A polyethylene film material suitable for high speed gravure printing and a method of making the same

Abstract

The application discloses a polyethylene film material suitable for high-speed gravure printing and a preparation method. The polyethylene film material is prepared from polyethylene with a density of 0.92-0.97 g / cm3 as raw material by adopting a 'five-layer co-extrusion blow molding+online longitudinal stretching' process, through step density layer design, the thickness ratio between layers is 1:1:2:1:1, and the polyethylene film material with a thickness of 20-25 mu is prepared through online twelve-roll longitudinal stretching. The polyethylene film material prepared by the application has high tensile strength (longitudinal), good elongation at break, and a 1% quadratic modulus (longitudinal) of 1356 MPa, and has good material rigidity. The polyethylene film material can meet the printing speed of 300-500 m / min in an ester-soluble ink system of a high-speed gravure printing machine, and the overlay precision is less than or equal to 0.2 mm. The polyethylene film material can provide technical guidance for the realization of polyethylene single material packaging.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of polymer material processing and molding, and particularly relates to a polyethylene film material suitable for high-speed gravure printing and a preparation method thereof. BACKGROUND

[0002] Gravure printing is one of the four printing methods, and is a direct printing method, that is, the ink contained in the pits of the gravure plate is directly printed on the printing material, and the light and shade levels of the printed picture are determined by the size and depth of the pits. If the pits are deeper, the ink contained is more, and the ink layer left on the printing material after printing is thicker. Conversely, if the pits are shallower, the amount of ink contained is less, and the ink layer left on the printing material after printing is thinner. Gravure printing occupies an extremely important position in the fields of printing packaging and graphic publishing due to its advantages of thick and solid ink layer, bright color, high saturation, printing plate durability, stable printing quality, and fast printing speed. At the same time, gravure printing can use water-based ink and alcohol-soluble ink, which meets the requirements of green and environmentally friendly printing, and can be widely applied to various media such as film, composite material, and paper, and thus is widely used in the field of packaging printing.

[0003] Polyethylene is a semi-crystalline non-polar polymer material, which is very sensitive to environmental stress (chemical and mechanical action), and thus can be processed into film, packaging material, container and other products by general thermoplastic plastic molding methods. Traditional polyethylene film material has the advantages of transparent softness, good heat sealing property, and water and moisture resistance, and thus has a wide application in the field of outer packaging. However, it also has some problems, such as low tensile strength, large tensile elongation, easy winding and wrinkling, and especially micron-level film is prone to deformation during printing, causing color matching difficulty, and thus is only suitable for low-speed printing and has low printing precision.

[0004] CN106273955A discloses a salad dressing packaging composite film and a preparation method thereof, the packaging composite film is tightly attached by a PET printing film layer, a functional polyethylene film layer and a PE film layer connected in turn, which prevents the penetration of the packaging content into the film and causes the delamination of the composite film, resulting in the decrease of the peeling strength of the composite film. CN114834171A discloses an environmentally-friendly printing process of polyethylene packaging material, and a three-layer polyethylene composite film is prepared, wherein the nanochitosan powder is blended and melted in the corona layer, the silane coupling agent and triethylene diamine are added in the cooking-resistant water-based polyurethane ink to adjust the pH value, and the three components synergistically enhance the adhesion of the ink while ensuring the hydrolysis resistance and antibacterial durability of chitosan. CN113059879A discloses a matt polyethylene film suitable for high-speed gravure printing and a preparation process thereof, and the PE film is obtained by adopting a three-layer co-extrusion technology, which improves the surface gloss and achieves the matt effect. However, in the preparation process of the polyethylene film in the prior art, other inorganic raw materials are added for blending, which can improve the surface gloss, antibacterial property and medium resistance effect, but the prepared polyethylene film has low rigidity and is only suitable for printing speed of about 150 m / min, and the overlaying precision is poor.

