membrane

Abstract

The present invention provides a transverse shrinkage film comprising an inorganic pore-forming agent having an average particle size greater than 3 micrometers.

Description

[0001] This invention relates to a transversely shrinkable membrane and a method for preparing the membrane.

[0002] Transverse (TD) shrink films are used to tightly wrap polymer films around articles, such as labels. These films are more oriented laterally than longitudinally, and therefore shrink more laterally than longitudinally when heated. This means that these films can be loosely fitted around an article and then heated to shrink primarily in one direction, thus tightly wrapping the article.

[0003] Articles encased in shrink film are typically made of a different material than the film itself. Therefore, separating these two materials during recycling is crucial. This is usually achieved by providing materials of different densities.

[0004] For example, in the recycling process of polyethylene terephthalate (PET) bottles, the polyolefin-based TD shrink film, after being crushed, can be easily separated from the PET using a flotation tank. In this tank, PET fragments sink to the bottom, while polyolefin label fragments float to the surface. The end result is high-purity PET recycling, free from label ink contamination. Currently, products in the dairy, home, and personal care sectors are increasingly turning to transparent PET bottles (derived from HDPE) for easier recycling in existing PET recycling facilities.

[0005] In many applications, the contents of a product need to be obscured by the label. Furthermore, in industries such as dairy, labels need to protect the contents from the harmful effects of ultraviolet light. Both situations require the use of fully enclosed shrink sleeves, which are completely opaque yet have a density sufficiently low (below 1) to allow label fragments to float during recycling after printing. Opaque labels also enhance the effect of the printed design.

[0006] To ensure 99% of the ultraviolet region of the electromagnetic spectrum is blocked without interfering with the near-infrared (NIR) region, a carbon-free black layer can be applied to the inner surface of the label. However, it is crucial that the NIR region is not interfered with so that the NIR detectors on the recycling line can see through the label to the product material for accurate identification and sorting.

[0007] Therefore, shrink film needs to have high opacity and high whiteness, so that it can be used alone as an opaque label, or, when there is a blocky ink / carbon-free black layer on its back, it can fully cover the ink / carbon-free black layer, making the label appear white rather than gray. It is generally considered that an opacity value of over 75 and a whiteness value of over 85 are the minimum requirements.

[0008] These levels can be easily achieved simply by adding sufficient pigment (such as titanium dioxide (TiO2)) to the membrane structure. However, since the density of TiO2 is approximately 4 g / cm³, this is not feasible. 3 The final membrane density will quickly exceed the ideal target value (the density of the finished membrane is less than 0.95 g / cm³). 3 The film density is approximately 0.92 g / cm³ when no TiO₂ is present. 3 At this density, reliable separation from other materials (such as PET) is not possible because the membrane may not float on water.

[0009] It is known in the art that pore-forming agents can be used to reduce membrane density, particularly inorganic pore-forming agents such as calcium carbonate. Commercially available calcium carbonate typically has an average particle size of 3 micrometers or less. These pore-forming agents can reduce the density to as low as 0.55 g / cm³. 3 However, all other properties of the membrane (including shrinkage, tensile properties, and coefficient of friction) must be kept within acceptable tolerances.

[0010] In a typical sequential tenter frame production line, which includes a longitudinal (MD) orientation step (typically stretched to 3 to 6 times the original size) and a subsequent transverse (TD) orientation step (typically stretched to 5 to 10 times the original size), cavities are more easily generated due to the higher strain. Cavities are initiated in the high-strain-rate MD orientation step and then elongated and grown in the TD orientation step. This produces sufficiently large cavities, thereby reducing the film density.

[0011] However, to achieve the desired TD shrinkage properties, TD shrink films are not manufactured using standard sequential tenter frame stretching; instead, the MD orientation step is typically not used at all. Even when the MD orientation step is used, the stretch ratio is very small (typically stretched to 1 to 1.6 times the original size), insufficient to induce significant cavitation. Therefore, the TD shrink labeling process relies almost entirely on the low-strain-rate TD orientation step to generate cavitation, a step that is extremely inefficient. Consequently, it is difficult to prepare TD shrink films with good cavitation, especially those where the degree of cavitation needs to be sufficient to affect the film density to compensate for the addition of opacifiers. Preparing TD shrink films with good cavitation under simultaneous stretching conditions is even more difficult because the process strain rates in both directions are low, making cavitation even harder to achieve.

