GB2132133A - Heat-sealable oriented polymer film - Google Patents

Heat-sealable oriented polymer film Download PDF

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Publication number
GB2132133A
GB2132133A GB08236148A GB8236148A GB2132133A GB 2132133 A GB2132133 A GB 2132133A GB 08236148 A GB08236148 A GB 08236148A GB 8236148 A GB8236148 A GB 8236148A GB 2132133 A GB2132133 A GB 2132133A
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United Kingdom
Prior art keywords
film
butene
copolymer
ethylene
heat
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Withdrawn
Application number
GB08236148A
Inventor
Johannes Hendricus La Choufoer
Petrus Joannes Kok
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Shell Internationale Research Maatschappij BV
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Shell Internationale Research Maatschappij BV
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Priority to GB08236148A priority Critical patent/GB2132133A/en
Publication of GB2132133A publication Critical patent/GB2132133A/en
Withdrawn legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/32—Layered products comprising a layer of synthetic resin comprising polyolefins
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/06—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material
    • B32B27/08—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
    • C08J5/18—Manufacture of films or sheets
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J7/00—Chemical treatment or coating of shaped articles made of macromolecular substances
    • C08J7/04—Coating
    • C08J7/0427—Coating with only one layer of a composition containing a polymer binder
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J7/00—Chemical treatment or coating of shaped articles made of macromolecular substances
    • C08J7/04—Coating
    • C08J7/052—Forming heat-sealable coatings
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2270/00—Resin or rubber layer containing a blend of at least two different polymers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2307/00—Properties of the layers or laminate
    • B32B2307/50—Properties of the layers or laminate having particular mechanical properties
    • B32B2307/514—Oriented
    • B32B2307/518—Oriented bi-axially
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2323/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
    • C08J2323/02—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers not modified by chemical after treatment
    • C08J2323/10—Homopolymers or copolymers of propene
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2423/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers

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  • Chemical & Material Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Medicinal Chemistry (AREA)
  • Polymers & Plastics (AREA)
  • Organic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Shaping By String And By Release Of Stress In Plastics And The Like (AREA)
  • Laminated Bodies (AREA)

Abstract

A process for preparing oriented film in which a film comprising a substrate layer of a propylene homopolymer or copolymer and on at least one surface of said film a layer comprising a blend of 10 to 40% wt of a propylene homopolymer having a M.I. of 5.0 to 10.0 g/10 min and a degree of crystallinity of at least 45% and 60 to 90% wt of a butene-1/ethylene copolymer, the ethylene content in thereof being from 0.2 to 9% mol, this copolymer having a M.I. of 0.4 to 5.0 g/10 min and a degree of crystallinity of at least 35%, is stretched at a temperature above the melting point of the butene-1/ethylene copolymer and the stretched film is subjected to a temperature treatment for a time sufficient to ensure the conversion of the butene-1/ethylene copolymer from the molten state into the I' crystalline state.

