CN1064892C

CN1064892C - Method for making a molded plastic container

Info

Publication number: CN1064892C
Application number: CN961902477A
Authority: CN
Inventors: 大库尔特H·鲁普曼
Original assignee: SR KURT H RUPPMAN
Current assignee: SR KURT H RUPPMAN
Priority date: 1995-03-27
Filing date: 1996-03-07
Publication date: 2001-04-25
Anticipated expiration: 2016-03-07
Also published as: CA2191093A1; EP0760737A4; CA2191093C; JPH10501481A; CN1148827A; MX9605868A; AU5420196A; WO1996030190A1; NZ306047A; BR9605942A; AU704903B2; EP0760737A1

Abstract

A polyethylene terephthalate (PET) preform (11) having a capped cylindrical body (13), a threaded top and collared neck (19) is preheated to soften the PET. The preform (11) is placed in a split mold whose walls are heated to a temperature between 150 DEG C and 177 DEG C. A stretch rod (35), inserted through the top of the preform (11), stretches the preform (11) axially until the preform is the length of the final product (49). The preform (11) is expanded using compressed ambient air, and is molded against the walls (27, 29) of the mold (26). The air is vented, and dry nitrogen at a temperature below -50 DEG C is injected into the molded preform (47) to purge and cool the molded preform (47) while maintaining pressure of at least 520 kPag. The molded preform (47) is held against the mold (36) to anneal the inner and outer surfaces of the molded preform (47). The nitrogen supply is shut off and the final product (49) is released from the mold (26).

Description

The manufacture method of improved thermoplastic containers

The application is March 27 nineteen ninety-five application, and application number is the part continuation application of 8/412,535 U. S. application, now abandons, and this is disclosed in this in conjunction with as a reference.

Background of the present invention

Field of the present invention

The present invention relates to the manufacture method of the thermoplastic of modification, particularly relate to by the PETG (PET) or the similar manufacture method of the mold container of the biaxial orientation made of thermoplastic polymer, heat setting, this container has the thermomechanical property and the diffusion of improvement.

Description of related art

Organic thermoplastic such as PET are because its transparency, impact resistance and two-dimensional stability are widely used in the manufacturing mold container.Yet carbon dioxide is with certain speed diffusion or penetrate PET, thereby has limited the storage life of soda.The product that the result did not sell in several weeks becomes " insipid " and have to throw away.This is all the more so concerning the beer of carbonic acid content sensitivity to its taste.

There is a kind of known method to be used to produce the energy heated fluid injection and non-shrinking container with heat setting.In this method, amorphous PET is blown in the mold heat, is heated to above the glass transition temperature of PET and keeps certain hour in this temperature, slowly cooling then.Heating makes the PET of suitable deal by the amorphous crystalline state that is transformed into.Unbodied or non-crystalline PET is softening and contraction under the normally used processing temperature of food industry.Crystalline PET is an opaque and white, is fragility rather than flexibility.Yet, to compare with amorphous PET, crystalline PET is can be under higher temperature strong and keep its shape and do not shrink or softening.The commerce of heat setting process is implemented normally complicated, need control its heating and cooling speed according to many measures, and each production cycle needs more time than cold blowing method.

US4039641 grants Collins, has disclosed a kind of method of using die wall to be heated to 140 ℃ split cavity production heat setting plastic containers.Preferred embodiment use the liquid cools container, another kind of embodiment uses the nitrogen of the about room temperature of certain pressure to avoid the contraction of container when mold cools down to 40 ℃.When heat setting took place, container was close to hot-die and was kept 25 seconds under pressure, followed (its) mold cools down to 40 ℃.The whole production time is several times of conventional cold molding production cycle.

US4385089 grants people such as Bonnebat, has also informed a kind of method of heat setting bottle.There is not the used equipment of this method of public use.On the contrary, Bonnebat has emphasized that temperature with moulding material remains on minimum biaxial orientation temperature and exceeds between 30～50 ℃ of this temperature.The biaxial orientation temperature is defined as and can obtains draftability and can make the well distributed minimum possibility temperature of material.For PET, Bonnebat sets the highest possible temperature at 120 ℃.This temperature drops on industrial already used before beginning thermal finalization in the temperature range of preheating parison or preform.Bonnebat also requires longer cycle time simultaneously, and is main because with mould there be 5～20 second time of contact.