[0005] Therefore, it is an urgent task for the industry to develop a polyethylene film material suitable for high-speed gravure printing. SUMMARY

[0006] In view of the above technical problems, the present application provides a polyethylene film material suitable for high-speed gravure printing and a preparation method thereof, which is prepared by adopting a "five-layer co-extrusion blow molding + online longitudinal stretching" technology, and has small overlaying deviation, high rigidity and meets the high-speed gravure printing speed of 300-500 m / min.

[0007] In order to achieve the above purpose, the present application provides a polyethylene film material suitable for high-speed gravure printing, the thickness of the polyethylene film material is 20-25 μm, the density is 0.92-0.97 g / cm 3 .

[0008] Preferably, the polyethylene film material is composed of five layers, which are an outer layer (1), a secondary outer layer (2), a middle layer (3), a secondary inner layer (4) and an inner layer (5), and the thickness ratio of each layer is 1:1:2:1:1.

[0009] Further preferably, the density of the outer layer is 0.96-0.97 g / cm 3 , the density of the secondary outer layer is 0.94-0.95 g / cm 3 , the density of the middle layer is 0.92-0.93 g / cm 3 , and the density of the secondary inner layer is 0.94-0.95 g / cm 3, the density of the inner layer is 0.96-0.97 g / cm 3 .

[0010] The application further provides a preparation method of the polyethylene film material suitable for high-speed gravure printing, comprising the following steps:

[0011] (1) different densities and masses of the copolymerized polyethylene are respectively put into corresponding five extruders to extrude the polyethylene at high temperature to form a melt;

[0012] (2) the melt is blow molded into a ring shape, and then air-cooled to form a primary film;

[0013] (3) the primary film is rolled flat and stretched in the longitudinal direction to obtain a stretched film;

[0014] (4) the stretched film is subjected to corona treatment, edge cutting and winding to obtain the polyethylene film material.

[0015] Preferably, the blow molding temperature in step (2) is 190-200 DEG C, and the blow ratio is 2.0-3.0.

[0016] Preferably, the longitudinal stretching in step (3) is online twelve-roll longitudinal stretching, and the twelve rolls are composed of four preheating rolls, two stretching rolls, four annealing rolls and two cooling rolls.

[0017] Further preferably, the temperature of the preheating roll 1 is 50-60 DEG C, the temperature of the preheating roll 2 is 80-90 DEG C, the temperature of the preheating roll 3 is 90-100 DEG C, the temperature of the preheating roll 4 is 100-110 DEG C, the temperature of the stretching roll 1 is set to 100-120 DEG C, the temperature of the stretching roll 2 is set to 100-120 DEG C, the temperature of the annealing roll 1 is set to 100-120 DEG C, the temperature of the annealing roll 2 is set to 100-120 DEG C, the temperature of the annealing roll 3 is set to 100-120 DEG C, the temperature of the annealing roll 4 is set to 100-120 DEG C, the temperature of the cooling roll 1 is set to 50-60 DEG C, and the temperature of the cooling roll 2 is set to 30-40 DEG C.

[0018] Further preferably, the pulling speed of the online twelve-roll longitudinal stretching is 15-25 m / min, and the comprehensive stretching ratio is 4.8-5.5.

[0019] Preferably, the corona treatment condition in step (4) is 38-42 dyne value.

[0020] The application further provides an application of the polyethylene film material in high-speed gravure printing, and the speed of the high-speed gravure printing is 300-500 m / min.

[0021] The application has the following beneficial effects:

[0022] 1. A copolymer polyethylene with a density of 0.92-0.97 g / cm 3 is used as raw material, a five-layer gradient density interlayer design is carried out, a polyethylene film material with high density of outer layer and inner layer and relatively low density of middle layer is prepared, which has a "sandwich" laminated structure, and the material has excellent balance of rigidity and toughness.

