JPS63237924A - Manufacture of multi-layer vessel - Google Patents

Abstract

PURPOSE:To prevent generation of surging, by performing coextrusion by interposing specific resin layers among an intermediate, inner and outer layers. CONSTITUTION:Specific layers obtained by blending scraps and polyolefin resin at a weight ratio of 90:10-10:90 are superposed on the top and bottom of an intermediate layer through an adhesive agent. Coextrusion is performed by superposing further an inner and outer layers of polyolefin resin on the top and bottom of the foregoing layer and a multi-layer vessel is molded. Dispersion in thickness is extremely few, surging is prevented effectively and deterioration also in flavor characteristics of the vessel is prevented, in the obtained vessel.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a multilayer container, and more specifically, the present invention relates to a method for manufacturing a multilayer container, and more specifically, a method for manufacturing a multilayer container using a scrap composition containing a gas barrier thermoplastic resin and a polyolefin resin as one of the raw materials. This article relates to a method for manufacturing a multilayer container to be used.

(Prior art) Ethylene-vinyl alcohol copolymer is one of the resins that has the best permeation resistance to substrates such as oxygen among various resins, and this property is used to make bottles, cups, etc. It is widely used in fields such as packaging containers and films. This ethylene-vinyl alcohol copolymer is sensitive to humidity, and has the disadvantage that, under high humidity conditions such as 100% RH, the oxygen permeability coefficient increases by two orders of magnitude or more. In order to improve this drawback, we created a layered structure in which a single layer of gas barrier containing an ethylene-vinyl alcohol copolymer was sandwiched between inner and outer surface layers of low water absorption resin such as polyethylene or polypropylene.
Techniques for reducing the effect of humidity on ethylene-vinyl alcohol copolymers are widely used.

When manufacturing packaging containers from this laminate, pinch-off particles are inevitably generated in blow molding of bottles and the like, and punching scraps are inevitably generated in cup molding. For this reason, it is necessary to reuse the scrap made of Paris etc. from the viewpoint of resource conservation.

Japanese Patent Publications No. 49-13868 and Japanese Patent Publication No. 13868-1989 use such a scrap layer as one layer of the above-mentioned laminate.
A container for frying is known from Japanese Patent No. 44155.

(Problems with the prior art) However, when manufacturing containers using scrap as described above, the scrap does not penetrate into the extruder screw during extrusion, so the discharge rate tends to fluctuate, and as a result, the layer There is a problem in that thickness variation, ie, surging occurs, and mechanical properties such as impact resistance strength deteriorate.

Furthermore, the ethylene-vinyl alcohol copolymer contained in this scrap is susceptible to thermal deterioration during extrusion, and the generation of such degraded products impairs the flavor characteristics of the container.

Therefore, the technical object of the present invention is to prevent deterioration of mechanical properties and flavor characteristics due to surging when manufacturing containers by reusing scraps generated during container molding.

(Means for Solving the Problems) The method for producing a multilayer container of the present invention includes forming a polyolefin resin into the inner and outer layers, a gas barrier thermoplastic resin into the middle layer, and optionally an adhesive resin between the inner and outer layers and the middle layer. It consists of coextrusion as an intervening layer and molding the coextrudate into a container, in which the scrap of the coextrudate produced during the molding of the container and the polyolefin resin are mixed in a ratio of 90:10 to 10:9.
At least one layer of this blend is supplied between the intermediate layer and at least one of the inner and outer layers to carry out coextrusion.

(Function) In the multilayer container manufacturing method of the present invention, as described above, the scraps of the coextrudate produced during container molding are not reused alone, but are blended with virgin polyolefin resin. It is an important feature to use.

In other words, the scraps of coextrudates produced during the molding of containers may be scraps or punched scraps, but these are all very irregular shapes, such as cylindrical shapes or coil shapes. Therefore, it is very bulky.

For this reason, when coextrusion is performed by feeding the scrap from a predetermined hopper into an extruder, the scrap does not penetrate into the extruder screw well, making it impossible to maintain a constant discharge rate. Surging will occur.

In this case, it is possible to prevent the screw from digging into the extruder screw by forcibly feeding the scrap by installing a suitable feeder in the upper part of the hopper, but this requires the use of special equipment. It's not valid.

According to the present invention, by blending the scrap with virgin polyolefin resin and reusing it, it is possible to solve the problem of surging without requiring special equipment during extrusion.

In other words, scrap itself is bulky and does not penetrate the extruder screw very well, but by blending it with virgin polyolefin resin, the blend has a lower bulk than scrap alone. As a result, the extruder screw is well penetrated, a constant discharge amount can be maintained, and surging is effectively prevented.