The someone finds out the problem that way solves cycle length and slough the moulding material contraction from mold heat.These methods are mostly used a kind of cooling fluid, liquid or gas.The temperature of cooling fluid is in a little higher than room temperature and be low to moderate variation between 0 ℃.

US4883631 grants Ajmera, has disclosed a kind of method of heat setting molded plastic container.In the method, liquid carbon dioxide or liquid nitrogen gasify under a little higher than atmospheric pressure, are used for purge vessel after container is close to mould.Still continue for some time at container demoulding afterflush.The plunger rod structure comprises complicated network channel and aperture, and it is extremely important that the distribution of cooling fluid spray orifice obtains consistent performance to entire container.Though this method is to want to reduce the whole cycle, the Agmera method is still much longer than the cold blowing method production cycle.

Known heat setting method has several shortcomings.First shortcoming be the highest hot charging of reality of this container to fill out temperature be about 90 ℃, so food that this container can not the splendid attire boiling.Second shortcoming is the thermomechanical property of the improvement that obtains by known heat setting method most of disappearance the in 72 hours after heat-set container.Therefore this container must use after heat setting immediately, otherwise in stowing operation unacceptable contraction can take place, and takes place as the cold blowing container.Also having a shortcoming is that conventional heat setting meeting causes that container keeps a large amount of reductions of gas and ability water conservation.The manufacturer has to make one's options between hot injectability and good gas and steam reserve capability.Most of beer will pass through heat sterilization before tinning, the container that therefore needs the energy hot charging to fill out.Because carbon dioxide permeates the relative two-forty of conventional heat setting PET bottle, beer is not packed immediately.The relatively poor water-retaining property of conventional heat setting bottle, how some fruit juice of injection are brought down below the amount of indicating on the label so that the quality that guarantees product in the container is unlikely because seeing through the gasification of bottle in bottle to force the fruit drink producer.

The present invention's general introduction

Therefore one of purpose of the present invention is to make biaxial orientation, heat setting molded plastic container, and this container has maintenance gas ability and the water-retaining property that can compare with cold blowing method institute container made at least.Another purpose is to make ability 100 ℃ of fillings temperature and the molded plastic container that not have obviously contraction or loss of strength.The 3rd purpose is that the required All Time of this method of enforcement is short as far as possible, so that productivity ratio is high as far as possible.A further object of the invention is to use the equipment similar to existing system plastic containers method to make the method for plastic containers.Last purpose is that this method adopts minimal steps.

These purposes are by the preform of a preheating being put into die wall through heated mold, in preform, insert the plunger that has stretching rod, make preform be stretched to the length of the cavity of mould formation, by the gas that pressurizes preform is expanded to and is adjacent to mould, make the preform internal pressure keep the scheduled time, be lower than-50 ℃ pressure with temperature then and be at least the purging with nitrogen gas of 520kPag and cool off molding preform inside, then final products are taken out from hot-die.The All Time that PET contacts with the hot-die wall influences the crystallization content of PET final products.Cold nitrogen makes the molding preform enough cold, in order to avoid stick on the hot-die wall during final products demoulding.Final products can bear nearly 100 ℃ hot charging and fill out temperature, and linear shrinkage is less than 1%.This hot charging ability of filling out keeps constant substantially at least in 90 days after heat setting.In addition, have suitable with the cold blowing container at least gas and the steam loss ability of preventing by the final products of the method manufacturing of claim.Because the step of this method and implement similar in this method device therefor and the known molding technology is transformed existing production line only minimum investment of need and new equipment.At last, the whole production cycle equates with the cold molding method, and wants much shorter than the conventional heat setting method cycle, thereby has guaranteed high production rate.

In conjunction with the accompanying drawing of the preferred embodiment for the present invention, of the present invention these will show by following description with other purpose, advantage and characteristic.

Brief description of drawings

Fig. 1 is the cut-away section view of device therefor in the preceding molded plastic container method constructed in accordance of stretched plastic preform.

Fig. 2 is the side plan view of the typical preform that uses in this method.

