Resin composition for injection forming

Abstract

A resin composition for injection forming containing a high-density polyethylene, an ethylene-vinyl alcohol copolymer and an acid-modified linear low-density polyethylene, characterized in that the ethylene-vinyl alcohol copolymer is contained in an amount of 35 to 90 parts by mass and the acid-modified linear low-density polyethylene is contained in an amount of 10 to 35 parts by mass per 100 parts by mass of the high-density polyethylene.

Claims

1. An injection-formed body formed by a resin composition comprising a high-density polyethylene, an ethylene-vinyl alcohol copolymer, and an acid-modified linear low-density polyethylene, wherein the high-density polyethylene has a density in a range of not less than 0.942 g/cm.sup.3 and an MFR at 190° C. in a range of 0.1 to 10 g/10 min, wherein the ethylene-vinyl alcohol copolymer has an MFR at 210° C. in a range of 20 to 100 g/10 min and is contained in an amount of 35 to 90 parts by mass of the high-density polyethylene, wherein the acid-modified linear low-density polyethylene has an MFR at 190° C. in a range of 0.1 to 10 g/10 min and is contained in an amount of 10 to 35 parts by mass per 100 parts by mass of the high-density polyethylene, and wherein the injection-formed body is a cap or a spout.

Description

MODES FOR CARRYING OUT THE INVENTION

(1) The resin composition for injection forming of the present invention contains a high-density polyethylene (HDPE) as the main component and an ethylene-vinyl alcohol copolymer (EVOH) that works to improve the oxygen-barrier property as the sub-component. In addition to these basic components, the resin composition for injection forming, further, contains an acid-modified linear low-density polyethylene (acid-modified LLDPE).

(2) <High-Density Polyethylene>

(3) The high-density polyethylene (HDPE) used as the main component has a density which is as high as not less than 0.942 g/cm.sup.3, has almost no branch, is highly crystalline, has excellent mechanical strength and surface slipperiness, and can be favorably used for forming, specifically, caps with a screw thread and spouts. The caps and spouts formed by using the above HDPE feature a large mechanical strength and, therefore, a high degree of slipperiness at the screw portions and excellent screw engagement. Therefore, the caps and spouts can be favorably used for packaging aseptic and sterilized contents.

(4) The resin composition for injection forming of the present invention is, further, used for producing an injection-formed body to secure a high degree of oxygen-barrier property by permitting the ethylene-vinyl alcohol copolymer (EVOH) to be oriented and dispersed in the form of a layer or a belt. For this purpose, the invention uses the HDPE of the so-called injection forming grade having, preferably, an MFR (melt flow rate) at 190° C. of, for example, 0.1 to 10 g/10 min. When the MFR is too large, the fluidity is so high that the EVOH may not be dispersed in the form of the layer (belt). When the MFR is too small, on the other hand, the fluidity may become so small that the resin composition cannot be injection-formed.

(5) <Ethylene-Vinyl Alcohol Copolymer>

(6) The ethylene-vinyl alcohol copolymer (EVOH), as is well known, is a representative oxygen-barrier resin, and is used for imparting oxygen-barrier property to the injection-formed body.

(7) As the EVOH of this kind, there is usually used an ethylene-vinyl acetate copolymer having an ethylene content of 20 to 60% by mol that is saponified to acquire a saponification degree of not less than 96% by mole and, specifically, not less than 99% by mol.

(8) To form the body through the injection forming, the present invention uses the EVOH having an MFR of the injection grade. Here, the invention uses, specifically, the EVOH having the MFR in a range of 20 to 100 g/10 min. at 210° C. to have it oriented and dispersed in the form of a layer or a belt in the HDPE. Namely, the invention uses the EVOH having a suitable degree of fluidity relative to the HDPE; i.e., the EVOH is oriented and dispersed in the form of a layer or a belt so as to exhibit a high degree of oxygen-barrier property. The EVOH can be injection-formed even when it has an MFR that lies outside the above-mentioned range. In this case, however, the EVOH is dispersed homogeneously or in a granular form in the HDPE. As a result, the oxygen-barrier property tends to decrease.

