JPH08207193A - Multilayered injection-molded article - Google Patents

Abstract

PURPOSE: To obtain a transparent injection-molded article having ultraviolet blocking effect by providing a resin layer composed of a thermoplastic resin containing fine particles of metal oxide. CONSTITUTION: A multilayered injection-molded article has a resin layer composed of a thermoplastic resin containing fine particles of metal oxide. In such a case that the multilayered injection-molded article is constituted of three layers, a core layer 1 is set to a resin layer A containing fine particles of metal oxide and adhesive layers 2 are arranged on both sides of the resin layer A. Fine particle metal oxide is an ultraviolet absorbing material based on ZnO or TiO2 and the particle size thereof may be set to 0.1μm or less so that the resin layer containing fine particles of metal oxide does not become opaque within a visible light region and the addition amt. thereof is determined in consideration of the ultraviolet blocking properties and transparency required corresponding to the use purpose of the injection molded article. The multilayered injection-molded product is molded by a multilayered injection molding method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plastic injection-molded article, and more particularly, it is suitable as a material used for various machine parts, containers, lids, caps, covers and the like which are transparent and block ultraviolet rays.

[0002]

2. Description of the Related Art At present, there are resins having good transparency among thermoplastic resins, and many products that make use of the transparency are manufactured. It may be desirable for some of these products to be opaque to ultraviolet light. Examples thereof include a light-cutting film mounted on windows of automobiles and buildings, liquid containers such as an ultraviolet absorbing container made of polyethylene terephthalate, a bag made of an ultraviolet absorbing film for foods, beverages, medicines and the like. Organic materials and inorganic materials (metal oxides) are known as these ultraviolet absorbers.

Examples of organic materials include benzotriazole-based materials, benzophenone-based materials, and cyanoacrylate-based materials. These materials are often selected and improved from the viewpoint of safety, processability, ultraviolet absorptivity, etc. depending on the resin used and used. However, when manufacturing by injection molding,
Organic ultraviolet absorbers have problems such as sublimation and thermal decomposition at the time of molding, and also have problems such as elution into contents and leaching when used as products and containers, quality, function,
I am not satisfied with the appearance. As an inorganic material,
Metal oxides, especially ZnO-based and TiO ₂ -based materials are known.

These materials exhibit an ultraviolet absorbing function by being dispersed in various solvents and coated on a resin film. Alternatively, it is added to a thermoplastic resin and processed into a film. However, it is known that the inorganic material reduces the mechanical strength of the resin when added to the resin. Therefore, it cannot be used alone.

[0005]

DISCLOSURE OF THE INVENTION The present invention has the above-mentioned drawbacks, that is, a problem in terms of molding, quality of a molded product and mechanical problems in the case of adding an ultraviolet absorbing material to a thermoplastic resin, particularly in injection molding. It is an object of the present invention to provide a multilayer injection-molded article that solves the reduction in strength.

[0006]

The present invention is to solve the above-mentioned problems, and is a multilayer injection-molded article containing a resin layer made of a thermoplastic resin containing fine particle metal oxides, and further, A multilayer injection-molded article comprising at least a thermoplastic resin layer containing fine particle metal oxide and a thermoplastic resin layer containing no fine particle metal oxide provided on both sides of the thermoplastic resin layer. The details will be described below.

When the multilayer injection-molded article has a three-layer structure, the core layer (1) is a resin layer (A) containing fine particle metal oxide as shown in FIG. When the multilayer injection-molded article has a five-layer structure, as shown in FIG. 2, only the central core layer (1) can be the resin layer (A) containing the particulate metal oxide. In addition, as shown in FIG. 3, the central core layer (1) and the adhesive layers (2) on both sides thereof are resin layers (A) containing fine particle metal oxides, and a thermoplastic resin layer (3) is provided on the outside thereof. In addition, as shown in FIG. 4, the central core layer (1) does not contain particulate metal oxide, and the adhesive layer (2) outside the core layer (1) is made of metal oxide. The resin layer (A) containing can also be used.

The fine particle metal oxide used in the present invention is Z
It is an ultraviolet absorber containing nO or TiO ₂ as a main component. Various modifiers such as a dispersant can be added to the extent that the transparency of the thermoplastic resin is not impaired. The particle size of the particulate metal oxide may be such that the resin layer containing the particulate metal oxide does not become opaque in the visible light region, and is 0.1 μm or less,
It is generally preferable to select 0.04 μm or less.

The particle size and the addition amount of the fine particle metal oxide are determined in consideration of the ultraviolet ray blocking property (transmittance) and transparency required depending on the purpose of use of the injection molded product. Increasing the amount of the particulate metal oxide added improves the ultraviolet blocking effect of the injection molded product, but deteriorates the transparency. Further, if the particle size of the fine particle metal oxide is increased, the transparency of the multilayer injection-molded product becomes poor (JP-A-58-73535). Further, the ultraviolet blocking property and transparency of the injection molded product vary depending on the thickness of the molded product and the number and thickness of the resin layer containing the fine particle metal oxide. In order to increase the transparency in the visible light region and suppress the ultraviolet light transmission to be low, the object can be achieved by decreasing the particle size of the fine particle metal oxide and increasing the addition amount.