Description

SPECIFICATION Heat-sealable oriented polymer film The present invention is concerned with a process for preparing oriented polymer film, particularly biaxially oriented polypropylene film.
For packaging applications oriented polymer film should have good heat-sealing properties. These can be realized by providing the film on at least one of its surfaces with a special coating comprising a polymer having a lower melting point than the polymer of the substrate film. Examples of such low melting polymers are butene-l/propylene copolymers (UKP 1,452,424), butene-1/ethylene copolymers (EP 0,001,490), and butene-1/octene or butene-llhexene copolymers (UKP 1,582,186). Polymeric blends have also been proposed, cf. UKP 1,495,577, which is i.a. concerned with heat-sealing coatings comprising a blend of a propylene/ethylene copolymer with an ethylene content of 0.25 to 5%wt and a butene-1/propylene copolymer, with a propylene content above 80%wt.Although these prior art references suggest that heat-sealing would be possible at temperatures from 100to upwards, none of these references provide adequate data to show that one can achieve satisfactory heat-seal strength at heat-sealing temperatures in the range of 100 to 115"C when employing modern high-speed packaging equipment.
Butene-1/ethylene copolymers with an ethylene content of less than 10% mol have a crystalline melting point in the fairly narrow range of 123 to 1 28"C. In the solid, crystalline state four different crystalline modifications can be distinguished, viz. the Ill modification, the I', II and I modification. The transition temperatures at which upon heating one modification passes into the other are respectively about 90 C, 104"C and 117"C, upon further increasing the temperature the I-modification reaches eventually the crystalline melting point. The ease at which the formation of the various modifications and the transitions thereof take place is increased by incorporating a minor amount of a crystalline polypropylene into the butene-1/ethylene copolymer.
The orientation of heat-sealable polypropylene films by stretching is normally effected at temperatures in the range of 145 to 1600C, i.e. at temperatures above the crystalline melting point of the butene-1 ethylene copolymer. In commercial practice, the stretched film, upon leaving the stretching equipment, is exposed to ambient temperature which effects a slow cooling of the film. Upon such slow cooling, the copolymer crystallizes to form the II modification.Whilst it would in principle be possible to achieve good heat sealing of the film so produced at temperatures in the order of 105 to 1 C, the instability of II modification unfortunately results in the disadvantage that the good heat-sealing properties are completely lost when, in accordance with customary practice, the stretched film is wound-up on reels for storage and further handling at a later stage.
The present invention aims at the heat-seal temperature of oriented polypropylene film to be effectively reduced to temperatures in the order of 85 to 95"C. Thereto, the invention provides a process for preparing an oriented film comprising a substrate layer of a homopolymer or copolymer of propylene and on at least one of the surfaces of said film a layer comprising a blend of 10 to 40%wt of a propylene homopolymer havng a M.l. of 5.0 to 10.0 9/10 min and a degree of crystallinity of at least 45% and 60 to 90%wit of a copolymer of butene-1 and ethylene having an ethylene content of from 0.2 to 9% mol, a M.l. of 0.4 to 5.0 g/10 min and a degree of crystallinity of at least 35%, is stretched at a temperature above the melting point of the butene-1/ethylene copolymer and the stretched film is subjected to a temperature treatment for a time sufficient to ensure the conversion of the butene-llethylene copolymer from the molten state into the I' crystalline state.
Suitable polymers forming the substrate film are propylene homopolymers and propylene copolymers comprising less than 30%wt, preferably less than 10%wt, of another alpha-olefin, e.g. butene-1 or butene-2, but more preferably ethylene. The copolymers may be random or block copolymers and the polymer forming the substrate film may comprise the usual additives, e.g. colouring agents, nucleating agents, thermo-stabilizers, antioxidants, fillers and U.V. absorbers.
The specified degree of crystallinity is determined in accordance with Differential Scanning Calorometric Analysis, employing extruded polymer nibs which are directly obtained from the (co)polymerization plant.
The Melt Index of the polymer is determined in accordance with ASTM-1 238 at 230;C for the propylene polymer and 190"C for the butene-l/ethylene copolymer.
Whilst the process of this invention is of particular interest for the production of co-extruded heat-sealable film, other techniques for producing multi-layered film may be employed as well, such as lamination of two or three extruded films, extrusion coating, and emulsion coating. The film may be oriented by stretching in the machine direction or in the transverse direction, or, more preferably, in both directions which is the case for biaxially oriented film. In the latter process the transverse stretching will normally be applied next to stretching in the machine direction, which is of particular interest as to the required obtaining of stretched film wherein the butene-Ilethylene copolymer is present in the molten state.Therefore, the first (lengthwise) stretching will normally be carried out at temperatures of from 120 to 135C and the second (transverse) stretching at higher temperatures, preferably from 150 to 165 & .
In between extrusion and stretching the film may be subjected to chill-roll cooling or water-bath quenching but this is not of critical importance for obtaining the benefits of this invention. However, since in the majority of the commercial film stretching lines chill-roll cooling is common practice, this will therefore be the preferred mode of operation.
Normally the stretched substrate film will have a thickness of from 10 to 80 microns, that of the copolymer coating will usually be from 1 to 6 microns. Corona treatment may be employed to improve the printability and other properties of the oriented film.
Particularly suitable butene-1/ethylene copolymers for the coating layer are those having an ethylene content of from 0.5 to 5% mol. The butene-l/ethylene copolymers are random copolymers and their degree of crystallinity is determined as set out hereinabove. The preferred blending ratio for producing the coating layer is 70 to 85%wt of butene-l/ethylene copolymer and 15 to 30%wt of propylene homopolymer. The coating layer is applied to at least that surface of the film which is subjected to sealing. The other surface of the film may be non-coated, coated with the same composition as employed in this invention or with another copolymer composition, e.g. a random ethylene-propylene copolymer comprising from 1 to 6% ethylene. In the latter case one obtains heat-sealed films with outstanding haze properties.
Propylene homopolymers and butene-l/ethylene copolymers having the required degree of crystallinity are commercially available. They can be prepared by conventional (co)polymerization methods employing Ziegler/Natta coordination catalysts.
