JP2005171082A - Polyester resin for compression molding, and preform and polyester container composed of the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyester resin for compression molding which is suppressed in a drawing-down tendency at the time of melt extrusion and smoothly flowable at the time of compression molding, and to provide a manufacturing method of a preform which has reduced molding strain and excellent mechanical strength and is suppressed in scratch generation. <P>SOLUTION: The polyester resin for compression molding has melt viscosity of 100-200 Ns/m<SP>2</SP>at 265°C and a shear rate of 2,000 (1/sec). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a polyester resin for compression molding, and more specifically, a polyester resin in which drawdown during melt extrusion into a compression mold is effectively prevented, and a preform and a polyester container molded using this resin And a method for producing a preform using the resin.

Stretch blow molded plastic containers, in particular biaxially stretched polyester containers, are now commonplace, and liquids such as liquid detergents, shampoos, cosmetics, soy sauce, sauces, etc. due to their excellent transparency and moderate gas barrier properties. In addition to containers for products or foods, they are widely used for carbonated drinks such as beer, cola, and cider, and other drink containers such as fruit juice and mineral water.
When forming a biaxially stretched polyester container, a bottomed preform having a size considerably smaller than the final container and having an amorphous polyester is formed in advance by injection molding of a polyester resin, and the preform is brought to its stretching temperature. A method of preheating, stretching in the axial direction in the blow mold and blow-stretching in the circumferential direction is employed (for example, Patent Document 1).

As the shape of the bottomed preform, a mouth-and-neck portion corresponding to the mouth-and-neck portion of the container and a bottomed cylindrical portion to be stretch blow molded are generally used, and the shape as a whole is a test tube. The mouth / neck portion is formed with, for example, a sealing opening end or an engaging means with a lid. In addition, a gate portion that protrudes outward from the center of the bottom portion is always formed on the bottom portion because of the necessity of injection molding.
However, in general, in the manufacture of a preform by injection molding, the melt-plasticized resin is injected into the cavity through the nozzle, sprue, runner, and gate, so that the residence time of the resin in the injection molding machine is long. A long stay in a simple molding machine may cause deterioration of the resin. In particular, the polyester resin has a problem in that satisfactory mechanical strength cannot be obtained because the intrinsic viscosity and molecular weight decrease due to thermal decomposition.

  From this point of view, it has already been proposed to produce a bottomed preform by compression molding of a resin. For example, Patent Document 2 discloses a method of cutting a molten resin mass (drop) by cutting a molten resin extruded from an extruder. ) Is held and supplied into the female mold, and then a male mold is press-fitted into the female mold and compression molding is performed in the female mold.

JP-A-4-154535 JP 2000-280248 A

  Crystalline resins that can be stretched and oriented, such as thermoplastic polyester resins, generally have a large tendency to draw down, and when the intrinsic viscosity (IV) decreases greatly during plasticization, that is, during melt-kneading, drawdown is performed during drop molding. Occurs, it becomes difficult to accurately hold the molten resin lump, and the transportability of the molten resin lump to the compression molding machine is reduced, so that the intrinsic viscosity of the molten resin at the time of extrusion is required to be high On the other hand, a molten resin lump with high intrinsic viscosity, which is excellent in transportability, has poor melt flowability due to its high melt viscosity, so that molding distortion during compression in the compression mold remains in the preform. The problem is that the mechanical strength of the container to be molded is inferior, and the cutter mark is formed on the cut edge of the molten resin lump, and the molded container is scratched.

Accordingly, an object of the present invention is to provide a polyester resin for compression molding capable of suppressing a draw-down tendency at the time of melt extrusion while allowing a smooth flow during compression molding.
Another object of the present invention is to provide a method for producing a preform in which molding distortion is reduced and mechanical strength is excellent, and generation of scratches is suppressed.

