WO2015154849A1 - Process for moulding and co-moulding ultra-low density expanded tpu with static injection machines and product obtained with this process - Google Patents

Process for moulding and co-moulding ultra-low density expanded tpu with static injection machines and product obtained with this process Download PDF

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Publication number
WO2015154849A1
WO2015154849A1 PCT/EP2015/000619 EP2015000619W WO2015154849A1 WO 2015154849 A1 WO2015154849 A1 WO 2015154849A1 EP 2015000619 W EP2015000619 W EP 2015000619W WO 2015154849 A1 WO2015154849 A1 WO 2015154849A1
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WO
WIPO (PCT)
Prior art keywords
injection
moulding
expanded
mould
compact
Prior art date
Application number
PCT/EP2015/000619
Other languages
French (fr)
Inventor
Leonardo PROCACCINI
Federico PROCACCINI
Original Assignee
Co.Bo. S.R.L.
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Publication date
Application filed by Co.Bo. S.R.L. filed Critical Co.Bo. S.R.L.
Publication of WO2015154849A1 publication Critical patent/WO2015154849A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
    • B29C45/0001—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor characterised by the choice of material
    • A—HUMAN NECESSITIES
    • A43—FOOTWEAR
    • A43B—CHARACTERISTIC FEATURES OF FOOTWEAR; PARTS OF FOOTWEAR
    • A43B13/00—Soles; Sole-and-heel integral units
    • A43B13/02—Soles; Sole-and-heel integral units characterised by the material
    • A43B13/12—Soles with several layers of different materials
    • A43B13/122—Soles with several layers of different materials characterised by the outsole or external layer
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
    • B29C44/02—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles for articles of definite length, i.e. discrete articles
    • B29C44/04—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles for articles of definite length, i.e. discrete articles consisting of at least two parts of chemically or physically different materials, e.g. having different densities
    • B29C44/0461—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles for articles of definite length, i.e. discrete articles consisting of at least two parts of chemically or physically different materials, e.g. having different densities by having different chemical compositions in different places, e.g. having different concentrations of foaming agent, feeding one composition after the other
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
    • B29C44/34—Auxiliary operations
    • B29C44/36—Feeding the material to be shaped
    • B29C44/38—Feeding the material to be shaped into a closed space, i.e. to make articles of definite length
    • B29C44/42—Feeding the material to be shaped into a closed space, i.e. to make articles of definite length using pressure difference, e.g. by injection or by vacuum
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29D—PRODUCING PARTICULAR ARTICLES FROM PLASTICS OR FROM SUBSTANCES IN A PLASTIC STATE
    • B29D35/00—Producing footwear
    • B29D35/0009—Producing footwear by injection moulding; Apparatus therefor
    • B29D35/0018—Moulds
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29D—PRODUCING PARTICULAR ARTICLES FROM PLASTICS OR FROM SUBSTANCES IN A PLASTIC STATE
    • B29D35/00—Producing footwear
    • B29D35/12—Producing parts thereof, e.g. soles, heels, uppers, by a moulding technique
    • B29D35/14—Multilayered parts
    • B29D35/142—Soles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
    • B29C44/34—Auxiliary operations
    • B29C44/36—Feeding the material to be shaped
    • B29C44/38—Feeding the material to be shaped into a closed space, i.e. to make articles of definite length
    • B29C44/42—Feeding the material to be shaped into a closed space, i.e. to make articles of definite length using pressure difference, e.g. by injection or by vacuum
    • B29C44/424—Details of machines
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
    • B29K2021/00—Use of unspecified rubbers as moulding material
    • B29K2021/003—Thermoplastic elastomers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
    • B29K2075/00—Use of PU, i.e. polyureas or polyurethanes or derivatives thereof, as moulding material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
    • B29K2101/00—Use of unspecified macromolecular compounds as moulding material
    • B29K2101/12—Thermoplastic materials
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
    • B29K2995/00—Properties of moulding materials, reinforcements, fillers, preformed parts or moulds
    • B29K2995/0037—Other properties
    • B29K2995/0063—Density
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29L—INDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES
    • B29L2031/00—Other particular articles
    • B29L2031/48—Wearing apparel
    • B29L2031/50—Footwear, e.g. shoes or parts thereof
    • B29L2031/504—Soles

