White opaque bopet films with dead-fold properties

Abstract

The present invention relates to a multi-layer biaxially-oriented, white-opaque polyester (BOPET) film with dead-fold properties, a process for producing the multi-layer biaxially oriented polyester film. In particular the present invention describes BOPET films with folding characteristics with white opaque appearance to be used in industry, primarily in packaging applications.

Description

[0001] DESCRIPTION

[0002] WHITE OPAQUE BOPET FILMS WITH DEAD-FOLD PROPERTIES

[0003] Technical Field

[0004] The present invention relates to multilayer oriented films having a dead-fold property for packaging applications which comprise polyesters. This invention also relates a process for producing this multi-layer biaxially oriented polyester films.

[0005] Prior Art

[0006] Biaxially oriented polyester films, such as biaxially oriented polyethylene terephthalate (BOPET) films, which are also known as oriented polyester films, are used in a wide variety of technical applications such as packaging products, paper and glass coverings, insulating materials, solar, marine and aviation applications, science, electronic and acoustic applications, wires, cables, radio frequency identifications, flexible circuits, graphic arts, filter products, cosmetic products, household products, imaging and recording media or industrial products due to its superior mechanical and thermal performance in comparison to other packaging materials such as polyethylene or polypropylene films. The films can be oriented in one direction or both directions to be used in packaging applications. The films can be either transparent or opaque in terms of appearance, however opacity is required in order to protect the packed goods from UV light or just in terms of aesthetics of the packaging design.

[0007] Dead fold property is a measure of the ability of the packaging material to retain a fold or crease.

[0008] One common problem that relates to polyester films are that the films tend to recover its original position when it is given a shape to cover up the product to be packed. That property is easily achieved by using ductile materials such as aluminum foil or cellulose based packaging materials such as paper or board. However due to elasticity of thermoplastic polymers, the films tent to recover to its unfolded shape or state. White opaque BOPET films are known from prior art. US Patent no 8,487,044 discloses an oriented white polyester film comprising of a cavitation additive with luminance (L value) of larger than 50%, light transmission of lower than 50%, whiteness of larger than 50% and density of lower than l,lg / cm3. US Patent no 8,487,044 provides a solution for well dispersion of the cavitating agent in BOPET films as well as a solution to overcome the dust problem during slitting process.

[0009] US Patent no 6,326,431 describes a milkily translucent, BOPET film which comprises of COC. In WO 2017141205 a thin sheet having dead fold properties, comprised of cellulose fibers with either translucent or transparent appearance is described. US Patent no 6,326,431 describes a solution to an economic processing and production of milky BOPET film and use of regrind material in the process with different concentrations.

[0010] Patent no WO 2017141205 discloses a sheet with improved dead fold properties however the sheet comprises of cellulose to a great extent and therefore loses its elastic properties as in polymeric films.

[0011] In previous studies, translucent or white opaque BOPET films are described. However, none of the publications recognizes any solution to overcome the folding problem. Consequently, there is a need to find a solution to improve the dead fold properties of BOPET films.

[0012] Aims of the Invention and Brief Description

[0013] The object of the present invention is to provide a biaxially oriented polyester films having dead-fold property.

[0014] Another object of the present invention is the provision of an inorganic voiding (cavitating) agent for biaxially oriented polyester films.

[0015] Due to nature of the polymeric film, folding problem appears since there is no dead fold property. Processing like stretching (orientation) or annealing of the film also increases the tendency of polymeric film to go back to its original form. In this existing invention, this affinity is reduced to great extent by incorporation of inorganic agents to core layer of the film. Also, annealing temperatures of the film after stretching is reduced. The density of the film is reduced from 1.4 g / cm3to less than 1.0 g / cm3. The value of density is between 0,9 to 1,0 g / cm3. Therefore, the yield value of the film is increased proportionally. In addition, the translucent appearance is achieved by incorporation of inorganic additive and biaxial orientation.

[0016] Definition of the Figures of the Invention

[0017] The figures that have been prepared in order further describe the laminated composite film assembly have been defined below.

[0018] Figure 1: Cross-section view of laminated composite film assembly

[0019] Definitions of the parts / aspects / sections forming the invention

[0020] The parts and sections provided in the figures that have been prepared in order to further describe the laminated composite film assembly that have been developed by this invention, have each been numbered and the description of each reference number has been given below.