According to the present invention, there is provided a polyester resin for compression molding having a melt viscosity of 100 to 200 Ns / m ² at a temperature of 265 ° C. and a shear rate of 2000 (1 / sec).
According to the present invention, a molten resin lump made of a polyester resin is supplied to a compression molding machine, and the molten resin lump is compressed at a temperature of 265 ° C. and a shear rate of 2000 ( 1 / sec), a preform manufacturing method comprising a polyester resin having a melt viscosity of 100 to 200 Ns / m ² is provided.
According to the present invention, there is further provided a preform characterized by being produced by the above production method, and a polyester container characterized by being formed by stretching the preform.

According to the polyester resin for compression molding of the present invention, the occurrence of resin drawdown during melt extrusion is effectively suppressed, and the flow of molten resin during compression molding is smooth, so that molding distortion is reduced. It becomes possible to mold the preform without leaving it. Further, since the cut edge of the molten resin lump (drop) is uniform and the cutter mark is not formed, it is possible to effectively prevent the preform from being damaged.
Further, the preform made of the compression-molded polyester resin of the present invention is excellent in mechanical strength and appearance characteristics.

In the polyester resin for compression molding according to the present invention, it is an important characteristic that the melt viscosity at a temperature of 265 ° C. and a shear rate of 2000 (1 / sec) is 100 to 200 Ns / m ² , and thereby drawdown While the tendency is suppressed, the molten resin can be smoothly flowed during compression molding, and the moldability can be improved.
That is, a general polyester resin (polyethylene terephthalate) has a low melt tension, and drawdown occurs during melt extrusion, making it difficult to efficiently supply the molten resin mass to the compression molding machine. Although it is required to increase the intrinsic viscosity, if the intrinsic viscosity of the resin is increased, the melt viscosity is also increased, so that the fluidity of the resin is reduced during compression in the compression molding machine, and the molding distortion is increased. Since this remains in the preform, it becomes inferior in mechanical strength. Molding of the molten resin mass is performed by cutting the molten resin continuously extruded from the molding extruder with a cutter. At this time, if the viscosity of the molten resin mass is high, the cutting edge in the moving direction of the cutter. Flows, and there is a tendency that a cutter mark having a corner at its end is formed. When a molten resin mass having such a cutter mark is compression-molded, scratches caused by the cutter mark enter the preform to be molded, and when the preform with this scratch is stretch-molded, the molded product is also scratched. It is.

  In the present invention, the problem of the melt viscosity at a shear rate of 2000 (1 / sec) at a temperature of 265 ° C. is that the flow strain generated on the molten resin by the female mold and the male mold surface during compression molding is the reference. By setting the melt viscosity in the above range to the above range, it becomes possible to satisfy both contradictory properties of suppressing the drawdown tendency during melt extrusion and the fluidity of the molten resin during compression molding. is there.

Such operational effects of the present invention are also apparent from the results of Examples described later. That is, when a polyester resin having a melt viscosity smaller than 100 Ns / m ^{2 at a} shear rate of 2000 (1 / sec) at a temperature of 265 ° C. is used (Comparative Example 1), the resin draws down and compression molding is performed. Polyester that cannot efficiently convey the molten resin mass to the mold and is inferior in productivity, while the melt viscosity at a shear rate of 2000 (1 / sec) at a temperature of 265 ° C. is greater than 200 Ns / m ² When the resin is used, a cutter mark is formed on the cut edge of the molten resin lump, the preform is scratched, and the body of the stretch blow molded polyester container is scratched (Comparative Example 2). Or it turns out that the shaping property at the time of preform molding is inferior (comparative example 3). On the other hand, when a polyester resin having a melt viscosity in the above range at a shear rate of 2000 (1 / sec) at a temperature of 265 ° C. is used, the molten resin lump is excellent in transportability and molded. The preform has no cutter mark, and the stretch blow molded polyester container is excellent in appearance characteristics (Examples 1 to 4).

  In the production method of the preform of the present invention by compression molding, it is important that the molten resin mass obtained by cutting the molten resin extruded from the extruder with a cutter has the above-described melt viscosity. This suppresses drawdown of the molten resin lump, enables reliable holding by the conveying jig and supply to the compression mold, prevents formation of cutter marks on the molten resin lump, and damages the preform. Can be prevented. In addition, when the molten resin mass is compressed in the compression mold, the molten resin spreads in the space formed by the female mold and the male mold with good fluidity, and it becomes possible to mold the preform without leaving molding distortion. is there.