(9) The invention uses the EVOH in an amount of 35 to 90 parts by mass and, specifically, 45 to 70 parts by mass per 100 parts by mass of the high-density polyethylene. When used in an amount in excess of the above range, the EVOH cannot be easily oriented or dispersed in the form of a layer or a belt and it becomes difficult to obtain a high degree of oxygen-barrier property. When used in an amount smaller than the above range, on the other hand, the EVOH exhibits decreased oxygen-barrier property, as a matter of course.

(10) <Acid-Modified Linear Low-Density Polyethylene>

(11) As described already, the acid-modified linear low-density polyethylene (acid-modified LLDPE) is used for improving the adhesiveness between the HDPE and the EVOH, and works as a compatibilizer.

(12) The linear low-density polyethylene (LLDPE) to be modified with an acid is obtained by copolymerizing an ethylene which is a recurring unit with a small amount of α-olefin (e.g., 1-butene, 1-hexene, 4-methylpentene-1, 1-octene, etc.), has short branches that are introduced therein in a random fashion, has branches shorter than those of the LDPE, has a low density (e.g., 0.910 to 0.925 g/cm.sup.3), comprises molecules which are highly linear, and is highly flexible.

(13) The invention uses the acid-modified LLDPE obtained by modifying the LLDPE with an acid, and makes it possible to prevent the cracks and surface abrasion. When there is used, for example, an ordinary low-density polyethylene (LDPE) that is modified with an acid, it is not possible to prevent the cracks and surface abrasion. That is, the LDPE has an ethylene chain that includes branches of long chains. Due to this structure, the LDPE has a low density yet flexibility. Due to the possession of branches of long chains, however, the LDPE has a small degree of linearity and cannot be oriented in the direction in which it flows during the injection forming. Namely, the LDPE is not suited for forming a distribution structure in which it is oriented around the EVOH that is distributed in the form of a layer or a belt. It is, therefore, considered that the interfacial delamination easily occurs between the HDPE and the EVOH, and, as a result, the cracks and surface abrasion cannot be prevented.

(14) As the acid for modifying the LLDPE, the invention uses an unsaturated carboxylic acid such as maleic acid, itaconic acid, fumaric acid or (meth)acrylic acid, or an acid anhydride thereof. Upon modifying the LLDPE with the above acid, a carbonyl group (>C═O) is introduced therein, and a high degree of adhesiveness is exhibited to the HDPE and the EVOH. The invention preferably uses the maleic acid or the maleic anhydride from the standpoint of cost and availability.

(15) Further, to modify the LLDPE while maintaining its specific properties such as linearity and flexibility, it is desired that the acid has been introduced through the graft copolymerization. It is, further, desired that the degree of modification with acid (percentage of acid mass per the LLDPE) is in a range of 1.10 to 0.80.

(16) From the standpoint of having the acid-modified LLDPE oriented and dispersed around the EVOH through the injection forming, furthermore, it is desired that the acid-modified LLDPE has the MFR (190° C.) in a range of 0.1 to 10 g/10 min.

(17) The invention uses the acid-modified LLDPE in an amount of 10 to 35 parts by mass and, specifically, 15 to 30 parts by mass per 100 parts by mass of the high-density polyethylene. When the amount thereof is larger than the above range, the oxygen-barrier property of the EVOH is impaired. When the amount thereof is smaller than the above range, on the other hand, the interfacial delamination takes place easily between the EVOH and the HDPE, and the cracks and surface abrasion cannot be prevented.

(18) <Other Components>

(19) The resin composition for injection forming of the present invention can be blended with various kinds of blending agents that have been known per se., such as ultraviolet absorber, pigment, dye and filler depending upon the properties required for the body obtained through the injection forming in such amounts that would not impair the properties that would be exhibited by the components.

(20) <Injection-Formed Body>

(21) The resin composition for injection forming is formed into a predetermined shape through the injection forming.

(22) The injection conditions are so set as to form such a structure that the HDPE serves as the matrix and the EVOH is distributed in the form of a layer or a belt in the matrix. For example, the resin composition is thrown into a kneading portion of a predetermined injection-forming machine, maintained at a temperature of 160 to 240° C. therein, and is injected into a mold maintained at a temperature of about 10 to about 50° C. at a rate of 5 to 80 mm/sec.

