JPS6026008B2 - Method for manufacturing multilayer containers - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a multilayer container that has high impact strength, excellent gas permeation resistance, solvent permeation resistance, and soundproofing effect.

Large polyethylene hollow-molded containers are used in a variety of fields, including kerosene drums, water tanks, various industrial chemical cans, and automobile gasoline tanks, but their major drawback is that they allow a large amount of permeation of various solvents and gases. It is being

As an improvement method, it is possible to layer resins with excellent permeation prevention effects for various solvents and gases, such as polyester, nylon, saponified ethylene-vinyl acetate copolymer, vinylidene chloride, etc., but if you simply do this, Impact strength is significantly reduced, and large containers in particular must not be damaged if dropped, and gasoline tanks must not be damaged in a car collision.
It becomes difficult to use it for these purposes. Furthermore, in response to social demands for reducing noise in automobile gasoline tanks and the like, there is a desire to develop containers in which noise due to vibrations of the contents is less likely to be transmitted to the outside.

In order to satisfy these problems, the inventors of the present invention have made extensive studies and have found a method for producing a container that has excellent gas permeability, solvent permeation resistance, high impact strength, and also has excellent soundproofing effects. I got it.

That is, the gist of the present invention is that the outer layer has a melt index of 0.
Melt index using polyethylene of 01 to 0.3 evening/1 hour (regarded as MI sail) and modifying the polyethylene with at least one monomer selected from unsaturated carboxylic acids or their derivatives for the intermediate layer. Using modified polyethylene of 0.1 to 5.0 m/h (referred to as skin [B'), the inner layer {C) has an ethylene content of 25 to 5 hol%.
(Xmol%) Ethylene with saponification degree of 95% or more
When manufacturing a multilayer container by extruding and blowing a saponified vinyl acetate copolymer through circular dies arranged in the same direction, the average thickness ratio of each layer is T:T'B':T{C
' = 1: (o.oaog(MI'B}/MI■+o.o5
)~0.5:2.0×10-4X~3.5×10-3×
This is a method for manufacturing a multilayer container, characterized in that the method is characterized in that:

Melt index here refers to the value measured by the method according to JIS K6760, and if the value of the polyethylene used for the outer layer is less than 0.01 Tano 10, the fluidity during melting is poor and normal extrusion molding is difficult. If it exceeds .3 pm/1 pm, the impact strength of the resulting multilayered container will deteriorate, making it unsuitable.

The monomers used in the modified polyethylene for the intermediate layer (immediately) include unsaturated carboxylic acid or its derivatives; specific examples include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, acrylic anhydride, and methacrylic acid. Acid anhydride, maleic anhydride, itaconic anhydride, methyl acrylate, methyl methacrylate, ethyl acrylate,
Ethyl methacrylate, butyl acrylate, butyl methacrylate, monoethyl maleate, diethyl maleate, monomethyl fumarate, dimethyl fumarate, acrylamide, methacrylamide, monoamide maleate, diamide maleate, Maleic acid-N-monoethylamide, maleic acid-N.N-diethylamide, maleic acid-N-monobutylamide,
Maleic acid, mono-N/N-dibutylamide, fumaric acid monoamide, fumaric acid diamide, fumaric acid-N/N-jethylamide, fumaric acid-N-monobutylamide, fumaric acid-N/N-dibutylamide, maleimide, N -butylmaleimide, N-phenylmaleimide, sodium acrylate, potassium acrylate, sodium methacrylate,
Examples include potassium methacrylate. Among these, it is preferable to use maleic anhydride because it can be easily grafted by a normal melt extrusion method and is inexpensive.
Methods for grafting these monomers onto polyethylene include simultaneous melting and homogenization of polyethylene, monomers, and a radical initiator such as peroxide, and methods for grafting polyethylene suspended or dissolved in a suitable medium. There is a method of adding a monomer and an initiator.

Here, the amount of monomer grafted is 0.1 to 0.
．． 5% by weight is desirable. In addition, if the melt index of this modified polyethylene is less than 0.1 m/1 h, the adhesion to the saponified ethylene-vinyl acetate copolymer will be poor, and if it exceeds 5.0 m/10 h, the adhesion will be poor. The impact strength of the resulting multilayer container decreases due to the weakening of the body. Note that high, medium, and low density polyethylene can be used as appropriate for the polyethylene of the outer layer and the intermediate layer (B), but it is preferable to use low density polyethylene for the polyethylene of the intermediate layer legs from the viewpoint of impact resistance.