In addition, in the present invention, the blend of scrap and virgin polyolefin resin to be coextruded can be prepared by simply tri-blending it into a car, and the blend can be fed as it is into the extruder hopper to perform the extrusion operation. Can be done. That is, since there is no particular need for heat melting means such as melt blending or pelletizing, thermal deterioration of the ethylene-vinyl alcohol copolymer in the scrap can be effectively suppressed, and thus the deterioration of the flavor characteristics of the container can be prevented. It becomes possible to prevent this.

Furthermore, according to the present invention, since the virgin polyolefin resin is present in the scrap-containing blend physics, the blend physics itself has extremely good adhesion with other polyolefin resin layers and adhesive resin layers. The resulting container has excellent delamination resistance.

(Preferred embodiment of the invention) Container material In the present invention, polyolefin resin,
A gas barrier thermoplastic resin is used as the intermediate layer, and an adhesive resin layer is interposed between the inner and outer layers and the intermediate layer.

This polyolefin resin includes propylene resin,
For example, tactical polypropylene, ethylene-propylene copolymer, propylene-butene-1 copolymer, ethylene-propylene-butene-1 copolymer, etc. can be used alone or in combination of 2 ff1 or more.

Of course, in addition to these, other crystalline olefin polymers such as high-9 medium- or low-pressure polyethylene, ethylene/vinyl acetate copolymers of two or more of them, and polymethylpentene resin mixtures may also be used. can.

In particular, propylene resin is a thermoplastic resin with low water absorption, and is preferably used because it has rigidity, transparency (contact clear property), and other characteristics.

As the gas barrier thermoplastic resin for the intermediate layer, an ethylene-vinyl alcohol copolymer having a vinyl alcohol content of 40 to 85 mol%, particularly 45 to 80 mol%, is particularly preferably used.

That is, ethylene-vinyl alcohol copolymer is one of the resins with the best gas barrier properties, and its gas barrier properties and thermoformability depend on the vinyl alcohol unit content. When the vinyl alcohol content is less than 40 mol %, the permeability to oxygen and carbon dioxide gas tends to be higher than when it is within the above range, and the gas barrier properties tend to decrease. On the other hand, if this content exceeds 85 mol%,
This is not preferable because the permeability to water vapor increases and the melt formability decreases.

The ethylene-vinyl alcohol copolymer is obtained by saponifying a copolymer of ethylene and a vinyl ester such as vinyl acetate so that the degree of saponification is 96% or more, particularly 99% or more, In addition to the above-mentioned components, this copolymer may contain 3-carbon atoms such as propylene, butylene-1, isobutylene, etc., within a range that does not impair the barrier properties against oxygen, carbon dioxide, etc., for example, within a range of up to 3 mol%. The above olefin may be contained as a comonomer component.

In addition to the above-mentioned ethylene-vinyl alcohol copolymer, vinylidene chloride resins and various homopolyamides and copolyamides can also be used as the gas barrier thermoplastic resin. Among these polyamides, aromatic polyamides such as xylylene group-containing polyamides are particularly preferred.

In addition, in the present invention, since gas barrier thermoplastic resins such as ethylene-vinyl alcohol copolymer, vinylidene chloride resin, and aromatic polyamide and polyolefin resins such as polypropylene usually do not have thermal adhesive properties, it is necessary to An adhesive resin layer is provided if necessary, and such adhesive resins include carbonyl (-C-) groups based on carboxylic acids, carboxylic acid anhydrides, carboxylic acid salts, carboxylic acid amides, carboxylic acid esters, etc. in the main chain or side chain, 1 to 900 mEq/1
00g resin, especially thermoplastic resins containing at a concentration of 10 to 700 meq/100g resin. Suitable examples of adhesive resins include ethylene-acrylic acid copolymers, ionically crosslinked olefin copolymers, maleic anhydride grafted polyethylene, maleic anhydride grafted polypropylene, acrylic acid grafted polyolefins, ethylene-vinyl acetate copolymers, These include polymerized polyester, copolymerized polyamide, etc.

Blend product In the present invention, at least one blend layer is provided between the intermediate layer and at least one of the inner and outer layers (olefin resin layer).

This blend consists of scraps of the coextrudate produced during container molding and virgin polyolefin resin, and the ratio of the scraps and polyolefin resin to each other is preferably 90:10 to 10:90 on a weight basis. They are blended in a ratio of 80:20 to 15:85.