Fig. 3 to Fig. 5 is the view similar to Fig. 1 of different phase in the display packing.

The explanation of preferred embodiment

Will know that in the following discussion accompanying drawing and the description of implementing the equipment of this method only are to think functionally to describe equipment, rather than it is defined in any specific configuration.

With reference to the accompanying drawings, particularly Fig. 2 has shown typical preform 11.Preform 11 is made by PET or polystyrene, and other thermoplastic polymer with biaxial orientation molecular structure also can use.Preform 11 has cylinder body 13 and sphenoid part 17 of a band dome 15.Sphenoid part 17 links to each other with neck 19 with the axle collar 23 by buffering ring 21.

At first, according to known systems, preform 11 in a stove (not shown) preheating so that it is softening.Chuck with two jaws 25 is caught the axle collar 23 then, and two pawls of chuck 25 can be caught the axle collar 23 tightly and provide support the plane of buffering ring 21.Chuck with two jaws 25 moves to next step with preform 11, and here preform 11 is placed in the split cavity 26 of being made up of two-

half die

27 and 29 of

opening.Half module

27 and 29 is incorporated in around the preform 11 then.

Half module

27 and 29 is heated to 150～177 ℃ of preferred temperature by the recycle oil in the pipeline in 27 and 29 31 then, and other heating means described in the prior art also can be used.The mould temperature can be at 130～232 ℃.Higher temperature generally makes thermo setting time reduce.

In next step, plunger 33 inserts in the preform neck 19 with hermetic seal preform 11, as shown in Figure 1.Form hermetic seals with the stretching bar 35 of hole 38 close-fitting band round ends 37 in the plunger 33.Plunger 33 and stretching bar 35 all have the passage (not shown) to pressurize and decompression to preform 11 with gas.Hole 36 in the stretching bar 35 is discharged into preform 11 with gas.Hole 36 diameters are 1/16 inch (1.6mm), and having overall diameter is 45 ° of bore holes of 1/8 inch (3.2mm), and (12～25mm) along stretching bar axially-aligned at a distance of half inch to one inch.Bore hole opening 36 is used as nozzle so that gas balance ground is full of preform 11.Actuator 39 is connected on stretching bar 35 and the plunger 33, enters plunger 33 to drive stretching bar 35.

Actuator 39 pushed away plunger with stretching bar 35, and contacted with skull 15.Along with bar 35 continues its motion, preform 11 extends the bottom that touches the cavity 40 that is formed by die

wall

27 and 29 until skull 15, as shown in Figure 3.The inside stop mechanism (not shown) of actuator 39 stops 35 further motion.This extensional motion makes the thermoplastic biaxial orientation.The gas of container and steam retention property depend primarily on this biaxial orientation.

At next step, supply valve 41 is opened, and the about compressed air person who lives in exile preform 11 of room temperature makes preform 11 expansions and press

half module

27 and 29 models, as shown in Figure 4.Air should not contain steam, oil and foreign particle.The thermomechanical property decline in time that it is believed that the container appearance of producing with known heat setting method is mainly relevant with the steam of PET absorption in the conventional heat setting process.Other dry oil free gas such as nitrogen also can use.This step can be come the pre-blowing container by logical people's low-pressure air (not shown), then blows people's pressure-air (not shown) and finishes blowing and the pre-type body 47 of pressure moulding and realize.The open hour altogether of supply valve 41 are about 0.3 second to about 0.8 second, just close then.Though this time can increase to change thermo setting time.And then breather valve 43 is opened with discharged air.

In logical people's pressure-air or after a while nitrogen supply valve 45 is opened.The pressure of the check valve 46 on the nitrogen supply line 42 is arranged to be lower than the pressure of described pressure-air.This can be avoided flowing through nitrogen supply line 42 at this step nitrogen.Preferably using check valve 46, because it has simplified design (not needing extra timer etc.) and stoped air people's nitrogen supply line that flows backwards once in a while, but is not necessary.