When the film leaves the stretching equipment it is of essential importance that the butene-l/ethylene copolymer is still in the molten state and not in the I or II crystalline modification, otherwise the advantage of a stable, low heat-sealing temperature is not obtained. The film is then subjected to a temperature treatment for a time which is short enough to ensure formation of the butene-l/ethylene copolymer in the I' crystalline modification. To this end the film may be passed through an annealing chamber which is kept at temperature of 60 to 105"C, provided the circulation of gaseous medium, e.g. air, in this chamber is such as to ensure that the temperature of the film is lowered fast enough to achieve the desired formation of the I' modification.This annealing may improve the heat-set properties of the film. It is however preferred to separate the heat-setting operation from the operation in which the I' modification is formed. To this end the film is subjected to a forced cooling operation upon leaving the stretching equipment, e.g. by blowing cooled air with a temperature of 10 to + 1 20C onto the film, or, which is more convenient, by contacting the film with a chill-roll which is kept at an internal temperature of at most 60"C. Instead of chill-roll quenching, it is also possible to employ quenching in a water-bath or to spray cold cooling liquid, e.g. water, onto the film.
Heat-setting of the film may then be carried out either before or after the quenching operation. When effecting a preceding heat-setting operation it is important to keep the butene-l/ethylene copolymer in the molten state during heat-setting and when effecting a subsequent heat-setting operation it is important to maintain the I' modification of the butene-l/ethylene copolymer. This sets certain temperature restrictions for the possible heat-setting operations: for a preceding operation the temperature should not be reduced to a value below 135"C and for a subsequent heat-setting operation the temperature of the film should not be increased to a value above 125"C.
Example I Oriented polypropylene film was manufactured employing a commercial coextrusionlstretching production iine having a final linear film transport speed of 100 m/min. Upon leaving the extrusion orifice the flat film was cast on a chill-roll which was operated on an internal cooling temperature of 20"C. The film had a core-thickness of 1.4 mm and was provided on each side with a coating with a thickness of 0.05 mm.
Stretching in the longitudinal direction was effected at a ratio of 5:1 and a temperature of 125"C, the subsequent stretching in the transverse direction was effected at a ratio of 10:1 and a temperature of 155"C.
The core of the film was prepared from a commercial polypropylene grade with a Melt-lndex(M.l.) of 3 dg/min. For the coating layers a number of different compositions was investigated.
For film A1, a blend was employed comprising 25%wt of a polypropylene grade having a crystallinity of 50% and a M.l. of 8 dg/min and 75%wt of a commercial butene-l/ethylene copolymer with an ethylene content of 2.8% mol, a M.l. of 1 dg/min and a crystallinity of 40%. Film A2, was made using a coating composition comprising 25%wt of the same propylene homopolymer as employed for film A1, and 75%wt of a commercial butene-l/ethylene copolymer having an ethylene content of 1.4% mol, a crystallinity of 45% and a M.l. of4dg/min.
For comparison films B to F were produced: Film B, using a coating composition comprising 75%wt of the butene-1 copolymer of film A1, and 25%wt of a commercial ethylene-propylene block copolymer, with an ethylene content of 7%wt, a crystallinity of 41% and a M.I. of 3 dg/min; Film C using a coating composition comprising 75%wt of the same butene-1 copolymer employed in film A1 and 25%wt of a random ethylene-propylene copolymer with an ethylene content of 3.8%wt, a crystallinity of 35% and a M.l. of 7 dg/min;Film D using a coating composition of 75%wt of the same butene-11 ethylene copolymer employed in Film A1 and 25%wt of a commercial propylene homopolymer having a crystallinity of 50% and a M.l. of 3.5 dgimin; Film E using a coating composition of 75%wt of the same butene-l/ethylene copolymer employed in Film A1 and 25%wt of a commercial propylene homopolymer having a crystallinity of 50% and a M.l. of 2 dg/min; Film F using a coating comprising 100%wt of a butene-1 homopolymer having a crystallinity of 50% and M.I. of 8 dg/min.
At a distance of 0.5 m from the exit of the transverse stenter a chill-roll was placed which was operated at an internal cooling temperature of 20"C and which could be raised and lowered to vary the contact-angle of the film. In the lower position the contact-angle was 0 , hence there was no contact and thus no quenching of the film, in the higher position the contact angle was 1200. The chill-roll had an external diameter of 0.3 m.
The film was wound-up on a reel which was placed at a distance of 2 m from the exit of the transverse stenter.
Heat-seal threshold temperatures were determined using the method disclosed in U.K. P 1,452,424 taking as the threshold value the lowest heat-seal temperature yielding a heat-seal strength of 300 g/25 mm.
The results are presented in Table I wherein HSTT' stands for the heat-seal threshold temperature of non-quenched film.
TABLE I Film HSTT, "C HSTT, "C A1 85 105 A2 87 110 B 95 115 C 110 118 D 99 115 E 110 118 F 115 121 Example II Flat uncoated film was cast on a quench roll using the polymeric blend of 25%wt propylene homopolymer and 75%wt butene-l/ethylene copolymer described in Example I for producing film A1.
This film was subjected to differential scanning calorimetry (DSC). The resulting diagram showed one peak at 90"C, marking the presence of the I' crystalline modification, one lower peak at 1 140C for the II modification and one peak at 159"C. When the molten film was slowly cooled to room temperature at a rate of 20"C/min. DSC analysis of the cooled film showed a diagram with only two peaks at 1 14" and 159"C, thus marking the complete disappearance of the I' modification.
From the quenched and non-quenched films A1, B, C and E the coating layers were peeled-off from the substrate film and subjected to DSC analysis. In each quenched sample the DSC diagram showed larger peaks at 900C than at 1040C thus marking the presence of the I' modification in a significantly larger proportion than the Il modification.
Samples of non-quenched film A1, which were stored for 100 hours at room temperature showed upon DSC analysis the complete disappearance of the II modification and the presence of the I modification having a peak at 1 170C. This disappearance corresponds with a significant increase in HSTT; the latter was found to be 1 140C for non-quenched film stored for 100 hours at room temperature.
Example 111 Heat-setting experiments were carried out by employing 10% relaxation at 115 C, respectively 138"C. The film employed was film A1 described in Example I. The heat-setting at both temperatures was effected before quenching of the film and after transverse stretching ("preceding heat-setting"), respectively subsequent to quenching of the film ("following heat-setting"). The HSTT data of the heat-set films are included in Table II.
TABLE II Operation Temp. 0C HSTT, "C Preceding heat-setting 115 105 Preceding heat-setting 138 85 Following heat-setting 115 85 Following heat-setting 138 105