[0012] US2004213981 describes a simultaneously oriented polyolefin film containing incompatible particles to induce void formation, wherein the cast polyolefin is simultaneously stretched 8 times in both the MD and TD directions. Therefore, this film is a biaxially stretched film, with equal stretching in both the MD and TD directions, and thus does not belong to the TD film category, even though some TD shrinkage may be observed.

[0013] Therefore, there is still a need for a TD shrink film with a sufficiently low density so that it can be recycled during the recycling process when it is used as part of packaging materials containing other polymers.

[0014] According to a first aspect of the invention, a transverse shrinkage film is provided, the transverse shrinkage film comprising an inorganic pore-forming agent having an average particle size greater than 3 micrometers.

[0015] Transverse (TD) shrinkage film refers to a film that is more oriented in the transverse direction than in the longitudinal direction. This means that when subjected to a heating treatment, the film shrinks more in the transverse direction than in the longitudinal direction.

[0016] The lateral shrinkage rate can be more than 3 times or 4 times the longitudinal shrinkage rate, preferably more than 5 times. Therefore, the ratio of TD to MD shrinkage rates can be greater than 3:1, greater than 4:1, or greater than 5:1.

[0017] This can be achieved with a transverse stretch ratio of approximately 3 to 20 times, or approximately 5 to 10 times, while the longitudinal stretch ratio can be approximately 0.5 to 3 times, or approximately 1 to 2 times. The transverse stretch ratio is significantly higher than the longitudinal stretch ratio. Therefore, the membrane is considered to be oriented only in the transverse direction, although there may also be a small amount of stretching (and thus shrinkage) in the longitudinal direction.

[0018] When tested by exposure to a 95°C water bath for 10 seconds, the lateral shrinkage rate can be approximately 30% to 95%, or approximately 40% to 90%, or approximately 50% to 85%. When tested by exposure to 95°C for 10 seconds, the longitudinal shrinkage rate can be less than approximately 20%, less than approximately 15%, less than approximately 10%, or optionally less than approximately 6%.

[0019] The temperature of the annealing roller during film stretching also affects the degree of MD shrinkage; higher temperatures reduce MD shrinkage. Therefore, the temperature of the annealing roller can be 75°C or higher, preferably 80°C or higher.

[0020] In this case, the average particle size refers to D50 (i.e., the 50th percentile of the particle size distribution).

[0021] It has been unexpectedly discovered that using inorganic pore-forming agents with a larger average particle size can create sufficiently large voids in TD shrink films. This is unexpected because TD shrink films have almost no longitudinal orientation and the strain rate of the transverse orientation is very low, making it difficult to form the desired voids. However, the inventors have found that only larger particles, exceeding the natural particle size distribution range, can generate any cavities, and larger particles generate larger cavities.

[0022] Therefore, using large-particle-size inorganic pore-forming agents can remove many particles that cannot create voids and ensure that the remaining particles contribute to the cavitation of the membrane, even in the low-strain-rate TD orientation step.

[0023] The inorganic pore-forming agent can be any suitable pore-forming agent known in the art, including calcium carbonate (CaCO3), barium carbonate (BaCO3), alumina, aluminum sulfate, barium sulfate, magnesium carbonate, silicates (such as aluminum silicate (kaolin), mica, and magnesium silicate (talc)), and silica, and mixtures thereof. Calcium carbonate may be the inorganic pore-forming agent.

[0024] The average particle size of inorganic pore-forming agents can be greater than 4 micrometers; the average particle size can be greater than 4.5 micrometers, optionally greater than 5 micrometers; the average particle size can be from approximately 4.5 micrometers to 10 micrometers. It has been found that the larger the average particle size, the higher the degree of cavitation within the membrane. Therefore, the particle size can be adjusted according to the desired degree of cavitation and density.