(23) The thus formed body is capable of effectively preventing the cracks or the surface abrasion from taking place despite its surface is rubbed. Therefore, the formed body can be preferably used as a product that has a sliding portion such as a threaded portion yet featuring oxygen-barrier property, e.g., a container like a bottle, or a cap or a spout. Specifically, the formed body is best suited as the spout or the cap (particularly, threaded cap).

(24) Further, by using such means as co-injection or insertion forming, the body can also be formed in a multilayered structure including the layer of the above-mentioned resin composition as the intermediate layer. Here, however, the injection-formed body of the present invention effectively prevents the cracks or the surface abrasion from taking place despite the surface is rubbed. Therefore, the body simply needs be formed in a single-layered structure using only the resin composition for injection forming. This is a great advantage of the present invention.

EXAMPLES

(25) Excellent effects of the invention will now be described by way of Examples and Comparative Examples.

(26) Also described are the materials used in these Examples and methods of evaluation.

(27) High-density polyethylene (HDPE)

(28) B5803R produced by Keiyo Polyethylene Co.

(29) Density: 0.958 g/cm.sup.3

(30) MFR (190° C.): 0.3 g/10 min.

(31) Ethylene-vinyl alcohol copolymer (EVOH)

(32) K3850B produced by Nihon Gosei Kagaku Kogyo Co.

(33) Ethylene content: 38% by mol

(34) MFR (210° C.): 50 g/10 min.

(35) Compatibilizer;

(36) A. Maleic acid-modified linear low-density polyethylene (maleic acid-modified LLDPE)

(37) 41E710 produced by du Pont Co.

(38) Modified degree: 1%

(39) MFR (190° C.): 2.7 g/10 min.

(40) B. Maleic acid-modified low-density polyethylene (maleic acid-modified LDPE)

(41) L553 produced by Mitsubishi Chemical Co.

(42) MFR (190° C.): 1.5 g/10 min.

(43) C. Maleic acid-modified high-density polyethylene (maleic acid-modified HDPE)

(44) 4033 produced by du Pont Co.

(45) Modified degree: 1%

(46) MFR (190° C.): 2.0 g/10 min.

(47) D. Maleic acid-modified polyethylene (maleic acid-modified PP)

(48) 50E806 produced by du Pont Co.

(49) Modified degree: 0.5%

(50) MFR (230° C.): 25 g/10 min.

(51) E. Maleic acid-modified styrene elastomer (maleic acid-modified SEBS)

(52) M1943 produced by Asahi Kasei Co.

(53) MFR (230° C.): 8.0 g/10 min.

(54) F. Ionomer

(55) 1855 produced by Mitsui⋅du Pont Polychemical Co.

(56) MFR (190° C.): 1.0 g/10 min.

(57) The resin compositions prepared in Examples and Comparative Examples were evaluated in a manner as described below. Namely, each composition was injection-formed into a spout (opening diameter: 11 mm, thickness of body portion: 2 mm, height: 32 mm). A threaded cap of a polypropylene (surface hardness: Rockwell hardness of 90) was fitted to the threaded portion formed on the outer surface of the cylindrical body of the spout to evaluate as described below.

(58) (Abrasion)

(59) The formed spout was capped with the threaded polypropylene cap at a predetermined double-seaming angle, and was treated with the shower of hot water presuming the hot packing. Thereafter, the operation for opening the cap and closing the cap was repeated 20 times, and abrasion of the cylindrical body of the spout was observed with the eye and was evaluated:

(60) ◯: No abrasion was recognized.

(61) X: Abrasion was recognized.

(62) (Cracks)

(63) The formed spout was capped with the threaded polypropylene cap at a predetermined double-seaming angle, and was treated with the shower of hot water presuming the hot packing. Thereafter, the cap was opened, and any cracks in the cylindrical body of the spout were observed with the eye and were evaluated:

(64) ◯: No crack was recognized.

(65) X: Cracks were recognized.

(66) (Oxygen-Barrier Property)

(67) An aluminum film was stuck to the opening of the formed spout to make a sample for measurement. By using an oxygen permeability measuring apparatus “OX-IRAN (registered trademark) 2/21 manufactured by MOCON Co.”, the amount of oxygen that has permeated through per a day under the condition of a temperature of 23° C. was measured.

