JPS5841182B2 - Method for manufacturing hot-fillable plastic containers - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a biaxially stretched plastic container that can be hot filled, and more particularly to an improvement that enables the production of heat-set two-wheel stretched containers with high productivity and at low cost. Regarding the manufacturing method.

The plastic container obtained by stretching a parison or preform made of saturated polyester resin in the axial direction and expanding it with a fluid in a mold has biaxial molecular orientation, and has transparency and impact resistance. , gas barrier
However, when the contents are hot-filled in order to preserve them in a sterile state, there is a problem of significant shrinkage.

It has been known for a long time that biaxially stretched products of saturated polyester resins are heat treated under tension to prevent shrinkage at high temperatures and improve dimensional stability.

It is also well known that this heat setting technique can be applied to biaxially stretched plastic containers, and all such conventional techniques maintain the mold temperature at a temperature above the hot filling temperature of the contents and stretch and blow. After molding, the plastic container is heat-set by holding it for a predetermined period of time while keeping the internal pressure high for blowing, and then when it is taken out as it is, the container lacks self-retention and deforms, so the mold must be replaced again. Cool to a low temperature and remove the heat-set stretched plastic container.

However, in this known method, the plastic container after stretch molding is held in a heated mold for a predetermined period of time, and the product cannot be taken out until the mold is further cooled. The drawbacks are that the time required for each mold to be occupied is significantly longer, productivity is lower, and equipment costs are higher.

Furthermore, since the mold must be heated and cooled for each cycle of the bottom shape, there is also the drawback that the cost of thermal energy increases.

Thus, if a container can be taken out of the mold during or after heat setting without cooling the mold, the time occupied by the mold per single plastic container can be significantly reduced, increasing productivity. It is possible to improve the efficiency and reduce equipment costs, and it is also possible to save heat energy costs.

The present inventors used a multilayer parison or preform in which the inner layer was made of a saturated polyester resin and the intermediate layer or outer layer was made of a thermoplastic resin having a lower thermal conductivity than the saturated polyester resin, and Alternatively, if a fluid with a temperature of 90°C or higher is used as the fluid to be blown into the preform and the mold surface temperature is maintained below the temperature at which the outermost layer resin has self-retaining properties, the container will be exceptionally cooled within the mold. The biaxially stretched container can be taken out of the mold without the need for additional operations, and the biaxially stretched container can be heat-fixed at the same time as blow molding by leaving the container after being taken out. I found it.

That is, an object of the present invention is to provide a method for manufacturing, with high productivity and low cost, a biaxially stretched multilayer plastic container that can be hot-filled with contents and has excellent flavor retention of the contents. .

Another object of the present invention is to provide a biaxially stretched multilayer plastic container that can be hot filled and that allows the biaxially stretched molded container to be taken out of the mold during or after heat setting without cooling the mold. To provide the manufacturing method.

Still another object of the present invention is to provide a method for manufacturing a biaxially stretched multilayer plastic container that skillfully utilizes the temperature gradient from the inner surface to the outer surface of the biaxially stretched multilayer plastic container for heat setting and self-shape retention of the container. It is in.

According to the present invention, a multilayer parison or preform is manufactured in which the inner layer is made of a saturated polyester resin and the intermediate layer or outer layer is made of a thermoplastic resin having a lower thermal conductivity than the saturated polyester resin, and the multilayer parison is An operation of stretching the preform in the axial direction at a temperature lower than the melting point of the saturated polyester resin and higher than its glass transition point, and holding the multilayer parison or preform in a mold and introducing a fluid into the inside thereof. Blowing and expanding operations are performed simultaneously or in this order, and a fluid with a temperature of 90°C or higher is used as the fluid to be blown into the multilayer parison or preform, and the temperature at which the outermost layer resin has self-shape retention. A method for manufacturing a heat-set biaxially stretched plastic container is provided below, which is characterized by maintaining the mold surface temperature.

As mentioned above, an important feature of the present invention is that a thermoplastic resin having a lower temperature conductivity than a saturated polyester resin, particularly a thermoplastic resin having a temperature conductivity of 3.50 x 10 'm''/hr or less, is used in the intermediate layer or Combined with an inner layer of saturated polyester resin in the form of a multilayer, and used in the form of a multilayer parison or preform for a stretch-blown bottom shape, and this multilayer parison is used in combination with a saturated polyester resin inner layer in the form of a multilayer parison or preform; It is a combination of maintaining the temperature below the temperature at which the resin in the outermost layer has self-retaining properties and stretching and blowing it into a bottom shape.

In this specification, temperature conductivity (α) is a value defined by the following formula, where thermal conductivity is λ, specific heat is C1 density is d; is a value with dimension .

This value relates to the temperature gradient during heat transfer, and the smaller the value, the larger the temperature gradient during heat transfer.

