JPH02215529A - Multi-layer plastic vessel superior in surface gloss property - Google Patents

Abstract

PURPOSE:To give excellent surface gloss and sanitary properties, by making use of specific ethylene-propylene/random copolymer for the outermost surface layer of a multi-layer plastic vessel. CONSTITUTION:A vessel wall of a multi-layer plastic vessel is constituted of outer surface layers 10, 11, an intermediate layer 12 and a base material resin layer 13 which are comprised respectively of an ethylene-propylene/random copolymer, gas barrier resin and polyolefin resin. When those resin layers are short of adhesion to each other, adhesive agent resin 14a, 14b are interposed among the layers each. The ethylene-propylene/random copolymer whose ethylene content, melt flow rate and ratio between a weight-average molecular weight and number-average molecular weight (molecular weight distribution) are respectively 2-8wt.%, at least 2.5g/10 minutes and 3-5 is used.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to multilayer plastic containers, and more particularly to multilayer plastic containers with excellent surface gloss.

(Prior Art) It is well known that plastic blow-molded containers have a multi-layered laminated structure. In this case, the inner and outer surface layers of the container are made of polyolefin such as polyethylene or polypropylene from the viewpoint of hygienic properties and moisture resistance. resin is used, and
From the viewpoint of the gas barrier of the container, both surface layers are made of a gas barrier such as ethylene-vinyl alcohol copolymer.
A laminated structure is used in which the resin is sandwiched.

Polyolefin resins for blow molding are generally of a different grade from those used for normal molding. That is, during blow molding, a phenomenon in which the molten parison sags due to its own weight (called drawdown) or a phenomenon in which the molten parison itself becomes rippled or has a shark's skin (melt fracture) tends to occur, and in order to prevent this, , a melt flow rate (MFR) of 2.0 g 710 minutes or less and a wide range of molecular weight distribution defined by MwZMn,
That is, resins in the range of 3.5 to 7 are used. Although this resin is effective in preventing the above-mentioned drawdown and melt fracture, the formed container wall has poor surface gloss and lacks transparency. The problem was that the appearance of the contents was inferior to the actual product, and the product value was poor, and the gloss level was about 60% at most.

Accordingly, one object of the present invention is to provide a multilayer plastic container having excellent surface gloss, hygienic properties, etc.

(Means for Solving the Problems) According to the present invention, in a multilayer plastic container having a structure in which two or more types of resin layers are laminated, the outermost surface layer has an ethylene content of 2 to 8% by weight, Melt flow rate is 2
．． 5g/10 minutes or more and the ratio of M w / M n is 3
A multilayer plastic container with excellent surface gloss is provided, which is characterized by being made of the ethylene-propylene random copolymer of 5 to 5.

(Function) In FIG. 1 showing an example of the multilayer plastic container of the present invention, the container 1 is connected to a body 2, a lower end of the body 2,
Moreover, the bottom 3 formed by pinching off the parison
, consists of a mouth and neck part 5 that is connected to the upper end of the body part 2 via a shoulder part 4, and this mouth part 5 includes a mouth part 6 that is sealingly engaged with a lid (not shown) and a lower part of the mouth part 6. A lid attachment part 7 is provided which is made of a screw, a bead, a flange, a step layer, or the like.

In FIG. 2, which shows an enlarged cross-section of the wall of this multilayer plastic container, the wall is made of an outer surface layer 10 and an outer surface layer 11 made of the ethylene-propylene random copolymer of the present invention, and a gas barrier resin. The middle layer consisting of 12. It is composed of a base resin layer 13 made of polyolefin resin, and if these resin layers have poor adhesiveness to each other, adhesive resins 14a and 14b can be interposed between each layer.

One of the important features of the multilayer plastic container of the present invention is that the outermost surface layer has an ethylene content of 2 to 8% by weight, a melt flow rate of 2.5 g/10 minutes or more, and M w / M n The point is that an ethylene-propylene random copolymer having a ratio of 3 to 5 is used.