[0025] The D90 (i.e., the 90th percentile of the particle size distribution) of the inorganic pore-forming agent can be greater than 10 μm, and optionally greater than 15 μm.

[0026] TD shrink film is polymeric and can be a polyolefin-based TD shrink film. "Polyolefin-based" means that the majority of the film's weight is composed of one or more polyolefins. Optionally, more than 75% of the film's weight is composed of one or more polyolefins. The TD shrink film can also be a polypropylene-based TD shrink film, meaning that the majority of the film's weight is composed of one or more polypropylene-containing polymers. The TD shrink film can contain a polypropylene / polyethylene / polybutene terpolymer and / or a polypropylene / polyethylene copolymer.

[0027] TD shrink film can be a single-layer or multi-layer film. TD shrink film may include a core layer, one or more intermediate layers, and / or one or more outer layers. TD shrink film may include a core layer, one intermediate layer on each side of the core layer, and an outer layer on each intermediate layer.

[0028] The outer layer may be a printable layer, a sealable layer, a metallized / metallable layer, and / or a barrier layer (gas or moisture barrier layer). The outer layer may be treated, for example, with corona treatment. The outer layer may be printed. The outer layer and / or the intermediate layer are polymers, which may be polyolefins and may contain cyclic olefin copolymers.

[0029] The membrane is self-sealing, allowing it to seal and form a tubular structure. This seal can be achieved through heat sealing or solvent welding. The tubular structure can then be fitted around the article and heated, causing the membrane to shrink and tightly enclose the article.

[0030] The film may contain one or more conventional additives, including anti-caking agents, slip agents (such as waxes), tack reducers (such as fumed silica, silica, silicone sealant), UV absorbers, dyes, pigments, colorants, fillers, lubricants, crosslinking agents, antistatic agents (cationic, anionic and / or nonionic, such as polyoxyethylene sorbitan monooleate), antioxidants (such as phosphorous acid, tris(2,4-di-tert-butylphenyl) ester), gloss improvers, degradation promoters, additives that improve ink adhesion and / or printability, additives that increase the coefficient of friction (such as silicon carbide), additives that increase stiffness (such as hydrocarbon resins) and / or additives that increase shrinkage (such as hard resins).

[0031] The core layer may contain the majority of the membrane thickness. The core layer may contain more than 60%, optionally more than 70%, of the membrane thickness. Inorganic pore-forming agents may be located in the core layer of the membrane.

[0032] The content of inorganic pore-forming agent in the TD shrink film can be from 2% to 15% by weight, optionally from 4% to 13% by weight. The content of inorganic pore-forming agent in the film can be less than 12% by weight. When using pore-forming agents with larger particle sizes, less amount is required because each particle can form a larger cavity; conversely, more opaque agent can be used while still remaining below the density target.

[0033] TD shrink film may contain a light-blocking agent. The light-blocking agent can be any commonly used light-blocking agent, including titanium dioxide, aluminum oxide, aluminum sulfate, barium sulfate, calcium carbonate, magnesium carbonate, silicates (aluminum, magnesium), silicon dioxide, and combinations thereof. Titanium dioxide is used due to its extremely high refractive index.

[0034] Optaneous light-blocking agents can also be used as pigments and can be selectively applied to achieve desired colors, such as white. The average particle size of the opaque light-blocking agent can range from 0.01 μm to 1 μm, which provides optimal light scattering (depending on the refractive index of the opaque agent). The density of the opaque light-blocking agent can be higher than that of the membrane polymer. Cavitation generated by the inorganic pore-forming agent can offset the density increase caused by the opaque light-blocking agent, thereby maintaining the desired overall density of the membrane.

[0035] The opacifier can be located in the same layer of the membrane as the inorganic pore-forming agent. This layer can be the core layer of a multilayer membrane.

[0036] Inorganic pore-forming agents and the cavitation they generate also contribute to the opacity of the membrane. A component that creates voids is considered a pore-forming agent, while one that contributes to the membrane's opacity is considered a light-blocking agent. Typically, the particle size of light-blocking agents is insufficient to form cavities.

[0037] The thickness of the TD shrink film can be from 20 micrometers to 100 micrometers, and optionally from 30 micrometers to 80 micrometers.

