A low-temperature wrinkle-resistant biaxially stretched polypropylene label film and preparation method thereof

Abstract

The present invention relates to a low-temperature wrinkle-resistant biaxially stretched polypropylene label film and a preparation method thereof, and belongs to the technical field of label films. The low-temperature wrinkle-resistant biaxially stretched polypropylene label film of the present invention comprises an upper surface layer, an intermediate layer and a lower surface layer arranged in sequence; the upper surface layer comprises copolymerized polypropylene, high-density polyethylene and 20-30wt% trifluoroethyl acrylate copolymer; the intermediate layer comprises polypropylene, pearlescent masterbatch and 3-7wt% polyolefin elastomer. The low-temperature wrinkle-resistant biaxially stretched polypropylene label film of the present invention has 20-30wt% trifluoroethyl acrylate copolymer added to the upper surface layer, and 3-7wt% polyolefin elastomer added to the intermediate layer. Through the synergistic effect of the upper surface layer and the intermediate layer, the label made of the low-temperature wrinkle-resistant biaxially stretched polypropylene label film does not have obvious wrinkles during storage in a beverage cabinet between 2-8°C, meeting the aesthetic and low-temperature storage requirements of beverages.

Description

Technical Field

[0001] The invention relates to the technical field of label films, in particular to a low-temperature wrinkle-resistant biaxially stretched polypropylene label film and a preparation method thereof. Background Art

[0002] Biaxially oriented polypropylene label film is a single-sided corona, white opaque BOPP film. One of the application scenarios of biaxially oriented polypropylene label film is in the field of beverage packaging. As an application method, the surface of biaxially oriented polypropylene label film is printed to make a wrap-around label for PET beverage bottles. This label is widely used in beverage packaging of major brands.

[0003] In order to keep the freshness and taste of beverages and to prevent them from being too cold or too hot, most supermarkets and stores place beverages in beverage cabinets at a temperature between 2 and 8 degrees Celsius. However, in summer or other high-temperature environments, due to the low temperature of the beverage bottle and the high ambient temperature, the label will have obvious wrinkles, which affects the appearance of the beverage and is not conducive to repeated low-temperature storage of the beverage. Summary of the invention

[0004] Based on this, the object of the present invention is to provide a low-temperature wrinkle-resistant biaxially stretched polypropylene label film and a preparation method thereof, wherein the low-temperature wrinkle-resistant biaxially stretched polypropylene label film can be applied to frozen beverage label packaging scenarios, and the labels made of the low-temperature wrinkle-resistant biaxially stretched polypropylene label film do not have obvious wrinkles during storage in a beverage cabinet between 2 and 8°C, thereby meeting the aesthetic and low-temperature storage requirements of the beverage.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A low-temperature anti-wrinkle biaxially stretched polypropylene label film comprises an upper surface layer, an intermediate layer and a lower surface layer which are arranged in sequence; the upper surface layer comprises copolymerized polypropylene, high-density polyethylene and 20-30wt% of trifluoroethyl acrylate copolymer; the intermediate layer comprises polypropylene, pearlescent masterbatch and 3-7wt% of polyolefin elastomer, and the glass transition temperature of the polyolefin elastomer is -35--20°C.

[0007] The low-temperature anti-wrinkle biaxially oriented polypropylene label film of the present invention has 20-30wt% of trifluoroethyl acrylate copolymer added to the upper surface layer, and 3-7wt% of polyolefin elastomer added to the middle layer. Through the synergistic effect of the upper surface layer and the middle layer, the problem of wrinkles on labels made of the existing biaxially oriented polypropylene label film during low-temperature storage or switching between high and low temperature environments is effectively improved.

[0008] In the low-temperature wrinkle-resistant biaxially stretched polypropylene label film described in the present invention, polyolefin elastomer is added to the middle layer. Polyolefin elastomer is a type of saturated polymer containing only carbon and hydrogen elements. Its structure generally has side chains or side groups with a certain carbon chain length, and has a low glass transition temperature, which can provide support for the polypropylene in the middle layer at low temperatures; in addition, since the polyolefin elastomer and the polypropylene in the middle layer have the same constituent elements and are both saturated structures, the polyolefin elastomer and polypropylene have good compatibility, so the polyolefin elastomer has a good toughening effect on polypropylene. The present invention utilizes the above characteristics and designs the middle layer to include polypropylene, pearlescent masterbatch and 3~7wt% polyolefin elastomer, so that the middle layer has low-temperature resilience and toughness.

[0009] The addition of the pearlescent masterbatch in the intermediate layer will inevitably cause the mechanical properties of the film to decrease. The present invention adds the polyolefin elastomer to the intermediate layer and uses the polyolefin elastomer to toughen the polypropylene in the intermediate layer, thereby compensating for the loss of mechanical properties caused by the addition of the pearlescent masterbatch. The present invention adds 3-7wt% polyolefin elastomer to the intermediate layer. After the polyolefin elastomer is mixed with the polypropylene, the ductility of the polypropylene molecular chain is improved. Between the polypropylene layer stacking areas or at the spherulite boundaries, the polyolefin elastomer and the polypropylene form a lamellae interlocking structure, which fixes the molecular chains that diffuse mutually in the interface layer and prevents the relaxation of the entangled chain segments. The presence of the polyolefin elastomer enhances the low-temperature toughness of the blend in the intermediate layer, compensating for the loss of mechanical properties caused by the addition of the pearlescent masterbatch, thereby making the low-temperature anti-wrinkle biaxially stretched label film have good resilience without wrinkles during low-temperature storage or high-low temperature environment switching. In the present invention, the content of the polyolefin elastomer in the intermediate layer is limited to 3-7wt%. If the content of the polyolefin elastomer in the intermediate layer is lower than 3wt%, it will not have an effective low-temperature anti-wrinkle effect; if the content of the polyolefin elastomer in the intermediate layer is higher than 7wt%, the mechanical properties of the low-temperature anti-wrinkle biaxially stretched label film will decrease, that is, the tensile strength will decrease, which will affect the labeling process of the low-temperature anti-wrinkle biaxially stretched label film in subsequent applications.