(Polyester resin)
The polyester resin used in the present invention is conventionally known except that the melt viscosity at a shear rate of 2000 (1 / sec) at a temperature of 265 ° C. is 100 to 200 Ns / m ² , particularly 110 to 190 Ns / m ² . A polyester resin comprising a dicarboxylic acid component and a diol component can be used.
As the dicarboxylic acid component, 50% or more, particularly 80% of the dicarboxylic acid component is preferably terephthalic acid from the viewpoint of mechanical properties and thermal properties, but it is of course possible to contain a carboxylic acid component other than terephthalic acid. Examples of carboxylic acid components other than terephthalic acid include isophthalic acid, naphthalenedicarboxylic acid, p-β-oxyethoxybenzoic acid, biphenyl-4,4′-dicarboxylic acid, diphenoxyethane-4,4′-dicarboxylic acid, 5- Examples thereof include sodium sulfoisophthalic acid, hexahydroterephthalic acid, adipic acid, sebacic acid and the like.

  As the diol component, 50% or more, particularly 80% or more of the diol component is preferably ethylene glycol in view of mechanical properties and thermal properties. As diol components other than ethylene glycol, 1,4-butanediol, Examples thereof include propylene glycol, neopentyl glycol, 1,6-hexylene glycol, diethylene glycol, triethylene glycol, cyclohexane dimethanol, an ethylene oxide adduct of bisphenol A, glycerol, and trimethylolpropane.

  In addition, the dicarboxylic acid component and the all-time component may contain a tribasic or higher polybasic acid and a polyhydric alcohol. For example, trimellitic acid, pyromellitic acid, hemimellitic acid, 1,1,2, 2-ethanetetracarboxylic acid, 1,1,2-ethanetricarboxylic acid, 1,3,5-pentanetricarboxylic acid, 1,2,3,4-cyclopentanetetracarboxylic acid, biphenyl-3,4,3 ′, Polybasic acids such as 4′-tetracarboxylic acid, and polybasic acids such as pentaerythritol, glycerol, trimethylolpropane, 1,2,6-hexanetriol, sorbitol, 1,1,4,4-tetrakis (hydroxymethyl) cyclohexane And monohydric alcohols.

The polyester resin of the present invention suppresses drawdown during melt extrusion to improve the transportability up to the compression molding process, and also performs stringing when cutting the molten polyester resin to obtain a drop, and the correctness in the compression mold. In addition to improving the standing stability and from the viewpoint of removing acetaldehyde, the inherent viscosity measured at 30 ° C. using a phenol / tetrachloroethane mixed solvent with a weight ratio of 1: 1 is 0.60 to 0.75 dL / g, particularly It is preferably in the range of 0.67 to 0.73 dL / g.
Furthermore, in order to satisfy the heat resistance and workability of the preform or polyester container, it is preferable to have a melting point (Tm) of less than 250 ° C., particularly 220 to 245 ° C. The glass transition point is preferably 30 ° C. or higher, particularly 50 to 120 ° C.

  The polyester resin of the present invention contains known compounding agents for resins such as colorants, antioxidants, stabilizers, various antistatic agents, mold release agents, lubricants, nucleating agents, etc. It can mix | blend according to a well-known prescription in the range which is not.

(preform)
The preform of the present invention is obtained by compression-molding the above-mentioned compression-molding polyester resin, but it is made of the above-mentioned compression-molding polyester resin as well as a single layer composed only of the above-mentioned compression-molding polyester resin. A multilayer preform having a layer made of another thermoplastic resin in the layer may be used.
As the thermoplastic resin other than the polyester resin, any resin can be used as long as it is a resin that can be stretch blow molded and thermally crystallized, and is not limited thereto. However, polyethylene, polypropylene, ethylene-propylene copolymer, ethylene- Examples thereof include olefin resins such as vinyl alcohol copolymers and cyclic olefin polymers, and polyamide resins such as xylylene group-containing polyamide. In addition, oxygen-absorbing gas barrier resin compositions containing diene compounds and transition metal catalysts in polyamides containing xylylene groups, recycled polyesters (PCR (resin that recycles used bottles), SCRs (generated in production plants) Resin) or a mixture thereof) can also be used. These recycled polyester resins preferably have an intrinsic viscosity (IV) measured by the method described above in the range of 0.60 to 0.75 dL / g.