For example, the temperature conductivity of stretched and unstretched saturated polyester resin is 6.40×10′ to 7.80×, respectively.
10'm/hr and 4.90X10-4~5.50
X 10'vl/hr, while the thermal conductivity of polypropylene is 2.50X10'~3.00
X 10 'rrr'/hr, and it can be seen that the saturated polyester resin, especially the stretched one, exhibits a large temperature conductivity.

Thus, for example, a thermoplastic resin whose thermal conductivity is lower than that of a saturated polyester, in particular a thermoplastic resin whose thermal conductivity is 3.50×
When a plastic wall with a multilayer structure, consisting of an intermediate layer of thermoplastic resin of 10' i/hr or less and inner and outer layers of saturated polyester resin, is placed under heat transfer conditions in a certain direction, the heat transfer rate shown in Figure 1 is shown. In the saturated polyester inner layer 1, the temperature gradient is small between the innermost surface 4 and the inner interface 5 of both phase resin layers, while in the low temperature conductive resin intermediate layer 2,
The temperature gradient becomes extremely steep between the inner interface 5 and the outer interface 60, and in the saturated polyester outer layer 3, the temperature gradient becomes smaller again between the interface 6 and the outermost surface 7.

That is, under the heat transfer conditions shown in FIG. 1 where the inside is hot and the outside is cold, the saturated polyester inner layer 1 is maintained at a relatively uniform high temperature, while the saturated polyester outer layer 3 is maintained at a relatively uniform low temperature. It can be seen that as a result, a relatively large temperature difference can be formed between the inner and outer layers.

This applies not only to a three-layer structure but also to a multilayer structure of two layers or four or more layers.

The present invention cleverly exploits this phenomenon for the heat setting of the saturated polyester inner layer and the self-retention necessary for ejecting the container from the mold.

That is, the present invention uses a fluid at a temperature of 90° C. or higher for stretch blow molding of a multilayer plastic parison or preform, so that heat fixation of biaxially oriented saturated polyester proceeds at a relatively high temperature. On the other hand, since the resin constituting the outer layer comes into contact with the mold at the above-mentioned temperature and becomes below its self-shape retention temperature, problems such as deformation of the container can be effectively eliminated even when the resin is taken out from the mold immediately. be done.

Moreover, since heat transfer is effectively blocked between the inner surface of the container and the outer surface of the container, the above-mentioned heat fixation of the inner layer and self-retention of the outer layer proceed fairly quickly. It is recognized that the process continues effectively even if the container is left outside the mold.

In the present invention, the inner layer of the parison or preform is made of saturated polyester because this material has excellent flavor retention properties, and especially the stretched unsaturated polyester has transparency and impact resistance. It is important because it has excellent properties such as hardness, creep resistance, and gas barrier properties.

As the saturated polyester, a polymeric polyester derived from an aromatic dicarboxylic acid and an alkylene glycol, particularly a polyester mainly containing ethylene terephthalate units, is advantageously used.

As the low temperature conductivity thermoplastic resin, for example, etc. can be used.

Of course, in the present invention, the low temperature conductivity resin is not limited to those exemplified above, and this value (α) is 3.50
Any resin can be used as long as it is 10'm/hr or less, and these resins can be used alone,
It can also be used in the form of a blend of two or more types, and also in the form of a blend with other thermoplastic resins, such as adhesion promoter resins.

The multilayer parison or preform may have any layer structure as long as the saturated polyester (A) is the inner layer and the low temperature conductivity resin (B) is the middle layer or outer layer. Thermoplastic resin (q may be used as an outer layer, and an adhesive resin layer 0 may be used between each of these resin layers.
may be interposed.

Suitable examples of layer configurations such as multilayer parisons are as follows.

Examples of the adhesive resin layer include acid- or acid anhydride-modified olefin resins, ionomers, ethylene-acrylic acid ester copolymers, ethylene-vinyl acetate copolymers, urethane resins, and other thermoplastic resins. Examples of the resin include polycarbonate, polyamide, polyethylene, and the like.

The thickness ratio between the saturated polyester resin A and the low temperature conductive material J]mB) is preferably within the following range from the above-mentioned object of the present invention.

Further, when the inner layer (A) and the outer layer (A) are made of saturated polyester, it is preferable that the thickness ratio of the two is within the range of from the viewpoint of balance between heat fixation and self-shape retention.

The parison or preform is molded using multilayer injection molding,
It can be carried out by any means such as multilayer extrusion, multilayer extrusion-pre-blow molding, etc.

Alternatively, the low temperature conductivity resin can be made into a solution or latex, applied to a preformed polyester preform, dried, and further extruded or injected with polyester or other resin as needed. The preform can have two or three layers.

In the present invention, stretch blow molding of the multilayer parison or preform described above involves using the multilayer parison or preform described above, using a blowing fluid of 90°C or higher, and controlling the mold surface temperature to the outermost layer resin. This can be carried out by means known per se, except that the temperature is below the self-shape retention temperature.

