Immediately after the mold opening is completed, it is preferable to perform injection compression molding of the next thermoplastic resin. By performing the injection compression molding of the next thermoplastic resin before the surface of one thermoplastic resin molded product cools, the adhesion between the laminated thermoplastic resins is good, and the molding of the next thermoplastic resin The warpage of the thermoplastic resin layer caused by shrinkage on the inner side is reduced, and a thin molded article excellent in surface appearance can be obtained. In the injection compression molding, in order to reduce the warpage of a thin molded product and obtain a thin molded product of a predetermined thickness, 60 to 90 wt% of the total injection amount of the thermoplastic resin is injected into a mold. It is preferable to start compression from a point in time. [0016] Even in the case of a thin-walled molded product in which three or more kinds of thermoplastic resins are laminated, if this method is sequentially repeated, a molded product having good adhesion, less warpage and excellent surface appearance can be efficiently obtained. be able to. According to the method for producing a thin-walled molded product of the present invention, the warpage caused by the orientation of the thermoplastic resin is small, and the adhesiveness between the laminated thermoplastic resins is good. A thin molded product made of a laminate of a plurality of thermoplastic resins having excellent appearance can be obtained. Therefore, it can be used for a molding method for automobile parts such as instrument panels, pillars, trims, bumpers, and wheel caps, and housings for electric equipment. The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these examples. Prior to the examples, an injection compression molding machine, a mold, and a method of evaluating a molded product used in the examples will be described. (1) Injection compression molding machine A double-toggle injection compression molding machine equipped with two in-line screw injection devices having a clamping force of 100 tons and a screw diameter of 35 mm was used. Injection cylinder temperature is 22 for both units
It was set to 0 ° C. In addition, the cylinder temperature at the time of injecting polyamide was set to 260 ° C. (2) Die Injection compression molding having the structure shown in FIG. 1 and having a cavity with a length of 200 mm, a width of 150 mm, a thickness variable from 1.0 mm to 5.0 mm, and two sets of hot runners. A mold was used. The mold temperature was set at 40 ° C. (3) Method of Evaluating Molded Product Surface roughness of the molded product surface, flow marks, and sink marks were observed with the naked eye. Warpage of Molded Article A molded article is warped with the thermoplastic resin injected first facing outward. Therefore, the difference between the height of the center portion and the height of the end portion when the thermoplastic resin layer obtained by first injection-molding the obtained molded article was placed down on the thermoplastic resin layer was measured and defined as the amount of warpage. Adhesion The adhesion between the laminated thermoplastic resin layers is poor, especially at the end of the molded article. Therefore, the two thermoplastic resin layers laminated at the end of the molded product were peeled off by a razor about 10 mm,
The adhesiveness was evaluated by pulling the two separated thermoplastic resins in opposite directions by hand. Example 1 A homopolypropylene having a melt flow rate of 15 g / 10 min was passed through one hot runner into a mold having a cavity thickness of 1.5 mm, and a predetermined amount was injected into the mold cavity. Then, a gap of 0.8 mm (1.6 times the thickness of the thermoplastic resin to be subjected to injection compression molding) was formed between the thermoplastic resin and the fixed mold. Immediately after the gap is formed, an olefin-based thermoplastic elastomer (manufactured by Tokuyama Corporation, PER,
The injection of the grade name M142E) is started through the other hot runner, and the injection amount is 8 times the total injection amount of the thermoplastic resin.
The movable side mold was moved from the time when it reached 0%, and compression was started. The thickness of the obtained thermoplastic resin was 0.5 mm. The surface appearance of the obtained two-layer thin-walled molded product was excellent with no surface roughness or sink marks observed. Warpage is 0.2
mm. The adhesiveness of the two laminated layers resulted in cohesive failure of the olefin-based thermoplastic elastomer, and was excellent. Example 2 The molding of the homopolypropylene in Example 1 was performed using 1.8
