JPS6365097B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a resin composition for injection molding. More specifically, the present invention relates to an injection molding resin composition which uses an ethylene-vinyl ester copolymer or an ethylene-α,β-unsaturated carboxylic acid ester copolymer as a main raw material and does not cause flow marks on the surface of the injection molded product. Ethylene-vinyl ester copolymers such as ethylene-vinyl acetate copolymers produced by high-pressure radical polymerization have excellent processability, transparency, strength,
Due to its impact resistance, it is used in automobile and bicycle supplies (mud flaps, saddles, etc.), sporting goods (golf bag bottoms, etc.), construction supplies (mats, water faucets, etc.), and general industrial supplies (electrical insulation). cover,
It is widely used in injection molded products such as packing materials, rubber feet for light electrical appliances, etc.), household goods (lids for sealed containers, inner stoppers, etc.), and decorative items (cap visors, etc.). In this way, ethylene-vinyl acetate copolymers are used in many applications because they have excellent properties as injection molding materials, but the appearance of molded products made from them also depends on the product. It is extremely important as it influences value. One important item that poses a problem in the appearance of molded products is flow marks. With Flowmark, molten resin flows through the mold during injection molding, and after it solidifies,
This is a phenomenon that produces tree-ring-like striped patterns centered around gates on the surface of molded products. The reason for this is that the temperature of the molten resin decreases in the mold and becomes highly viscous as it is filled. As a result, the molten resin that comes into contact with the mold surface moves in a semi-solid state. This is thought to be due to the formation of countless fine folds at right angles. The occurrence of flow marks is largely related to the design of the mold, but if the molds are the same, one way to prevent this is to change the molding conditions by changing the temperature of the molding machine cylinder, in other words, the molten resin. Another method is to raise the temperature of the mold. However, all of these methods lengthen the cooling time, in other words, the molding cycle, resulting in a decrease in workability. Furthermore, in terms of the basic physical properties of this copolymer, it is true that flow marks are less likely to occur if a resin with a high melt index is used. This results in cycle extension, etc. The present inventors have intensively investigated ways to prevent the occurrence of flow marks from the molecular structure and composition aspects of ethylene-vinyl ester copolymers, and have found that they can be used by mixing a small amount of ionomer resin with this copolymer. , found it to be very effective. Furthermore, it has been found that similar effects can be obtained in the case of an ethylene-α,β-unsaturated carboxylic acid ester copolymer which has a similar problem. Therefore, the present invention relates to an injection molding resin composition containing an ethylene-vinyl ester copolymer or an ethylene-α,β-unsaturated carboxylic acid ester copolymer as a main component.
Vinyl ester copolymer or ethylene-α,β
- 80 to 98 parts by weight of an unsaturated carboxylic acid ester copolymer and 20 to 2 parts by weight of an ionomer resin of an ethylene-α,β-unsaturated carboxylic acid copolymer. Here, to describe the circumstances that led to the completion of the present invention, the present inventors made flow marks for injection molded products of ethylene-vinyl ester copolymer or ethylene-α,β-unsaturated carboxylic acid ester copolymer. In order to prevent the occurrence of this by blending other resins, we selected low-density or high-density polyethylene, linear low-density polyethylene, polypropylene, ethylene-methacrylic acid copolymer, ionomer resin, etc. as blend materials and conducted various studies. did. As a result, it was found that ionomer resins other than ionomer resins were not effective in preventing the occurrence of flow marks, and only ionomer resins were effective. Ethylene-
Compared to vinyl ester copolymers and ethylene-α,β-unsaturated carboxylic acid ester copolymers, flow marks occur less often, but depending on the mold size and molding conditions, flow marks may sometimes occur. In contrast, even when blending ionomer resin with low-density polyethylene, the effect of preventing flow marks is not observed.
Vinyl ester copolymer and ethylene-α,β
-The fact that the effect was observed only when blended with an unsaturated carboxylic acid ester copolymer indicates that ionomer resins do not universally have the effect of preventing flow marks. The ethylene-vinyl ester copolymer modified by the present invention is a copolymer of ethylene and a vinyl ester such as vinyl acetate or vinyl propionate, which is produced by high-pressure radical polymerization. Ethylene-vinyl acetate copolymers are most widely used. Ethylene-α,β-unsaturated carboxylic acid ester copolymers are also produced by high-pressure radical polymerization, and examples of α,β-unsaturated carboxylic acid esters include methyl, acrylic acid, methacrylic acid, etc. ethyl, n-butyl,
Isobutyl esters are used, generally methyl or ethyl esters are widely used. There are no particular restrictions on the comonomer content and melt index of these ethylene-based copolymers, but copolymers that are particularly effective when applied to the resin composition of the present invention include vinyl ester or α , β-unsaturated carboxylic acid ester content of about 1 to 14 mol%, preferably about 1 to 5 mol%, and a melt index of about 0.8 to 100. To explain in more detail using an ethylene-vinyl acetate copolymer as an example, a copolymer with a vinyl acetate content of about 1 mol% (about 3% by weight) or less has physical properties similar to ethylene homopolymer. Therefore, no particular effect is observed even if an ionomer resin is mixed with such a copolymer. On the other hand, copolymers with a vinyl acetate content of about 14 mol% (about 33% by weight) or more have extremely good transparency, so if even a small amount of ionomer resin is added, the transparency will be impaired. Therefore, taking these into consideration, the vinyl acetate content is approximately 1 to 5 mol% (approximately 3 to 14% by weight).
A copolymer of is most preferred. Also, copolymers with a melt index of less than about 0.8 and greater than about 100 are generally not used in injection molding applications. Ethylene-α,β-unsaturated carboxylic acid copolymer or ethylene-α,β-unsaturated carboxylic acid-α,β-unsaturated carboxylic acid ester used to form ionomer resin used as a modifier 3
The ethylene-α,β-unsaturated carboxylic acid copolymer such as the original copolymer is produced, for example, by the method described in Japanese Patent Publication No. 39-6810. That is, copolymers of ethylene and α,β-unsaturated carboxylic acids having 3 to 8 carbon atoms, such as acrylic acid, methacrylic acid, itaconic acid, and fumaric acid, or copolymers of ethylene with methyl acrylate, ethyl acrylate, and acrylic butyl acid, methyl methacrylate, ethyl methacrylate,
A terpolymer copolymerized with an alkyl ester of an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms such as butyl methacrylate or dimethyl fumarate as a third component is produced by this method. Ru.
The content of α,β-unsaturated carboxylic acid in these copolymers is generally about 0.5 to 15 mol%, preferably about 1 to 8 mol%, and the content of α,β-unsaturated carboxylic acid ester is generally about 0.5 to 15 mol%, preferably about 1 to 8 mol%. When further copolymerized, the content is generally about 0.2 to 10 mol%, preferably about 1 to 6 mol%. The metal ion crosslinking of the carboxylic acid groups in these copolymers is as described in the same patent publication.
Generally, crosslinking is carried out in a range of about 10 to 100%, preferably about 15 to 85%, and the degree of crosslinking is determined by the melt index of the copolymer, the content of α,β-unsaturated carboxylic acid in the copolymer, the metal The selection is made taking into account the type of ion and its intended use. As metal ions,
Monovalent metal ions such as lithium, sodium, potassium, and cesium, magnesium, calcium,
Divalent metal ions such as strontium, barium, copper, and zinc, or trivalent metal ions such as aluminum and iron.
Valent metal ions are used. The resin composition is prepared by dry blending or melt blending the above components simultaneously or sequentially. In the case of dry blending, when the ethylene-vinyl ester copolymer or ethylene-α,β-unsaturated carboxylic acid ester copolymer is melt-plasticized in the injection molding machine, the ionomer resin is also mixed with these copolymers. Easily melted and mixed uniformly. In the case of a melt blend, melt mixing may be carried out using a single screw extruder, a twin screw extruder, various mixers such as a Banbury mixer, coals, various kneaders, etc., and there is no particular restriction on the mixing order. The ionomer resin is preferably 2 to 20 parts by weight, based on 80 to 98 parts by weight, preferably 85 to 98 parts by weight of the ethylene-vinyl ester copolymer or ethylene-α,β-unsaturated carboxylic acid ester copolymer. They are used by mixing in a proportion of about 2 to 15 parts by weight.
If the mixing ratio is less than this, the copolymer will not have a sufficient effect in preventing the occurrence of flow marks, and if it is used in a larger amount, the physical properties of the injection molded product, such as stiffness and transparency, will be improved. deviates from the intrinsic physical properties of Next, the present invention will be explained with reference to examples. Examples 1 to 4 Each predetermined amount of ethylene-vinyl acetate copolymer (Mitsui Polychemical product Evaflex P-
0607; Vinyl acetate content 7% by weight, melt index 25) and ionomer resin (Mitsui Polychemical product Himilan H-1652; Zn type, melt index 5) were melted at 160°C using a 65 mm diameter extruder. Blended. Using this mixed resin, a Toshiba Machine IS60B small injection molding machine (screw diameter 36 mm) was used, with a nozzle temperature of 160°C and a molding cycle of 10 seconds for injection and 15 seconds for cooling.
Under the conditions of seconds, with pin gate type mold,
A round lid for a sealed container with a diameter of 100 mm and a thickness of 1 mm was molded. Comparative Example 1 In Examples 1 to 4, only the ethylene-vinyl acetate copolymer was used without using the ionomer resin.
After passing through a diameter extruder, injection molding was performed. Container lids molded in Examples 1 to 4 and Comparative Example 1 above were visually judged for flow marks that appeared on the molded product surface, and evaluated in four grades from A (good) to D (poor). . The composition and evaluation results of the mixed resin are shown in Table 1 below.

