JPH04345635A - Lightweight resin molding and its production - Google Patents

Abstract

PURPOSE:To provide a lightweight resin molding expanded at a low expansion ratio and a process for producing the same. CONSTITUTION:A lightweight resin molding is prepared by adding at most 3wt.% blowing agent to a base resin prepared by mixing a polystyrene resin with a polyphenylene resin in a suitable mixing ratio and expanding the obtained mixture at an expansion ratio of 1.5-15; and a process for producing the same comprises pre-expanding a base resin prepared by mixing a polystyrene resin with a polyphenylene resin in a suitable mixing ratio, adding at most 3wt.% blowing agent to the base resin thus pre-expanded, and post-expanding the resulting mixture at an expansion ratio as low as 1.5-15 in a desired mold.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is directed to a lightweight resin molded article that has sufficient strength at a low expansion ratio of about 1.5 to 15 times and can be used as a constituent material for equipment, and to produce such a molded article in a short time. The present invention relates to a possible manufacturing method.

0002

2. Description of the Related Art In recent years, from the viewpoint of energy conservation, efforts have been made to reduce the weight of automobiles and improve their fuel consumption rates. Weight reduction has been achieved by replacing metal materials with resin molded products, but thin-walled molding is now being adopted in order to obtain even lighter structural materials. However, since many large molded products are hollow, there is a limit to their strength, and it is difficult to make them extremely thin.

Foam molding is attracting attention as an alternative to such thin wall molding. Reducing the weight of a molded article by foaming must be carried out in a state that exhibits the mechanical or physical properties of functional resins, that is, various resins called engineering plastics.

[0004] Conventional foam molding, in which injection molding is carried out simply by mixing a chemical or physical blowing agent with a base resin, can only achieve a weight reduction of 5 to 10% at most. It is known that foam molding using polystyrene beads is effective in achieving significant weight reduction. However, conventional polystyrene foam moldings have an expansion ratio of 40.
There were many cases of high foaming of about 100 to 100 times, and it was not possible to obtain sufficient strength as a structuring agent.

If one attempts to carry out foam molding at a relatively low expansion ratio of, for example, about 15 times, which can maintain sufficient strength as a structural material, the molding time, which conventionally takes about 2 minutes, will take 10 to 20 minutes. This results in a long process and a significant drop in productivity. This tendency becomes more pronounced the more one attempts to obtain a resin molded article with a lower expansion ratio.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a lightweight resin molded article in a foamed state with a relatively low magnification that maintains mechanical or physical properties that can be used as a constituent material. An object of the present invention is to provide a method for manufacturing a lightweight resin molded body.

[0007]

[Means for Solving the Problem] This problem is achieved by adding 3% by weight or less of a blowing agent to a base resin that is a mixture of 95 to 5% by weight of a polystyrene resin and 5 to 95% by weight of a polyphenylene ether resin. 1.
．． A lightweight resin foam molded body formed with an expansion ratio of 5 to 15 times, and a base resin consisting of 95 to 5% by weight of polystyrene resin and 5 to 95% by weight of polyphenylene ether resin are pre-foamed, and then A lightweight resin that is prepared by mixing 3% by weight or less of a blowing agent with the pre-foamed base resin and performing secondary foam molding at a low expansion ratio of 1.5 to 15 times in a desired mold. The problem is solved by a method for manufacturing a foam molded article.

The polystyrene resin used in the present invention refers to polymer resins containing styrene as a main component, such as polystyrene, polystyrene-butadiene copolymer, polystyrene-acrylonitrile copolymer, styrene graft copolymer, etc. It is a general term for copolymer resins, etc. It also includes mixed resins with multiple resins containing these as main components.

[0009] The polyphenylene ether resin used in the present invention has the general formula

(Here, R1, R2, R3 and R4 are each independently a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, and at least two carbon atoms between the halogen atom and the phenyl ring) represents a monovalent substituent selected from a haloalkyl group or a haloalkoxy group having a tertiary α-carbon, and n is an integer representing the degree of polymerization), Even if one kind of the polymer represented by the above general formula (Chemical formula 1) is used alone,
It may also be a copolymer in which two or more types are combined. In a preferred embodiment, R1 and R2 are C1-C4 alkyl groups, and R3 and R4 are hydrogen atoms or C1-C4 alkyl groups. For example, poly(2,6-dimethyl-1,4-phenylene)
Ether, poly(2,6-diethyl-1,4-phenylene) ether, poly(2-methyl-6-ethyl-1,4)
-phenylene) ether, poly(2-methyl-6-propyl-1,4-phenylene) ether, poly(2,6-
dipropyl-1,4-phenylene) ether, poly(2
-ethyl-6-propyl-1,4-phenylene) ether and the like.

Examples of the PPE copolymer include copolymers containing a portion of alkyl trisubstituted phenol, such as 2,3,6-trimethylphenol, in the polyphenylene ether repeating unit. Moreover, a copolymer obtained by grafting a styrene compound onto these PPEs may also be used.

The base resin of the present invention is a mixture of 95 to 5% by weight of a polystyrene resin and 5 to 95% by weight of a polyphenylene ether resin. A desired expansion ratio can be obtained by mixing an appropriate amount of PPE resin with the PS resin. In the above range, 1.
Relatively low expansion ratios of the order of 5 to 15 times can be achieved.