The recycled polyester can be used alone or as a blend with virgin polyester. When the recycled polyester has a reduced intrinsic viscosity, it is preferably used by blending with the virgin polyester. In this case, the ratio of the recycled polyester: virgin polyester is 1: 5 to 5: 1. Preferably there is.
Moreover, in order to adhere | attach an inner layer or an outer layer, and an intermediate | middle layer, adhesive resin can also be interposed. As the adhesive resin, an acid-modified olefin resin obtained by graft polymerization of maleic acid or the like, an amorphous polyester resin, a polyamide resin, or the like can be used.
Moreover, various additives for resin can be mix | blended with thermoplastic resins other than the said polyester resin similarly to the said polyester resin for compression molding.

Although the layer structure of the multilayer preform of the present invention is not limited to this, the following can be exemplified. The following abbreviations in the multilayer structure are: PET: polyester resin for compression molding of the present invention, GBR: gas barrier resin, PCR: recycled polyester resin, ADR: adhesive resin, OAR: oxygen-absorbing resin composition, COC : Cyclic olefin copolymer.
Three-layer structure: PET / GBR / PET, PET / PCR / PET
PET / (PET + PCR) / PET
Four-layer structure: PET / GBR / PCR / PET,
PET / GBR / OAR / PET,
PET / GBR / COC / PET
Five-layer structure: PET / ADR / GBR / ADR / PET
PET / ADR / OAR / ADR / PET
PET / GBR / PCR / GBR / PET
PET / ADR / (GBR + OAR) / ADR / PET
Six-layer structure: PET / ADR / GBR / AR / PCR / PET
PET / ADR / OAR / ADR / PCR / PET
Seven-layer structure: PET / PCR / ADR / GBR / ADR / PCR / PET
PET / ADR / GBR / ADR / OAR / ADR / PET

(Preform molding)
As described above, the preform of the present invention can be molded from the compression molding polyester resin by a conventionally known compression molding method.
In compression molding, since the residence time of the resin is short, there is little thermal deterioration of the resin as in injection molding, so that a general-purpose resin can also be used. In addition, the gate part that causes whitening of the bottom is not formed at the bottom as in the case of injection molding, and the flow orientation of the resin hardly occurs at the bottom of the preform, and the residual strain due to the fluid orientation occurs at the bottom. Therefore, there is an advantage that the physical properties of the molded product are less affected.

The preform of the present invention can be molded by a conventionally known compression molding method as long as the polyester resin for compression molding of the present invention is used.
That is, the extruder continuously extrudes the melt and cuts it to produce a molten resin lump (drop) that is a preformed preform for a preform in a molten state. The molten resin lump is compression molded. It is put into the cavity mold of the machine, and this is compression molded with the core mold. At this time, as described above, the molten resin has a melt viscosity of 100 to 200 Ns / m ² , particularly 110 to 190 Ns / m ² when the molten resin mass has a shear rate of 2000 (1 / sec) at a temperature of 265 ° C. It is preferable in terms of lump transportability and fluidity.
Further, when a large number of compression molding dies are arranged circumferentially on the rotating turret, the preform can be molded with high efficiency in an intermittent but nearly continuous state.

  In the preform production method of the present invention, the melt extrusion temperature of the molten polyester resin is preferably in the range of Tm + 5 ° C. to Tm + 40 ° C., particularly Tm + 10 ° C. to Tm + 30 ° C., based on the melting point (Tm) of the polyester resin. At a temperature lower than the above temperature, the shear rate becomes too high, and it may be difficult to form a uniform melt extrudate. On the other hand, at a temperature higher than the above range, the degree of thermal degradation of the resin increases. Or the drawdown becomes too large, and it becomes difficult to form a preform having the above-mentioned characteristics.