Claims (7)

1. A process for preparing oriented polymerfilm in which a film comprising a substrate layer of a propylene homopolymer or copolymer and on at least one of the surfaces of said film a layer comprising a blend of 10 to 40%wt of a propylene homopolymer having a M.I. of 5.0 to 10.0 gIlO min and a degree of crystallinity of at least 45% and 60 to 90%wt of a copolymer of butene-1 and ethylene, the ethylene content in this copolymer being from 0.2 to 9% mol, this copolymer having a M.l. of 0.4 to 5.0 g/1 0 min and a degree of crystallinity of at least 35%, is stretched at a temperature above the melting point of the butene-1/ethylene copolymer and the stretched film is subjected to a temperature treatment for a time sufficient to ensure the conversion of the butene-l/ethylene copolymer from the molten state into the I' crystalline state.
2. A process as claimed in claim 1, wherein biaxially oriented film is produced.
3. A process as claimed in claim 1 or 2, wherein the butene-1/ethylene copolymer comprises from 0.5% to 5% mol ethylene.
4. A process as claimed in claims 1 to 3, wherein the temperature treatment comprises a forced cooling operation.
5. A process as claimed in claim 4, wherein the cooling operation comprises contacting the stretched film with a chill roll which is kept at an internal temperature of at most 60"C.
6. A process as claimed in claims 1 to 5, wherein the stretched film is heat-set at a temperature above 135"C before subjecting the film to the aforesaid temperature treatment.
7. A process as claimed in claims 1 to 5, wherein the stretched film is heat-set at a temperature of less than 1 250C next to subjecting the film to the aforesaid temperature treatment.
GB08236148A 1982-12-20 1982-12-20 Heat-sealable oriented polymer film Withdrawn GB2132133A (en)

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GB08236148A GB2132133A (en) 1982-12-20 1982-12-20 Heat-sealable oriented polymer film

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2210825A (en) * 1987-10-12 1989-06-21 Courtaulds Films & Packaging Oriented polymeric films having writeable surfaces
EP0343943A2 (en) * 1988-05-24 1989-11-29 Shell Oil Company A composition comprising polymers of but-1-ene and propylene

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2210825A (en) * 1987-10-12 1989-06-21 Courtaulds Films & Packaging Oriented polymeric films having writeable surfaces
GB2210825B (en) * 1987-10-12 1992-03-04 Courtaulds Films & Packaging Polymeric films
EP0343943A2 (en) * 1988-05-24 1989-11-29 Shell Oil Company A composition comprising polymers of but-1-ene and propylene
EP0343943A3 (en) * 1988-05-24 1990-10-24 Shell Oil Company A composition comprising polymers of but-1-ene and propylene

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