A molded product was obtained in the same manner as in Example 1 except that homopolypropylene was injection-compressed and formed in a mold set to a thickness of 1.5 mm, and the final thickness of the thermoplastic resin was adjusted to 1.5 mm. . The surface appearance of the obtained molded product was extremely excellent without any surface roughness or sink marks, and the warpage was 0.1 mm or less, and the adhesion was a cohesive failure of the olefin-based thermoplastic elastomer. Comparative Example 1 In Example 1, the injection molding of the olefin-based thermoplastic elastomer was performed in the same manner as in Example 1 except that the gap was set to 0.5 mm, injection compression molding was not performed, and ordinary injection molding was performed. A molded product was obtained. The thickness of each layer of the obtained molded article was the same as that of Example 1. Further, slight irregularities were observed on the surface of the molded product. The warpage was 2.2 mm, and the two layers were not adhered at the end of the molded product, and could be easily peeled off by hand. Comparative Example 2 In Example 1, the gap was set to 2.0 mm (4.0 times the thickness of the thermoplastic resin to be subjected to injection compression molding) during the injection compression molding of the olefin thermoplastic elastomer. Except for the above, a molded article was obtained in the same manner as in Example 1. Roughness was observed on the surface of the obtained molded article, particularly at the end of the molded article. The warpage was 3.8 mm, the adhesiveness was poor at the end of the molded product, and it could be easily peeled off by hand. Example 3 In a mold in which the thickness of the mold cavity was set to 3.0 mm,
The same homopolypropylene as in Example 1 containing 0.5% by weight of azodicarbonamide as a foaming agent was injection-molded, and then only the same homopolypropylene as in Example 1 was injection-compressed and molded in the same manner as in Example 1. Product was obtained. The surface appearance of only the homopolypropylene side of the obtained molded article was excellent, the warpage was 0.4 mm, and the adhesion was good. Example 4 In Example 1, homopolypropylene having a melt flow rate of 0.1 g / 10 min was used as the next thermoplastic resin, and the gap was 1.0 mm (2 mm of the thickness of the thermoplastic resin layer of the molded product). A molded product was obtained in the same manner as in Example 1 except that injection compression molding was performed in a metal mold of (1.0 times). The surface appearance of the obtained molded product was excellent, the warpage was 0.5 mm, and the adhesiveness was good. Example 5 In Example 1, maleic anhydride was first added to 0.03
Melt flow rate 22g / 10 wt% grafted
After injection molding of the block polypropylene, a 0.55 mm gap (1.1 times the thickness of the thermoplastic resin to be subjected to injection compression molding) was formed in the mold, and the injection cylinder was set at 260 ° C. From polyamide (Unitika Nylon 6, manufactured by Unitika Ltd., grade name A1030)
BRL) was injected into a mold, and a molded article was obtained in the same manner as in Example 1 except that injection compression molding was performed. The surface appearance of the obtained molded product was excellent, the warpage was 0.3 mm, and the adhesiveness was also good.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view showing a typical example of a mold structure used in the present invention. FIG. 2 is a schematic view showing another example of a mold structure used in the present invention. [Description of Signs] 1 Fixed mold 2 Moving mold 3 Mold cavities 4 and 5 Hot runners 6 and 7 Nozzles 8 and 9 Gate 10 Switching valve

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B29C 45/00-45/84

Claims (1)

(57) [Claim 1] An injection compression molding apparatus in which a plurality of different thermoplastic resins and a plurality of injection devices for injecting each thermoplastic resin into a mold are connected to the mold. First, one thermoplastic resin is injected into the mold to perform molding, then the mold is opened, and then injection compression molding is performed between the molded thermoplastic resin and the mold. A gap having a thickness of 1.05 to 3.00 times the thickness of the thermoplastic resin to be formed is formed, and the next thermoplastic resin is injected into the gap, and the injection amount is 60 to 90 wt% of the total injection amount of the thermoplastic resin. %
A method for producing a thin-walled molded product, comprising performing injection compression molding from the point of time of obtaining a thin-walled molded product in which a plurality of different thermoplastic resins are laminated.