Conventionally, when polyolefin resin such as polypropylene is used for this type of container, the melt flow rate (MFR)
In order to prevent drawdown, it was necessary that the amount was 1-5 g/10 minutes or less. However, with an MFR of 1.5 g/IQ min or less, a satisfactory surface gloss could not be obtained. Furthermore, polybropylene tends to have poor transparency due to crystallization.

In the present invention, the ratio of M w /M n is 3 to 5. Especially 3.
By using an ethylene-propylene random copolymer that has a molecular weight distribution of 5 to 4.5 and an ethylene content of 2 to 8% by weight, particularly 3 to 5% by weight, this resin can be made into a multi-layered copolymer. By making it the outer layer of the bottle, the melt flow rate is 2.5g/10 minutes or more, especially 3.
This is based on new knowledge regarding multilayer bottles that drawdown can be prevented even at large values of 5 to 5 g/10 minutes, and the surface gloss, stain resistance, transparency, etc. of multilayer plastic containers can be significantly improved.

That is, in the present invention, it is important that the ratio of M w /M n (molecular weight distribution) is 3 to 5, particularly 3.5 to 4.5, and that the ratio of M w / M n is less than the above range. If it is too large, the surface of the container will lose its luster, and if it is smaller than the above range, the wall of the molded container will become sharkskin. This molecular weight distribution can be determined by obtaining a molecular weight distribution curve using gel permeation chromatography and calculating the weight average molecular weight and number average molecular weight using a universal calibration method using polystyrene as a standard.

Furthermore, the ethylene content of this ethylene-propylene random copolymer is 2 to 8% by weight, particularly 3 to 5% by weight.
It is also important that If the ethylene content is less than the above range, the gloss of the container surface will decrease, and if it is more than the above range, the container wall will be too soft and easily scratched, and the rigidity will be poor.

It is also important from the viewpoint of moldability of the container that the melt flow rate (MFR) of this ethylene-propylene random copolymer is 2.5 g/10 minutes or more, particularly 3 to 5 g/10 minutes. That is, if the melt flow rate is lower than the above range, the fluidity will be poor and if the load during extrusion becomes large, the moldability will deteriorate and the gloss will be lost. Furthermore, a material having an MFR larger than the above range will have large drawdown even if used as part of a multilayer polyester within the above range, making blow molding generally difficult, and will also have poor impact resistance.

In the present invention, by using an ethylene-propylene random copolymer that satisfies these conditions as a resin constituting the outermost surface layer, the resulting multilayer plastic container has excellent surface gloss and gloss. degree (JIS K 7
105, the incident angle (60°) is 8°㎢%, which is the same level of surface gloss as that obtained from polycarbonate or polyester bottles.

(Preferred embodiment of the invention) In the present invention, hydrogenated petroleum resin is used in place of the above ethylene-propylene random copolymer.
It is also possible to use ethylene-propylene random copolymers containing 10% by weight, in particular 10 to 20% by weight. This hydrogenated petroleum resin is colorless, transparent, odorless, and has excellent heat resistance, weather resistance, etc. Similar effects can be obtained by using this resin in the outermost surface layer instead of the ethylene-propylene random copolymer. As this hydrogenated petroleum resin, 1, for example, Alcon P-140
(manufactured by Arakawa Chemical Industry Co., Ltd.) can be suitably used.

The ethylene-propylene random copolymer used in the present invention itself has poor moldability, and it is necessary to combine this resin with a base resin having excellent moldability. As this base resin, olefin resin is suitable, and among them, polypropylene, high density polyethylene, etc. can be used.

Voribrolepin may be a homopolymer of propylene, or it may be a homopolymer of propylene and ethylene or other α-
It may be a copolymer with olefin, for example, butene-1, pentene-1, hexene-1, etc., or it may be a blend of two or more of these, or a homopolymer or blend thereof. should be crystalline in terms of X-ray diffraction, and the content of propylene units in the entire polymer should be 85 mol% or more, especially 90 mol% or more, and if the melt flow rate is polypropylene, 2g/
Should be no more than 10 minutes.

In addition, other examples of polyolefin resins include MFRo
, 5 or less can be used.

In this case, an adhesive is required, and suitable adhesives include linear low density polyethylene and ethylene acrylate copolymer.