[0021] 10: Multilayer biaxially oriented polyethylene terephthalate (BOPET) film

[0022] 101: First outer layer of the multilayer BOPET film

[0023] 102: Core layer of the multilayer BOPET film

[0024] 103: Second outer layer of the multilayer BOPET film

[0025] Detailed Description of the Invention

[0026] The present invention relates to multilayer oriented films for packaging applications which comprise polyesters. The present invention also relates to the multilayer biaxially oriented polyethylene terephthalate (BOPET) film comprising at least two outer layers comprising polyethylene terephthalate and / or its copolymers in an amount ranging from 0 to 100 wt. % and at least one core layer comprising polyethylene terephthalate in amount ranging from 70 to 90 wt. % and inorganic additive in an amount ranging from 10 to 30 wt. %, wherein said layers are coextruded. According to one aspect of the present invention, t the film comprises a first outer layer (101) comprising polyethylene terephthalate and / or its copolymers in an amount ranging from 0 to 100 wt. %, a second outer layer (103) comprising polyethylene terephthalate and / or its copolymers in an amount ranging from 0 to 100 wt. % and a core layer (102) comprising polyethylene terephthalate in amount ranging from 70 to 90 wt. % and inorganic additive in an amount ranging from 10 to 30 wt. %, wherein said layers (101), (103), and (102) are coextruded.

[0027] The invention provides a white opaque biaxially oriented polyester film comprising; at least one layer has a cavitating agent that creates voids in the film structure wherein said cavitating agent comprises of organic substances such as polyethylene imine or inorganic fillers such as calcium carbonate, silica or combinations thereof; at least one layer comprises of antiblocking agents to provide easy separation of layers of film in roll formation wherein said anti-blocking agent comprises of silicate, siloxane and derivatives of siloxane or combinations thereof. In order to provide the desired dead fold characteristics the white opaque polyester comprises of 10-30% by weight of the cavitating agent.

[0028] The white opaque polyester film has a thickness of 10 micron to 200 mic, preferably 12 to 75 mic; has an opacity of 50 to 90%, preferably 70 to 80% and has a whiteness index of 70 to 130, preferably 80 to 100.

[0029] The white opaque polyester film is produced according to this invention exhibits further features such as high surface tension which enables printing, coating or lamination; low oxygen transmission rate (OTR) for extending the Product shelf life by preventing detoriation of goods such as food products. The film has a surface tension of 36 - 60 dyne / cm surface tension, preferably 38 - 56 dyne / cm and the film has an OTR of 0,5 to 1000 cc / sqm / day, preferably 40 to 200 cc / sqm / day.

[0030] The white opaque polyester film described in this art may be produced either with uniaxial stretching of the polymer or biaxial stretching of the polymer after extrusion stage. During uniaxial stretching the polymer film is stretched in the machine direction typically with a drawing ratio of 2,0 to 8,0 times, preferably 3,0 to 5,0 times; during biaxial stretching the polymer film is stretched in the machine direction typically with a drawing ratio of 2,0 to 8,0 times, preferably 3,0 to 5,0 times and in the transverse direction typically with a drawing ratio of 2,0 to 10,0 times, preferably 3,0 to 6,0 times.

[0031] To fold the structure, it is required to apply a force under certain period of time. In elastic region of the stress strain curve, the polymer tends to recover back to its original shape. In plastic strain area it is known that the resistance to deform of polymers are greatly reduced. In order to reduce the elastic region of the polymer the temperature setting of the stretching process is adapted in a way to reduce to elastic region. The inventors of this art suprisingly found that the behaviour of lower elastic deformation of polymer films are greatly reduced with similar process conditions with the abovementioned white opaque polyester film structure. The resultant dead fold characteristics of the white opaque polyester film is found to be improved at a great extent. Dead fold retention value which can be evaluated as angle after the film is being folded onto itself and released back. The angle for standard BOPET films ranges from 120 ° to 180 °. The angle for the film described in the invention ranges from 30 ° to 60 °.

[0032] The first outer layer of multilayer BOPET film (101) comprises polyethylene terephthalate and / or its copolymers. The first outer layer of multilayer BOPET film (101) may also comprise additives such as anti-blocking, slip or other functional masterbatches to ease the handling and converting of the film.

[0033] The core layer of multilayer BOPET film (102) forms the backbone of the multilayer BOPET film (10), that provides the stiffness and mechanical strength of the film and also dead fold property. The core layer of multilayer BOPET film (102) also comprises polyethylene terephthalate resin and inorganic additive.

[0034] The second outer layer of multilayer BOPET film (103) is the same as the first outer layer of multilayer BOPET film (101).

