JP2002292723A - Multi-layered preform and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive multi-layered preform having excellent mechanical properties obtained by using a recovered polyester resin and to provide its manufacturing method. SOLUTION: A multi-layered preform has an inner layer composed of a virgin polyester and an outer layer composed of a recovered polyester wherein the multi-layered preform is obtained by compression-molding a co-extruded item of the multi-layered preform having an inner layer composed of the virgin polyester and the outer layer composed of the recovered polyester, a mouth portion and a bottom portion of the preform are formed of only the virgin polyester and the outer layer of the recovered polyester exists only at a body portion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a multilayer preform and a method for producing the same, and more particularly, to a multilayer preform using a recovered polyester as a raw material resin and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, industrial waste has increased, and disposal of the waste has become a problem. In particular, the demand for polyester containers has been rapidly increasing, and the amount of waste has been increasing year by year. Therefore, it has been required to effectively reuse such waste. In polyester containers,
Various attempts have been made to recover the polyester resin container from the market, remove the adherence of contents, dust, foreign materials, etc., wash and then recycle the recovered polyester resin obtained by grinding to form a container. ing.

For example, Japanese Patent Application Laid-Open No. 8-253222 discloses a composite container comprising a new material and a recycled material,
The mouth, a support ring provided at the lower end of the mouth, a shoulder, a body, and a bottom following the support ring, and the mouth, the support ring, the shoulder and the body, The bottom portion is composed of a mixed layer of a nascent material or a nascent material of a composition mainly composed of a regenerated material or a composition mainly composed of the recycled material. A non-food composite container characterized by the following has been proposed. Also, Japanese Patent Application Laid-Open No. 10-3377
Japanese Patent Application Publication No. 70-70139 discloses a multilayer preform for stretch blow molding comprising an inner layer and an outer layer, wherein the inner layer is a primary molded article formed by primary injection of a virgin polyester resin, and the outer layer is a recovered polyester resin. Is formed on the outer surface of the primary molded body by secondary injection and is formed of at least a two-layer structure, and the outer layer has a thickness of 0.5 to 2.5 mm.
A multilayer preform having a recovered polyester characterized by the following has been proposed.

[0004]

In the prior art utilizing the above-mentioned recovered polyester resin, as in the former technique, a multi-layer is formed by co-injection molding such that the recovered polyester resin is an intermediate layer and the virgin polyester resin is an inner and outer layer. In the preform, whitening due to crystallization occurs in the intermediate layer, and whitening tends to occur also in the bottom which is highly processed, resulting in poor mechanical strength. Further, in the latter technique, even if the problem as in the former technique does not occur, in each of these conventional techniques, a multilayer preform which is a precursor of a final molded product is formed by injection molding. Always have a gate part that protrudes outward from the center at the bottom, and this gate part has many problems in terms of productivity, manufacturing cost, and characteristics of the final blow molded product .

[0005] That is, a special cutting step is required to cut the gate portion, which is a factor of lowering the productivity. In addition, the cut gate portion becomes scrap resin, and resources are wasted. Furthermore, the remaining portion of the gate is thick, which tends to cause crystallization and whitening of the final blow-molded product, which causes a deterioration in appearance characteristics. This causes uneven orientation and non-uniform structure during molding, and also causes bottom cracks due to drop impact and the like.
Further, in the former technique, since the recovered polyester resin of the intermediate layer is exposed on the inner surface side in the remaining portion of the gate, there is a problem that impurities in the recovered polyester resin elute into the contents.

In addition, in injection molding, a large shearing force acts during molding, so that molding at high temperature is required, and this thermal history causes a problem that thermal degradation (thermal degradation) of the resin occurs. For this reason, in the production of a conventional polyethylene terephthalate (PET) container, PET having a high intrinsic viscosity by a solid-state polymerization method must be used in anticipation of a decrease in the intrinsic viscosity occurring during injection molding, which increases costs. Has been brought. Furthermore, since not only the cooling of the injected resin but also the flow of the resin is required for the mold at the same time, the degree of freedom in setting the mold temperature is small, and the injection molding time becomes longer. There are also problems.

[0007] Accordingly, an object of the present invention is to provide a multilayer preform which uses a recovered polyester resin at low cost and has excellent mechanical properties, and a method for producing the same.

[0008]

SUMMARY OF THE INVENTION According to the present invention, there is provided a multilayer preform having an inner layer made of virgin polyester and an outer layer made of recovered polyester, comprising: an inner layer made of virgin polyester and an outer layer made of recovered polyester. The multilayer preform is formed by compression molding of a co-extruded product, wherein the mouth and bottom of the preform are substantially formed only of virgin polyester, and the outer layer of the recovered polyester is present only in the body. Provided. In the multilayer preform of the present invention, the recovered polyester preferably accounts for 25% or more of the weight of the multilayer preform.