If the ethylene content of the saponified ethylene-vinyl acetate copolymer is less than 28 hol%, the melting point will be high and the temperature difference from the decomposition temperature will be small, making melt molding difficult. Permeability and solvent permeability deteriorate.

If the degree of saponification is less than 95%, the gas permeability and solvent permeability will similarly deteriorate, making it unsuitable. The average thickness ratio of each layer of a multilayer container is appropriately adjusted by the extrusion base or injection pressure molding temperature of each layer, slit interval, etc., but the average thickness of each layer of a multilayer container referred to here means Select any point, measure it, and average it.

'If the thickness of the outer layer leg is 1 as the average thickness ratio of each layer, then the middle layer'
The ratio of B} needs to be 0.061og (MI{B}/MI)10.05 or more and 0.5 or less. 0
．． The formula of 0 mother og (MI'B}MI) + 0.05 is obtained from an experiment that depends on the melt index of the outer layer (MI style) and the melt index of the middle layer [B] (MI {B-). This is an empirical formula, and when the ratio is lower than this, the strength of the pinch-off part becomes weaker, and the impact strength (drop strength) of the entire multilayer container becomes weaker.If the ratio exceeds 0.5, the impact strength also decreases in areas other than the pinch-off part. This weakens the impact strength of the entire multilayer container.

The thickness ratio of the inner layer {q is 2.0×10-4× or more and 3.5× when the ethylene content (mol%) of the saponified ethylene-vinyl acetate copolymer is X mol%.
It is necessary that it is 10-3× or less.

If it is less than 2.0×10-4×, the soundproofing effect, solvent permeation resistance, and gas permeation resistance will deteriorate;
If it exceeds 5×10-3×, the strength of each part forming the multilayer container decreases, and the impact strength (drop strength) of the multilayer container becomes significantly weaker. Regarding the soundproofing effect, although the details of the mechanism are still unknown, it is known that significant effects can be obtained by keeping the ethylene content and thickness ratio in the saponified ethylene-vinyl acetate copolymer within the above range. I found it.

A coextrusion multilayer blow molding machine having a plurality of extruders is used as an apparatus for manufacturing this container.

The method includes both an extrusion method and an accumulator method, and although both are possible, it is more desirable to use the accumulator method as the container becomes larger. In the case of this accumulator method, in order to achieve the thickness structure of the present invention, the injection of each layer should be performed at the same time as or before the injection of the layer using a resin with a low melt viscosity and the layer using a resin with a high melt viscosity. This is desirable because resin with high melt viscosity does not fill the flow path and block the flow of resin with low melt viscosity. Further, the molding temperature at this time is desirably higher than the melting point of each resin and lower than 240 oo. As mentioned above, this container can be used for a variety of purposes, including kerosene cans, drums, water tanks, various industrial chemical cans, food containers for juice and mayonnaise, and gasoline tanks for automobiles. It may be used by adding one to three layers to it, or by applying inserts, surface treatment, printing, etc. Hereinafter, the present invention will be explained in more detail with reference to Examples.

Examples 1 to 12 and Comparative Examples 1 to 8 The melt index (MI index) of the outer layer was 0.
04 Melt index (M1 [B') of high-density polyethylene of 0.23% by weight and 0.21% by weight of maleic anhydride grafted into the middle layer [B] is 0.4 and 1.5%, respectively. /1 denatured high-density polyethylene, and the inner layer 'q has an ethylene content (x) of 35 mol%
One extruder (for the outer layer) with a diameter of 9 mm and using saponified ethylene-pinyl acetate copolymer with a saponification degree of 99.1%.
A square bottle with an inner capacity of 30 mm was molded using an accumulator head type three-layer blow molding machine equipped with two extruders (one for the middle layer and one for the inner layer) each having a diameter of 4 mm.

The molding temperature was 210°C in the die part, the total thickness of the molded multilayer container was about 3 ribs, and the thickness ratio of the middle layer was varied by adjusting the injection pressure, and the thickness ratio of the inner layer was about 0. I went there on 025.

