JPS603338B2 - Injection molded product with excellent heat deformation properties - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an injection molded product mainly composed of an ethylene-Q/B-unsaturated carboxylic acid ester copolymer, which is highly flexible and has excellent thermal deformation properties.

Ethylene-Q.B-unsaturated carboxylic acid ester copolymer (hereinafter referred to as ethylene copolymer).

) is already used as a variety of molding resins because it is highly flexible and has excellent low-temperature properties, weather resistance, and processability. However, one of the major drawbacks of these ethylene copolymers is that they have low crystallinity and poor heat resistance due to the large side chains of the comonomers. Particularly in molding methods that involve resin orientation, such as injection molding, it is unavoidable that orientation strain remains inside the molded product, so when the molded product is reheated, this strain causes dimensional deformation and deformation. This is problematic and therefore limits practical use to temperatures well below the melting point of the resin.
Once this deformation occurs, it will not recover even if the temperature is lowered, so it is not only possible to use the molded product in a high-temperature atmosphere, but also to use it outdoors and expose it to direct sunlight, or to use it in a drying oven during other processes. If the temperature of the molded product rises even temporarily due to the molded product being placed inside the molded product, this will cause a serious problem. The present inventors have determined that these drawbacks of these ethylene copolymers can be overcome. As a result of extensive research, the inventors have found that polyethylene with a density within a certain range is added to the above ethylene copolymers at a ratio within a specific range. The inventors have discovered that the thermal deformation characteristics of injection molded products can be significantly improved without impairing their flexibility, and have completed the present invention.

That is, the present invention provides an ethylene-Q/8-unsaturated carboxylic acid ester copolymer with polyethylene having a density of 0.920 m/m or more in a blending ratio of polyethylene in the composition.
Y] is the formula, 25≦≦625 (wherein, Y is the blending ratio of polyethylene in the composition (
% by weight), and x indicates the density (ta') of polyethylene.

The present invention relates to an injection molded product having excellent heat deformation properties obtained by injection molding a resin composition obtained by adding and mixing within a range that satisfies the following.

Compositions of ethylene copolymers and polyethylene have been known for a long time. For example, in order to improve the strength of polyethylene, compositions in which ethylene-vinyl acetate copolymers are blended with polyethylene (Japanese Patent Publication No. -24913
), or a blend in which an ethylene-Q/8-monounsaturated carboxylic acid alkyl ester copolymer or an ethylene-saturated carboxylic acid vinyl ester copolymer is added to polyethylene in order to improve the stress cracking resistance of polyethylene. (Japanese Patent Publication No. 47-26367) is well known.

However, all of these basically relate to improving the properties of polyethylene, whereas the present invention
The purpose of this composition is to improve the thermal deformation properties of injection molded products made of flexible ethylene copolymers, and in this respect it differs from known polyethylene compositions. Examples of the ethylene-Q.8 monounsaturated carboxylic acid ester used in the present invention include ethylene-ethyl acrylate copolymer, ethylene-methyl acrylate copolymer, etc. Among these, ethylene-acrylic acid Ethyl copolymers are preferred.

The ethylene-ethyl acrylate copolymer used in the present invention has a content of ethyl acrylate as a comonomer component of 5 to 5.
2% by weight can be used, but 10 to 2% by weight is particularly preferred.

Those with a comonomer content of less than 5% by weight do not have sufficient flexibility, and those with a comonomer content of more than 2% by weight have the disadvantage of extremely poor heat resistance, and it is no longer possible to obtain sufficient heat resistance even with the addition of polyethylene. Can not. Furthermore, the polyethylene used in the present invention has a density of 0.9 when measured at 23°C.
As long as it is 20 min/block or more, it may be produced by a high-pressure process or by copolymerization with a Q-olefin such as propylene or butene in a medium-low pressure process. In the present invention, the effect of reducing the heat shrinkage rate of the injection molded article is greater as the density of the polyethylene becomes higher, and the effect is almost negligible when the density of the polyethylene is less than 0.920 ta'.

Regarding the amount of polyethylene added, the larger the amount added, the greater the effect of stabilizing the dimensions of the injection molded product, but on the other hand, the higher the density of the polyethylene used and the larger the amount added, the more flexible the molded product becomes. This results in a disadvantage that the tensile strength, especially the elongation rate, tends to decrease.

Therefore, in order to suppress the heat shrinkage rate without significantly impairing the flexibility, the density X (ta') of the added polyethylene and the blending ratio Y (wt%) in the composition should be within a range that satisfies the following relational expression. something is required.