According to the present invention, there is also provided a step of co-extruding a virgin polyester as an inner layer and a recovered polyester as an outer layer, a step of cutting the co-extruded product into a cylindrical molten mass, and a step of converting the molten mass into a cavity mold. Supplying the core mold substantially in the axial direction and pressing the core mold into the inner layer of the molten mass in the cavity mold, and the mouth and bottom of the preform are substantially formed only of virgin polyester;
Compression molding into a preform in which the outer layer of the recovered polyester is present only in the trunk. In the method for producing a multilayer preform of the present invention, it is preferable that the cylindrical molten mass has a structure in which the thickness of the inner layer is small at the cutting edge and the thickness of the outer layer is large at the middle.

According to the present invention, there is further provided a bottle characterized in that the multilayer preform is formed by biaxial stretch blow molding.

[0011]

DETAILED DESCRIPTION OF THE INVENTION In the present invention, there is provided a multilayer preform having an inner layer made of virgin polyester and an outer layer made of recovered polyester, wherein a coextrudate of an inner layer made of virgin polyester and an outer layer made of recovered polyester is provided. It is an important feature that the mouth and bottom of the preform are substantially formed only of virgin polyester, and the outer layer of recovered polyester is present only in the trunk.

Most of the recovered polyester resin used in the present invention is polyethylene terephthalate (PE).
T) Containers called bottles are collected from the market, and are PET resins regenerated from these containers; PET resins for heat-resistant bottles such as hot packs; PET resins for pressure-resistant bottles such as carbonated beverages; and tea and beverages. P for aseptic filling bottles such as water
It is made of various PET resins having different compositions such as the intrinsic viscosity and the diethylene glycol content of the ET resin and the like, and has a high crystallization rate and is once subjected to heat history, so that it is particularly easy to whiten. Further, some impurities are mixed in the recovered polyester resin, and the impurities function as a nucleating agent, so that it is considered that the recovered polyester resin is more easily crystallized than the virgin resin.

[0013] The multilayer preform is subjected to stretch blow molding to obtain a final molded product. In this stretch blow molding, the bottom is highly processed and is a site where whitening is most likely to occur. It is not preferable to use a recovered polyester resin which is liable to cause the following. Further, since the mouth portion is a portion that comes into contact with the contents, use of the recovered polyester resin that may contain impurities is not sanitary. Therefore, in the present invention, by using the recovered polyester resin only for the outer layer of the trunk, in the stretch blow molding, the cooling of the recovered polyester resin is accelerated to prevent whitening due to crystallization, and also, the trunk inner layer, the bottom and By using a virgin polyester resin for the mouth, it is possible to provide a hygienic multilayer preform.

Further, since the multilayer preform of the present invention is formed by compression molding, there is no remaining gate at the bottom, so that the cutting step is not required, no scrap resin is generated, and the bottom is further reduced. The center is also smooth and homogeneous, and there is an advantage that there is no cause of whitening in stretch blow molding. Moreover, as described above, compression molding allows processing at a relatively low temperature, unlike injection molding, so that the degree of thermal deterioration of the resin is small, and tensile strength, pressure resistance, impact resistance, heat resistance, etc. In addition to providing a multilayer preform capable of producing a blow-molded product having excellent physical properties, there is an advantage that a material once subjected to a heat history such as a recovered polyester resin is not further thermally deteriorated.

That is, according to the multilayer preform of the present invention, a cheaper resin can be used to produce a blow-molded product having the same physical properties (strength and impact resistance). This makes it possible to produce a blow-molded product excellent in quality.

(Multilayer Preform) In FIG. 1 showing a side cross-sectional view of the multilayer preform of the present invention, the multilayer preform of the present invention, which is indicated as a whole by 1, comprises a mouth and neck portion 2, a trunk portion 3 and a bottom portion 4. A support ring 5 is formed below the mouth and neck 2. In this multilayer preform, the body 3 is composed of an inner layer 6 made of the same virgin polyester resin as the mouth and neck 2 and the bottom 4, and an outer layer 7 made of a recovered polyester resin. In this multilayer preform, the trunk outer layer made of the recovered polyester resin is 10 to 90% of the thickness of the trunk, particularly 30 to 9%.
The thickness is preferably about 0%.

The multilayer preform can be used as it is for stretch blow molding, and in order to impart heat resistance and rigidity to the mouth of the preform, the mouth is crystallized by heat treatment at the preform stage, and whitened. May be
Alternatively, after the preform is formed into a bottle by biaxial stretch blow molding described later, the mouth of the obtained plastic bottle may be crystallized and whitened.