[0010] In the low-temperature wrinkle-resistant biaxially stretched polypropylene label film of the present invention, the trifluoroethyl acrylate copolymer is added to the upper surface layer. 3 group, so that the surface of the upper surface layer is -CF 3The surface of the upper surface layer has a lower surface energy (i.e., a lower surface tension). Since the label made of the low-temperature wrinkle-resistant biaxially stretched polypropylene label film is in direct contact with the beverage bottle, when the beverage bottle is taken out of the beverage cabinet at 2-8°C, condensed water will be generated on the beverage bottle due to condensation. When the condensed water contacts the label, the low surface energy of the upper surface layer is used to improve the distribution and flow of the condensed water on its surface, so that the condensed water is quickly gathered into water droplets and quickly drained away. In addition, the rigidity of the acrylate main chain in the trifluoroethyl acrylate copolymer is strong, which can improve the hardness of the polymer, and the ester side chain can provide a certain degree of flexibility. The addition of the trifluoroethyl acrylate copolymer effectively improves the hardness of the upper surface layer, and through the synergistic effect with the intermediate layer, the wrinkle problem of the label made of the low-temperature wrinkle-resistant biaxially stretched polypropylene label film is effectively improved. In the present invention, the content of the trifluoroethyl acrylate copolymer in the upper surface layer is limited to 20-30wt%. If the content of the trifluoroethyl acrylate copolymer in the upper surface layer is lower than 20wt%, the surface energy of the upper surface layer is relatively high, and the surface energy of the upper surface layer cannot be reduced. If the content of the trifluoroethyl acrylate copolymer in the upper surface layer is higher than 30wt%, the hardness of the upper surface layer is too large, which easily leads to cracking of the upper surface layer. As a preferred solution, the glass transition temperature of the polyolefin elastomer is -35--20℃. By using a polyolefin elastomer with a glass transition temperature within the above range, the balance between the mechanical strength and low-temperature toughness of the low-temperature wrinkle-resistant biaxially stretched polypropylene label film is optimal. If the glass transition temperature of the polyolefin elastomer is lower than -35℃, the mechanical strength of the low-temperature wrinkle-resistant biaxially stretched polypropylene label film is significantly reduced. If the glass transition temperature of the polyolefin elastomer is higher than -20℃, the toughening effect of the low-temperature wrinkle-resistant biaxially stretched polypropylene label film is poor, which is not conducive to the low-temperature resilience of the low-temperature wrinkle-resistant biaxially stretched polypropylene label film.

[0011] As a preferred solution, in the upper surface layer, the trifluoroacrylate copolymer is formed by polymerization of trifluoroethyl acrylate and hydroxyethyl methacrylate; in the trifluoroacrylate copolymer, the content of trifluoroethyl acrylate is 20-40wt%. The present invention adopts a trifluoroethyl acrylate copolymer formed by polymerization of trifluoroethyl acrylate and hydroxyethyl methacrylate as raw materials, which has -CF 3The group can make the surface of the upper surface layer have a lower surface energy; at the same time, the methyl group on the acrylate main chain restricts the mobility of the acrylate main chain, strengthens the rigidity of the main chain, and further improves the hardness of the polymer. In the trifluoroethyl acrylate copolymer, the content of trifluoroethyl acrylate is 20~40wt%, and the effect of reducing the surface energy of the upper surface layer is the best. If the content of trifluoroethyl acrylate is less than 20wt%, the effect of reducing the surface energy of the upper surface layer is not obvious; if the content of trifluoroethyl acrylate is greater than 40wt%, due to the -CF covering the surface of the upper surface layer 3 The groups are nearly saturated and can no longer significantly reduce the surface energy of the upper surface.

[0012] As a preferred solution, the trifluoroethyl acrylate copolymer is prepared by solution polymerization using methyl isobutyl ketone as solvent, azobisisobutylnitrile as initiator, trifluoroethyl acrylate monomer and hydroxyethyl methacrylate monomer as raw materials. In the preparation process, the amount of trifluoroethyl acrylate monomer is 20-40wt% of the total amount of trifluoroethyl acrylate monomer and hydroxyethyl methacrylate monomer.

[0013] As a preferred solution, the trifluoroethyl acrylate copolymer has a melt index of 10.5-12.5 g / 10 min (measurement conditions: 190° C., 2.16 kg).

[0014] As a preferred solution, in the upper surface layer, the content of the copolymerized polypropylene in the upper surface layer is 40-50wt%, and the content of the high-density polyethylene in the upper surface layer is 30-40wt%. The upper surface layer of the present invention is a matte layer, and the copolymerized polypropylene and the high-density polyethylene form an "island" structure to achieve a matte effect. By designing the content of the copolymerized polypropylene in the upper surface layer to be 40-50wt%, and the content of the high-density polyethylene in the upper surface layer to be 30-40wt%, the matte effect of the upper surface layer is more excellent.

[0015] As a preferred solution, the copolymerized polypropylene is a random ethylene-propylene copolymer; the melt index of the copolymerized polypropylene is 6-10 g / 10 min (measurement conditions: 230° C., 2.16 kg).

[0016] As a preferred solution, the melt index of the high-density polyethylene is 9-20 g / 10 min (measurement conditions: 190° C., 2.16 kg).

[0017] As a preferred solution, in the intermediate layer, the polyolefin elastomer is an ethylene-octene copolymer elastomer.