[0023] 2. The polyethylene film material is prepared by using "five-layer co-extrusion blow molding + online longitudinal stretching" technology. The melt extruded by five-layer co-extrusion is blow molded, the polyethylene material is stretched for the first time during the blow molding process, the strength of the polyethylene material is enhanced, then the blow molding bubble film is flattened and stretched longitudinally online, the tensile strength of the polyethylene film material is increased to 110-130 MPa, the 1% secant modulus is increased to 1000-1400 MPa, the material has good rigidity and transparency, and can adapt to the printing speed of 300-500 m / min in the ester-soluble ink system of high-speed gravure printing machine, and still has the advantages of good light screen transfer, excellent ink adhesion and overlay accuracy ≤0.2 mm. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The polyethylene film material prepared by the present application has a five-layer structure, wherein 1 is the outer layer, 2 is the secondary outer layer, 3 is the middle layer, 4 is the secondary inner layer, and 5 is the inner layer. DETAILED DESCRIPTION

[0025] The technical solutions of the present application will be further explained and described in combination with the drawings and specific embodiments. It should be noted that the following embodiments are only preferred embodiments of the present application, and should not be understood as limiting the present application. The protection scope of the present application should be based on the content recorded in the claims. The modifications and replacements of the technical solutions of the present application made by those skilled in the art without creative labor fall within the protection scope of the present application.

[0026] In the following embodiments, the conventional polyethylene film is an example of blow molding a 20 micron film using low density polyethylene LDPE granules Exxon Mobil Exceed 2018HA, the density of which is 0.918 g / cm3, the haze is 30%, the tensile strength (longitudinal) is 60 MPa, the elongation at break is 700%, and the 1% secant modulus (longitudinal) is 160 MPa.

[0027] Example 1

[0028] (1) According to the outer layer 1, the secondary outer layer 2, the middle layer 3, the secondary inner layer 4 and the inner layer 5, different densities of copolymer polyethylene raw materials are weighed and put into the corresponding five extruders for high temperature extrusion to form a solution, wherein the outer layer 1 adopts copolymer polyethylene with a density of 0.96 g / cm 3co-polyethylene with density of 0.94 g / cm 3 co-polyethylene with density of 0.92 g / cm 3 co-polyethylene with density of 0.94 g / cm 3 co-polyethylene with density of 0.96 g / cm 3 co-polyethylene with density of 0.96 g / cm

[0029] (2) The melt obtained in step (1) is blown into a ring-shaped barrel film at 195℃, and after air cooling, a primary film is obtained; wherein the blowing ratio is 2.5;

[0030] (3) After the primary film is cooled and rolled by a guide roller, it is stretched longitudinally by an online twelve-roller longitudinal stretching process, wherein the online twelve-roller includes four preheating rollers, two stretching rollers, four annealing rollers and two cooling rollers, and the specific temperature settings are as follows:

[0031] The temperature of the preheating roller 1 is 50℃,

[0032] The temperature of the preheating roller 2 is 80℃,

[0033] The temperature of the preheating roller 3 is 90℃,

[0034] The temperature of the preheating roller 4 is 100℃,

[0035] The temperature of the stretching roller 1 is set to 100℃,

[0036] The temperature of the stretching roller 2 is set to 100℃,

[0037] The temperature of the annealing roller 1 is set to 100℃,

[0038] The temperature of the annealing roller 2 is set to 100℃,

[0039] The temperature of the annealing roller 3 is set to 100℃,

[0040] The temperature of the annealing roller 4 is set to 100℃,

[0041] The temperature of the cooling roller 1 is set to 50℃,

[0042] The temperature of the cooling roller 2 is set to 30℃;

[0043] The pulling speed of the primary film is 15 m / min, and the comprehensive stretching ratio is 4.8;

[0044] (4) The outer layer of the film after longitudinal stretching is subjected to corona treatment with a value of 38 dynes, and a polyethylene film material is obtained.