The fine particle metal oxide is ZnO or TiO.
_{One of the two} can be used by mixing both. The selection of the fine particle metal oxide is determined by the transparency of the injection molded product, the ultraviolet ray transmittance, the economical efficiency, the problem with the thermoplastic resin, and the like.
As an example, it has been reported that the mechanical strength of a TiO ₂ system decreases when it is added to a single layer of PP (JP-A-2-29).
6726). In general, ZnO is preferable because ZnO has a smaller refractive index and the ultraviolet absorption wavelength region is closer to visible light.

Any material can be used as the thermoplastic resin to which the fine particle metal oxide is added and the thermoplastic resin of the resin layer constituting both sides thereof. It can be appropriately selected depending on the application of the multilayer injection-molded product, but in consideration of transparency, for example,
When used for containers, caps, etc., it is possible to use a resin with low light transmittance as long as it is transparent enough to observe the remaining amount of liquid contents, and when enhancing the display effect in food and beverages. It is also possible to use a resin having a high light transmittance. In addition, a resin having a high light transmittance can also be used when it is used as a control panel of various devices or a cover of a display unit.

Further, although the present invention is transparent and has a function of blocking ultraviolet rays, it is possible to add other functions and performances by utilizing the characteristics of the multilayer structure. For example, as the resin forming the surface of the injection molded article, weather resistance, chemical resistance, abrasion resistance,
Materials having excellent printability, mechanical strength, dimensional stability, etc. can be used. Further, as the resin of the core layer to which the metal oxide is added, a gas barrier material such as oxygen gas, an odor barrier material such as a fragrance, a heat resistant material, a low cost material, a recycled material and the like can be used. By combining materials having these functions, a multifunctional injection-molded product or a low-cost injection-molded product becomes possible. Furthermore, by adding various resin layers, it is possible to obtain a higher-performance injection-molded product.

The shape of the injection-molded article using the above materials can be arbitrarily selected. When it is used for the purpose of protecting contents that are altered or deteriorated by ultraviolet rays, the shape of the container, cap or lid can be selected. In the case of a container or a cap, the resin layer containing the particulate metal oxide must be provided over the entire area of the molded product. Alternatively, the resin layer containing the particulate metal oxide may not be provided on the leg portion provided on the bottom of the cup-shaped container, the fitting portion of the cap with the container, etc., where ultraviolet blocking is not required. Also, in the case of various machine parts, covers, etc., it is possible to provide a resin layer containing fine particle metal oxide over the entire area of the molded product, or to provide a resin layer containing fine particle metal oxide only in a specific region. Is.

In order to manufacture an injection-molded article having the above-mentioned shape and layer structure, it is possible to use a multi-layer injection molding method. As the multilayer injection molding method, various methods such as a sequential injection method, a simultaneous injection method, a core slide method, and a core rotation method are known. Each of these molding methods has its own characteristics, and it is necessary to select the molding method depending on the shape and layer structure of the molded product.

The shape of the container, cap, etc. is circular,
Further, when the core layer is not exposed on the surface of the molded product, it is desirable to use the simultaneous injection molding method. The simultaneous injection molding method is a method in which a material forming a surface is first injected into a cavity, then a core material is simultaneously injected while injecting the resin, and finally only a material forming a surface is injected. A flat molded product such as a panel cover can be similarly molded.

[0016]

The multilayer injection-molded product of the present invention has a high light transmittance in the visible light region by using the transparent thermoplastic resin, and the resin layer containing the fine particle metal oxide shields the ultraviolet rays, so that it is transparent and blocks the ultraviolet rays. It is a molded product. The metal oxide has an effect of absorbing ultraviolet rays, and by making it into fine particles, scattering of visible light can be suppressed and transparency can be maintained. Further, when the resin layer containing the fine particle metal oxide is not formed on the surface, precipitation, elution, separation or the like of the metal oxide from the surface does not occur. In addition, when used in containers, there is no risk of elution into the contents. Further, even if the mechanical strength is deteriorated by the influence of the metal oxide, the strength of the molded product is maintained by the resin layers on both sides.

[0017]

EXAMPLES Examples of the multi-layer injection-molded article of the present invention will be described below, but the present invention is not limited to the following examples without departing from the gist thereof.

<Examples 1 to 3> A cup-shaped two-layer, three-layer structure having a thickness of 0.8 mm was prepared by a multilayer injection molding method using polypropylene as the inner and outer layers of the molded product and polypropylene mixed with ZnO as the core layer. The container was molded. The core layer had a thickness of 0.4 mm, and the surface layer had a thickness of 0.2 mm. As the polypropylene, a highly transparent random copolymer was used.
The particle size and the compounding ratio of the added ZnO were set as shown in (Table 1), the light transmittance was measured by a spectrophotometer, and the total light transmittance was measured by a haze meter. As Comparative Example 1,
The evaluation was also performed when ZnO was not added.