[0038] The density of TD shrink film before shrinkage can be less than 0.95 g / cm³. 3Choose any value less than 0.93 g / cm³ 3 Choose any value less than 0.9g / cm³ 3 This ensures that even after printing and shrinking, the shrink film can be separated from other polymer materials during recycling via a flotation tank, as the shrink film floats on the water.

[0039] TD shrink film can be opaque. The opacity of TD shrink film can be greater than 75, optionally greater than 80. Opacity can be determined using a contrast ratio method (e.g., using a Diffusion Systems Anglia Opacimeter Model 12 instrument). This ensures the film has the desired optical properties while effectively blocking any UV-blocking layers (e.g., carbon-free black layers) that may be present on one side of the film. The film blocks more than 99% of the ultraviolet spectral region of the electromagnetic spectrum without interfering with the near-infrared region.

[0040] The whiteness of TD shrink film can be greater than 85. Whiteness can be measured with a spectrophotometer.

[0041] The shrinkage rate of TD shrink film at 95℃ (in water for 10 seconds) can be: greater than 30% in the transverse direction and less than 20% in the longitudinal direction; or greater than 40% in the transverse direction and less than 15% in the longitudinal direction; or greater than 50% in the transverse direction and less than 10% in the longitudinal direction; or optionally greater than 60% in the transverse direction and less than 6% in the longitudinal direction.

[0042] The shrinkage rate of TD shrink film at 80℃ (10 seconds in water) can be: greater than 25% in the transverse direction and less than 6% in the longitudinal direction; or optionally greater than 35% in the transverse direction and less than 4% in the longitudinal direction.

[0043] The shrinkage properties of the membrane can be adjusted according to the intended application and required performance. The degree of orientation in the longitudinal and transverse directions can be used to change the shrinkage rate, because the higher the degree of orientation (caused by a higher draw ratio and / or a lower draw temperature), the more shrinkage occurs when heating is applied.

[0044] The tensile modulus of TD shrink film can be greater than 600 MPa in the longitudinal direction and greater than 800 MPa in the transverse direction; optionally, it can be greater than 700 MPa in the longitudinal direction and greater than 1000 MPa in the transverse direction.

[0045] According to a second aspect of the invention, a label is provided that comprises the aforementioned TD shrink film. The label may contain printed content on at least one side.

[0046] The label can be cut from the aforementioned TD shrink film. This label can be used as a sleeve label, covering the entire height of the product.

[0047] Labels can be printed on both sides. The side closest to the product can be printed with a UV-blocking layer, such as a carbon-free black layer. The side furthest from the product can be printed with text and / or graphics.

[0048] The film can self-seal to form a tubular label, which is then fitted around the product. Heating causes the label to shrink and tightly wrap the product. The seal can be achieved through heat sealing or solvent welding.

[0049] According to a third aspect of the invention, an article is provided that is at least partially surrounded by the aforementioned TD shrink film or label. "At least partially surrounded" means that the TD shrink film extends circumferentially around the article, continuously covering at least a portion of the article.

[0050] The product can be completely enclosed by TD shrink film. Alternatively, TD shrink film can form a label that surrounds a portion of the product, leaving the rest exposed. For example, the film can form a tubular label that surrounds a portion of the product circumferentially, or a sleeve label that covers the entire height of the product.

[0051] The product may be a container or other packaging. For example, the product may be a bottle or can. The product may contain a polymer material different from the polymer in the film. For example, the TD shrink film may be a polyolefin, while the product may be formed from PET or other materials.

[0052] The film can extend laterally around the circumference of the product (the circumference of the tubular label). When heating is applied, the height of the film remains unchanged, but the circumference of the tubular label decreases to tightly wrap the product.

[0053] Therefore, the present invention provides a method for marking or decorating articles, the method using a shrink film that can be easily separated from the articles during recycling.

[0054] According to a fourth aspect of the invention, a method for manufacturing the above-described article is provided, comprising loosely surrounding at least a portion of the article with the TD shrink film or label, and exposing the TD shrink film or label to an elevated temperature, causing the shrink film to shrink in the TD direction to tightly surround at least a portion of the article. The TD shrink film may first self-seal to form a tubular shape before being fitted around the article. The seal may be a heat seal or produced by solvent welding.