[0012] When the PPE resin is less than 5% by weight, it becomes difficult to maintain the desired low expansion ratio. If you try to mold it in a short time, the expansion ratio will be high, for example around 30 times,
Desired strength cannot be obtained. Although it is possible to achieve a low foaming ratio by lowering the molding temperature and performing molding for a longer time, the productivity will be lower and production costs will inevitably increase.

In contrast to the above, when the base material is a resin containing more than 95% by weight of polyphenylene ether resin, the temperature required for foaming increases rapidly, and the time required for foaming also increases. This increases production costs, including equipment costs.

In the present invention, the foaming agent content of the base resin must be 3% by weight or less. The blowing agent content here refers to the content of the blowing agent after the pre-foaming (primary foaming) in foam molding and before the so-called foam molding (or secondary molding) that creates the shape of the product that is practically required. Refers to quantity. The content of the blowing agent before pre-foaming is practically arbitrary, but considering the cost of industrial production, it is set at 7%.
The following is desirable.

[0015] As described above, the characteristic that the foaming agent content in the base resin after pre-foaming and before foam molding is 3% by weight or less is that a low-foam molded article can be produced in a short molding cycle. This is particularly important in the present invention. Further, if the content is 3% by weight or more, long-term dimensional stability is poor, and a dimensional change of 5/1000 or more is observed when left at room temperature. On the other hand, it was confirmed that by setting the blowing agent content to 3% by weight or less as in the present invention, the dimensional change was suppressed to 1/1000 or less.

[0016]

[Examples] The contents of the present invention will be disclosed below with reference to Examples. FIG. 1 is a graph in which the horizontal axis represents the foaming agent content and the vertical axis represents the foaming ratio. As is clear from the figure, if the blowing agent content is 3% by weight or more, even if the PS resin contains PP.
Even when E-based resin is mixed, rapid foaming occurs, resulting in high foaming. However, when the content of the foaming agent is 3% by weight or less, the foaming speed becomes slower and easier to control. In this case, the foaming can produce a molded article with uniform fine closed cells and a low expansion ratio of 1.5 to 15 times, which is necessary for a structural body. Molded bodies with such a relatively low expansion ratio are useful as constituent materials for automobiles, home appliances, office automation equipment, etc., and have high industrial utility value.

In the examples of the present invention, a mixture of polystyrene resin and polyphenylene ether resin in the proportions shown in Table 1 was used as the base resin. The beads made of this base resin were impregnated with n-butane, which is a foaming agent, at the ratio shown in Table 1.

[Table 1]

The beads thus formed were heated with water vapor for 2 minutes as shown in Table 1 to obtain pre-foamed beads. The expansion ratio and foaming agent content of the pre-expanded beads are shown in Table 1.

Furthermore, the above pre-expanded beads were subjected to foaming processing (secondary foaming) under the molding conditions shown in Table 1, and the initial foaming ratio, foaming agent content, and appearance of the molded product were evaluated.

Furthermore, the molded product thus obtained was aged in a hot air oven for 10 hours under the conditions shown in Table 1, and the expansion ratio, foaming agent content, and appearance of the molded product were similarly evaluated.

Note that the expansion ratio is based on the specific gravity of the base resin (=1
．． 06) by the specific gravity of the molded article. Moreover, the content of the foaming agent refers to the volatilization loss rate when heated at 250 degrees C for 10 minutes.

Comparative Examples 1 and 2 are cases where the composition of the base resin is outside the range of the present invention, and Comparative Examples 3 and 4 are cases where the content of the blowing agent during foam molding is outside the range of the invention. This shows a certain case.

[0023]

Effects of the Invention According to the present invention, the molding time required to obtain a low-foam molded product 1.5 to 15 times that of conventional polystyrene resin foam molded products can be significantly shortened, and the foamed state can be reduced. As a result, productivity has improved significantly. Furthermore, since polyphenylene ether resin was mixed, heat resistance was improved. Furthermore, the amount of blowing agent used can be reduced, and depending on the application, it is also possible to omit the aging step, which can also contribute to improving productivity.

[0024] The lightweight resin foam molded article according to the present invention uses less blowing agent and has a lower residual foaming material content, so it can be left at room temperature or heated in a hot air oven after secondary molding. Long-term dimensional stability after aging is also significantly improved. Such characteristics are particularly important when producing large molded objects, for example, parts with a long overall length such as an automobile instrument panel. Conventional molded products that undergo large long-term dimensional changes require a long period of stabilization time after manufacture before being attached to a predetermined location. In contrast, the lightweight resin molded article according to the present invention has the advantage that its long-term dimensional stability is greatly improved, and its dimensional change, mainly shrinkage, is about a fraction of that of conventional products.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between foaming agent content and foaming ratio.

Claims (2)

[Claims] [Claim 1] Polystyrene resin 95 to 5
The base resin is a mixture of 5% to 95% by weight of polyphenylene ether resin and 3% by weight or less of a foaming agent to form a foaming ratio of 1.5 to 15 times. A lightweight resin foam molded product characterized by: [Claim 2] Polystyrene resin 95 to 5
Pre-foaming a base resin consisting of 5 to 95 wt% of a polyphenylene ether resin, and then mixing 3 wt% or less of a blowing agent with respect to the pre-foamed base resin; A method for producing a lightweight resin foam molded article, which comprises performing secondary foam molding at a low expansion ratio of 1.5 to 15 times in a desired mold.