[0018] As a preferred solution, the melt index of the polyolefin elastomer is 9-13 g / 10 min (measurement conditions: 230°C, 2.16 kg). If the melt index of the polyolefin elastomer is lower than 9 g / 10 min, the polyolefin elastomer cannot be effectively dispersed in the polypropylene matrix of the intermediate layer, and cannot achieve an effective low-temperature wrinkle resistance effect. If the melt index of the polyolefin elastomer is higher than 13 g / 10 min, the intermolecular interaction force with the polypropylene of the intermediate layer will be reduced, resulting in a decrease in the tensile strength of the intermediate layer, thereby affecting the mechanical strength of the low-temperature wrinkle-resistant biaxially stretched polypropylene label film.

[0019] As a preferred solution, in the middle layer, the content of the polypropylene in the middle layer is 73-87wt%.

[0020] As a preferred solution, the polypropylene in the middle layer is homopolypropylene, the melt index of the homopolypropylene is 3-8 g / 10 min (measurement conditions: 230° C., 2.16 kg), and the isotacticity is 96%.

[0021] As a preferred solution, in the intermediate layer, the content of the pearlescent masterbatch in the intermediate layer is 10-20wt%.

[0022] As a preferred solution, the pearlescent masterbatch is mixed with 25-35wt% homopolypropylene and 65-75wt% inorganic filler, and the inorganic filler is at least one of calcium carbonate and titanium dioxide. The particle size of the calcium carbonate is 0.5-1.5μm, and in order to balance the foaming effect and cost considerations, it is preferably 0.8-1.3μm; the particle size of the titanium dioxide is 0.2-0.7μm, and in order to balance the foaming effect and cost considerations, it is preferably 0.35-0.45μm. Preferably, the homopolypropylene in the pearlescent masterbatch and the homopolypropylene in the intermediate layer are the same type of homopolypropylene to improve the compatibility of the homopolypropylene in the intermediate layer with the pearlescent masterbatch.

[0023] As a preferred solution, the lower surface layer is composed of homopolypropylene and 1~5wt% anti-adhesion masterbatch. Adding an appropriate amount of anti-adhesion masterbatch to the lower surface layer is beneficial to the smoothness of winding and unwinding the label film. If the content of the anti-adhesion masterbatch in the lower surface layer is lower than 1wt%, it will not have an effective anti-adhesion effect. If the content of the anti-adhesion masterbatch in the lower surface layer is higher than 5wt%, the anti-adhesion agent is likely to fall off during the production process, resulting in contamination of the guide roller, while increasing the haze and reducing the gloss, affecting the appearance of the product. Preferably, the homopolypropylene in the lower surface layer and the homopolypropylene in the middle layer are the same type of homopolypropylene to improve the compatibility of the middle layer and the lower surface layer.

[0024] As a preferred solution, the anti-blocking masterbatch is mixed with 90wt% homopolypropylene and 10wt% anti-blocking agent. Preferably, the homopolypropylene in the lower surface layer and the homopolypropylene in the anti-blocking masterbatch are the same type of homopolypropylene to improve the compatibility of the homopolypropylene in the lower surface layer and the anti-blocking masterbatch.

[0025] As a preferred solution, the anti-adhesive agent is at least one of silicon dioxide, talc and calcium carbonate, and the particle size of the anti-adhesive agent is 3-6 μm, preferably 4-5 μm in order to take into account the thickness of the lower surface layer and the problem of shedding.

[0026] The present invention also provides a method for preparing any of the above-mentioned low-temperature wrinkle-resistant biaxially stretched polypropylene label films, comprising the following steps:

[0027] Step 1: Batching and plasticization: The proportion of each layer of raw materials is set in the control system of the biaxial stretch film production line, and then the batching system will automatically transport the dried raw materials of each layer to the corresponding extruders according to the input ratio. After melting and plasticizing in the extruders of each layer, the melt enters the die head through the runner and distributor;

[0028] Step 2: Slice casting: After being extruded through the die, the melt immediately contacts the cooling roller to form a thick sheet;

[0029] Step 3: Longitudinal stretching: The thick sheet is heated to the set temperature by multiple sets of preheating rollers, and then begins to be longitudinally stretched and then shaped;

[0030] Step 4: Transverse stretching: After preheating the thick sheet that has been longitudinally stretched to the set temperature, transverse stretching begins, and after transverse stretching, shaping and cooling are performed;

[0031] Step 5: Traction and reeling: The multi-layer film from the transverse stretching unit enters the traction unit, and after thickness measurement and corona treatment, enters the reeling unit to obtain a parent roll;

[0032] Step 6: Slitting: Slitting the aged mother roll to obtain film rolls of specified width and length.

[0033] As a preferred scheme, in the above process, the melt extrusion temperature of the upper surface layer is: 200~260℃; the melt extrusion temperature of the middle layer and the lower surface layer is: 230~260℃; in the process of the melt contacting the cooling roller, the temperature of the chilling water and the chilling roller is: 15~50℃; the temperature of the longitudinal stretching zone is: 90~130℃; the temperature of the transverse stretching zone is: 155~165℃; the longitudinal stretching ratio is 4.5~5.5 times; the transverse stretching ratio is: 8~10 times; the corona power factor of the matte layer is: 20~25W•min / m. DETAILED DESCRIPTION

[0034] The present invention will be described in more detail below. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. The experimental methods in the following examples or comparative examples without specifying specific conditions are generally carried out according to conventional conditions in the art or according to conditions recommended by the manufacturer; the raw materials, reagents, etc. used, unless otherwise specified, are all raw materials and reagents that can be obtained from commercial channels such as conventional markets.