The tensile impact strength (ASTM D-1822) and drop strength (ASTM
, D-2463), and the results are shown in Table 1. Table 1 Examples 13 to 10 Comparative Examples 9 to 10 Melt index (MI) in the outer layer was 0.0, respectively.
005, 0.04, 0.08, 0.12, 0.23, 0
．． 50 minutes/1 skin inch of high-density polyethylene, middle layer B
)'The melt index (M1[B}) grafted with 0.2% by weight of maleic anhydride was 0.51/1 hour.
In the same manner as in Examples 1 to 12, a saponified ethylene-vinyl acetate copolymer with an ethylene content of 35 hol% and a saponification degree of 99.3% was used for the inner layer [CI]. The strength of the resulting multilayer container was measured.

The results are shown in Table 2. Table 2 Example 17
-20, Comparative Examples 11-12 High-density polyethylene with a melt index (MI) of 0.03 m/IQhjn was grafted to the outer layer (■), and 0.021% by weight of maleic anhydride was grafted to the intermediate layer [B}. Melt index (MI{B') is 0.05 and 0.05, respectively.
3 0.8 1.33. The following 6.2 evenings/1 hour of modified high-density polyethylene was used, and for the inner layer (C), a saponified ethylene-vinyl acetate copolymer with an ethylene content of 38 hol% and a saponification degree of 99.3% was used. Example 1~
The strength of a multilayer container obtained by molding in the same manner as No. 12 was measured.

The results are shown in Table 3.

Table 3 Examples 21-32, Comparative Examples 13-21 The outer layer was made of high-density polyethylene with a melt index (MI style) of 0.05 mm, and the middle layer (B'' was made of maleic anhydride of 0.01 mm). Neck weight% grafted melt index (M1[B}) is 0.51 min/1 hin
The inner layer {C} is made of modified high-density polyethylene with an ethylene content of 3 hol% and a saponification degree of 98.9.
%,■Ethylene content 35hol%, saponification degree 99.2
%, ■Ethylene content 3 shoes ol%, saponification degree 99.6%
, ■Ethylene content 44 mol%, degree of renanization 99.0
%, and an accumulator head type three-layer blow molding machine equipped with one extruder with a diameter of 65 bars (for the outer layer) and two extruders with a diameter of 30 bars (for the middle layer and inner layer). A cylindrical bottle with an inner capacity of 10 was formed using the following method.

The molding temperature was 210°C in the die part, the total thickness of the molded multilayer container was about 2.7 ribs, the thickness ratio of the middle layer was kept constant at about 0.2, and the thickness ratio of the inner layer was kept constant. It was molded in various ways.

For comparison, a single layer of high-density polyethylene with a thickness of 2.7 mm was also tested. Tensile impact strength, drop strength, gasoline permeability (determined from the change in weight over time of the lid filled with 50% unleaded gasoline in a 40° temperature bath), and soundproofing effect of the flat part of the resulting multilayer container (A container filled with 50% unleaded gasoline was vibrated at an amplitude of 15% and a frequency of 1 vibration per second, and a sound level meter was installed 50 cm away from the vibrating position to monitor the vibration at a frequency of 500 H.
Z, the sound pressure at 1000 days 2 and 1500 days 2 was measured.

The results are shown in Table 4.

Table 4

Claims (1)

[Claims] 1. The outer layer (A) has a melt index of 0.01 to 0.3.
g/10 min (referred to as MI (A)), and the intermediate layer (B) is a polyethylene modified with at least one monomer selected from unsaturated carboxylic acids or derivatives thereof, with a melt index of 0.1 to 5. .0g/10
min (referred to as MI (B)) is used, and the inner layer (C) has an ethylene content of 25 to 50 mol% (X
When manufacturing a multilayer container by extruding and blowing a saponified ethylene-vinyl acetate copolymer with a saponification degree of 95% or more through a circular die arranged concentrically, the average thickness ratio of each layer is T(A):T(B):T(C) =1:(0.06log(MI(B)/MI(A))
+0.05)~0.5:2.0×10^-^4X~3
．． A method for manufacturing a multilayer container, characterized in that the container has a size of 5×10^-^3X.