This high-density polyethylene also has the advantage of preventing drawdown.
It should have a melt flow rate of less than 0.5g710min.

The polyolefin resin used in the present invention may contain other resins, such as other olefin resins, as long as the main resin is the above-mentioned polypropylene and/or high-density polyethylene. A scrap resin or the like may be blended with the polyolefin resin, or the scrap resin may be provided as a single layer.

In the present invention, the gas barrier resin generally has an oxygen permeability coefficient (Pot) of 5.5 Xl0-" cc-
Cs7cm”sec-cmHg or less, especially 4.5 xt
o-" cc-c+++/Cm!・5ec-c+mHg
In the following, those having the above-mentioned transparency are preferably used, especially ethylene-vinyl alcohol having an ethylene content of 20 to 50 mol% and a content of unsaponified vinyl ester residues of 5 mol% or less. Polymer or carbon number 10
The number of amide groups per 0 is 3 to 30, especially 4 to 2
Homopolyamides, copolyamides or blends thereof containing in the range of 5 are preferably used.

Of course, the above-mentioned ethylene-vinyl alcohol copolymer and polyamide can be used in the form of a blend, and other thermoplastics can be used within a range that does not impair the essence of the product, for example, within a range of 20% by weight or less. Blends of resins, such as polyolefins and resins that provide adhesion to polyolefins, can also be used.

The gas barrier resin preferably has an absolute value of the difference in refractive index between the inner and outer surface layers of 0.1 or less, and most preferably has a refractive index equivalent to that of the inner and outer surface layers. Preferably, a gas barrier resin is used.

If there is no adhesion between the gas barrier resin and the inner and outer surface layers, add 1 acid-modified olefin resin between both side resin layers.
For example, it is preferable to interpose an adhesive layer of polyethylene, polypropylene, or the like graft-modified with an ethylenically unsaturated carboxylic acid such as maleic anhydride, acrylic acid, methacrylic acid, or itaconic anhydride or its anhydride. Instead of interposing a layer, the above-mentioned resin can be contained in at least one of the gas barrier layer and the inner and outer surface layers.

The layer structure of the multilayer plastic container wall of the present invention includes the above-mentioned ethylene-propylene random copolymer/base resin from the outer layer, and in the case of improving gas barrier properties, and in the case of obtaining a transparent bottle, When using the ethylene-propylene random copolymer/adhesive/gas barrier resin/adhesive/base resin and scrap resin in order from the outer layer to the inner layer, the ethylene-propylene random copolymer/adhesive/gas barrier resin/adhesive/base resin and scrap resin are used in order from the outer layer to the inner layer. The layered structure of propylene random copolymer/scrap resin/adhesive/gas barrier resin/adhesive/base resin makes it possible to obtain a multilayer plastic container each having excellent surface gloss.

It goes without saying that the laminated structure of these resins is not limited to the layered structure described above, and various changes can be made.

It is also important that this outermost surface layer has a thickness ratio of 3 to 40%, especially 5 to 30%, of the total thickness. That is, if the thickness ratio is larger than the above range, the moldability will deteriorate, and
If the thickness ratio is smaller than the above range, sufficient surface gloss cannot be expected.

In addition, the base resin accounts for 50 to 90% of the total thickness, especially 6
The thickness ratio is preferably 0 to 70%, and the gas barrier resin is preferably 2 to 15%, particularly 3 to 10%.
As the final container, the thickness of the vessel wall is 0.3 to 1.5 ar
m, preferably within the range of 0.5 to 1.2 m intestine.

According to the present invention, 1, for example, an ethylene-propylene random copolymer is used as the outermost surface layer, a gas barrier resin is used as the intermediate layer, a base resin is used as the inner layer, and if necessary, adhesive resin or ethylene is used as the innermost surface layer. -Providing a brobylene random copolymer and coextruding it through multiple dies in the form of a parison,
There are restrictions that must be observed at this time.