If the amount of scrap blended is greater than the above range, the objectives of the present invention of preventing surging and reducing flavor characteristics will not be achieved, and if it is less than the above range, it is undesirable from the standpoint of scrap reuse. .

The blending of scrap and virgin polyolefin resin may be a simple tri-blend, and means such as melt blending are not desirable. In the case of melt blending, thermal deterioration progresses as the ethylene-vinyl alcohol copolymer etc. in the scrap undergoes thermal history again.
This is because it deteriorates the flavor characteristics of the container.

Further, it is preferable to use a pellet-shaped polyolefin resin to be blended with the scrap so that the bulky scrap can easily fit into the extruder screw.

In the present invention, the resins and blends corresponding to each of the layers described above are subjected to coextrusion molding, which is known per se, to obtain a coextrusion molded product.

The resulting extrudate may take the form of a film, a sheet, a parison or pipe for forming bottles or tubes, a preform for forming bottles or tubes, and the like.

In addition, during coextrusion, as an extruder for the blend layer,
The angle of repose of the extruder hopper wall is between 5 and 85 degrees, especially 10 degrees.
It is desirable to use a hopper having an angle of 75 degrees and a hopper outlet hole diameter of 15 to 200 mm, particularly 20 to 170 mm, in order to smoothly feed the blend into the extruder screw.

In addition, the layer structure of the extruded product can adopt various aspects as long as blend physics is provided between the inner and outer polyolefin resin layers and the intermediate layer. For example, it is also possible to provide a plurality of blend physics. can. A specific example thereof is shown below.

The polyolefin resin layer is indicated by PO, the gas barrier thermoplastic resin is indicated by BR1, the adhesive layer is indicated by AD, and the blend physics is indicated by SC.

■PC/SO/8El/BR to AD/PO■PO/SC
/AD10R/AD/SC/PO■PO/Sfl:/P
O/AD/BR/AD/PO■PO/SC/PO/8I
)/BR/eight[)/l'o/SC/PO■PO/toC/
BR/SC/PO ■PO/BR/SC/PO ■PO/SC/PO/BR/PO/S(:/PO■PO
/BR/PO/SC/PO Forming into containers Forming bottles from parisons, pipes or preforms is facilitated by pinching off the extrudate with a pair of split dies and blowing fluid into the interior. . Also, after cooling the pipe or preform, it is heated to the drawing temperature,
By stretching in the axial direction and also in the circumferential direction using fluid pressure, a stretched blow bottle or the like can be obtained.

Furthermore, the film or sheet can be processed by vacuum forming, pressure forming,
A packaging container in the shape of a cup, tray, etc. can be obtained by subjecting it to stretch molding, plug assist molding, or the like.

Alternatively, the films can be stacked or folded into a bag and the periphery heat-sealed to form a bag-like packaging container (pakuchi).

(Effects of the Invention) According to the manufacturing method of the present invention, the poor bite of the scrap into the extruder screw is effectively improved, a constant discharge amount can be ensured, and the occurrence of surging is effectively prevented.

In addition, when blending scrap with virgin polyolefin resin, it is possible to simply tri-blend the mixture without thermal melting as in melt blending, which is effective in accelerating the thermal deterioration of the ethylene-vinyl alcohol copolymer in the scrap. It is possible to prevent the deterioration of the flavor characteristics of the container.

(Example) Example 1 The following 7-layer configuration, from the inside: PO+ / SC+ / ADI / BR / AC3
/SC2/PO2 open-ended parisons were formed by coextrusion. The resins constituting each layer were as follows.

Innermost layer and outermost layer (POo and PO2); density is 0.
91g/cc (ASTM D-1505), melt flow rate (ASTM D-1238) is 1.4g/cc
10m1n of tactical polypropylene.

Middle layer (BR).

Ethylene content 48 mol%, saponification degree 96.1%, melt flow rate (8STM D-1238, 190℃
) is 5.5g710m1n of ethylene-vinyl alcohol copolymer.

Adhesive layer (ADI and AC3).

Acid-modified polypropylene (Modic P-300F, manufactured by Mitsubishi Yuka ■).

Blend physics (sc, and SC,): A blend of the scraps of molded products of the polypropylene, the acid-modified polypropylene, and the ethylene-vinyl alcohol copolymer, and the virgin polypropylene. The blend ratio is 33:87 (by weight).

When coextruding, the outermost layer and the innermost layer have a diameter of 65 mm.
An extruder with a metering type screw with a % L/D (effective length/diameter) of 22, an intermediate layer with a diameter of 40 mm, L/D
Similar extruder with D 20, adhesive layer diameter 32 m+n
A similar extruder with a % L/D of 20 and blending physics used a similar extruder with a diameter of 651 m and a L/D of 22.