Definitions

  • the present invention relates to the footwear sector and more specifically concerns a process for moulding and co-moulding ultra-low density expanded TPU (0.25 - 0.45 g/cm ) with static injection machines that use injection nozzles, moulds and operating conditions of pressure, flow rate, cooling time and temperature of the moulds that are different from those necessary in the state of the art for moulding a compact TPU, as well as the product obtained with this process.
  • a compact material 2.5-3.5 mm thick, is injected into a mould having a temperature of about 60-80°C for a cooling time of about 60-70 sec.
  • processes for moulding compact polymeric materials such as for example TPU, TR, SBS, that are moulded using static injection machines having injection nozzles with an outlet hole of smaller diameter than the diameter of the barrel of the reciprocating screw.
  • the inlet hole of a nozzle has a diameter of 12 mm, whereas the outlet hole of the injection nozzle has a diameter of 3 mm, so as to obtain a constriction that produces the necessary and sufficient injection pressure of the order of 50-80 bar which is variable depending on the design of the sole to be moulded, on the material to be moulded and on its viscosity, since lower viscosity polymeric materials will be moulded at lower flow rate and lower pressure; but higher viscosity polymeric materials will be moulded at higher flow rate and higher pressure.
  • first layer consists of a low-density polyurethane having a rigidity of between 45 and 50 degrees
  • the second layer consists of a high density polyurethane having a rigidity of between 65 and 70 degrees.
  • the products resulting from the molding processes described above should be processed and assembled with other parts to get finished soles because, through these processes, it is not possible to obtain soles of different materials without having to subsequently glue them; furthermore, the polyurethanes therein used are characterized by having a low, but not ultra-low, density. Disclosure of the Invention
  • Fig. 1 shows an axonometric and section view of a known injection nozzle, used in processes for moulding compact polymeric materials and having an inlet hole 12 mm in diameter and an outlet hole 3 mm in diameter;
  • FIG. 2 shows an axonometric and section view of an injection nozzle (1) according to the present invention, used in processes for moulding expanded polymeric materials and having an inlet hole (1A) 12 mm in diameter and an outlet hole (IB) 6 mm in diameter, which is double the diameter of the outlet hole of the injection nozzle for compact materials shown in Fig. 1.
  • the 6 mm diameter of the outlet hole (IB) inside the nozzle (1) is constant for a section that is between 10 and 15 mm long and in any case long enough to avoid a drastic constriction;
  • FIG. 3 shows an axonometric view of a back plate (2) of a mould having runners (3) and (4) in which the sprue flows and a vent valve (5) located on the outer side;
  • FIG. 4 shows a view from above of an intermediate plate (6) where the upper part of the product is made, having:
  • the figure also shows a section view of the nozzle (1) to highlight the fact that runners (7) and (8) are characterized by a diameter equal to that of the outlet hole (IB) of the injection nozzle (1).
  • - Fig. 5 shows an axonometric view of the correct superimposition between the back plate (2) and the intermediate plate (6) so as to form the cover of the mould of the expanded material.
  • FIG. 6 shows an axonometric view of a shoe outsole that is one of the products that can be obtained with this moulding process, in which:
  • FIG. 1 - shown with (A) is a shoe outsole obtained with a process for bi- injection moulding of an expanded material (16) with an expanded material (16);
  • (B) is a shoe outsole obtained with a process for bi- injection moulding of a compact material (17) with an expanded material (16);
  • (C) is a shoe outsole obtained with a process for mono- injection moulding of an expanded material (16).
  • the present invention concerns a process for moulding and co-moulding ultra-low density expanded TPU (0.25 - 0.45 g/cm 3 ) with static injection machines that use injection nozzles (1) characterized by an outlet hole (IB) with diameter of 6 mm that is double the diameter of the outlet hole of known nozzles used for moulding TPU and other compact materials to prevent the constriction of a conventional nozzle, normally used for injecting compact materials, from causing pre-compaction of the expanded material, and increasing its density.
  • IB outlet hole
  • the present invention also concerns a process for moulding and co-moulding ultra-low density expanded TPU (0.25 - 0.45 g/cm ) using suitably modified moulds, with runners for the flow of low density expanded TPU characterized by a diameter of 6 mm, equal to that of the outlet hole (IB) of the modified injection nozzle.
  • the process for moulding a material such as ultra-low density expanded TPU (0.25 - 0.45 g/cm 3 ) that is the subject of the present patent application does not take place "by cushion” as in the known processes for moulding compact materials, but "by volume”; namely, the volume parameter is set on the static injection machine so as to inject the exact volume quantity of material necessary for filling the shape of the mould, so preventing compaction with the consequent increase in its density.
  • the mould consists of two parts or, alternatively, of three parts depending on the moulding method that one wants to use: mono-injection or bi-injection.