[0035] In the following examples or comparative examples:

[0036] Glass transition temperature: tested by DSC tester. Under nitrogen protection, the temperature was raised from -50°C to 190°C at a rate of 20°C / min, and stayed at 200°C for 1 min to eliminate the influence of thermal history. The temperature was then cooled to -50°C at a rate of 20°C / min, stayed for 1 min, and then raised to 200°C at a rate of 20°C.

[0037] The melt index (melt mass flow rate MFR) is determined according to GB / T3682-2018.

[0038] The melt index of high-density polyethylene is: 10g / 10min (measurement conditions: 190℃, 2.16kg);

[0039] The copolymerized polypropylene is a random ethylene-propylene copolymer with a melt index of 7.5 g / 10 min (measurement conditions: 230 ° C, 2.16 kg);

[0040] The melt index of the homopolymer polypropylene in the middle layer is: 3.0 g / 10 min (measurement conditions: 230°C, 2.16 kg); the isotacticity is 96%;

[0041] The pearlescent masterbatch is a mixture of 30wt% homopolymer polypropylene and 70wt% calcium carbonate; the melt index of the homopolymer polypropylene in the pearlescent masterbatch is 3.0g / 10min (measurement conditions: 230℃, 2.16kg); the isotacticity is 96%; the particle size of the calcium carbonate is 0.8μm;

[0042] The trifluoroethyl acrylate copolymer is prepared by solution polymerization using methyl isobutyl ketone as solvent, azobisisobutylnitrile as initiator, trifluoroethyl acrylate monomer and hydroxyethyl methacrylate monomer as raw materials.

[0043] The polyolefin elastomer is an ethylene-octene copolymer elastomer.

[0044] The melt index of the homopolymer polypropylene in the lower surface layer is: 3.0 g / 10 min (measurement conditions: 230°C, 2.16 kg); the isotacticity is 96%;

[0045] The anti-blocking masterbatch is a mixture of 90wt% homopolypropylene and 10wt% anti-blocking agent; the melt index of the homopolypropylene in the anti-blocking masterbatch is 3.0g / 10min (measurement conditions: 230°C, 2.16kg); the isotacticity is 96%; the anti-blocking agent is silicon dioxide with a particle size of 4μm.

[0046] Example 1

[0047] This embodiment provides a low-temperature anti-wrinkle biaxially stretched polypropylene label film, comprising an upper surface layer (matte layer), an intermediate layer and a lower surface layer arranged in sequence. The formula of each layer is as follows:

[0048] Matt layer: 50wt% copolymerized polypropylene, 30wt% high-density polyethylene and 20wt% trifluoroethyl acrylate copolymer (melt index is 11.2g / 10min, melt index measurement conditions: 190℃, 2.16kg, trifluoroethyl acrylate content is 30wt%);

[0049] Middle layer: 87wt% homopolypropylene, 10wt% pearlescent masterbatch and 3wt% polyolefin elastomer (polyolefin elastomer is ethylene-octene copolymer elastomer, melt index is 9g / 10min, melt index measurement conditions: 230℃, 2.16kg, glass transition temperature is -28℃);

[0050] Lower surface layer: 97wt% homopolymer polypropylene and 3wt% anti-blocking masterbatch.

[0051] The total thickness of the biaxially oriented polypropylene label film of this embodiment is 30 μm, the thickness of the upper surface layer is 1.8 μm, and the thickness of the lower surface layer is 1.0 μm.

[0052] This embodiment also provides a method for preparing a low-temperature wrinkle-resistant biaxially stretched polypropylene label film, comprising the following steps:

[0053] Step 1: Batching and plasticization: The proportion of each layer of raw materials is set in the control system of the biaxial stretch film production line, and then the batching system will automatically transport the dried raw materials of each layer to the corresponding extruders according to the input ratio. After melting and plasticizing in the extruders of each layer, the melt enters the die head through the runner and distributor;

[0054] Step 2: Slice casting: After being extruded through the die, the melt immediately contacts the cooling roller to form a thick sheet;

[0055] Step 3: Longitudinal stretching: The thick sheet is heated to the set temperature by multiple sets of preheating rollers, and then begins to be longitudinally stretched and then shaped;

[0056] Step 4: Transverse stretching: After preheating the thick sheet that has been longitudinally stretched to the set temperature, transverse stretching begins, and after transverse stretching, shaping and cooling are performed;

[0057] Step 5: Traction and reeling: The multi-layer film from the transverse stretching unit enters the traction unit, and after thickness measurement and corona treatment, enters the reeling unit to obtain a parent roll;

[0058] Step 6: Slitting: Slitting the aged mother roll to obtain film rolls of specified width and length.

[0059] In the above process, the melt extrusion temperature of the matte layer is 235°C; the melt extrusion temperature of the middle layer and the lower surface layer is 250°C; in the process of the melt contacting the cooling roller, the temperature of the chilled water and the chilled roller is 40°C; the temperature of the longitudinal stretching zone is 125°C; the temperature of the transverse stretching zone is 160°C; the longitudinal stretching ratio is 5.3 times; the transverse stretching ratio is 8.5 times; the corona power factor of the matte layer is 23.5W•min / m.

[0060] Example 2

[0061] This embodiment provides a low-temperature anti-wrinkle biaxially stretched polypropylene label film, comprising an upper surface layer (matte layer), an intermediate layer and a lower surface layer arranged in sequence. The formula of each layer is as follows:

[0062] Matt layer: 45wt% copolymerized polypropylene, 30wt% high-density polyethylene and 25wt% trifluoroethyl acrylate copolymer (melt index is 11.2g / 10min, melt index measurement conditions: 190℃, 2.16kg, trifluoroethyl acrylate content is 30wt%);

[0063] Middle layer: 80wt% homopolypropylene, 15wt% pearlescent masterbatch and 5wt% polyolefin elastomer (polyolefin elastomer is ethylene-octene copolymer elastomer, melt index is 11g / 10min, melt index measurement conditions: 230℃, 2.16kg, glass transition temperature is -28℃);

[0064] Lower surface layer: 97wt% homopolymer polypropylene and 3wt% anti-blocking masterbatch.