, 25≦Old≦625 (However, XZO.920) Polyethylene can be added to the ethylene copolymer by melting and kneading it in advance using an extruder, Banbury mixer, etc., or by adding both to the ethylene copolymer immediately before injection molding. It is also possible to blend Novelette comrades.

Further, if necessary, pigments such as carbon black, fillers such as calcium carbonate, and other resins may be added to this composition. No special equipment is required to obtain injection molded products from these compositions, and an ordinary injection molding machine for plastics is sufficient.

Further, as the molding temperature, a temperature higher than the melting point of the resin can be applied, but usually a range of 140 to 220 degrees Celsius is mainly used. The appropriate injection molding pressure is 500 to 1500 k9/s. In the present invention, the heat deformation properties (molding shrinkage rate, heating shrinkage rate, Shrinkage rate) can be significantly improved.

That is, according to the present invention, it is possible to make the molding shrinkage rate and heat shrinkage rate of injection molded products of these mixtures much smaller than expected from the values of each individual component. Here, the heat shrinkage rate means the rate of change in dimensions of a molded article at room temperature before and after heating under certain conditions. Surprisingly, with an appropriate blending ratio, it is possible to suppress the heat shrinkage of the mixture not only to that of the copolymer but also to an even smaller value than that of polyethylene, which is a component with better heat resistance. The present invention is effective when the temperature at which thermal deformation of the ethylene copolymer starts to become a problem, that is, when the resin temperature of the molded article rises to 50 to 6 pi or more.

Moreover, unlike expansion and contraction caused by general thermal expansion, heat shrinkage and heat deformation caused by orientational strain in the resin do not return to their original state even if the temperature is lowered once the resin temperature rises and changes. It has extremely high practical value in applications where the temperature of the product may rise. For example, when molded products made by adding a small amount (1 to 2% by weight) of carbon black to an ethylene copolymer are used outdoors, such as for protective covers for power lines or parts around automobile bumpers, these black The temperature of a molded product rises to 60 to 70 oo when exposed to direct sunlight in the summer, which may cause dimensional changes and deformations such as twisting and waving, but the injection molded product of the present invention suppresses these phenomena. be able to. In addition, when painting these ethylene copolymer molded products, they are sometimes placed in a furnace at a temperature of 50 oo or more to accelerate the aggregation of the paint, and the molded products of the present invention are also effective in preventing thermal deformation in this case. be. Of course, the molded product of the present invention is not limited to these examples of use, but is extremely effective for all applications of injection molded products in which the resin temperature rises to 50° C. or higher, even temporarily. Example 7 parts by weight of ethylene-ethyl acrylate copolymer (ethyl acrylate content: 1% by weight, melt index 6) and polyethylene (Mitsui Petrochemicals Neozex 2540R; ethylene-Q-olefin copolymer called L-LOPE) 30 parts by weight of the polymer, density 0.925/base, melt index 4) were blended in pellet form and injection molded at a cylinder temperature of 220° to form a square plate.

The dimensions of the mold used were 140 x 80 x 2 sails, and markings were made at 12 ratio intervals in the length direction corresponding to the flow direction of the resin. After leaving this injection molded product in a 2300 room for 24 hours, the length between the markings was determined.
Leave it in the air oven at 0:00 for 3 hours, and then heat it for another 23q.
After leaving it in a room for 24 hours, its length and curve were determined again, and the heat shrinkage rate was determined using the following formula, and a value of 1.1% was obtained.

Heating shrinkage rate (%) = A33XI. Comparative Example 1 When the heat shrinkage rate of the injection molded product of the polyethylene used in the example was determined, a value of 1.25% was obtained.

Comparative Example 2 Regarding the ethylene-ethyl acrylate copolymer used in the example, the heating shrinkage rate of the injection molded product was determined as follows.
A value of 2.0% was obtained.

Claims (1)

[Claims] 1 α/β-unsaturated carboxylic acid ester content is 5 to 2
Polyethylene with a density of 0.920 g/cm^3 or more is added to 0% by weight of ethylene-α/β-unsaturated carboxylic acid ester copolymer, and the blending ratio of polyethylene in the composition is expressed by the formula 125≦Y/(1 -X)≦625Y: Blending ratio of polyethylene in the composition (wt%) X: Density of polyethylene (
An injection molded product with excellent thermal deformation properties, made by injection molding a resin composition obtained by adding and mixing within a range that satisfies the g/cm^3). 2. The injection molded article according to claim 1, wherein the polyethylene is an ethylene-α-olefin copolymer.