  • mono-injection a cavity and a cover used for moulding low density expanded material are used; in the case of bi-injection moulding, a cavity, a cover of known construction for moulding compact material and a cover used for moulding expanded material are used.
  • the cover of the mould consists of:
  • the central runner (7) will be used in the case of mono-injection moulding, while the side runner (8) will be used in the case of bi-injection moulding.
  • the unused runner in either type of moulding is closed with a barrier obtained by static screwing-in of a metal grub screw.
  • Both low density expanded TPU runners (7) and (8) are characterized by a diameter equal to that of the outlet hole (IB) of the injection nozzle (1) of the present invention.
  • the through slot (9) situated in the central part of the intermediate plate (6) is in line with the central runner (7).
  • All the moving parts of the mould must have gaskets, as a vacuum is activated when they are closed to remove the gases and air present in the mould during injection.
  • the vacuum system is obtained by means of channels (not shown) situated at the back of the intermediate plate (6) that are connected to the cores (12) and (13), that is, the parts embedded in the intermediate plate (6).
  • the embedded cores (12) and (13) act as a large vent, and extract the air or gas that is released through very narrow slits (14) and (15) situated around the outer edge of the shape of the object to be moulded.
  • the air is conveyed through the slits (14) and (15) into the cores (12) and (13) that, through holes (not shown), convey it into channels (not shown) situated at the back of the intermediate plate (6), which in turn are connected with a hole (not shown) to a channel (not shown) inside the back plate (2) that will take the air or gas outside through the vent valve (5) located on the outer side of the back plate (2).
  • the stages of the process for mono-injection moulding of an ultra-low density expanded TPU are the following:
  • the material is loaded into the reciprocating screw of the injection machine where the polymerization stage starts due to the parameters that are set on the machine in terms of temperature of the order of 110- 130°C.
  • the temperature of the mould is about 20-50°C.
  • the vacuum pump is started to remove all the gases or air present in the mould to prevent the creation of empty spaces in the outsole to be moulded that would prevent the material from flowing and cause holes to be created.
  • the material cools for a cooling time that varies between 100 and 130 sec. as the thickness (of the order of about 7-20 mm) of the ultra-low density expanded TPU varies.
  • the static injection machine opens the mould to extract the moulded item.
  • the pressures and flow rates are set with high values to optimize the flowing of the material and the filling of the shape in the mould.
  • the volume of the material to be injected varies depending on the product to be moulded, and this means a variation in the cooling time of the item since the larger the volume of the product to be moulded the longer the cooling time, and an incorrect cooling time is the cause of abnormal swelling and expansion of the injected product.
  • stage 2 In the mono-injection moulding variant with loading of inserts, before stage 2, there is a further stage that consists of manual loading of semi-finished products over which the polymeric material is then injected so as to incorporate the insert in the moulded shape of the outsole of the shoe (process of over-injection of the insert) in order to complete the injected product.
  • semi-finished product refers to a fabric that is chemically similar to the polymeric material to be moulded, a moulded polymeric material, a chemically similar material that does not need pre-treatment, or a material that needs pre-treatment such as, for example, halogenation or mastic application.
  • the process described above regards the mono-injection moulding of an ultra- low density expanded material; however, with the same mould described above, in a further variant, it can also be decided to mould using bi-injection moulding:
  • the stages relevant to the bi-injection moulding process are the following:
  • the expanded and compact materials are loaded into two different reciprocating screws where the polymerization stage starts due to the parameters that are set on the machine in terms of temperature, which is different for the expanded material and for the compact material.
  • the volume, flow rate and pressure parameters for the compact material are set on the machine and the machine is given the OK to inject; the first cover (known) of the mould is closed and the compact material is injected into the runner that then ends up in the shape of the object to be moulded.
  • the machine rotates the head where the covers of the two materials are positioned and closes on the cavity above the previously injected compact material.
  • the volume, flow rate and pressure parameters for the expanded material are set on the machine and these are read by the machine when the OK to inject is given; the second cover of the mould is closed and the expanded material is injected into the side runner (8).
  • the injection machine opens the mould to extract the moulded item.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Chemical & Material Sciences (AREA)
  • Materials Engineering (AREA)
  • Injection Moulding Of Plastics Or The Like (AREA)