[0055] According to a fifth aspect of the present invention, a method for preparing the above-mentioned TD shrink film is provided, comprising adding an inorganic pore-forming agent with an average particle size greater than 3 micrometers to one or more layers of the film, and then stretching the film in the transverse direction at least three times that in the longitudinal direction.

[0056] The membrane can be stretched laterally to 3 to 20 times its original size, optionally 5 to 10 times.

[0057] The membrane can be stretched longitudinally to less than 3 times its original size, optionally less than 1.6 times. The membrane can also be stretched longitudinally to 1 times its original size, i.e., without any longitudinal stretching.

[0058] It has been unexpectedly discovered that even at such low stretching, cavities can still be generated in the membrane, which are sufficient to reduce the membrane density to compensate for the density increase caused by other additives.

[0059] The film can be produced on a tenter frame. Stretching can be sequential or simultaneous. Alternatively, the film can be produced using a bubble method.

[0060] The film can then be printed on at least one side to form a label. The film can also self-seal to form a tubular label.

[0061] The features described above also apply to other aspects of this application.

[0062] The present invention will now be described in more detail with reference to the following embodiments.

[0063] Example 1

[0064] Several five-layer membranes were prepared, each containing two layers of cyclic olefin copolymer on each side of the core layer, which contains the components listed in the table below. The outermost layers on both sides also contain 2500 ppm of silica antiblocking agent.

[0065] The film was oriented using a sequential tenter frame process. The orientation parameters listed in the table below were used, with a TD stretch ratio of 9.2, followed by a 1.6% relaxation treatment. The MDO stretching rollers were set to 70°C throughout the process. As is customary, the TDO preheating zone temperature decreased sequentially, starting from preheating zone 1 and ending at the stretching zone set point. Subsequently, one side of the film underwent corona treatment.

[0066] The polypropylene copolymer elastomer in the membrane is Vistamaxx 3980FL (ExxonMobil Chemical), and the polypropylene / polyethylene / polybutene terpolymer in the membrane is Adsyl 6C (Lyondell Basell). The recycled membrane is an internally recycled membrane (APO type product manufactured by Innovia Films), and its components are the same except for the light-blocking agent and pore-forming agent.

[0067] Table 1a

[0068] Table 1b

[0069] The membrane performance was then evaluated, as shown in the table below. Opacity was measured using the contrast method (Diffusion Systems Angla Opacimeter Model 12). Whiteness was measured using the X-Rite Spectrophotometer Ci62, employing the CIELab method.

[0070] Table 2a

[0071] Table 2b

[0072] The sample prepared with an MD stretch ratio of 1.5 (Table 1a) showed an MD shrinkage rate of 5% at 95°C. Although other properties were good, this shrinkage rate was too high for many applications, so subsequent samples had a lower MD stretch ratio (Table 1b). For sample 9, the MD stretch ratio was reduced to 1.2, and the MD shrinkage rate decreased to -1% at 95°C. Therefore, the remaining samples were prepared with an MD stretch ratio of 1.35, achieving an MD shrinkage rate of 1.5%. In subsequent tests (sample 14), by increasing the annealing roll temperature to 80°C and using an MD stretch ratio of 1.5, a film with an MD shrinkage rate of less than 4% at 95°C was produced.

[0073] Comparing the data from samples 8, 3, 5, 12, and 13 clearly shows the effect of using larger calcium carbonate particles, as shown in Table 3 below. These data indicate that increasing the average particle size significantly reduces density when the TiO2 masterbatch concentration is 15% and 22%. Specifically, for a 15% TiO2 masterbatch, increasing the average particle size from 3.0 μm to 4.5 μm reduces the density from 0.93 g / cm³. 3 Reduced to 0.873 g / cm³ 3 For 22% TiO2 masterbatch, when the average particle size increases from 4.5 micrometers to 7 micrometers, the density increases from 0.93 g / cm³. 3 Reduced to 0.88 g / cm³ 3 .