[0045] The prepared polyethylene film material has a thickness of 20 μm, a haze of 6.2%, a tensile strength (longitudinal direction) of 114 MPa, an elongation at break of 64%, and a 1% secant modulus (longitudinal direction) of 1023 MPa, which is more than 5 times that of a conventional polyethylene film, and has good material rigidity and transparency.

[0046] The prepared polyethylene film material is subjected to high-speed gravure printing, and the ester-soluble ink is used during printing. When the printing speed is 300 m / min, the ester-soluble ink has good light web transfer and excellent adhesion, and the printed pattern is clear (the overlaying precision is ±0.2 mm), indicating that the prepared polyethylene film material is suitable for use as a transparent packaging material.

[0047] Example 2

[0048] The method and steps are the same as in Example 1, and the densities of the layers from outside to inside in step (1) are 0.96 g / cm 3 , 0.945 g / cm 3 , 0.925 g / cm 3 , 0.945 g / cm 3 , 0.96 g / cm 3 , respectively.

[0049] The temperature of the preheating roller 1 is 55℃,

[0050] The temperature of the preheating roller 2 is 85℃,

[0051] The temperature of the preheating roller 3 is 95℃,

[0052] The temperature of the preheating roller 4 is 105℃,

[0053] The temperature of the stretching roller 1 is set to 105℃,

[0054] The temperature of the stretching roller 2 is set to 105℃,

[0055] The temperature of the annealing roller 1 is set to 115℃,

[0056] The temperature of the annealing roller 2 is set to 115℃,

[0057] The temperature of the annealing roller 3 is set to 115℃,

[0058] The temperature of the annealing roller 4 is set to 115℃,

[0059] The temperature of the cooling roller 1 is set to 50℃,

[0060] The temperature of the cooling roller 2 is set to 30℃.

[0061] The polyethylene film material was prepared by the method, wherein the drawing line speed was 20 m / min, and the comprehensive stretching ratio was 5.0.

[0062] It was detected that the thickness of the prepared polyethylene film material was 25 μm, the haze was 6.7%, the tensile strength (longitudinal direction) was 115 MPa, the elongation at break was 47%, and the 1% secant modulus (longitudinal direction) was 1162 MPa.

[0063] The prepared polyethylene film material was subjected to high-speed gravure printing, wherein ester-soluble ink was used during printing. When the printing speed was 400 m / min, the ester-soluble ink was well transferred by the light mesh, had excellent adhesion, and the printing pattern had a register accuracy of ±0.15 mm, indicating that the prepared polyethylene film material was suitable for use as a medium-rigid packaging material and could be used as a substitute film for BOPP.

[0064] Example 3

[0065] The method and steps were the same as in Example 1, wherein the densities of the layers from outside to inside in step (1) were 0.97 g / cm 3 , 0.45 g / cm 3 , 0.93 g / cm 3 , 0.95 g / cm 3 , 0.97 g / cm 3 , respectively; the blowing temperature in step (2) was 200 ℃, and the blow-up ratio was 3.0; and the temperature settings of the twelve rollers in step (3) were as follows:

[0066] The temperature of the preheating roller 1 was 60 ℃;

[0067] The temperature of the preheating roller 2 was 90 ℃;

[0068] The temperature of the preheating roller 3 was 100 ℃;

[0069] The temperature of the preheating roller 4 was 110 ℃;

[0070] The temperature of the stretching roller 1 was set to 120 ℃;

[0071] The temperature of the stretching roller 2 was set to 120 ℃;

[0072] The temperature of the annealing roller 1 was set to 120 ℃;

[0073] The temperature of the annealing roller 2 was set to 120 ℃;

[0074] The temperature of the annealing roller 3 was set to 120 ℃;

[0075] The temperature of the annealing roller 4 was set to 120 ℃;

[0076] The temperature of the cooling roller 1 was set to 60 ℃;

[0077] The temperature of the cooling roller 2 is set to 40°C.

[0078] The polyethylene film material is prepared by using the polyethylene melt obtained in step (1) as the raw material, and by using a method of cooling and stretching.