[0065] The total thickness and thickness of each layer of the low-temperature wrinkle-resistant biaxially oriented polypropylene label film of this embodiment are the same as those of Embodiment 1.

[0066] The preparation method of the low-temperature anti-wrinkle biaxially stretched polypropylene label film of this embodiment is the same as that of Example 1.

[0067] Example 3

[0068] This embodiment provides a low-temperature anti-wrinkle biaxially stretched polypropylene label film, comprising an upper surface layer (matte layer), an intermediate layer and a lower surface layer arranged in sequence. The formula of each layer is as follows:

[0069] Matt layer: 40wt% copolymerized polypropylene, 30wt% high-density polyethylene and 30wt% trifluoroethyl acrylate copolymer (melt index is 11.2g / 10min, melt index measurement conditions: 190℃, 2.16kg, trifluoroethyl acrylate content is 30wt%);

[0070] Middle layer: 73wt% homopolypropylene, 20wt% pearlescent masterbatch, 7wt% polyolefin elastomer (polyolefin elastomer is ethylene-octene copolymer elastomer, melt index is 13g / 10min, melt index measurement conditions: 230℃, 2.16kg, glass transition temperature is -28℃);

[0071] Lower surface layer: 97wt% homopolymer polypropylene and 3wt% anti-blocking masterbatch.

[0072] The total thickness and thickness of each layer of the low-temperature wrinkle-resistant biaxially oriented polypropylene label film of this embodiment are the same as those of Embodiment 1.

[0073] The preparation method of the low-temperature anti-wrinkle biaxially stretched polypropylene label film of this embodiment is the same as that of Example 1.

[0074] Comparative Example 1

[0075] This comparative example provides a biaxially oriented polypropylene label film, comprising an upper surface layer (matte layer), an intermediate layer and a lower surface layer arranged in sequence. The formula of each layer is as follows:

[0076] Matt layer: 50wt% copolymerized polypropylene and 50wt% high-density polyethylene;

[0077] Middle layer: 80wt% homopolypropylene, 15wt% pearlescent masterbatch and 5wt% polyolefin elastomer (polyolefin elastomer is ethylene-octene copolymer elastomer, melt index is 11g / 10min, melt index measurement conditions: 230℃, 2.16kg, glass transition temperature is -28℃);

[0078] Lower surface layer: 97wt% homopolymer polypropylene and 3wt% anti-blocking masterbatch.

[0079] The total thickness and thickness of each layer of the biaxially oriented polypropylene label film of this comparative example are the same as those of Example 1.

[0080] The preparation method of the biaxially oriented polypropylene label film of this comparative example is the same as that of Example 1.

[0081] Comparative Example 2

[0082] This comparative example provides a biaxially oriented polypropylene label film, comprising an upper surface layer (matte layer), an intermediate layer and a lower surface layer arranged in sequence. The formula of each layer is as follows:

[0083] Matt layer: 50wt% copolymerized polypropylene, 40wt% high-density polyethylene and 10wt% trifluoroethyl acrylate copolymer (melt index is 11.2g / 10min, melt index measurement conditions: 190℃, 2.16kg, trifluoroethyl acrylate content is 30wt%);

[0084] Middle layer: 80wt% homopolypropylene, 15wt% pearlescent masterbatch and 5wt% polyolefin elastomer (polyolefin elastomer is ethylene-octene copolymer elastomer, melt index is 11g / 10min, melt index measurement conditions: 230℃, 2.16kg, glass transition temperature is -28℃);

[0085] Lower surface layer: 97wt% homopolymer polypropylene and 3wt% anti-blocking masterbatch.

[0086] The total thickness and thickness of each layer of the biaxially oriented polypropylene label film of this comparative example are the same as those of Example 1.

[0087] The preparation method of the biaxially oriented polypropylene label film of this comparative example is the same as that of Example 1.

[0088] Comparative Example 3

[0089] This comparative example provides a biaxially oriented polypropylene label film, comprising an upper surface layer (matte layer), an intermediate layer and a lower surface layer arranged in sequence. The formula of each layer is as follows:

[0090] Matt layer: 30wt% copolymerized polypropylene, 30wt% high-density polyethylene and 40wt% trifluoroethyl acrylate copolymer (melt index is 11.2g / 10min, melt index measurement conditions: 190℃, 2.16kg, trifluoroethyl acrylate content is 30wt%);

[0091] Middle layer: 80wt% homopolypropylene, 15wt% pearlescent masterbatch and 5wt% polyolefin elastomer (polyolefin elastomer is ethylene-octene copolymer elastomer, melt index is 11g / 10min, melt index measurement conditions: 230℃, 2.16kg, glass transition temperature is -28℃);

[0092] Lower surface layer: 97wt% homopolymer polypropylene and 3wt% anti-blocking masterbatch.

[0093] The total thickness and thickness of each layer of the biaxially oriented polypropylene label film of this comparative example are the same as those of Example 1.

[0094] The preparation method of the biaxially oriented polypropylene label film of this comparative example is the same as that of Example 1.

[0095] Comparative Example 4

[0096] This comparative example provides a biaxially oriented polypropylene label film, comprising an upper surface layer (matte layer), an intermediate layer and a lower surface layer arranged in sequence. The formula of each layer is as follows:

[0097] Matt layer: 45wt% copolymerized polypropylene, 30wt% high-density polyethylene and 25wt% trifluoroethyl acrylate copolymer (melt index is 11.2g / 10min, melt index measurement conditions: 190℃, 2.16kg, trifluoroethyl acrylate content is 10wt%);

[0098] Middle layer: 80wt% homopolypropylene, 15wt% pearlescent masterbatch and 5wt% polyolefin elastomer (polyolefin elastomer is ethylene-octene copolymer elastomer, melt index is 11g / 10min, melt index measurement conditions: 230℃, 2.16kg, glass transition temperature is -28℃);

[0099] Lower surface layer: 97wt% homopolymer polypropylene and 3wt% anti-blocking masterbatch.