[Table] Examples 5 to 7 In Examples 2 to 4, after dry blending the ethylene-vinyl acetate copolymer and the ionomer resin, a square plate (150 ×80×2mm)
was molded. Examples 8-10 In Examples 5-7, another ionomer resin (Mitsui Polychemical product Himilan H-1802; Na
type, melt index 4.0) was used. Example 11 In Example 6, another ethylene-vinyl acetate copolymer (Mitsui Polychemical product Evaflex P-1207; vinyl acetate content 12% by weight, melt index 12) was used. Example 12 In Example 6, another ethylene-vinyl acetate copolymer (Mitsui Polychemical product Evaflex P-1907; vinyl acetate content 19% by weight, melt index 15) was used. Comparative Example 2 In Examples 5-10, no ionomer resin was used. Comparative Example 3 In Example 11, no ionomer resin was used. Comparative Example 4 In Example 12, no ionomer resin was used. Comparative Example 5 In Example 6, polyethylene (Mitsui Polychemical product Mirason M-11; density 0.917 g/cm ³ , melt index 7) was used in place of the ethylene-vinyl acetate copolymer. Comparative Example 6 In Comparative Example 5, only polyethylene was used alone without using an ionomer resin. Regarding the square plates molded in Examples 5 to 12 and Comparative Examples 2 to 6, the degree of occurrence of flow marks was visually evaluated, and the transparency (ASTM D-
1746-70T) was also measured. The results obtained are shown in Table 2 below, along with the composition of the mixed resin.