Abstract

The present invention relates to the footwear sector and more specifically concerns a process for moulding and co-moulding ultra-low density expanded 5 TPU (0.25 - 0.45 g/cm3) with static injection machines that use injection nozzles, moulds and operating conditions of pressure, flow rate, cooling time and temperature of the moulds that are different from those necessary in the state of the art for moulding a compact TPU, as well as the product obtained with this process.

Description

Process for moulding and co-moulding ultra-low density expanded TPU with static injection machines and product obtained with this process.
Description
Field of the Invention
The present invention relates to the footwear sector and more specifically concerns a process for moulding and co-moulding ultra-low density expanded TPU (0.25 - 0.45 g/cm ) with static injection machines that use injection nozzles, moulds and operating conditions of pressure, flow rate, cooling time and temperature of the moulds that are different from those necessary in the state of the art for moulding a compact TPU, as well as the product obtained with this process.
Background of the Invention
Currently, a compact material, 2.5-3.5 mm thick, is injected into a mould having a temperature of about 60-80°C for a cooling time of about 60-70 sec. Known in the state of the art are processes for moulding compact polymeric materials, such as for example TPU, TR, SBS, that are moulded using static injection machines having injection nozzles with an outlet hole of smaller diameter than the diameter of the barrel of the reciprocating screw. On average, the inlet hole of a nozzle has a diameter of 12 mm, whereas the outlet hole of the injection nozzle has a diameter of 3 mm, so as to obtain a constriction that produces the necessary and sufficient injection pressure of the order of 50-80 bar which is variable depending on the design of the sole to be moulded, on the material to be moulded and on its viscosity, since lower viscosity polymeric materials will be moulded at lower flow rate and lower pressure; but higher viscosity polymeric materials will be moulded at higher flow rate and higher pressure.
This moulding method is not applicable to ultra-low density expanded polymeric materials (0.25 - 0.45 g/cm3) since the constriction of the nozzle
l would produce an inevitable pre-compacting of the material near the injection nozzle, thereby preventing correct injection into the mould and making it impossible to make the outsole.
Known in the state of the art are the moulding conditions of compact polymeric materials whose average flow rate is of the order of 15-60 g/second and is variable depending on the design of the product to be moulded, on the material to be moulded and on its viscosity.
In the state of the art, also used in the process for moulding compact materials is the "cushion" method, so called because the injection conditions are set so that, inside the reciprocating screw, a permanent cushion is generated consisting of a portion of material that, by remaining in the reciprocating screw as the injection stage ends, serves to compact the material and create further injection pressure, in order to prevent creation of shrinkage of the material injected into the mould. This moulding method cannot be applied to ultra-low density expanded polymeric materials since the cushion method would compact the material to the maximum, thereby increasing its density and generating dangerous overpressures.
In the state of the art, molding processes disclosed in the following patent applications are known:
- US 2010/019088 Al which discloses a method for molding a polyurethane having a density of 150-350 g/1.
- WO 201 1/050389 Al which discloses a sole for footwear wherein the first layer consists of a low-density polyurethane having a rigidity of between 45 and 50 degrees, while the second layer consists of a high density polyurethane having a rigidity of between 65 and 70 degrees.
- US5674439 which discloses a system and a molding apparatus for producing articles of polymeric material.
The products resulting from the molding processes described above should be processed and assembled with other parts to get finished soles because, through these processes, it is not possible to obtain soles of different materials without having to subsequently glue them; furthermore, the polyurethanes therein used are characterized by having a low, but not ultra-low, density. Disclosure of the Invention
It is an object of the present invention to mould an ultra-low density expanded TPU by means of a static injection machine having a suitably modified injection nozzle in order to obtain correct injection of the expanded material, and prevent the constriction of a conventional nozzle, normally used for injecting compact materials, from causing its compaction and increasing its density.