[0074] Therefore, larger particle sizes result in lower densities due to increased cavitation. Using a low degree of MD stretching can increase void initiation, thereby enhancing the degree of cavitation.

[0075] By calculating the theoretical density of each membrane under cavitation-free conditions, the theoretical density reduction factor can also be calculated.

[0076] Table 3

[0077] Therefore, there is a clear trend: particle size increases and density decreases, especially when the effect of MD stretch ratio is considered.

[0078] The original target specifications can be met by using calcium carbonate with an average particle size greater than 3.0 micrometers.

[0079] The density change of the membrane due to shrinkage was also tested. This was achieved by evaluating the buoyancy of the selected membranes in different test solutions, and the results are summarized in Table 5 below.

[0080] The shrinkage rate of the membrane was tested within the standard shrinkage test temperature range to track the change in membrane density under different degrees of shrinkage.

[0081] Cut a 25 mm × 25 mm square membrane sample and immerse it in a water bath at the set temperature for 10 seconds (temperatures are shown in Table 5). Then cut the sample into small pieces of approximately 5 mm × 5 mm. Add these pieces to a beaker containing the test solution (Table 4) and gently stir for 2 minutes. Stop stirring and allow the sample to settle in the solution. Visually observe the solution and record whether the sample sinks to the bottom of the beaker or floats to the surface.

[0082] If the sample settles, the result is recorded as "-"; if the sample floats, the result is recorded as "F". The results are summarized in Table 5.

[0083] Since membrane samples can only float in solutions with a density higher than that of the membrane sample, this can be used to estimate the membrane's density. Furthermore, in the recovery process, it is typically required that the membrane can float in water (density 1 g / cm³). 3 )superior.

[0084] Table 4

[0085] A series of test solutions and their specific densities were prepared using water and isopropanol, as detailed below.

[0086] Table 5

[0087] The results show that as the degree of membrane shrinkage increases (i.e., the shrinkage temperature rises), the membrane density also increases. Specifically, the increased shrinkage due to higher temperature leads to increased membrane density, which in turn allows the membrane to float in less solution. In other words, after shrinkage, the amount of solution with a density higher than the membrane density decreases.

[0088] This increase in density can be quite abrupt, even at lower shrinkage temperatures (such as 75°C). For example, when observing sample 12, the film precipitated in all solutions when the temperature exceeded 75°C due to the sharp increase in density.

[0089] Observation of sample 3 shows that the membrane contains CaCO3 with an average particle size of 3 micrometers. 32 Only when the density is 0.96 g / cm³ 3 It floats in solutions of 0.98 g / cm³ at a shrinkage temperature of 80°C or higher. 3 ).

[0090] Conversely, samples 12 and 5 contained CaCO3 with an average particle size of 4.5 μm, at a concentration as low as 0.9 g / cm³. 3 (Sample 5) and 0.94 g / cm 3 (Sample 12) floated in the solution. This shows that a larger particle size is sufficient to reduce the membrane density, allowing it to float in a variety of solutions even after shrinkage.

[0091] Samples 13 and 14 contained CaCO3 with an average particle size of 7 micrometers, and their concentrations were 0.92 g / cm³. 3 The above (sample 13) and 0.9 g / cm 3 The above (sample 14) floated in the solution.

[0092] These data indicate that the initial density decreases when larger particle sizes are present in the membrane, meaning the membrane can float in more test solutions even after shrinkage. The data also suggest that a sufficiently low density before shrinkage (ideally below 0.95 g / cm³) is desirable. 3 If it is below 0.93 g / cm 3 (Even better) is crucial to ensure that the film remains buoyant even after shrinkage during recycling. However, these are not printable films. Therefore, for printing on the film to be considered, the density before printing needs to be even lower, ideally below 0.9 g / cm³. 3 .

Claims

1. A transverse shrinkage film comprising an inorganic pore-forming agent having an average particle size greater than 3 micrometers.

2. The TD shrink film according to claim 1, wherein the inorganic pore-forming agent is calcium carbonate.

3. The TD shrink film according to claim 1 or 2, wherein the average particle size of the inorganic pore-forming agent is greater than 4 micrometers, optionally greater than 4.5 micrometers or greater than 5 micrometers.