When air bleeding valve 43 is opened, when the pressure in the molding preform 47 was brought down below the set point of check valve 46, the next step in the method began.At this moment, nitrogen is immediately by nitrogen supply line 42 person who lives in exile's molding preforms 47.Nitrogen flooding is the air in the molding preform 47 to the greatest extent, cooling molding preform and to 47 pressurizes of molding preform.The nitrogen supply pressure is 690kPag (100psig) at least, preferred supply pressure is that (300～450psig), the pressure in this step in the molding preform 47 must remain on 520kPag (75psig) and fill out and steam/gas barrier properties to realize the hot charging that improves 2070～3100kPag at least.

Nitrogen provides by the gasification liquid nitrogen and through air throttle, and the air throttle (not shown) is positioned at the upstream of supply valve 45.When nitrogen passed through air valve, it thoroughly gasified, and produced the nitrogen of certain pressure and deep cooling, and generally its temperature is between-209 ℃ to-100 ℃.Be cooled to-50 ℃ nitrogen, the nitrogen that preferably is lower than-100 ℃ also can use.Necessary, gas supply line 42 must suitably be isolated, to guarantee to be in required temperature range when nitrogen enters molding preform 47.

Air bleeding valve 43 keeps opening about 1.3～1.5 seconds in this step.Nitrogen valve 45 was closed about 0.1～0.2 second before this step contact.Under given heat setting degree, the open hour altogether of nitrogen valve 45 become inverse variation with the die wall temperature.Open hour altogether long under the uniform temperature will cause bigger heat setting.It is open that air bleeding valve 43 keeps in next step.

In this step with purging with nitrogen gas molding preform 47 inside of pressurization to influence plastics, the PET molecular structure hardening that contacts with nitrogen has increased the density of PET.Nitrogen also infilter PET and with molding preform 47 in the PET bonding.Simultaneously, the nitrogen of deep cooling cools off PET rapidly, thereby makes PET annealing.The container crystallization that produces that combines of these mechanism changes the little of more conventional heat setting method, fills out temperature yet can bear higher hot charging.In addition, container is without any the gas that container took place and the forfeiture of gas barrier properties of conventional heat setting method production.Also remove the undesirable volatile component that in the heat setting process, produces with the container of purging with nitrogen gas.These components can be brought offending pleasant impression to the content of container.

In last step of the present invention,

half module

27 and 29 is opened, and plunger and relevant apparatus are removed, and chuck 25 moves to final products 49 the local (not shown) of factory.Breather valve 43 begins just to keep open-minded from previous step, therefore before plunger 33 is removed final products is decompressed to atmospheric pressure.It is very crucial to the time delay of opening between the mould 26 to close nitrogen valve 45.Cooling stopped when nitrogen valve 45 was closed, and the pressure that makes final products 49 be close to mould 26 also sharply descends.Therefore, if the time that final products 49 contact with mould 26 surpasses 0.3 second, container is with overheated and contraction.

To the method for heat setting described in the prior art, often require cooling die 26 in the taking-up process, to stick on the mould to avoid final products 49.If use present method, this is not necessary.Because cold nitrogen makes final products 49 enough cold, thereby avoid adhering to, even die

wall

27 and 29 keeps heating.Therefore

half module

27 and 29 can remain at heat-set temperature, has reduced the thermal cycling fatigue of mould 26 and has shortened the production cycle greatly.

Use the bottle bottom of known heat setting method production, the zone and the neighboring area thereof of stretching bar 35 contacts often to suffer stress cracking.Crystallization is excessive owing to be heated too much for this regional PET.Because the conduction heat that passes to another cycle from one-period heats stretching rod 35 repeatedly, followed by stretching rod not exclusively cooling again, overheated once connecing once taken place.Use this method, avoided the heat history and the corresponding stress cracking of stretching rod owing to following two reasons: the first, greatly shorten than conventional method the heat time heating time of stretching rod, and this makes the stretching rod minimizing of being heated.The second, the nitrogen of cooling preform 47 inside also cools off stretching rod 35 simultaneously fully.

Use gasification shape liquid nitrogen also to make the defective in the final products 49 reduce.Because steam, dirty particle or oil content are very little in the liquid nitrogen, content is then more in the compressed air, thereby has avoided the defective that caused by these pollutants.As previously mentioned, can think the nitrogen of being supplied not moisture be a factor of producing the container can after 72 hours, still keep its thermomechanical property.