It is another object of the present invention to mould an ultra-low density expanded TPU (0.25 - 0.45 g/cm ) with a process with moulding pressures, moulding flow rates, moulding temperatures and cooling times that are different from those known in the state of the art and normally used in the process of injection moulding TPU and other compact materials.
It is another object of the present invention to mould an ultra-low density expanded TPU by means of a static injection machine having a different nozzle from the known ones that injects material into the mould with temperatures that are much lower than those used up to now for injecting a compact TPU without causing the mould to break.
Finally, it is an object of the present invention to mould an ultra-low density expanded TPU using a mould at a temperature between 20 and 50°C, depending on the type of product, so as to obtain a reduction in the cycle times and guarantee correct expansion of the material in the mould.
Further features and advantages of the invention will be apparent from the description of a preferred, but not exclusive, embodiment of the process for moulding and co-moulding ultra-low density expanded TPU (0.25 - 0.45 g/cm ) that is the subject of the present patent application, illustrated by way of non-limiting example in the drawing units in which:
- Fig. 1 shows an axonometric and section view of a known injection nozzle, used in processes for moulding compact polymeric materials and having an inlet hole 12 mm in diameter and an outlet hole 3 mm in diameter;
- Fig. 2 shows an axonometric and section view of an injection nozzle (1) according to the present invention, used in processes for moulding expanded polymeric materials and having an inlet hole (1A) 12 mm in diameter and an outlet hole (IB) 6 mm in diameter, which is double the diameter of the outlet hole of the injection nozzle for compact materials shown in Fig. 1. The 6 mm diameter of the outlet hole (IB) inside the nozzle (1) is constant for a section that is between 10 and 15 mm long and in any case long enough to avoid a drastic constriction;
- Fig. 3 shows an axonometric view of a back plate (2) of a mould having runners (3) and (4) in which the sprue flows and a vent valve (5) located on the outer side;
- Fig. 4 shows a view from above of an intermediate plate (6) where the upper part of the product is made, having:
- a central runner (7);
- a side runner (8);
- a central through slot (9) that connects runners (7) and (8) with runners (3) and (4) made in the back plate;
- two slots (10) and (11) located in the centre of shape of the object to be moulded;
- two embedded, screwed-on "core" parts (12) and (13) that usually, since depending on requirements the manufactured product can be made upside down, reproduce the upper part of the product, having very narrow slits (14) and (15) situated around the outer edge of the shape of the object to be moulded.
The figure also shows a section view of the nozzle (1) to highlight the fact that runners (7) and (8) are characterized by a diameter equal to that of the outlet hole (IB) of the injection nozzle (1). - Fig. 5 shows an axonometric view of the correct superimposition between the back plate (2) and the intermediate plate (6) so as to form the cover of the mould of the expanded material.
- Fig. 6 shows an axonometric view of a shoe outsole that is one of the products that can be obtained with this moulding process, in which:
- shown with (A) is a shoe outsole obtained with a process for bi- injection moulding of an expanded material (16) with an expanded material (16);
- shown with (B) is a shoe outsole obtained with a process for bi- injection moulding of a compact material (17) with an expanded material (16);
- shown with (C) is a shoe outsole obtained with a process for mono- injection moulding of an expanded material (16).
Detailed description of the Invention
According to a preferred - but non-limiting - embodiment, the present invention concerns a process for moulding and co-moulding ultra-low density expanded TPU (0.25 - 0.45 g/cm3) with static injection machines that use injection nozzles (1) characterized by an outlet hole (IB) with diameter of 6 mm that is double the diameter of the outlet hole of known nozzles used for moulding TPU and other compact materials to prevent the constriction of a conventional nozzle, normally used for injecting compact materials, from causing pre-compaction of the expanded material, and increasing its density. The process for moulding and co-moulding ultra-low density expanded TPU (0.25 - 0.45 g/cm ), which is the subject of the present patent application, is characterized by moulding pressures, moulding flow rates, moulding temperatures and cooling times, as will be more clearly specified in the description below and in any case different from those known in the state of the art and normally used in the process of injection moulding TPU and other compact materials. The present invention also concerns a process for moulding and co-moulding ultra-low density expanded TPU (0.25 - 0.45 g/cm ) using suitably modified moulds, with runners for the flow of low density expanded TPU characterized by a diameter of 6 mm, equal to that of the outlet hole (IB) of the modified injection nozzle.