[0019]

[Table 1]

<Examples 4 to 6> An adhesive having polypropylene as the inner and outer layers of the molded article, an ethylene vinyl alcohol copolymer (EVOH) as the core layer, and ZnO on both sides of the core layer was formed to form a three-kind five-layer structure. And The particle size and the compounding ratio of ZnO added to the adhesive layer were set as shown in (Table 1) and evaluated in the same manner as in Example 1. As Comparative Example 2, evaluation was performed even when ZnO was not added.

Example 7 A cup-shaped container having a thickness of 0.8 mm was molded by a multi-layer injection molding method using polystyrene (GPPS) on the surface of the molded product and GPPS with ZnO mixed in the core layer. The core layer had a thickness of 0.4 mm and a surface area of 0.2 mm. GPPS used for surface layer and core layer
Used the same resin. The particle size and the compounding ratio of the added ZnO were set as shown in (Table 1), the light transmittance was measured by a spectrophotometer, and the total light transmittance was measured by a haze meter. Except that mixed with TiO ₂ to <Example 8> Core layer was molded as in Example 7 was evaluated. <Comparative Example 3> Using GPPS in which no fine particle metal oxide was mixed, molding was performed in the same manner as in Example 7 and Example 8 and evaluated. The results of measuring the light transmittance of Example 7 and Comparative Example 3 are shown in (Table 1), and the results of measuring the light transmittance of Example 8 are shown in (Table 2).

[0022]

[Table 2]

As shown in (Table 1) and (Table 2), the addition of the fine particle metal oxide has the effect of blocking ultraviolet rays. When ZnO is added, compared with the case where TiO ₂ is added, the effect of blocking ultraviolet rays is large and the total amount of transmitted light is high.

Further, the ultraviolet ray blocking ratio and the transparency change depending on the particle size and the addition amount of ZnO. When the amount of ZnO is small or the particle size is small, the transmittance of ultraviolet rays is high.
Further, when the amount of ZnO is large or the particle size is large, the transmittance of ultraviolet rays is small, but the transparency of the injection molded product itself is lowered.

[0025]

EFFECT OF THE INVENTION The present invention is constructed as described above, and by adding a fine particle metal oxide having an ultraviolet absorbing effect to the intermediate layer of a multilayer injection molded article, a transparent injection having an ultraviolet shielding effect can be obtained. A molded product can be provided.

By using the fine particle metal oxide as the ultraviolet absorber, problems such as sublimation and thermal decomposition during injection molding do not occur as compared with the case of using the organic ultraviolet absorber. Further, when the fine particle metal oxide is used, the mechanical strength of the resin may be deteriorated, but since the multilayer structure is used, the strength of the molded product itself can be supplemented by the outer layer resin, so that the problem of strength deterioration occurs. Absent. At this time, the UV blocking effect is not affected.

Further, since it has the multi-layered structure as described above, there is no problem such as desorption or elution of fine particle metal oxides from the surface of the molded product, and the range of use as a container, etc. is expanded, and containers for foods, beverages, medicines, etc. It can be used as a cap. It is also possible to provide the ultraviolet absorbing layer only in a specific area of the molded product.

[0028]

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a first embodiment of the present invention.

FIG. 2 is a sectional view showing a second embodiment of the present invention.

FIG. 3 is a sectional view showing a third embodiment of the present invention.

FIG. 4 is a sectional view showing a fourth embodiment of the present invention.

[Explanation of symbols]

 1: core layer 2: adhesive layer 3: thermoplastic resin layer

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Claims (7)

[Claims] 1. A multi-layer injection-molded article comprising a resin layer made of a thermoplastic resin containing a particulate metal oxide. 2. The multilayer according to claim 1, comprising at least a thermoplastic resin layer containing a particulate metal oxide and thermoplastic resin layers provided on both sides of the thermoplastic resin layer and containing no particulate metal oxide. Injection molding. 3. The multilayer injection-molded article according to claim 1 or 2, wherein there are two or more resin layers made of a thermoplastic resin containing fine particle metal oxide. 4. The multilayer injection-molded article according to claim 1, wherein all the resin layers are transparent. 5. The multilayer injection-molded article according to claim 1, wherein the fine particle metal oxide is ZnO. 6. The multilayer injection-molded article according to claim 1, wherein the fine particle metal oxide is TiO ₂ . 7. The fine particle metal oxide has a UV transmittance of 20% or less and a visible light transmittance of 6 in the entire multilayer injection molded article.
It is 0% or more, The multilayer injection-molded article of Claim 1 thru | or 5 characterized by the above-mentioned.