[Table] From this result, the following can be said. (1) As the mixing ratio of ionomer resin to ethylene-vinyl acetate copolymer increases,
The degree of occurrence of flow marks is reduced. however,
Mixing ionomer resins tends to reduce transparency, so care must be taken depending on the application. (2) The above tendency is hardly affected by the vinyl acetate content in the ethylene-vinyl acetate copolymer (however, about 3 to 33% by weight, preferably about 3 to 33% by weight)
within 14% by weight). (3) In the case of polyethylene, flow marks occur relatively little even when used alone, and no particular effect is observed even when mixed with ionomer resin. Example 13 In Example 6, ethylene-ethyl acrylate copolymer [] (ethyl acrylate content: 9% by weight, melt index 6) was used in place of the ethylene-vinyl acetate copolymer. Example 14 In Example 6, ethylene-ethyl acrylate copolymer [] (ethyl acrylate content: 19% by weight, melt index 5) was used in place of the ethylene-vinyl acetate copolymer. Example 15 In Example 6, ethylene-ethyl acrylate copolymer [] (ethyl acrylate content 25% by weight, melt index 5) was used in place of the ethylene-vinyl acetate copolymer. Example 16 In Example 7, the ethylene-ethyl acrylate copolymer [] was used instead of the ethylene-vinyl acetate copolymer. Example 17 In Example 10, the ethylene-ethyl acrylate copolymer [] was used instead of the ethylene-vinyl acetate copolymer. Comparative Example 7 In Example 13, no ionomer resin was used. Comparative Example 8 In Example 14, no ionomer resin was used. Comparative Example 9 In Example 15, no ionomer resin was used. The square plates molded in Examples 13 to 17 and Comparative Examples 7 to 9 described above were visually evaluated for the degree of occurrence of flow marks. The results obtained are shown in Table 3 below, along with the composition of the mixed resin.

[Table] Examples 18-19 In Example 6, another ionomer resin (Mitsui Polychemical product Himilan H-1855; Zn type, melt index 1.0 or Himilan H-1856; Na type, melt index 1.0)
was used. Examples 20-21 In Example 7, the ionomer resin used in Examples 18-19 was used. Examples 22-23 In Example 12, the ionomer resin used in Examples 18-19 was used. Regarding the square plates molded in Examples 18 to 23 above, the degree of occurrence of flow marks was visually evaluated. The results obtained are shown in Table 4 below, along with the composition of the mixed resin.

【table】

Claims (1)

[Scope of Claims] 1. 80 to 98 parts by weight of an ethylene-vinyl ester copolymer or an ethylene-α,β-unsaturated carboxylic acid ester copolymer and an ethylene-α,β-unsaturated carboxylic acid copolymer. Ionomer resin 20~
A resin composition for injection molding prepared by mixing 2 parts by weight. 2. The resin composition for injection molding according to claim 1, wherein the ethylene-vinyl ester copolymer is an ethylene-vinyl acetate copolymer.