The process that is the subject of the present patent application concerns mono-injection moulding, mono-injection with loading of inserts, this last consisting of manual loading of semi-finished products into the mould, over which the polymeric material is then injected so as to incorporate the insert in the moulded shape of the outsole of the shoe (process of over-injection of the insert).
The process for moulding a material such as ultra-low density expanded TPU (0.25 - 0.45 g/cm3) that is the subject of the present patent application does not take place "by cushion" as in the known processes for moulding compact materials, but "by volume"; namely, the volume parameter is set on the static injection machine so as to inject the exact volume quantity of material necessary for filling the shape of the mould, so preventing compaction with the consequent increase in its density.
The mould consists of two parts or, alternatively, of three parts depending on the moulding method that one wants to use: mono-injection or bi-injection. In the case of mono-injection, a cavity and a cover used for moulding low density expanded material are used; in the case of bi-injection moulding, a cavity, a cover of known construction for moulding compact material and a cover used for moulding expanded material are used.
When expanded material is moulded, the cover of the mould consists of:
- a back plate (2) having runners (3) and (4) into which the sprue flows (left-over material that flows along the runners);
- an intermediate plate (6), where the upper part of the moulded product is made, that has the following: - a central runner (7) or, alternatively, a side runner (8) for injecting the ultra-low density expanded material. The central runner (7) will be used in the case of mono-injection moulding, while the side runner (8) will be used in the case of bi-injection moulding. The unused runner in either type of moulding is closed with a barrier obtained by static screwing-in of a metal grub screw. Both low density expanded TPU runners (7) and (8) are characterized by a diameter equal to that of the outlet hole (IB) of the injection nozzle (1) of the present invention.
- Embedded, screwed-on parts called "core" (12) and (13) that usually reproduce the upper part of the product.
In the central part of the intermediate plate (6), there is a through slot (9) that connects runners (7) and (8) made in the intermediate plate (6) with runners (3) and (4) made in the back plate (2). In this slot (9) runs the sprue that ends up in the back plate (2) of the mould, goes through the runners (3) and (4) situated to the left and to the right of the central slot (9) and orthogonal to the direction of the first runner (7) to then go back into another two slots (10) and (11) located in the centre of the shape of the object to be filled on the intermediate plate (6).
The through slot (9) situated in the central part of the intermediate plate (6) is in line with the central runner (7).
All the moving parts of the mould must have gaskets, as a vacuum is activated when they are closed to remove the gases and air present in the mould during injection.
The vacuum system is obtained by means of channels (not shown) situated at the back of the intermediate plate (6) that are connected to the cores (12) and (13), that is, the parts embedded in the intermediate plate (6). The embedded cores (12) and (13) act as a large vent, and extract the air or gas that is released through very narrow slits (14) and (15) situated around the outer edge of the shape of the object to be moulded. The air is conveyed through the slits (14) and (15) into the cores (12) and (13) that, through holes (not shown), convey it into channels (not shown) situated at the back of the intermediate plate (6), which in turn are connected with a hole (not shown) to a channel (not shown) inside the back plate (2) that will take the air or gas outside through the vent valve (5) located on the outer side of the back plate (2). Once the mould is closed, it becomes hermetic; whereas, when the head of the injection machine is open, the springs keep the two parts separate to make it easier to extract the sprue.
The stages of the process for mono-injection moulding of an ultra-low density expanded TPU are the following:
1. The material is loaded into the reciprocating screw of the injection machine where the polymerization stage starts due to the parameters that are set on the machine in terms of temperature of the order of 110- 130°C.
2. The following parameters are set on the machine:
- volume, which varies depending on the geometry of the outsole to be moulded;
- flow rate of about 90-99 g/second;
- pressure of the order of 150-160 bar;
and the material is injected into the runner (7) of the mould, which will pour into the slot (9) located in the central part of the intermediate plate (6) and in line with runner (7), go along two orthogonal runners (3) and (4) located in the back plate (2) and then flow back through another two slots (10) and (11) located in the centre of the shape to be filled. The temperature of the mould is about 20-50°C.
3. During the injection stage, the vacuum pump is started to remove all the gases or air present in the mould to prevent the creation of empty spaces in the outsole to be moulded that would prevent the material from flowing and cause holes to be created. 4. The material cools for a cooling time that varies between 100 and 130 sec. as the thickness (of the order of about 7-20 mm) of the ultra-low density expanded TPU varies.
5. Once the cooling stage has ended, the static injection machine opens the mould to extract the moulded item.
The pressures and flow rates are set with high values to optimize the flowing of the material and the filling of the shape in the mould.
The volume of the material to be injected, as also mentioned above, varies depending on the product to be moulded, and this means a variation in the cooling time of the item since the larger the volume of the product to be moulded the longer the cooling time, and an incorrect cooling time is the cause of abnormal swelling and expansion of the injected product.
In the mono-injection moulding variant with loading of inserts, before stage 2, there is a further stage that consists of manual loading of semi-finished products over which the polymeric material is then injected so as to incorporate the insert in the moulded shape of the outsole of the shoe (process of over-injection of the insert) in order to complete the injected product.
The term semi-finished product refers to a fabric that is chemically similar to the polymeric material to be moulded, a moulded polymeric material, a chemically similar material that does not need pre-treatment, or a material that needs pre-treatment such as, for example, halogenation or mastic application. The process described above regards the mono-injection moulding of an ultra- low density expanded material; however, with the same mould described above, in a further variant, it can also be decided to mould using bi-injection moulding:
1. expanded material→ expanded material
2. compact material→ expanded material.
The stages relevant to the bi-injection moulding process are the following:
1. The expanded and compact materials are loaded into two different reciprocating screws where the polymerization stage starts due to the parameters that are set on the machine in terms of temperature, which is different for the expanded material and for the compact material.
2. The volume, flow rate and pressure parameters for the compact material are set on the machine and the machine is given the OK to inject; the first cover (known) of the mould is closed and the compact material is injected into the runner that then ends up in the shape of the object to be moulded.
3. Once the compact material cooling stage has ended, the mould is opened.
4. The machine rotates the head where the covers of the two materials are positioned and closes on the cavity above the previously injected compact material.
5. Before starting the moulding process, the volume, flow rate and pressure parameters for the expanded material are set on the machine and these are read by the machine when the OK to inject is given; the second cover of the mould is closed and the expanded material is injected into the side runner (8).
6. During injection of the expanded material, the vacuum pump is started, which is necessary to remove all the gases or air present in the mould.
7. There is a wait for the cooling time of the product in the mould that then opens.
8. Once the cooling stage has ended, the injection machine opens the mould to extract the moulded item.
As in the mono-injection moulding variant with loading of inserts, in the bi- injection process with loading of inserts, before stage 2, there is also a further stage that consists of manual loading of semi-finished products over which the polymeric material is then injected so as to incorporate the insert in the moulded shape of the outsole of the shoe (process of over-injection of the insert) in order to complete the finished product. The materials and dimensions of the invention as described above, illustrated in the accompanying drawings and claimed below, can be of any kind according to requirements. Moreover, all the details can be replaced with other technically equivalent ones without for this reason straying from the protective scope of the present patent application.