First, when manufacturing a parison for blow molding using this ethylene-propylene random copolymer as an outer surface, it is important to melt and cross-mix this resin through a cross-wire type screw. It is difficult to extrude parisons with the ethylene-propylene random copolymer having the above-mentioned molecular weight distribution, and in order to enable extrusion into parisons with smooth surfaces, it is necessary to prevent uneven melting in the resin. For this purpose, it is necessary to equalize the resin temperature to 200 to 230°C. Furthermore, it is also necessary to suppress pressure fluctuations that tend to occur in the plasticizing section of the extruder. For example, in the present invention, it is necessary to suppress pressure fluctuations in the plasticizing section to below +/-3%. By performing melt extrusion of the ethylene-propylene random copolymer using an extruder equipped with a mixed screw, such as a Dalmage type screw or a bottled screw, the above-mentioned uniform resin temperature can be achieved.
This makes it possible to prevent oxidation and pressure fluctuations, and to manufacture blow-molded containers with excellent surface smoothness, transparency, etc. Screws other than mixed type screws, e.g.
When a ring-type screw is used, it is difficult to manufacture the blow-molded container of the present invention.

In addition to using the above-mentioned cross-conductor type screw, it is also extremely important to polish the die surface at least near the exit in order to prevent the occurrence of guilines. Polishing the mold surface is also an important factor.

In the present invention, instead of directly pinching off the parison extruded from the die with a split mold and blow molding, the extruded parison is brought into contact with cold air or with a cooling mold so that the surface of the parison rises above the melting point. Although the temperature is low, the parison is cooled so that the center of the wall is still at a temperature above the melting point.
It is also possible to then subject this parison to blow molding.

In this case, the surface of the bottle to be formed will have some molecular orientation due to the expansion caused by blowing.

(Effects of the Invention) According to the present invention, in a multilayer plastic container having a structure in which two or more resin layers are laminated, the outermost surface layer has an ethylene content of 2 to 8% by weight and a melt flow rate of 2.
．． 5g/10 minutes or more and the ratio of M w / M n is 3
By using the ethylene-propylene random copolymer of 5 to 5, it is possible to mold a container using the resin, which was considered to have poor moldability, and the surface gloss of the container can be reduced to 0 (JIS Z 7105 incident light). 8 at an angle of 60°)
This makes it possible to improve it by more than 5%.

(Example) The invention is illustrated in the following examples.

Example 1 Melt flow rate (MFR) 3.0g/1 as outer layer
0 minutes, molecular weight distribution (M w /M n ) 3.5,
An ethylene-propylene random copolymer with an ethylene content of 4 mol% was fed to an extruder for the outer layer, and the MFR was used as the inner layer.
l, 5 g/I 0 min, M w /Mn 2.0,
An ethylene-propylene block copolymer with an ethylene content of 3.5 mol% is supplied to an extruder for inner layer to extrude a two-layer molten parison, and this parison is blow-molded in a blow mold to obtain an average wall thickness of the body. A bottle with a diameter of 800 μm and an internal volume of 500 cc was obtained.

The thickness of each layer of this bottle is 100U for the outer layer and 7U for the inner layer.
It was 00μ.

Example 2 A shell was made in the same manner as in Example 1, except that 10% by weight of hydrogenated petroleum resin Alcon P-140 (manufactured by Arayo Kagaku Kogyo ■) was added to the ethylene-propylene random copolymer of the outer layer of Example 1. A bottle with an average wall thickness of 800 u and an internal volume of 500 cc was molded.

The thickness of each layer of this bottle is 40μ for the outer layer and 76μ for the inner layer.
It was 0μ.

Example 3 The average wall thickness of the body was 800 in the same manner as in Example 1 except that a scrap resin layer was formed between the outer layer and the inner layer of Example 1.
A bottle with an internal volume of 500 cc was molded.

The thickness of each layer of this bottle was 40μ for the outer layer, 560μ for the scrap layer, and 200μ for the inner layer.