[0100] The total thickness and thickness of each layer of the biaxially oriented polypropylene label film of this comparative example are the same as those of Example 1.

[0101] The preparation method of the biaxially oriented polypropylene label film of this comparative example is the same as that of Example 1.

[0102] Comparative Example 5

[0103] This comparative example provides a biaxially oriented polypropylene label film, comprising an upper surface layer (matte layer), an intermediate layer and a lower surface layer arranged in sequence. The formula of each layer is as follows:

[0104] Matt layer: 45wt% copolymerized polypropylene, 30wt% high-density polyethylene and 25wt% trifluoroethyl acrylate copolymer (melt index is 11.2g / 10min, melt index measurement conditions: 190℃, 2.16kg, trifluoroethyl acrylate content is 50wt%);

[0105] Middle layer: 80wt% homopolypropylene, 15wt% pearlescent masterbatch and 5wt% polyolefin elastomer (polyolefin elastomer is ethylene-octene copolymer elastomer, melt index is 11g / 10min, melt index measurement conditions: 230℃, 2.16kg, glass transition temperature is -28℃);

[0106] Lower surface layer: 97wt% homopolymer polypropylene and 3wt% anti-blocking masterbatch.

[0107] The total thickness and thickness of each layer of the biaxially oriented polypropylene label film of this comparative example are the same as those of Example 1.

[0108] The preparation method of the biaxially oriented polypropylene label film of this comparative example is the same as that of Example 1.

[0109] Comparative Example 6

[0110] This comparative example provides a biaxially oriented polypropylene label film, comprising an upper surface layer (matte layer), an intermediate layer and a lower surface layer arranged in sequence. The formula of each layer is as follows:

[0111] Matt layer: 45wt% copolymerized polypropylene, 30wt% high-density polyethylene and 25wt% trifluoroethyl acrylate copolymer (melt index is 11.2g / 10min, melt index measurement conditions: 190℃, 2.16kg, trifluoroethyl acrylate content is 30wt%);

[0112] Middle layer: 80wt% homopolymer polypropylene and 20wt% pearlescent masterbatch;

[0113] Lower surface layer: 97wt% homopolymer polypropylene and 3wt% anti-blocking masterbatch.

[0114] The total thickness and thickness of each layer of the biaxially oriented polypropylene label film of this comparative example are the same as those of Example 1.

[0115] The preparation method of the biaxially oriented polypropylene label film of this comparative example is the same as that of Example 1.

[0116] Comparative Example 7

[0117] This comparative example provides a biaxially oriented polypropylene label film, comprising an upper surface layer (matte layer), an intermediate layer and a lower surface layer arranged in sequence. The formula of each layer is as follows:

[0118] Matt layer: 45wt% copolymerized polypropylene, 30wt% high-density polyethylene and 25wt% trifluoroethyl acrylate copolymer (melt index is 11.2g / 10min, melt index measurement conditions: 190℃, 2.16kg, trifluoroethyl acrylate content is 30wt%);

[0119] Middle layer: 84wt% homopolypropylene, 15wt% pearlescent masterbatch and 1wt% polyolefin elastomer (polyolefin elastomer is ethylene-octene copolymer elastomer, melt index is 11g / 10min, melt index measurement conditions: 230℃, 2.16kg, glass transition temperature is -28℃);

[0120] Lower surface layer: 97wt% homopolymer polypropylene and 3wt% anti-blocking masterbatch.

[0121] The total thickness and thickness of each layer of the biaxially oriented polypropylene label film of this comparative example are the same as those of Example 1.

[0122] The preparation method of the biaxially oriented polypropylene label film of this comparative example is the same as that of Example 1.

[0123] Comparative Example 8

[0124] This comparative example provides a biaxially oriented polypropylene label film, comprising an upper surface layer (matte layer), an intermediate layer and a lower surface layer arranged in sequence. The formula of each layer is as follows:

[0125] Matt layer: 40wt% copolymerized polypropylene, 25wt% high-density polyethylene and 35wt% trifluoroethyl acrylate copolymer (melt index is 11.2g / 10min, melt index measurement conditions: 190℃, 2.16kg, trifluoroethyl acrylate content is 30wt%);

[0126] Middle layer: 65wt% homopolypropylene, 15wt% pearlescent masterbatch and 20wt% polyolefin elastomer (polyolefin elastomer is ethylene-octene copolymer elastomer, melt index is 11g / 10min, melt index measurement conditions: 230℃, 2.16kg, glass transition temperature is -28℃);

[0127] Lower surface layer: 97wt% homopolymer polypropylene and 3wt% anti-blocking masterbatch.

[0128] The total thickness and thickness of each layer of the biaxially oriented polypropylene label film of this comparative example are the same as those of Example 1.

[0129] The preparation method of the biaxially oriented polypropylene label film of this comparative example is the same as that of Example 1.

[0130] Comparative Example 9

[0131] This comparative example provides a biaxially oriented polypropylene label film, comprising an upper surface layer (matte layer), an intermediate layer and a lower surface layer arranged in sequence. The formula of each layer is as follows:

[0132] Matt layer: 45wt% copolymerized polypropylene, 30wt% high-density polyethylene and 25wt% trifluoroethyl acrylate copolymer (melt index is 11.2g / 10min, melt index measurement conditions: 190℃, 2.16kg, trifluoroethyl acrylate content is 30wt%);

[0133] Middle layer: 80wt% homopolypropylene, 15wt% pearlescent masterbatch and 5wt% polyolefin elastomer (polyolefin elastomer is ethylene-octene copolymer elastomer, melt index is 11g / 10min, melt index measurement conditions: 230℃, 2.16kg, glass transition temperature is -65℃);

[0134] Lower surface layer: 97wt% homopolymer polypropylene and 3wt% anti-blocking masterbatch.