Claims

1. Process for mono-injection moulding of an expanded TPU having a density of between 0.25 and 0.45 g/cm3 and/or bi-injection moulding of an expanded TPU having a density of between 0.25 and 0.45 g/cm3 and of a compact material with static injection machines characterized in that it uses injection nozzles (1) having an inlet hole (1A) 12 mm in diameter and an outlet hole (IB) 6 mm in diameter, which is constant inside the injection nozzle (1) for a section that is between 10 and 15 mm long.
2. Process for mono-injection moulding of an expanded TPU having a density of between 0.25 and 0.45 g/cm according to claim 1 characterized by the following stages:
- loading of the material into the reciprocating screw of the injection machine;
- setting on the machine of temperature parameters of the order of 110-130°C;
- stage of polymerization of the material due to the above-mentioned temperature;
- setting on the machine of the following parameters:
- volume, which is variable depending on the geometry of the outsole to be moulded;
- flow rate of about 90-99 g/second;
- pressure of the order of 150-160 bar;
- injection of the material into a runner (7), which will pour into a slot (9) located in the central part of an intermediate plate (6) and in line with the runner (7), go along two orthogonal runners (3) and (4) located in a back plate (2) and then flow back through another two slots (10) and (11) located in the centre of a shape to be filled. The temperature of the mould is about 20-50°C. - starting of the vacuum pump during injection that removes all the gases or air present in the mould to prevent the creation of empty spaces in the outsole to be moulded that would prevent the material from flowing and cause holes to be created;
- cooling of the material for a cooling time that varies between 100 and 130 sec. according to variation in the thickness of the expanded TPU.
- opening of the mould of the static injection machine;
- extraction of the moulded item.
3. Process for bi-injection moulding of an expanded TPU having a density of between 0.25 and 0.45 g/cm and of a compact material according to claim 1 characterized by the following stages:
loading of the expanded and compact materials into two different reciprocating screws;
- setting on the machine of different temperature parameters for the expanded material and for the compact material;
stage of polymerization of the materials due to the above-mentioned temperature parameters;
setting on the machine of the volume, flow rate and pressure parameters for the known compact material;
closing of a first known cover of the mould;
injection of the compact material into the runner that then ends up in the shape of the object to be moulded;
compact material cooling stage;
- opening of the mould;
rotation of the head of the machine;
setting on the machine of the volume, flow rate and pressure parameters for the expanded material;
closing of the cover for the expanded material on the cavity containing the previously injected compact material; injection of the expanded material into a side runner (8);
starting of the vacuum pump during injection of the expanded material;
cooling of the expanded material;
opening of the mould of the static injection machine;
extraction of the moulded item.
4. Bi-injection moulding process according to claim 3, characterized in that it moulds, according to a further embodiment, two different expanded materials.
5. Moulding process according to the previous claims in which the cover of the mould of the expanded material is characterized in that it consists of:
- a back plate (2) having runners (3) and (4) in which the sprue flows;
- an intermediate plate (6), where the upper part of the moulded product is made, that has:
- a central runner (7) or, alternatively, a side runner (8) for injecting the expanded material, with a diameter equal to that of the outlet hole (IB) of the injection nozzle (1);
- embedded, screwed-on parts called "core" (12) and (13) that reproduce the upper part of the product.
6. Moulding process according to the previous claims in which the through slot (9) located in the central part of the intermediate plate (6) connects runners (7) and (8) made in the intermediate plate (6) with runners (3) and (4) made in the back plate (2).
7. Product obtained with the moulding processes for mono-injection and/or bi-injection according to the previous claims characterised in that it is a shoe outsole consisting entirely of an expanded material (16) or two different expanded materials (16) or even an expanded material (16) and a compact material (17).
PCT/EP2015/000619 2014-04-07 2015-03-20 Process for moulding and co-moulding ultra-low density expanded tpu with static injection machines and product obtained with this process WO2015154849A1 (en)

Applications Claiming Priority (2)

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ITAN2014A000057 2014-04-07

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SU503730A1 (en) * 1974-01-21 1976-02-25 Московский Институт Химического Машиностроения The mechanism of plasticization injection molding machine
US5674439A (en) * 1993-12-30 1997-10-07 Kona Corporation System and apparatus for injection molding articles of amorphous polyethylene terephthalate and similar materials
US20100190880A1 (en) * 2007-10-02 2010-07-29 Basf Se. Low-density polyurethane foams and use thereof in shoe soles
WO2011050389A1 (en) * 2009-11-02 2011-05-05 Andrea Bisaz Orthotic footwear

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SU503730A1 (en) * 1974-01-21 1976-02-25 Московский Институт Химического Машиностроения The mechanism of plasticization injection molding machine
US5674439A (en) * 1993-12-30 1997-10-07 Kona Corporation System and apparatus for injection molding articles of amorphous polyethylene terephthalate and similar materials
US20100190880A1 (en) * 2007-10-02 2010-07-29 Basf Se. Low-density polyurethane foams and use thereof in shoe soles
WO2011050389A1 (en) * 2009-11-02 2011-05-05 Andrea Bisaz Orthotic footwear

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