(Polyester Resin) As the virgin polyester resin used in the present invention, any thermoplastic polyester resin derived from a dibasic acid component and a glycol component can be used. In addition to homopolyester and copolyester, It is also possible to use a blend of two or more polyester resins.

Examples of the dibasic acid component include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid and orthophthalic acid, and aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid and dimer acid. And alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, and 1,2-cyclohexanedicarboxylic acid. Also, as the glycol component,
Ethylene glycol, 1,3-propanediol, 1,
3-butanediol, 1,5-pentanediol, 1,
6-hexanediol, diethylene glycol, dipropylene glycol, 1,4-cyclohexanedimethanol, p-xylylene glycol, 1,2-propylene glycol, 1,2-butanediol, 1,3-butanediol, 2, 3-butanediol, 2-methyl-1,3
-Propanediol, neopentyl glycol, di1,
2-propylene glycol, 1,4-pentanediol, 3-methyl-1,5-pentanediol, 2-ethyl-2-butyl-1,3-propanediol, 2,2-
Diethyl-1,3-propanediol, 2,4-diethyl-1,5-pentanediol, 1-methyl-1,8-
Octanediol, 3-methyl-1,6-hexanediol, 4-methyl-1,7-heptanediol, 4-methyl-octanediol, 4-propyl-1,8-octanediol and the like can be mentioned.

As the polyester resin which can be most preferably used, the ethylene terephthalate-based thermoplastic polyester used in the polyester container of the present invention contains most of ester repeating units, generally 70 mol% or more, especially 8 mol% or more.
The ethylene terephthalate unit occupies at least 0 mol%, and has a glass transition point (Tg) of 50 to 90 ° C., particularly 55 to 80 ° C., and a melting point (Tm) of 200 to 275.
C., especially 220 to 270.degree. C., is preferred. Further, the intrinsic viscosity [η] of the virgin polyester resin is preferably 0.6 dl / g or more, particularly preferably in the range of 0.7 to 0.9 dl / g. In addition, various additives such as a coloring agent, an ultraviolet absorber, a release agent, a lubricant, and a nucleating agent can be blended into the polyester resin within a range that does not impair the quality of the product.

(Recovered polyester resin) In the present invention,
The recovered polyester resin is 1% of the weight of the multilayer preform.
Preferably, it accounts for 0% or more, especially 25 to 65%. Further, as a resin serving as a base containing the recovered polyester resin, scrap resin generated in the container manufacturing process can be used in addition to the virgin polyester resin described above. The intrinsic viscosity [η] of the resin containing the recovered polyester resin is preferably 0.6 dl / g or more, particularly preferably in the range of 0.65 to 0.80 dl / g.
Incidentally, a polyester resin, polypropylene or the like may be added as an additive to the recovered polyester resin for the purpose of adjusting the viscosity.

(Method of Manufacturing Preform) The multilayer preform of the present invention is manufactured by compression-molding a coextrudate of an inner layer made of virgin polyester and an outer layer made of recovered polyester. The outline of the process will be described below.

(A) Melt Extrusion and Cutting Steps: The virgin polyester resin and the recovered polyester resin are supplied to the vacuum hopper of the extruder, respectively, and are kept in the extruder main body in a state where moisture absorption from outside air is shut off in a vacuum. Is melt-kneaded by a barrel and a screw, and is co-extruded with a virgin polyester resin as an inner layer and a recovered polyester resin as an outer layer. It is formed into a molten mass with a shape close to a cylinder.

In the present invention, as shown in FIG. 2, the molten mass is applied to an inner layer 11 made of a virgin polyester resin.
The outer layer 12 made of the recovered polyester resin having a uniform thickness may be used. However, as shown in FIG. 3, the outer layer 12a is thinner near the cut edge 13 and the outer layer 12b is thicker in the middle part 14. It is particularly desirable that the structure be a molten mass. This is to prevent the core mold 21 from contacting the recovered polyester resin 12 at the start of the compression molding. In order to change the thickness of the outer layer in the vicinity of the cutting edge and in the middle, the outer layer 12 may be used when coextruding the resin flow.
It can be formed by changing the amount of the resin containing the recovered polyester resin, ie, a.

(B) Supplying step: It is important that the molten mass is gripped by the gripping member and injected into the cavity from the cutting position so that the axial direction substantially coincides. Only the polyester resin of virgin can be formed in the mouth, the bottom, or the inner layer of the trunk portion.