For example, prior to stretch blow molding, a multilayer parison or preform is preheated to a temperature lower than the melting point of the saturated polyester resin and higher than its glass transition temperature, and the heated parison or preform is The operation of stretching the multilayer parison or preform in the same direction and the operation of holding the multilayer parison or preform in a mold and inflating it by blowing a fluid into the mold are performed simultaneously or sequentially in this order.

The temperature of the fluid blown into the parison or preform is 90℃
If the temperature exceeds the above, it is difficult to effectively heat set the fluid to withstand hot filling, and it is generally desirable that the temperature of this fluid be 160° C. or lower.

Fluids include hot air, steam, heated nitrogen gas,
Alternatively, a mixture thereof is preferably used.

In this specification, the self-shape retention temperature of the outermost layer resin is
It is defined as the maximum temperature at which the outermost layer resin can maintain the shape of the mold without deforming even under unrestrained conditions.

This self-retention temperature is - for example, approximately 85 DEG C. for saturated polyesters and approximately 135 DEG C. for polypropylene.

Although the mold can be cooled or heated as necessary to maintain the temperature below the mold surface temperature, it is understood that the present invention does not require a cyclic operation of heating and cooling for each molding cycle. It should be.

The heating fluid is blown onto the parison or preform and maintained at high pressure for at least 2 seconds, preferably 5 seconds.
If it is longer than seconds, necessary blow molding, initiation of heat setting, and self-shape retention are effectively performed.

The blowing and holding time of the fluid is preferably 60 seconds or less, particularly 30 seconds or less, from the viewpoint of productivity.

The molecular orientation of the inner layer polyester by stretching and blowing is
Satisfactory results can be obtained by setting the in-plane orientation coefficient (1+m) to 0.3 or more, particularly 0.4 or more.

The invention is illustrated by the following example.

Example 1 The outer layer has a thermal conductivity of 5.04 x 10' m/h and a density x
, 3sy/=, the intermediate layer is made of polyethylene terephthalate (thickness 0.2 mm) with an intrinsic viscosity of 0.7 and a temperature conductivity of 2.
．． 16X 10' = "h, a saponified product of ethylene vinyl acetate (thickness 0.2:3 m) with a density of 1.2 f/-, and the inner layer has a thermal conductivity of 5.04 x lO' m/h and a density of 1.
A three-layer preform made of polyethylene terephthalate (thickness 2.1 mm) with 35P/cIiL and an intrinsic viscosity of 0.7 was heated to a stretch molding temperature of 110°C, and the mold temperature was 7.
The preform was set in a blow mold at 0°C, and while being stretched in the longitudinal direction, high-temperature, high-pressure air (temperature 100°C) was applied.
A biaxially stretched bottle with an internal volume of 100cc was obtained by blowing in the bottle, stretching it in the transverse direction, and holding it for 5 seconds at high temperature and high pressure.

When this container is filled with hot water at 87℃, the shrinkage rate is 0.3.
%, there was no practical problem, and further improvement in gas barrier properties was observed.

Example 2 The outer layer is made of polyethylene terephthalate (thickness 0.2 mvt) with a temperature conductivity of 5.04X10' m/h, a density of 1.351/crrj, and an intrinsic viscosity of 0.7, and the middle layer has a temperature conductivity of 2.59X10'. m/h, density 1.3?
/- vinylidene chloride resin (thickness 0.22 mm), and the inner layer is polyethylene terephthalate (thickness 2.2 mm) with temperature conductivity 5.04 x 10' m/h, density 1.35 P/ffl, and intrinsic viscosity 0.7. A three-layer preform is heated to a stretch forming temperature of 105°C and placed in a blow mold with a mold temperature of 65°C.While stretching the preform in the longitudinal direction, high temperature and high pressure air ( temperature 10
A biaxially stretched bottle with an internal volume of 100cc was obtained by blowing 0° C. into the bottle, stretching it in the transverse direction and holding it for 5 seconds at high temperature and high pressure.

When this bottle is filled with hot water at 85°C, the shrinkage rate is 0.
．． No practical problem at 32%, appearance, strength, gas 7<I
It was a container rich in J. Goya.

Example 3 The outer layer has a thermal conductivity of 2.70×10-' m/h and a density of 1
．． 06 f/critI) Steel o-# resin (thickness 0.1
5mm), and the inner layer has a thermal conductivity of 5.04X10'
m”/h, density 1.35?/art, intrinsic viscosity 0.7
of polyethylene terephthalate (thickness 2.5 mm)
A two-layer preform made of ) was blown in, stretched in the transverse direction, and held at high temperature and high pressure for 5 seconds to obtain a biaxially stretched bottle with an internal volume of 1000 cc.