[0035] The film (10) is more preferably co-extruded film in which more than one extruder is used to form first outer layer of multilayer BOPET film (101), one of the outer layer (skin layer) of multilayer BOPET film (103) and core layer of multilayer BOPET film (102) (A / B / C structure) or one extruder for skin layers and at least one extruder for core layer (A / B / A structure). The core layer of multilayer BOPET film (102) may be a single layer or multilayer, meaning extruded through a single extruder or more than one extruder. Skin layer thickness ranges from 5 % to 15 %.

[0036] Polyethylene terephthalate materials are processed through extruder system where the raw materials turned into melt form and transferred to following mechanisms to form the final film. The polymers are extruded and after extrusion they are processed in different mechanisms to form the final structure or shape of the package.

[0037] Biaxial orientation process is a technique to stretch the polymer in two directions to provide molecular orientation. Depending on the design of the production line, BOPET films can be produced in multilayer form by coextrusion. Surface layers can be modified with additives such as silica to adjust the friction of the film and its winding properties. Depending on the layer structure, the feed block design differs for multilayer film lines. For a three layer BOPET line, the film layer design may be ABC or ABA.

[0038] Film lines are typically consisting of raw material handling system, extrusion system, casting system, Machine Direction Orientation (MDO) system, Transverse Direction Orientation (TDO) system, Pull Roll Stand (PRS) system and Film Winder (FW) system.

[0039] The orientation process brings many improvements to film properties typically can be grouped as mechanical (tensile strength and stiffness increase, increase of crack and impact resistance), optical (haze reduction and gloss increase) and the barrier properties (significant reduction in gas, particularly oxygen and water vapour transmission rates). The degree of orientation depends on the stretching temperature, the rate of stretching and the rate of quenching. Quenching occurs when the extruded film is passing through chill rolls. Lower stretching temperatures, higher rate of stretching and increased rate of quenching result in a higher degree of orientation.

[0040] Depending on the polymer type and processing conditions, the stretching ratio in machine direction and transverse direction may vary from 3: 1 to 5: 1 respectively

[0041] The MDO unit consists of a roll system, which realizes the stretching by the different and stepwise increasing circumferential speed of the stretching rolls. Stretching unit in TDO however works differently, basically web is held by clips system moving on a rail system and TD orientation achieved by increased distance between these clips. MDO and TDO units consist of preheating section, stretching section, relaxation and annealing sections respectively.

[0042] After the stretching steps, the film passes through a Pull Roll Stand (PRS) unit. In this unit, the clamped edges of the film, holding the film during TDO stretching are being trimmed. In PRS Unit edge of the films that clips held during TDO stretching is being trimmed. This is done because this part of the film did not stretch in transverse direction. Also thickness gauges placed in PRS unit to perform web thickness measurement. The web thickness profile is monitored and the data are transmitted to the extrusion system to align the die gap by heating or cooling the die-bolts in order to ensure uniform film thickness across the width.

Claims

CLAIMS1. A white opaque multi-layer biaxially oriented thermoplastic polyester film comprising at least two outer layers comprising polyethylene terephthalate and / or its copolymers in an amount ranging from 0 to 100 wt. % and at least one core layer comprising inorganic additive in an amount ranging from 10 to 30 wt. %, wherein said layers are coextruded2. The film according to Claim 1, comprising• A first outer layer (101) comprising polyethylene terephthalate and / or its copolymers in an amount ranging from 0 to 100 wt. %• A second outer layer (103) comprising polyethylene terephthalate and / or its copolymers in an amount ranging from 0 to 100 wt. %• A core layer (102) comprising polyethylene terephthalate in amount ranging from 70 to 90 wt. % and inorganic additive in an amount ranging from 10 to 30 wt. % wherein said layers (101), (103), and (102) are coextruded.

3. The film according to Claim 1 or Claim 2, which is characterized by a density in the range from 0,9 to 1,0 g / cm3.

4. The film according to Claim 1 or Claim 2, which is characterized by a thickness of 10 micron to 200 micron.

5. The film according to Claim 4, which is characterized by a thickness of 12 to 75 micron.

6. The film according to Claim 1 or Claim 2, wherein the at least one layer comprises additive.

7. The film according to Claim 6, wherein the additive is an anti-blocking agent, slip, other functional masterbatches or a combination thereof.

8. The film according to Claim 7, wherein anti-blocking agent comprises silicate, siloxane, derivatives of siloxane or a combination thereof.

9. The film according to Claim 1 or Claim 2, wherein the core layer of multilayer BOPET film (102) comprises polyethylene terephthalate resin and inorganic additive.

10. The film according to Claim 1 or Claim 2, wherein the inorganic additive is calcium carbonate (CaCCh).8

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