[0079] It is detected that the polyethylene film material prepared has a thickness of 25 μm, a haze of 5.3%, a tensile strength (longitudinal direction) of 129 MPa, an elongation at break of 33%, and a 1% secant modulus (longitudinal direction) of 1356 MPa. The material has good rigidity and flexibility.

[0080] The polyethylene film material prepared is subjected to high-speed gravure printing using ester-soluble ink. When the printing speed is 500 m / min, the ester-soluble ink has good light web transfer and excellent adhesion, and the printing pattern has a registration accuracy of ±0.1 mm. This indicates that the polyethylene film material prepared is suitable for use as a high-rigidity packaging material and can be used as a substitute film for PET.

[0081] Influence of polyethylene density on film performance

[0082] The method and steps are the same as in Example 1, except that the five-layer raw material in step (1) is replaced by copolymerized polyethylene having a density of 0.95 g / cm 3 . The polyethylene film material is obtained by blow molding, and the film surface is subjected to corona treatment at a value of 38 dynes. The thickness of the film is 20 μm. The performance test results are as follows: the material is not stretched and has a high density, the haze is as high as 20%, the tensile strength (longitudinal direction) is 50 MPa, which indicates that the film material is relatively soft, the elongation at break is 550%, which indicates that the film material is easy to stretch, and the 1% secant modulus (longitudinal direction) is 200 MPa, which indicates that the film material has poor rigidity. Therefore, when ester-soluble ink is used for high-speed gravure printing, the printing speed can only be 100-200 m / min, and the printing accuracy is only ±0.5 mm.

[0083] Influence of molding method on film performance

[0084] The method and steps are the same as in Example 1, except that the melt obtained by five-layer co-extrusion in step (1) is subjected to casting to obtain a primary film, and then the primary film is subjected to longitudinal stretching under the same stretching conditions as in Example 1 to prepare the polyethylene film material.

[0085] The prepared polyethylene film material has a thickness of 20 μm, and the material performance is good transparency, softness, but poor heat resistance. First, the casting forming is cooled by a water-cooled roller, which causes the polyethylene film molecular chain to be frozen, resulting in poor crystallization performance, which shows excellent transparency and a haze of only 5%; second, the melt index of the polyethylene measured by the casting forming is 4-8 g / min (the melt index of the polyethylene measured by the blow molding is 0.5-2.5 g / min), which shows that the film material is easily softened by heat, and the mechanical tensile elongation at break is 128%.

[0086] Influence of longitudinal stretching process on film performance

[0087] The method and steps are the same as those in Example 1. The primary film prepared in step (2) is subjected to corona treatment, edge cutting and winding to obtain a polyethylene film material.

[0088] The prepared polyethylene film material has not been subjected to a longitudinal stretching process, has a thickness of 20 μm, a haze of 27%, a tensile strength (longitudinal) of 67 MPa, an elongation at break of 714%, and a 1% secant modulus (longitudinal) of 169 MPa. After corona treatment, the film surface reaches a value of 42 dynes, and when using ester-soluble ink for high-speed gravure printing, the printing speed can reach 500 m / min, and the printing precision is 0.1 mm.

[0089] It is shown that polyethylene, as a high polymer material with a semi-crystalline state, is actually a process of chain segment orientation and recrystallization of polyethylene molecular chains after being stretched by external force during longitudinal stretching at high temperature. Therefore, the mechanical strength of the polyethylene film material without longitudinal stretching is poor.

[0090] Influence of longitudinal stretching degree on film performance

[0091] The method and steps are the same as those in Example 1. In step (3), the twelve-roll longitudinal stretching is replaced by six-roll longitudinal stretching, and the temperature settings are as follows:

[0092] The temperature of the preheating roller 1 is set to 55℃,

[0093] The temperature of the preheating roller 2 is set to 100℃,

[0094] The temperature of the stretching roller is set to 110℃,

[0095] The temperature of the annealing roller 1 is set to 110℃,

[0096] The temperature of the annealing roller 2 is set to 110℃,

[0097] The temperature of the cooling roller is set to 50℃;

[0098] The polyethylene film material is prepared, wherein the speed of the traction line is 15 m / min, and the comprehensive stretching ratio is 4.8.