  FIG. 1 is an explanatory view showing a compression molding apparatus when a multilayer preform is molded using the polyester resin for compression molding of the present invention. The compression molding apparatus generally indicated by 1 is a polyester for compression molding of the present invention. The resin A for inner and outer layers made of resin is continuously supplied from the main extruder 2 and the resin B for intermediate layer such as gas barrier resin is intermittently supplied from the sub-extruder 3 to join in the multilayer die 4. Then, the resin A is melt-extruded from the nozzle 5 provided below the multilayer die 4 so as to enclose the resin B, and the composite molten resin 7 extruded by the cutting means 6 movable in the horizontal direction is used as the intermediate layer. Cut to a predetermined dimension at the non-existing part. The cut composite molten resin lump 8 is conveyed into a female mold 9 of a compression molding apparatus composed of a female mold 9 and a male mold 10 immediately after cutting, sandwiched between jigs. The composite molten resin mass 8 in the female mold 9 is compression-molded by the male mold 10 to form a multilayer preform in which the intermediate layer is sealed with the inner layer and the outer layer.

  FIG. 2 is a cross-sectional view of an example of a multilayer preform among the preforms of the present invention. The multi-layer preform indicated as a whole by 20 consists of a mouth-and-neck part 21, a trunk part 22 and a bottom part 23. In the specific example shown in the figure, the preform is formed by compression molding having no gate portion at the bottom, and the portion excluding the end portion 21a of the mouth and neck portion 21 is the same as the three layers of the inner layer 24, the intermediate layer 25 and the outer layer 26. It has a structure.

(Polyester container)
The polyester container of the present invention can be obtained by stretching the preform.
In the stretch blow molding, the preform of the present invention is heated to a stretching temperature, the preform is stretched in the axial direction, and biaxial stretch blow molding is performed in the circumferential direction to produce a biaxially stretched container.
The preform molding and the stretch blow molding can be applied to a hot parison system in which stretch blow molding is performed without completely cooling the preform, in addition to the cold parison system.
Prior to stretching blow, if necessary, the preform is preheated to an appropriate stretching temperature by means of hot air, an infrared heater, high frequency induction heating or the like. In the case of polyester, the temperature range is 85 to 120 ° C., particularly 95 to 110 ° C.

The preform is supplied into a publicly known stretch blow molding machine, set in a mold, stretched in the axial direction by pushing a stretching rod, and stretched in the circumferential direction by blowing a fluid. In general, the mold temperature is preferably in the range of room temperature to 190 ° C. However, as described later, when heat setting is performed by the one mold method, the mold temperature is preferably set to 120 to 180 ° C.
The draw ratio in the final polyester container is suitably 1.5 to 25 times in terms of area magnification. Among these, the axial draw ratio is 1.2 to 6 times, and the circumferential draw ratio is 1.2 to 4.5. It is preferable to double.

The polyester container of the present invention can be heat-set by a means known per se. The heat setting can be performed by a one-mold method performed in a blow molding die, or can be performed by a two-mold method performed in a heat fixing die separate from the blow molding die. The temperature for heat setting is suitably in the range of 120 to 180 ° C.
As another stretch blow molding method, as illustrated in Japanese Patent No. 29178851 of the present applicant, a preform is subjected to primary blow molding having a size larger than that of a final molded product using a primary blow mold. A two-stage blow molding method may be employed in which the primary blow molded body is heated and shrunk, and then stretch blow molding is performed using a secondary blow mold to obtain a final molded product.

  An example of the multilayer structure of the polyester container of the present invention is shown in FIG. In FIG. 3, the biaxially stretched container generally indicated by 40 has a bottle shape and is composed of a mouth part 41, a body part 42 and a bottom part 43. The body part 42 and the bottom part 43 are composed of an inner layer 44a and an outer layer 44b. It consists of the intermediate | middle layer 45 enclosed in. The mouth portion 41 is formed of only the inner and outer layer resins as in the multilayer preform described above.