The angle of repose of the hopper of the extruder used for blending physics was 45 degrees, the outlet diameter of the hopper was 65 m+n, and the blend was prepared by triblending.

The set temperature at the screw tip of each extruder during coextrusion is polypropylene (outermost layer and innermost layer) 2
00℃, blend 200℃, acid-modified polypropylene (
The adhesive layer) was 210°C, and the ethylene-vinyl alcohol copolymer (intermediate Jli3) was 180°C.

This parison with both ends open was heated for about 30 minutes in a hot air circulation open air precisely set to an atmosphere of 155°C, and then a cylindrical bottle with an average wall thickness of about 600 μm and an internal volume of 280 cc was formed by a sequential biaxial stretching blow method. Molded. The average constituent thickness ratio is PO+ / SC+ / from the inside of the bottle.
ADI/BR/AC3/SC2/PO2=
The target was 515/1/1/11515.

(Hereinafter, this bottle will be referred to as the "Example Bottle.") For comparison, the same method as above was used, except that a scrap layer consisting of scrap alone to which no virgin polypropylene was added was used as the blending physics. A layered bottle was manufactured. (Hereinafter, this bottle will be referred to as a "comparative example bottle.") Regarding the two types of seven-layer bottles obtained, a blended layer containing scrap (in the example bottle) and a layer consisting of scrap alone (in the comparative example) were prepared using the following method. The average wall thickness value and the coefficient of variation indicating the variation in wall thickness (in the bottle) were measured, and each bottle was subjected to a drop impact test and flavor characteristics were evaluated.

(1) Average wall thickness and variation in wall thickness The blending physics in the example bottle and the wall thickness of the scrap layer in the cutting section of the comparative example bottle were measured at each intersection of 4 points in the vertical direction and 5 points in the circumferential direction of the bottle. That is, measurements were taken at a total of 20 positions.

Measurements were performed using the Congo red staining method. That is, about 70℃
After immersing the cut piece of the measurement part of the bottle in a 1 wt % Congo red aqueous solution kept warm for 3 minutes, the cut piece was taken out, dried, and then using a stereomicroscope with a magnification of 50 times. The blend physics and the thickness of the scrap layer were observed in the thickness direction of the cut surface of each measurement portion. This is because the ethylene/vinyl alcohol copolymer contained in the blend physics or scrap layer is dyed red with Congo red, making it possible to measure the thickness.

Then, the inner blend object (
or scrap) layer (SC+) and outer blend (
The coefficient of variation was calculated using the following formula as a guideline for indicating the average thickness and variation in wall thickness of the scrap) layer (SC2).

In the formula, the arithmetic mean value is the arithmetic mean value for the measurement positions (20 locations each) for the SC layer and the SC2 layer.

The results are shown in Table 1.

Table 1 From these results, it can be seen that the Example bottles obtained by the method of the present invention had significantly smaller variations in wall thickness than the Comparative Example bottles, and surging was effectively prevented.

(2) Drop Impact Test Tap water was drip-filled into 10 Example bottles and 10 Comparative Example bottles, the mouth of each bottle was capped, and the bottles were stored in a refrigerator at 5° C. for 7 days.

Next, 10 bottles each were vertically dropped in the same refrigerator room so that the bottoms touched the floor (concrete surface). The fall height was 2.0 m.

Each bottle was subjected to a drop test up to 10 times, and the presence or absence of bottle breakage and the presence or absence of peeling between the bottle layers at each drop were visually determined.

In the bottles of the present invention (example bottles) in which scraps are used in blends with virgin polyolefin, etc., all 10 bottles were tested 10 times each for bottle breakage and delamination between bottle layers. No peeling Il!i) was observed.

On the other hand, in the case of the comparative example bottle in which scrap was used alone, one bottle each was dropped on the 5th, 7th, 8th, and 9th drops, and 3 bottles were dropped on the 10th drop.
Damage occurred to the wooden bottle. Furthermore, interlayer delamination occurred in all the bottles (10 bottles) during the first drop.

(3) Flavor characteristics Example bottles and comparative example bottles were filled with distilled water and carbonated water to full capacity, capped, and stored at a temperature of 25°C for 7 days.
A comparative evaluation of flavor was conducted.

As a result, when the content was distilled water and carbonated water, all 10 panelists found that the flavor of each content filled in the example bottle was better than that of each content filled in the comparative example bottle. They answered that they clearly preferred it.