[0099] The twelve-roller longitudinal stretching is replaced by six-roller longitudinal stretching, which is essentially a simplification of the stretching process, that is, two preheating rollers, two annealing rollers and two cooling rollers are reduced, which mainly shows that one is that insufficient preheating in the early stage leads to material "cold drawing" deformation, and two is that insufficient "annealing" leads to material "stress concentration", and finally shows that the longitudinal shrinkage rate of the film is more than 15% (while the final longitudinal shrinkage rate of the fully stretched film is 5±1%), which leads to easy deformation in the application process of high-speed gravure printing in the later stage, cannot realize pattern overprinting, and cannot meet the printing requirement of more than 300 m / min.

Claims

1. A process for the preparation of a polyethylene film material suitable for high speed gravure printing, characterised in that: It comprises the following steps: (1) Different densities and masses of copolymerized polyethylene are weighed and put into corresponding five extruders to form a melt by high-temperature extrusion of polyethylene; (2) The melt is blown into a ring shape, and then wind-cooled to form a primary film; (3) The primary film is rolled flat and stretched longitudinally to obtain a stretched film; (4) The stretched film is subjected to corona treatment, edge cutting and winding to obtain a polyethylene film material; The polyethylene film material has a thickness of 20-25 μm and a density of 0.92-0.97 g / cm 3 ; The polyethylene film material is composed of five layers, namely an outer layer (1), a secondary outer layer (2), a middle layer (3), a secondary inner layer (4) and an inner layer (5), and the thickness ratio of each layer is 1:1:2:1:1; the density of the outer layer is 0.96-0.97 g / cm 3 the density of the sub-outer layer is 0.94-0.95 g / cm 3 the density of the middle layer is 0.92-0.93 g / cm 3 the density of the sub-inner layer is 0.94-0.95 g / cm 3 the density of the inner layer is 0.96-0.97 g / cm 3 ; The longitudinal stretching in step (3) is online twelve-roll longitudinal stretching, and the twelve rollers are composed of four preheating rollers, two stretching rollers, four annealing rollers and two cooling rollers, wherein the temperature of preheating roller 1 is 50-60 ℃; the temperature of preheating roller 2 is 80-90 ℃; the temperature of preheating roller 3 is 90-100 ℃; the temperature of preheating roller 4 is 100-110 ℃; the temperature of stretching roller 1 is set to 100-120 ℃; the temperature of stretching roller 2 is set to 100-120 ℃; the temperature of annealing roller 1 is set to 100-120 ℃; the temperature of annealing roller 2 is set to 100-120 ℃; the temperature of annealing roller 3 is set to 100-120 ℃; the temperature of annealing roller 4 is set to 100-120 ℃; the temperature of cooling roller 1 is set to 50-60 ℃; and the temperature of cooling roller 2 is set to 30-40 ℃.

2. A process for the preparation of a polyethylene film material suitable for high speed gravure printing according to claim 1, characterized in that: The blowing temperature in step (2) is 190-200 ℃, and the blowing ratio is 2.0-3.

0.

3. A process for the preparation of polyethylene film material suitable for high speed gravure printing according to claim 1, characterized in that: The pulling speed of the online twelve-roll longitudinal stretching is 15-25 m / min, and the comprehensive stretching ratio is 4.8-5.

5.

4. A process for the preparation of polyethylene film material suitable for high speed gravure printing as claimed in claim 1, wherein: The corona treatment condition in step (4) is 38-42 dynes.

5. Use of a polyethylene film material prepared according to the process of any one of claims 1 to 4 for high speed gravure printing, characterized in that: The speed of the high-speed intaglio printing is 300-500 m / min.

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