Example 4 MFR3.5g/l as outer layer 0 min, Mw/M
n4, B, an ethylene-propylene random copolymer with an ethylene content of 4 mol% was used as an extruder for the outer layer, and as an inner layer M
FRl, 9 g/l 0 min, My/Mn 2.5,
An extruder for the outer layer was made of an ethylene-propylene random copolymer with an ethylene content of 3 mol%, and an extruder for the intermediate layer was used for the gas barrier resin made of an ethylene-vinyl alcohol copolymer with an ethylene content of 32 mol%. As the adhesive layer interposed between the inner and outer layers and the intermediate layer, carboxylic acid-modified polypropylene with a carbonyl group concentration of 80 mmol/10 g polymer was supplied to an extruder for the adhesive layer, and a molten parison was extruded. Blow molding is performed in a blow mold, and the average wall thickness of the body is 1. Otmm, internal volume 10
A 00cc bottle was obtained.

The thickness of each layer of this bottle is 2 from the outer layer to the inner layer.
00μ/15μ/35μ/15μ/735μ.

Example 5 Example 3 except that 15% by weight of Alcon P-140 was added to the ethylene-propylene random copolymer of the outer layer of Example 3, and a scrap resin layer was formed between the inner layer and the adhesive layer. In the same manner as above, a bottle having an average body wall thickness of 450 μm and an internal volume of 100 cc was molded.

The thickness of each layer of this bottle is 80mm from the outer layer to the inner layer.
μ/10μ/20μ/10μ/230μ/100μ.

Comparative Example 1 MFRl, 5 g/I 0 min, M w /Mn 2.0
, an ethylene-propylene block copolymer with an ethylene content of 3.5 mol% is fed to an extruder to extrude a molten parison, and this parison is blow-molded in a blow mold to have a body with an average wall thickness of 800μ and an internal volume. A 500cc bottle was obtained.

Comparative Example 2 MFRl as outer layer, Og/l 0 min, Mv/M
n6.0, ethylene content 3.5 mol% ethylene-
A bottle was molded in the same manner as in Example 1 except that a propylene block copolymer was used.

These results are shown in Table 1.

table

[Brief explanation of the drawing]

FIG. 1 shows an example of a multi-layered plastic stitch according to the invention, and FIG. 2 shows an enlarged cross-sectional view of the multi-layered plastic wall of FIG. Container container L...container, 2...body, 3...bottom, 4...
Shoulder part, 5... Mouth and neck part, 6... Mouth part, 7... Lid attachment part, lO... Outer surface layer, 11... Inner surface layer, 12.
・Intermediate layer, 13-・Base resin layer, 14a, 14b・
...Adhesive resin layer.

Claims (7)

[Claims] (1) In a multilayer plastic container having a structure in which two or more resin layers are laminated, the outermost surface layer has an ethylene content of 2 to 8% by weight and a melt flow rate of 2.5 g/1
A multilayer plastic container with excellent surface gloss, characterized in that it is made of an ethylene-propylene random copolymer that lasts for at least 0 minutes and has a @M@w/@M@n ratio of 3 to 5. 2. The multilayer plastic container of claim 1, wherein the outermost surface layer comprises an ethylene-propylene random copolymer composition containing 5 to 25% by weight of hydrogenated petroleum resin. (3) The multilayer plastic container according to claim 1, wherein the outermost surface layer is present at a thickness ratio of 3 to 30% of the total thickness. (4) A multilayer plastic container, in which the laminated structure of the container wall is, in order from the outer layer to the inner layer, the ethylene-propylene random copolymer/adhesive/gas barrier resin/adhesive/polypropylene according to claim 1. (5) The laminated structure of the container wall is an ethylene propylene random copolymer containing the hydrogenated petroleum resin according to claim 2 in order from the outer layer to the inner layer/adhesive/gas barrier resin/adhesive/polypropylene. A multilayer plastic container. (6) The laminated structure of the container wall is arranged in order from the outer layer to the inner layer: ethylene-propylene random copolymer according to claim 1 / adhesive / gas barrier resin / adhesive / polypropylene + scrap resin / Ethylene-propylene
A multilayer plastic container that is a random copolymer. (7) The laminated structure of the container wall is an ethylene-propylene random copolymer containing the hydrogenated petroleum resin according to claim 1 in order from the outer layer to the inner layer/adhesive/gas barrier resin/adhesive/ A multilayer plastic container made of polypropylene + scrap resin/the ethylene-propylene random copolymer.