(C) Compression molding step: As shown in FIG.
The molten mass 10 is stored in an upright state so that the axial direction substantially coincides with the cavity mold 20. The core mold 21 starts to descend, the core mold 21 descends into the cavity 20,
After the molten mass 9 is substantially filled in the space defined by the cavity 20 and the core 21, the core mold and the 21 half ring 2
2, the mouth and the bottom of the preform are substantially formed only of virgin polyester, and only the outer layer of the body is made of the recovered polyester resin as shown in FIG. 23 are formed.

(Molding conditions) In the method for producing a multilayer preform of the present invention, the melt extrusion temperature of the resin (the temperature of the die head) varies depending on the type of resin used, but is generally based on the melting point (Tm) of the polyester resin. As T
It is preferably in the range of m + 100 ° C. to Tm + 10 ° C., particularly Tm + 40 ° C. to Tm + 20 ° C. At a temperature lower than the above range, the shear rate may be too high to form a uniform melt extrudate, while at a temperature higher than the above range, the degree of thermal degradation of the resin may be large. At the same time, the drawdown tends to be too large.

The weight of the molten mass to be cut, that is, the basis weight is naturally determined by the final blow-molded product, but an appropriate value is generally selected from the range of 5 to 70 g, particularly 15 to 65 g, depending on the required strength. Good to do.

It is advantageous in terms of handling that the molten mass has a cylindrical shape or a shape close to a columnar shape, but the ratio (H / D) of the diameter (D) to the height (H) of the molten mass is generally The range of 0.8 to 4 is advantageous in that the temperature of the molten mass can be prevented from lowering as much as possible and the molten mass can be easily put into the female mold. That is, when the H / D is outside the above range, the surface area of the molten mass becomes large, and the temperature tends to be easily lowered.

When the thickness of the outer layer is different between the cutting edge and the intermediate portion of the molten mass, it is preferable that the thickness of the outer layer near the cutting edge be 5% or less of the diameter (D) of the molten mass. Also, the thickness of the outer layer is reduced in the upper part of the molten mass (the side to be above the preform) by about 3 to 15% of the axial length of the entire molten mass, and in the lower portion of the molten mass (below the preform). On the other hand, the length is preferably about 3 to 15% of the axial length of the entire molten mass. Also,
The surface temperature of the compression mold may be any temperature at which solidification of the molten resin occurs, and generally a temperature range of 10 to 50 ° C. is appropriate.

[0031]

The present invention will be described more specifically with reference to the following examples.

(Example 1) A virgin PET resin having an intrinsic viscosity of 0.8 dl / g was subjected to a resin temperature of 270 ° C and a resin pressure of 12
The mixture was extruded from a single screw extruder into a cylindrical shape through a multilayer die under an extrusion condition of 0 kgf / cm2. At the same time, P
Intrinsic viscosity 0.72 dl /
g of flaked recovered polyester resin at a resin temperature of 2
Under a condition of extrusion at 70 ° C. and a resin pressure of 50 kgf / cm 2, the mixture was extruded from a twin screw extruder through a multilayer die to the outside of the above-mentioned virgin PET resin in a cylindrical shape. At this time, the extrusion rates of the two extruders were controlled such that the basis weight of the recovered polyester resin as the outer layer was 50% by weight of the total basis weight. As described above, the multilayer molten resin flow coextruded from the multilayer die using the virgin PET resin as the inner layer and the recovered polyester resin as the outer layer was cut into a cylindrical multilayer molten mass having a length of about 63 mm and a diameter of about 21 mm by a cutter. Next, this cylindrical multilayered molten mass was supplied into a female mold cooled to 15 ° C. so that their axial centers were aligned. Further, compression molding was carried out under the conditions of a mold clamping pressure of 100 kgf / cm2 by a synergistic action with a male mold cooled to 15 ° C. to obtain a two-layer preform having a recovered polyester resin as an outer layer and a virgin PET resin as an inner layer. The basis weight of this preform is 25.0 g, the weight of the mouth and neck including the neck ring is 5.5 g, the average thickness of the outer layer in the body is 2.08 mm, and the average thickness of the inner layer in the body is 0.
It was 92 mm. The mouth and neck including the neck ring and the bottom of the preform were all made of virgin PET resin.

(Comparative Example 1) Molding temperature of 28 using an injection machine
Under the conditions of 5 ° C. and a resin pressure of 400 kgf / cm 2, the above-mentioned virgin PET resin is co-injected into an injection mold cooled to 15 ° C. using the inner and outer layers and the above-mentioned recovered polyester resin as an intermediate layer. Got a reform. The weight of the multilayer preform was 25 g, the thickness of the trunk was 3 mm, and the ratio of the recovered polyester was 50% by weight. The gate was cut within 1 mm. The multilayer preform obtained in Example 1 and Comparative Example 1 was heated to 110 ° C., and blow-molded in a blow-molding die heated to 60 ° C. by a biaxial stretch blow-molding machine. Got a bottle.