The following examples have illustrated the method for claim and the performance of the improvement of the container produced according to the method for claim.

Embodiment 1

Be used for making 12 ounces of (355ml) bottle 21g preforms with design, make one group of 200 test chamber, the amorphous PET inherent viscosity of used commerical grade is 0.76, and density is 1.34g/ml.To each test chamber, preform is preheating to about 195 of temperature (90 ℃), and puts into the mould that remains on 285 (141 ℃).The preform drawn uses air to add compression swelling 0.2 second then under the pressure of 90psig (620kPag), then pressurizes 0.9 second at 300psig (2070kPag) with air, and the nitrogen check valve is set in 290psig (2000kPag).Air bleeding valve is opened, and-200 ℃ gasification nitrogen blows into the molding preform.About 1.2 seconds of purging with nitrogen gas container then stopped die sinking then 0.2 second.The whole time of preform in mould is no more than 3 seconds.

As a comparison, adopt the cold blowing method to prepare one group of 200 control container.Contrast containers preform and test chamber is used identical and be molded as identical shaped.Sample to container and experiment container all is to select immediately after production, and test its thermomechanical property and hot charging filled out performance under several temperature.Hot charging is filled out performance test and carry out repeated test with different samples after being produced 30 days.

Table 1 has been sketched the preceding result who tested in 30 days after production.The admission space data are adjusted to 68 °F (20 ℃).

Table 1

The average contrast piece of test block average test part is average

185/85 ℃-0.753-1.255-20.905 canful Volume Changes in (the 1st day) (the 30th day) (first day), %195/91 ℃-2.479-2.478-27.553 canful Volume Changes, %185/85 ℃-0.013-0.115-4.726 height change, %195/91 ℃-0.228-0.208-6.236 height change, %

A test container 230 (110 ℃) deep fats of having packed into.The high shrinkage rate of container is lower than 1%.Hot charging is filled out performance not significant change after 30 days.In fact, test is presented at 195 (91 ℃) its hot chargings and fills out performance and slightly improve.

In addition, the sample of container and test chamber all being sent to Plastic Technologies, Inc. (PTI) tests in the laboratory of Holland, Ohio.These laboratory tests its engineering properties, hot charging fill out performance, degree of crystallinity, density and surpass and produce carbon dioxide barrier properties after 90 days.Carbon dioxide stops that test carries out on a magnetron CIV pervasion test device.Container is injected into the carbon dioxide of 3.8 volume level and is retained in 73 °F (23 ℃).Table 2 has been sketched this test result.PTI has carried out 10 all carbon dioxide to some bottles and has kept experiment, and the result sketches sublist 3.

Table 2

Comparative sample test specimen degree of crystallinity (sidewall), % 26.5 33.8 degree of crystallinity (bottom), % 20.8 30.9 density (sidewall), g/ml 1.3647 1.3734 density (bottom), 1.3579 1.3699185 volume change of g/ml, %-7.11-0.055195 volume change, %-18.31-0.16210 volume change, %-34.97-0.25185 height change, %-5.14-0.266195 height change, %-6.32-0.423210 height change, %-7.96-0.550CO ₂Permeability, ml (STP)/sky 4.7 4.7

Table 3

The initial CO of comparative sample test specimen ₂, volume several 4.7 4.705 all CO ₂, volume several 3.788 all CO ₂, volume several 3.739 all CO ₂, volume several 3.4310 all CO ₂, volume several 3.23 3.23

The container contents that the crystalline PET content of test chamber is produced than conventional heat setting method is low.Container needs 38% or higher crystalline PET content that conventional heat setting method is produced are filled out performance to guarantee good hot charging.Although crystalline PET content is low, fill out performance than the hot charging that the container with known method production has improvement with the test chamber that the claim method is produced.

Embodiment 2

When preparing the container of embodiment 1, prepare group's test chamber and to container.Container adopt to be set the 19 gram preforms that are used for producing 12 ounces of (355ml) bottles and is made.The amorphous PET inherent viscosity of using of commerical grade is 0.76, and density is 1.34g/ml.The method for making of container is identical with embodiment's 1.This group container is also by its CO of PTI laboratory tests ₂Retention property.When beginning, comparative sample injects 4.36 volume CO ₂, 8 Zhou Houshang have 3.09 volumes, inject 4.36 volume CO when experiment container begins ₂, 8 Zhou Houshang have 2.93 volumes.