(68) ◯: Less than 0.002 cc/[pkg-day]

(69) X: Not less than 0.002 cc/[pkg-day]

Example 1

(70) 60 Parts by mass of the HDPE was blended with 30 parts by mass of the EVOH and 10 parts by mass of the compatibilizer A (maleic acid-modified LLDPE) to prepare a resin composition for injection forming. In other words, 100 parts by mass of the HDPE was blended with 50 parts by mass of the EVOH and 16.7 parts by mass of the compatibilizer A (maleic acid-modified LLDPE) to prepare a resin composition for injection forming.

(71) The composition was injection-formed into a spout of the above-mentioned form and was evaluated for its properties to obtain the following results.

(72) Abrasion: ◯

(73) Cracks: ◯

(74) Oxygen-barrier property: ◯

Example 2

(75) 55 Parts by mass of the HDPE was blended with 30 parts by mass of the EVOH and 15 parts by mass of the compatibilizer A (maleic acid-modified LLDPE) to prepare a resin composition for injection forming. In other words, 100 parts by mass of the HDPE was blended with 54.5 parts by mass of the EVOH and 27.3 parts by mass of the compatibilizer A (maleic acid-modified LLDPE) to prepare a resin composition for injection forming.

(76) The composition was injection-formed into a spout of the above-mentioned form and was evaluated for its properties to obtain the following results.

(77) Abrasion: ◯

(78) Cracks: ◯

(79) Oxygen-barrier property: ◯

Comparative Example 1

(80) 50 Parts by mass of the HDPE was blended with 30 parts by mass of the EVOH and 20 parts by mass of the compatibilizer A (maleic acid-modified LLDPE) to prepare a resin composition for injection forming. In other words, 100 parts by mass of the HDPE was blended with 60 parts by mass of the EVOH and 40 parts by mass of the compatibilizer A (maleic acid-modified LLDPE) to prepare a resin composition for injection forming.

(81) The composition was injection-formed into a spout of the above-mentioned form and was evaluated for its properties to obtain the following results.

(82) Abrasion: ◯

(83) Cracks: ◯

(84) Oxygen-barrier property: X

Comparative Example 2

(85) A resin composition for injection forming was prepared in the same manner as in Example 1 but changing the compatibilizer A into a compatibilizer B (maleic acid-modified LDPE).

(86) The composition was injection-formed into a spout of the above-mentioned form and was evaluated for its properties to obtain the following results.

(87) Abrasion: ◯

(88) Cracks: X

(89) Oxygen-barrier property: ◯

Comparative Example 3

(90) A resin composition for injection forming was prepared in the same manner as in Example 1 but changing the compatibilizer A into a compatibilizer C (maleic acid-modified HDPE).

(91) The composition was injection-formed into a spout of the above-mentioned form and was evaluated for its properties to obtain the following results.

(92) Abrasion: X

(93) Cracks: ◯

(94) Oxygen-barrier property: ◯

Comparative Example 4

(95) A resin composition for injection forming was prepared in the same manner as in Example 1 but changing the compatibilizer A into a compatibilizer D (maleic acid-modified PP).

(96) The composition was injection-formed into a spout of the above-mentioned form and was evaluated for its properties to obtain the following results.

(97) Abrasion: X

(98) Cracks: X

(99) Oxygen-barrier property: ◯

Comparative Example 5

(100) A resin composition for injection forming was prepared in the same manner as in Example 1 but changing the compatibilizer A into a compatibilizer E (maleic acid-modified SEBS).

(101) The composition was injection-formed into a spout of the above-mentioned form and was evaluated for its properties to obtain the following results.

(102) Abrasion: X

(103) Cracks: X

(104) Oxygen-barrier property: ◯

Comparative Example 6

(105) A resin composition for injection forming was prepared in the same manner as in Example 1 but changing the compatibilizer A into a compatibilizer F (ionomer).

(106) The composition was injection-formed into a spout of the above-mentioned form and was evaluated for its properties to obtain the following results.

(107) Abrasion: X

(108) Cracks: X

(109) Oxygen-barrier property: ◯