[Evaluation of Appearance] Ten multi-layer bottles obtained in each of the examples and comparative examples were extracted and observed visually for the presence or absence of whitening to determine the number of occurrences.

[Impact Resistance Test] A multilayer bottle sealed with 500 cc of water was dropped vertically onto a concrete floor from a height of 120 cm, and the number of damaged bottles was examined.

[Peeling Test] The body of the multilayer bottle was 15 m wide.
m, a strip having a length of 50 mm, and one end of the strip was partially peeled off, and the peel strength was measured with a T-peel strength measuring machine “Tensilon”. Table 1 shows the evaluation results of these multilayer bottles.

[0037]

Table 1 Appearance evaluation Impact resistance Peel strength Example 1 0/0 0/0 No peeling Comparative example 2 10/10 4/10 150

The multilayer bottle blow-molded using the multilayer preform of Example 1 did not have whitening of the body, and did not have any defects such as peeling or cracking even in the drop test. In addition, since there was no gate portion, the appearance was good.

On the other hand, in the multilayer bottle blow-molded using the multilayer preform of Comparative Example 1, the recovered polyester of the intermediate layer was milky white, and the whitening was particularly remarkable around the gate. Also, peeling and cracking occurred in the drop test.

[0040]

According to the multilayer preform of the present invention, the preform is formed by compression molding of a co-extrudate of an inner layer made of virgin polyester and an outer layer made of recovered polyester, and the mouth and bottom of the preform are substantially virgin. Since the outer layer of the recovered polyester is formed only in the trunk portion, a multilayer preform having excellent mechanical strength can be obtained while using a recovered polyester resin which is easily whitened. Further, according to the manufacturing method of the present invention, the recovered polyester resin is supplied to the outer layer and the multilayered molten resin block having the virgin PET resin as the inner layer is supplied into the female mold and compression-molded using the male mold, thereby obtaining the recovered polyester resin. Not only can it be effectively reused, it also has an excellent transparency without whitening even if the ratio of the recovered polyester resin is large, and the bottom is made of only virgin PET resin and has no gate, so it has low mechanical strength. An excellent multilayer preform can be obtained.

[Brief description of the drawings]

FIG. 1 is a side sectional view of an example of a multilayer preform of the present invention.

FIG. 2 is a view showing an example of a molten mass used in the method for producing a multilayer preform of the present invention.

FIG. 3 is a diagram showing another example of a molten mass used in the method for producing a multilayer preform of the present invention.

FIG. 4 is a diagram for explaining a method for producing a multilayer preform of the present invention.

FIG. 5 is a view for explaining a method for producing a multilayer preform of the present invention.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme court ゛ (Reference) B29L 9:00 B29L 9:00 22:00 22:00 (72) Inventor Makoto Eto Hodogaya-ku, Yokohama-shi, Kanagawa 22-4 Okazawacho F-term in Toyo Seikan Group Integrated Research Laboratory (reference) 4F201 AA24 AA50 AG03 AG07 AH55 BA03 BC01 BC02 BC12 BC21 BD06 BM07 BM13 4F204 AA24 AA50 AG03 AG07 AG22 AH55 FA01 FB01 FB22 FG02 4F208 AA24 A04 ALA03 LB01 LB22 LG06 LG16 LG32

Claims (4)

[Claims] 1. A multi-layer preform comprising an inner layer made of virgin polyester and an outer layer made of recovered polyester, formed by compression molding of a coextrudate of an inner layer made of virgin polyester and an outer layer made of recovered polyester. A multilayer preform wherein the mouth and bottom of the preform are formed substantially only of virgin polyester, and the outer layer of recovered polyester is present only in the trunk. 2. The recovered polyester comprises at least 10 to 80%, preferably 25 to 6% by weight of the multilayer preform.
The multilayer preform according to claim 1, wherein the multilayer preform accounts for 5% or more. 3. A step of co-extruding a virgin polyester as an inner layer and a recovered polyester as an outer layer; a step of cutting the co-extruded product into a cylindrical molten mass; Feeding the core mold into the inner layer of the molten mass in the cavity mold so that the mouth and bottom of the preform are substantially formed only of virgin polyester, and the outer layer of recovered polyester is Compression molding into a preform present only in the trunk. 4. The method according to claim 3, wherein the cylindrical molten mass has a structure in which the thickness of the outer layer is small at the cutting edge and the thickness of the outer layer is large at the middle.