Another embodiment (not shown) relates to extrusion die and blows over journey.In this embodiment, " preform " one got into the tubular plastic spare of mould, as polypropylene or polyethylene.Plastics are expressed into the length of final products, and the openend of preform is by the extruding sealing of the base of mould.Therefore there are not stretching rod 35 or stretching rod 35 that preform 11 is stretched to this step of product final lengths.Except that these differences, this method is with to have stated method identical.Preform is blown into mould, carries out of short duration pre-blowing with low-pressure air earlier, with pressure-air the molding preform is pressurizeed then.Container deep cooling N ₂At least purifying under 520kPag (75psig) pressure, then decompression and final products are taken out from mould.This process can be used to produce the extrudate of other shape except that container.

An advantage extruding blow molding method of claim is to accept the ink printing of outer surface with the polyethylene can of the method manufacturing of claim.Polyethylene extrusion container with the known method manufacturing need carry out the naked light post processing so that printing ink can stick on the frosting to container outer surface.

The method of claim is applicable to produces any slim thermoplastic that improves, and includes but not limited to sheet and slim membranaceous plastics.The slim average thickness that is defined as described herein reaches 1/4 cun (6.4mm).In this course, the one side of thermoplastic contacts with heated wall, as hot conveyer belt.The another side of material can be with the deep cooling gas pressurized of having stated.The gained plastics will have the thermomechanical property of improvement.Its gas and steam barrier properties will can obviously not reduce from the numeral before the method that adopts claim in addition.

From as can be seen aforementioned and other advantage that equipment is intrinsic together, the present invention can be by abundant remodeling to reach all targets proposed above and result.

Be appreciated that some characteristics and time combination are of great use, and do not need to use with reference to other characteristic and time combination.These had been considered and in the protection domain of claim.

Owing to can make many possibility embodiments and not break away from its scope at the present invention, be appreciated that content will be interpreted as descriptive explanation rather than restrictive shown in all the elements described herein and the accompanying drawing.

Claims

1. the preform of being made by thermoplastic polymer is made the method for thermoplastic containers, comprises the steps:

A) the preheating preform makes plastics softening;

B) the preform insertion is split in the mould, this die wall of splitting mould is heated to 130～232 ℃ of temperature ranges;

C) plunger is inserted in the preform,

D) in preform, inject first gas, so that preform expansion and be moulded to the mould die wall, and keep the pressure of molding preform at the fixed time;

E) first gas is discharged from the molding preform;

F) in the exhaust process, in the molding preform, inject second gas being higher than under the 690kPa pressure, this second gas enters preform inside with the temperature that is lower than-50 ℃, and with this second gas blow-washing and cool off the preform scheduled time, the molding preform is transformed into final products during this period; With

G) final products are taken out from mould.

2. make the method for thermoplastic containers as claim 1, the die wall of wherein splitting mould in the step (b) is heated to 150～177 ℃ temperature range.

3. make the method for thermoplastic containers as claim 1, wherein in the molding preform, inject second gas under the 2070kPa pressure being higher than in the step (f).

4. make the method for thermoplastic containers as claim 1, wherein second gas enters preform inside with the temperature that is lower than-100 ℃ in the step (f).

5. make the method for thermoplastic containers as claim 1, wherein first gas in the step (d) is chosen from compressed air and compressed nitrogen.

6. make the method for thermoplastic containers according to claim 1, wherein second gas in the step (f) is nitrogen.

7. make the method for thermoplastic containers as claim 6, wherein said nitrogen makes liquid nitrogen vaporization supply with through air throttle.

8. make the method for thermoplastic containers as claim 1, also comprise the stretching rod in the hole that is applied in the plunger, this rod can slide into plunger and therewith form hermetic seal.

9. make the method for thermoplastic containers as claim 8, at claim 1 step (c)) and (d) between also comprise with excellent axial tension preform to final products length.

10. make the method for thermoplastic containers as claim 1, the material of wherein making preform is selected from PETG, polyethylene, polypropylene, polystyrene.