When this bottle was filled with hot water at 85°C, the shrinkage rate was 0.
At 15%, there is no problem in practical use, both in terms of appearance and strength.
It was comparable to a single polyester container.

Example 4 The outer layer has a thermal conductivity of 2.86 x 10'm"/h
, density 0.9? /- homopolypropylene resin (thickness 0
．． 1), and the inner layer has a thermal conductivity of 5.04X10'm
/h, a two-layer preform made of polyethylene terephthalate (thickness 2.5 urn) with a density of 1.35P/CIfl and an intrinsic viscosity of 0.7 was heated to a stretch molding temperature of 140°C and then blown at a mold temperature of 70°C. A biaxial mold with an inner volume of 1000 cc was set in a mold, and while stretching the preform in the longitudinal direction, high-temperature, high-pressure air (temperature 110°C) was blown into it to stretch it in the transverse direction, and the preform was held at high temperature and high pressure for 5 seconds. A stretched bottle was obtained.

When this bottle is filled with hot water at 90℃, the shrinkage rate is 0.
3%, there were no practical problems, and the transparency of this container was 3.5% in terms of haze value, and its appearance was comparable to that of a single polyester container.

Comparative Example 1 A preform (thickness: 2.6 mm) made of polyethylene terephthalate used for the inner layer of Example 1 was heated to a stretch molding temperature of 95°C and set in a blow mold at room temperature (approximately 20°C). While stretching the preform in the longitudinal direction, high-pressure air at room temperature was blown into the preform to stretch it in the transverse direction to obtain a biaxially stretched bottle with an internal volume of 1000 cc.

When the bottle was filled with hot water at 85°C, the shrinkage rate was 5%, which was a practical problem as a container for filling hot contents.

Comparative Example 2 A preform (thickness: 2.7 mrn) made of polyethylene terephthalate used for the inner layer of Example 1 was heated to a stretch molding temperature of 95°C, set in a blow mold at 100°C, and the preform While stretching in the longitudinal direction, 1
A biaxially stretched bottle with an internal volume of 1000 cc was formed by blowing high-temperature and high-pressure air at 00°C and stretching it in the lateral direction.
The bottle did not have self-retention properties and could not be taken out as a product from the blow mold.

Comparative Example 3 The outer layer has a thermal conductivity of 4.7X10-4=/h and a density of 1.1.
A two-layer preform consisting of 5 g/- nylon 6.6 (0.1 mm thick) and polyethylene terephthalate (2.5 mm thick) used in Example 1 was stretched at a temperature of 160°C. The preform is heated and set in a blow mold with a mold temperature of 60'C, and while stretching the preform in the longitudinal direction, high temperature and high pressure air (temperature 100 °C) is blown in to stretch it in the transverse direction. A biaxially stretched bottle with an internal volume of 1000 cc was obtained by holding it under high pressure for 5 seconds.

When this bottle was filled with hot water at 85°C, the shrinkage rate was 2%, which was a practical problem for a container filled with high-temperature contents.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the temperature gradient of a multilayer plastic wall, where 1 is the inner layer, 2 is the middle layer, 3 is the outer layer, 4 is the innermost layer, and 5 is the inner layer.
6 indicates the inner interface, 6 indicates the outer interface, and 7 indicates the outermost surface.

Claims (1)

[Claims] 1. Produce a multilayer parison or preform in which the inner layer is made of a saturated polyester resin and the intermediate layer or outer layer is made of a thermoplastic resin whose temperature conductivity is lower than that of the saturated polyester resin; An operation of stretching the preform in the axial direction at a temperature lower than the melting point of the saturated polyester resin and higher than its glass transition point, and holding the multilayer parison or preform in a mold and introducing a fluid into the inside thereof. Blowing and expanding operations are performed simultaneously or in this order, and a fluid with a temperature of 90°C or higher is used as the fluid to be blown into the multilayer parison or preform, and the temperature at which the outermost layer resin has self-shape retention. A method for producing a heat-set biaxially stretched plastic container characterized by maintaining the mold surface temperature as follows. 2 The thermoplastic resin of the middle layer or outer layer is 3.5×1o'
2. The method for producing a biaxially stretched plastic container according to claim 1, wherein the biaxially stretched plastic container has a temperature conductivity of not more than m/h. 3. The biaxially oriented plastic container according to claim 1, characterized in that the thickness ratio of the polyester resin of the inner layer to the thermoplastic resin of the intermediate layer or outer layer is 1:1 to 200:1. manufacturing method. 4. Claims characterized in that the polyester resin of the inner layer is polyethylene terephthalate, and the thermoplastic resin of the intermediate layer or outer layer is mainly composed of polypropylene, ethylene-vinyl alcohol copolymer, polyvinylidene chloride, or polystyrene. A method for producing a biaxially stretched plastic container according to item 1.