Example 2 Using the multilayer extruder group described in Example 1 (however, the extruder for the adhesive layer was not used) and a flat mold with an internal volume of 360 m1, a 5-layer structure, that is, from the inside, PO+ / SI:+ / BR/ SC2/ PO2
A flat bottle (dropping internal volume: 356 mf) was molded by a coextrusion/direct blow method. The resins constituting each layer were as follows.

Innermost layer and outermost layer (po and po2).

Density (ASTM D-1505) is 0.922g/cc
, low density polyethylene with a melt flow rate (ASTM D-1238) of 0.56g710m1n.

Middle layer (BR).

Ethylene content is 31 mol%, saponification degree is 99.6%,
Melt flow rate (ASTM D-1238°190
For 100 parts by weight of a mixture of 1.3 g 710 m 1 n of ethylene vinyl alcohol copolymer (°C) and the low density polyethylene at a mixing ratio of 75:25 (weight ratio),
A three-component mixture consisting of 10 parts by weight of an ionomer (Himilan #1601, manufactured by Mitsui DuPont Polychemicals ■).

Blend Physics (SC, and 5C2).

A blend of scraps of molded products made of the ethylene-vinyl alcohol copolymer, the low-density polyethylene and the ionomer, and the virgin low-density polyethylene. The blend ratio is 67:33 (weight ratio).

The set temperature at the screw tip of each extruder during coextrusion is low density polyethylene (innermost layer and outermost layer).
temperature was 190°C, that of the blend was 190°C, and that of the composition layer (intermediate layer) mainly composed of ethylene/vinyl alcohol copolymer was 200°C.

Further, the total average wall thickness value of the molded bottle was 280 μm, and the average constituent thickness ratio was from the inside of the bottle. (Hereinafter, this bottle will be referred to as the "Example Bottle.") Also, for comparison, the blending physics is exactly the same as above, except that a scrap layer consisting of scrap alone without adding virgin low-density polyethylene was used. A 5-layer bottle was molded. (Hereinafter, this bottle will be referred to as a "comparative example bottle.") Regarding the two types of five-layer bottles obtained, according to the method described in Example 1, (1) Blend physics containing scrap (in the example bottle) The average wall thickness value and the coefficient of variation indicating the variation in wall thickness in the layer consisting of scrap alone (in the comparative example bottle) were measured, and (2) flavor characteristics were evaluated.

(1) Average wall thickness and wall thickness variation According to the measurement method and calculation method described in Example 1,
The average wall thickness and variation in wall thickness were determined for the "Example Bottle" and the "Comparative Example Bottle". The results are shown in Table 2.

From the results in Table 2, it can be seen that the Example bottles obtained by the method of the present invention had significantly smaller variations in wall thickness than the Comparative Example bottles, and surging was effectively prevented.

(2) Flavor characteristics Regarding the example bottle and the comparative example bottle, after filling the full amount of lactic acid bacteria beverage and capping the mouth, the bottle was heated to 25°C.
A panel of 10 people made a comparative evaluation of the flavor of the samples that had been stored for 7 days at a temperature of .

As a result, as in Example 1, even when the content was a lactic acid bacteria drink, all 10 panelists agreed that the flavor of the lactic acid bacteria drink filled in the example bottle was better than that of the lactic acid bacteria drink filled in the comparative example bottle. The respondents answered that the flavor was clearly preferable to that of .

Table 2 Patent applicant: Toyo Seikan Co., Ltd. ゛, -1-village/

Claims (5)

[Claims] (1) Multilayer consisting of coextrusion of polyolefin resin as an inner and outer layer, a gas barrier thermoplastic resin as an intermediate layer, and optionally an adhesive resin as an intervening layer between the inner and outer layers, and forming the coextrudate into a container. In the container manufacturing method, coextrudate scraps produced during container molding and polyolefin resin are blended at a weight ratio of 90:10 to 10:90, and at least one layer of this blend is used as an intermediate layer and an inner and outer layer. A method for producing a multilayer container, characterized in that coextrusion is carried out by supplying between at least one layer of (2) The manufacturing method according to claim 1, wherein the polyolefin resin is a propylene resin. (3) Polyolefin resin is polyethylene, ethylene-
The manufacturing method according to claim 1, which is either a vinyl acetate copolymer or a polymethylpentene resin. (4) The method according to claim 1, wherein the gas barrier thermoplastic resin is an ethylene-vinyl alcohol copolymer or a composition mainly composed of the copolymer. (5) The method according to claim 1, wherein the gas barrier thermoplastic resin is a vinylidene chloride copolymer.