[0135] The total thickness and thickness of each layer of the biaxially oriented polypropylene label film of this comparative example are the same as those of Example 1.

[0136] The preparation method of the biaxially oriented polypropylene label film of this comparative example is the same as that of Example 1.

[0137] Comparative Example 10

[0138] This comparative example provides a biaxially oriented polypropylene label film, comprising an upper surface layer (matte layer), an intermediate layer and a lower surface layer arranged in sequence. The formula of each layer is as follows:

[0139] Matt layer: 45wt% copolymerized polypropylene, 30wt% high-density polyethylene and 25wt% trifluoroethyl acrylate copolymer (melt index is 11.2g / 10min, melt index measurement conditions: 190℃, 2.16kg, trifluoroethyl acrylate content is 30wt%);

[0140] Middle layer: 80wt% homopolypropylene, 15wt% pearlescent masterbatch and 5wt% polyolefin elastomer (polyolefin elastomer is ethylene-octene copolymer elastomer, melt index is 11g / 10min, melt index measurement conditions: 230℃, 2.16kg, glass transition temperature is -10℃);

[0141] Lower surface layer: 97wt% homopolymer polypropylene and 3wt% anti-blocking masterbatch.

[0142] The total thickness and thickness of each layer of the biaxially oriented polypropylene label film of this comparative example are the same as those of Example 1.

[0143] The preparation method of the biaxially oriented polypropylene label film of this comparative example is the same as that of Example 1.

[0144] Performance Testing

[0145] The following performance tests were performed on the biaxially oriented polypropylene label films of Examples 1 to 3 and Comparative Examples 1 to 10, respectively. The test results are shown in Table 1:

[0146] Surface tension: Tested according to GB / T2410.

[0147] Mechanical properties (test conditions: place the sample in a low temperature environment (0°C) for 2 hours, and perform the following tests after the sample reaches a low temperature equilibrium state):

[0148] ① Tensile strength: Tested according to GB / T1040.3.

[0149] ② Impact strength (low temperature toughness): tested according to GBT 8809-2015 plastic film pendulum impact test method.

[0150] Appearance indicators:

[0151] ① Surface appearance of the matte layer: Observe whether there are cracks on the surface of the matte layer.

[0152] ② Wrinkle condition: Wrap the biaxially oriented polypropylene label film around a PET beverage bottle and place it in a beverage cabinet at an angle of 2 to 8 degrees. After 2 hours, take out the beverage bottle and observe whether the label film has wrinkles after 3 minutes.

[0153] Table 1 Test results of biaxially oriented polypropylene label film

[0154]

[0155] The low-temperature wrinkle-resistant biaxially stretched polypropylene label films of Examples 1 to 3 of the present invention have good mechanical properties, low surface tension of the matte layer, and will not crack. The low-temperature wrinkle-resistant biaxially stretched polypropylene label films of Examples 1 to 3 of the present invention have good resilience and do not have wrinkle problems during low-temperature storage or switching between high and low temperature environments.

[0156] The biaxially oriented polypropylene label film of Comparative Example 1 has a matte layer containing only high-density polyethylene and copolymerized polypropylene, and no trifluoroethyl acrylate copolymer is added to the matte layer. The surface tension of the matte layer of the biaxially oriented polypropylene label film of Comparative Example 1 is high, and the surface energy of the matte layer cannot be reduced. In addition, the biaxially oriented polypropylene label film of Comparative Example 1 has poor impact performance, that is, poor low-temperature toughness, and is prone to wrinkling.

[0157] In the biaxially oriented polypropylene label film of Comparative Example 2, the amount of trifluoroethyl acrylate copolymer added to the matte layer is too low, and the surface tension of the matte layer of the biaxially oriented polypropylene label film of Comparative Example 2 is high, which fails to reduce the surface energy of the matte layer; and the biaxially oriented polypropylene label film of Comparative Example 2 has poor impact performance, i.e., poor low-temperature toughness, and has a slight wrinkle problem.

[0158] In the biaxially stretched polypropylene label film of Comparative Example 3, the amount of trifluoroethyl acrylate copolymer added to the matte layer is too high, and the matte layer of the biaxially stretched polypropylene label film of Comparative Example 3 cracks during the stretching process.

[0159] In the biaxially oriented polypropylene label film of Comparative Example 4, the trifluoroethyl acrylate copolymer is added to the matte layer, wherein the content of trifluoroethyl acrylate is less than 20wt%, and the surface energy reduction effect of the matte layer surface of the biaxially oriented polypropylene label film of Comparative Example 4 is not obvious; and the biaxially oriented polypropylene label film of Comparative Example 4 has poor impact performance, i.e., poor low-temperature toughness.

[0160] In the biaxially oriented polypropylene label film of Comparative Example 5, the trifluoroethyl acrylate copolymer is added to the matte layer, wherein the content of trifluoroethyl acrylate is greater than 40wt%. 3 The group is close to saturation, and the biaxially oriented polypropylene label film of comparative example 5 can no longer significantly reduce the surface energy of the matte layer surface; and the biaxially oriented polypropylene label film of comparative example 5 has poor impact performance, that is, poor low-temperature toughness, and has a slight wrinkle problem.