[Example 1]
A homopolyethylene terephthalate resin having a melt viscosity of 102 Ns / m ² at a temperature of 265 ° C. and a shear rate of 2000 (1 / sec) is supplied to an extruder hopper and extruded under conditions of a die temperature of 270 ° C. and a resin pressure of 70 kgf / cm ^2. And cut into molten resin mass. When this molten resin mass was set in a compression mold at 20 ° C. and compression molding was performed under the condition of a clamping pressure of 100 kgf / cm ^2, a single layer preform was molded. In addition, the cutter mark was not observed on the molded preform. The obtained preform was heated to a stretching temperature of 110 ° C. and biaxially stretched and blow-molded in a mold at 25 ° C., and a single-layer PET excellent in appearance characteristics having a weight of 25 g and a capacity of 530 ml. Could get a bottle.

[Example 2]
Polyethylene terephthalate resin is supplied to an extruder for inner and outer layers, and metaxylylene adipamide resin (T600 manufactured by Toyobo Co., Ltd.) is supplied to an extruder with a vent for intermediate layer. Except that it was coextruded so as to enclose the amide resin and cut into a molten resin mass, the same molding as in Example 1 was carried out to obtain a two-type three-layer multilayer preform and a bottle having an intermediate layer ratio of 3 wt%. . The drawdown resistance and the transportability during compression molding were good, and neither preform nor bottle cutter marks were observed.

[Example 3]
Except for using a homopolyethylene terephthalate resin having a melt viscosity of 150 Ns / m ² at a temperature of 265 ° C. and a shear rate of 2000 (1 / sec), the same molding as in Example 1 was performed. Obtained. The drawdown resistance and the transportability during compression molding were good, and neither preform nor bottle cutter marks were observed.

[Example 4]
Except for using a homopolyethylene terephthalate resin having a melt viscosity of 195 Ns / m ² at a temperature of 265 ° C. and a shear rate of 2000 (1 / sec), the same molding as in Example 1 was performed, and a single layer preform and bottle were formed. Obtained. The drawdown resistance and the transportability during compression molding were good, and neither preform nor bottle cutter marks were observed.

[Comparative Example 1]
A compression molding was performed in the same manner as in Example 1 except that a homopolyethylene terephthalate resin having a melt viscosity of 90 Ns / m ² at a temperature of 265 ° C. and a shear rate of 2000 (1 / sec) was used. The conveyance was unstable.

[Comparative Example 2]
A single layer preform and bottle were molded in the same manner as in Example 1 except that a homopolyethylene terephthalate resin having a melt viscosity of 210 Ns / m ² at a temperature of 265 ° C. and a shear rate of 2000 (1 / sec) was used. Cutter marks at the time of compression molding remained on the preform and the bottle wall surface.

[Comparative Example 3]
Although compression molding was carried out in the same manner as in Example 2 except that a homopolyethylene terephthalate resin having a melt viscosity of 300 Ns / m ² at a temperature of 265 ° C. and a shear rate of 2000 (1 / sec) was used, it was inferior in formability. A good preform could not be obtained. Cutter marks also remained.

  The results of the above examples and comparative examples are shown in Table 1.

It is a figure which shows an example of the compression molding machine used for shaping | molding of the preform of this invention. It is a figure which shows an example of the preform of this invention. It is a figure which shows an example of the polyester container of this invention.

Claims (4)

A polyester resin for compression molding having a melt viscosity of 100 to 200 Ns / m ² at a temperature of 265 ° C. and a shear rate of 2000 (1 / sec). In the method of supplying a molten resin lump made of polyester resin to a compression molding machine and compression-molding it to produce a preform, the molten resin lump has a temperature of 265 ° C. and a shear rate of 2000 (1 / sec). A method for producing a preform, comprising a polyester resin having a melt viscosity of 100 to 200 Ns / m ² .   A preform manufactured by the preform manufacturing method according to claim 2.   A polyester container, wherein the preform according to claim 3 is stretch-molded.

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