4. The TD shrink film according to any one of claims 1 to 3, wherein the film is a polyolefin-based TD shrink film, optionally a polypropylene-based TD shrink film.

5. The TD shrink film according to any one of claims 1 to 4, wherein the film is a multilayer film, and the multilayer film may comprise one or more outer layers and / or one or more intermediate layers.

6. The TD shrink film according to any one of claims 1 to 5, wherein the TD shrink film comprises 2% to 15% by weight of an inorganic pore-forming agent, optionally comprising 4% to 13% by weight of an inorganic pore-forming agent.

7. The TD shrink film according to any one of claims 1 to 6, wherein the TD shrink film further comprises a light-blocking agent, optionally wherein the light-blocking agent is titanium dioxide.

8. The TD shrink film according to claim 7, wherein the light-blocking agent and the inorganic pore-forming agent are in the same layer of the film, optionally wherein the layer is the core layer of a multilayer film.

9. The TD shrink film according to any one of claims 1 to 8, wherein the inorganic pore-forming agent has a D90 greater than 10 μm, optionally greater than 15 μm.

10. The TD shrink film according to any one of claims 1 to 9, wherein the thickness of the TD shrink film is from 20 micrometers to 100 micrometers, optionally from 30 micrometers to 80 micrometers.

11. The TD shrink film according to any one of claims 1 to 10, wherein the density of the TD shrink film is less than 0.95 g / cm³. 3 Optionally less than 0.93 g / cm 3 Further optionally less than 0.9 g / cm 3 .

12. The TD shrink film according to any one of claims 1 to 11, wherein the opacity of the TD shrink film is greater than 75, optionally greater than 80.

13. The TD shrink film according to any one of claims 1 to 12, wherein the whiteness of the TD shrink film is greater than 85.

14. The TD shrink film according to any one of claims 1 to 13, wherein the shrinkage rate of the TD shrink film at 95°C (in water for 10 seconds) is: greater than 30% in the transverse direction and less than 20% in the longitudinal direction; or greater than 40% in the transverse direction and less than 15% in the longitudinal direction; or greater than 50% in the transverse direction and less than 10% in the longitudinal direction; optionally greater than 60% in the transverse direction and less than 6% in the longitudinal direction.

15. The TD shrink film according to any one of claims 1 to 14, wherein the ratio of TD shrinkage rate to MD shrinkage rate is about 3:1, or about 4:1, or about 5:

1.

16. The TD shrink film according to any one of claims 1 to 15, wherein the TD shrink film has a tensile modulus greater than 600 MPa in the longitudinal direction and a tensile modulus greater than 800 MPa in the transverse direction; optionally, it has a tensile modulus greater than 700 MPa in the longitudinal direction and a tensile modulus greater than 1000 MPa in the transverse direction.

17. A label comprising a TD shrink film as described in any one of claims 1 to 16 and printed content located on at least one side of the label.

18. An article of manufacture, said article of manufacture being at least partially surrounded by a TD shrink film or label as described in any of the preceding claims.

19. The article of claim 18, wherein the article is a container or other packaging containing a polymer material different from the polymer material in the film.

20. A method for preparing the article of claim 18 or 19, comprising: The TD shrink film of any one of claims 1 to 16 or the label of claim 17 loosely surrounds at least a portion of the article, and the TD shrink film or the label is exposed to an elevated temperature, causing the TD shrink film or the label to shrink laterally to tightly surround at least a portion of the article.

21. A method for preparing the TD shrink film according to any one of claims 1 to 16, comprising: An inorganic pore-forming agent with an average particle size greater than 3 micrometers is added to one or more layers of the membrane, and then the membrane is stretched in the transverse direction by at least 3 times more than in the longitudinal direction.

22. The method of claim 21, wherein the membrane is stretched laterally to 3 to 20 times, optionally 5 to 10 times, the original size of the membrane.

23. The method of claim 21 or 22, wherein the membrane is stretched longitudinally to less than 3 times the original size of the membrane, optionally less than 1.6 times.

24. The method according to any one of claims 21 to 23, wherein the film is produced on a tenter frame.

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