[0161] The biaxially oriented polypropylene label film of Comparative Example 6 does not have ethylene-octene copolymer elastomer added in the middle layer. The mechanical properties of the biaxially oriented polypropylene label film of Comparative Example 6 are low, and the impact performance is extremely poor, that is, the low-temperature toughness is extremely poor, and wrinkles are prone to occur. The film cannot meet the requirements of good resilience and wrinkle-free under low temperature conditions.

[0162] The biaxially oriented polypropylene label film of Comparative Example 7 has too low a content of the added ethylene-octene copolymer elastomer in the middle layer. The biaxially oriented polypropylene label film of Comparative Example 7 has low mechanical properties and extremely poor impact performance, i.e., extremely poor low-temperature toughness, and has slight wrinkles. The film cannot meet the requirements of good resilience and wrinkle-free performance under low temperature conditions.

[0163] In the biaxially oriented polypropylene label film of Comparative Example 8, the content of the added ethylene-octene copolymer elastomer in the middle layer is too high, and the mechanical properties of the biaxially oriented polypropylene label film of Comparative Example 8 are sharply reduced, causing the film to break easily during slitting and striping.

[0164] In the biaxially oriented polypropylene label film of Comparative Example 9, the glass transition temperature of the added ethylene-octene copolymer elastomer in the middle layer is lower than -35°C, and the mechanical strength of the biaxially oriented polypropylene label film of Comparative Example 9 is significantly reduced.

[0165] In the biaxially oriented polypropylene label film of Comparative Example 10, the glass transition temperature of the added ethylene-octene copolymer elastomer in the middle layer is higher than -20°C. The toughening effect of the biaxially oriented polypropylene label film of Comparative Example 10 is poor, which is not conducive to the low-temperature resilience of the film.

[0166] The above-mentioned embodiments only express several implementation methods of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, and the present invention is also intended to include these modifications and modifications.

Claims

1. A low-temperature wrinkle-resistant biaxially oriented polypropylene label film, characterized in that: It comprises an upper surface layer, an intermediate layer and a lower surface layer which are arranged in sequence; the upper surface layer comprises copolymerized polypropylene, high-density polyethylene and 20-30wt% trifluoroethyl acrylate copolymer; in the trifluoroethyl acrylate copolymer, the content of trifluoroethyl acrylate is 20-40wt%; the intermediate layer comprises polypropylene, pearlescent masterbatch and 3-7wt% polyolefin elastomer, and the glass transition temperature of the polyolefin elastomer is -35--20°C.

2. The low-temperature wrinkle-resistant biaxially oriented polypropylene label film according to claim 1, characterized in that: In the upper surface layer, the trifluoroethyl acrylate copolymer is obtained by polymerization of trifluoroethyl acrylate and hydroxyethyl methacrylate.

3. The low-temperature wrinkle-resistant biaxially oriented polypropylene label film according to claim 2, characterized in that: The preparation method of the trifluoroethyl acrylate copolymer is: using methyl isobutyl ketone as a solvent, azobisisobutyronitrile as an initiator, trifluoroethyl acrylate monomer and hydroxyethyl methacrylate monomer as raw materials, and preparing the copolymer by solution polymerization.

4. The low-temperature anti-wrinkle biaxially oriented polypropylene label film according to claim 1, characterized in that: The trifluoroethyl acrylate copolymer has a melt index of 10.5-12.5 g / 10 min under the measuring conditions of a melt temperature of 190° C. and a load weight of 2.16 kg.

5. The low-temperature anti-wrinkle biaxially oriented polypropylene label film according to claim 1, characterized in that: In the middle layer, the polyolefin elastomer is an ethylene-octene copolymer elastomer.

6. The low-temperature wrinkle-resistant biaxially oriented polypropylene label film according to claim 1, characterized in that: The polyolefin elastomer has a melt index of 9-13 g / 10 min under the measuring conditions of a melt temperature of 230° C. and a load weight of 2.16 kg.

7. The low-temperature wrinkle-resistant biaxially oriented polypropylene label film according to claim 1, characterized in that: In the upper surface layer, the content of the copolymerized polypropylene in the upper surface layer is 40-50wt%, and the content of the high-density polyethylene in the upper surface layer is 30-40wt%.

8. The low-temperature wrinkle-resistant biaxially oriented polypropylene label film according to claim 1, characterized in that: In the middle layer, the content of the polypropylene in the middle layer is 73-87wt%; the content of the pearlescent masterbatch in the middle layer is 10-20wt%.

9. The low-temperature wrinkle-resistant biaxially oriented polypropylene label film according to claim 1, characterized in that: The lower surface layer includes homopolymer polypropylene and 1-5 wt % anti-blocking masterbatch.

10. A method for preparing a low-temperature wrinkle-resistant biaxially oriented polypropylene label film according to any one of claims 1 to 9, characterized in that: The following steps are involved: Step 1: Batching and plasticization: The proportion of each layer of raw materials is set in the control system of the biaxial stretch film production line, and then the batching system will automatically transport the dried raw materials of each layer to the corresponding extruders according to the input ratio. After melting and plasticizing in the extruders of each layer, the melt enters the die head through the runner and distributor; Step 2: Slice casting: After being extruded through the die, the melt immediately contacts the cooling roller to form a thick sheet; Step 3: Longitudinal stretching: The thick sheet is heated to the set temperature by multiple sets of preheating rollers, and then begins to be longitudinally stretched and then shaped; Step 4: Transverse stretching: After preheating the thick sheet that has been longitudinally stretched to the set temperature, transverse stretching begins, and after transverse stretching, shaping and cooling are performed; Step 5: Traction and reeling: The multi-layer film from the transverse stretching unit enters the traction unit, and after thickness measurement and corona treatment, enters the reeling unit to obtain a parent roll; Step 6: Slitting: Slitting the aged mother roll to obtain film rolls of specified width and length.

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