A single-layer cast film production process

Abstract

The present invention discloses a single-layer cast film production process, which belongs to the field of film production technology. The ear material cut from the film blank is evenly cut into a number of waste strips through equidistant cutting. The waste strips are twisted and gathered to form a waste rope. During the twisting, the waste strips are twisted to form a spiral structure. The waste rope is heated so that the outer surfaces of the waste strips that fit together in the waste rope form a mutual fusion bond to form a primary material. Finally, the primary material is evenly cut to form waste sheets. The single-layer cast film production process of the present invention significantly improves the mixing uniformity and interface bonding strength of the recycled and reused waste sheets and the new material by forming waste sheets with specific gaps and mixing them with new material.

Description

Technical Field

[0001] The invention relates to the technical field of film production, in particular to a single-layer cast film production process. Background Art

[0002] PE cast film is a kind of film that uses an extruder to melt the resin particles that can be mixed with the masterbatch, and then extrude the molten material through a casting die to form a film blank. The film blank then passes through the casting roller, traction roller, edge roller and wind-up roller in sequence to be stretched, cooled and wound to form a thin film. During the transmission process of the edge roller, a cutter is usually set to cut the two sides of the film blank to trim the wavy lace structure formed on both sides of the film blank when it gradually cools down. The trimmed object is often called ear material.

[0003] Since the material properties of the materials constituting the single-layer film are highly consistent before and after casting, the existing process is to put the two ears of the single-layer film into a crusher to crush them, and then mix the waste flakes formed by the crushing with new materials. This method can ensure that the waste flakes are melted in the extruder and fully mixed with the new material put into the extruder with less pollution on the site.

[0004] During production, it was found that the existing waste sheets were formed by folding and extruding two ear materials in sequence by a crusher, hot-melting and fusing them, and finally cutting them. The waste sheets formed were mainly block structures with many layers and tight structures. Some waste sheets were granular because the edges and corners of the block structure were broken, affecting the factory environment. The block-structured waste sheets were folded and extruded, making it difficult for some of the extruded positions to be completely melted before reaching the die head. Finally, melt A was formed at the die head position. When it was extruded into a film blank together with melt B formed by melting the new material, the two were not fully and effectively mixed in the extruder, resulting in the cast film showing related characteristics with poor uniformity. Specifically, the distribution density of fish eyes on the surface of the finished cast film was uneven, affecting the quality and physical properties of the cast film. Summary of the Invention

[0005] The purpose of the present invention is to solve the problems in the prior art and to propose a single-layer cast film production process.

[0006] In order to achieve the above object, the present invention adopts the following technical solution: a single-layer cast film production process, comprising the following steps:

[0007] S1: Prepare additives and resin particles according to the formula;

[0008] S2: The additives and resin particles are weighed according to the ratio and mixed in the first mixing chamber, and the resulting new material is injected into the second mixing chamber;

[0009] S3: The second mixing chamber mixes all the materials inside it, and the resulting mixture is injected into the extruder to melt and form a melt;

[0010] S4: The die head connected to the extruder extrude the melt onto the casting roll to form a film blank, and then guides the film blank to pass through the traction roll and the edge roller in sequence. When the film blank passes through the edge roller, the two sides are cut and two ear materials are separated from the film blank;

[0011] S4.1: Cut the ear material cut from the film blank into several waste strips at equal intervals;

[0012] S4.2: A plurality of waste strips are twisted and gathered to form a waste rope, wherein the waste strips are twisted to form a spiral structure during twisting;

[0013] S4.3: Heating the scrap rope to melt and bond the outer surfaces of the scrap strips that fit together in the scrap rope to form a primary material, and finally cutting the primary material into pieces at equal intervals to form scrap sheets;

[0014] S5: After the ear material is cut, the film blank is cooled to form a cast film, and the cast film is wound by a winding roller;

[0015] In which, the mixed material includes new material and waste sheets, the resin particles are non-spherical structures, and the waste sheets are formed with multi-level gaps separated by their spiral structures. Several new materials filled in the gaps can be mutually constrained in the waste sheets through the supporting structure abutting against the sides of the gaps. The heat source for heating the waste rope evenly heats the sides of the waste rope. When heated, the waste rope twists around its axis. The gaps in the cross-section of the spiral structure of the waste sheet can accommodate new material filling. The gap area of ​​each waste strip in any cross-section of the waste sheet and its circumscribed circle account for 80%±5%.

[0016] The present invention is further configured such that the scrap rope is not sufficiently cooled before being cut, so that the scrap rope and the waste sheet retain indentations formed by the surface extrusion during cutting after cooling near the cross-sectional position to be cut, and maintain the supporting structure around the gap near the cross-sectional position.

[0017] The present invention is further configured such that the plurality of waste strips cut from one ear material are all in the same plane before being twisted.

[0018] The present invention is further configured such that the length of the waste pieces is not less than the diameter of the waste rope.

[0019] The present invention is further configured such that the width of the waste strip is 1.5 cm to 2.5 cm.

[0020] The present invention is further configured as follows: the number of waste strips in each waste rope is 10 to 14, and the diameter of the waste rope is 0.8 cm to 1.2 cm.

[0021] The present invention is further configured as follows: the number of turns of the spiral structure is 3 to 6, and the diameter of the resin particles is 0.5 mm to 1 mm.

[0022] The present invention is further configured such that the second mixing chamber uses a paddle stirrer to stir the material therein, and the stirring direction of the paddle stirrer is unidirectional stirring.

[0023] In summary, the present invention has the following beneficial effects: in this production process, by forming waste sheets with specific gaps and mixing them with new materials, the mixing uniformity and interface bonding strength of the recycled and reused waste sheets and new materials are significantly improved; since the waste sheets can form a melt earlier in the extruder and mix with the melt formed by the new material, the mass proportion of the waste sheets in the formula can be appropriately increased while ensuring the performance of the cast film, thereby improving the recovery rate of the waste sheets and effectively reducing the problem of oxidation and yellowing caused by long-term storage of waste sheets, and the amount of additives such as antioxidants added. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Flowchart of the production process of the present invention;

[0025] Figure 2 The structure of the present invention is schematically shown Figure 1 ;

[0026] Figure 3 The structure of the present invention is schematically shown Figure 2 .

[0027] In the figure: 1. Film blank; 2. Ear material; 3. Waste strip; 4. Waste rope; 5. First mixing chamber; 6. Second mixing chamber; 7. Extruder; 8. Casting roller; 9. Pulling roller; 10. Edge roller; 11. Winding roller. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. In the description of the present invention, it should be understood that the directions or positional relationships indicated by terms such as "upper", "lower", "front", "back", "left", "right", "top", "bottom", "inside" and "outside" are based on the directions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting the present invention. Obviously, the embodiments described are only some embodiments of the present invention, rather than all embodiments.

[0029] A single layer cast film production process, such as Figures 1 to 3 As shown, the following steps are included:

[0030] S1: Prepare additives and resin particles with a diameter of 0.5 mm to 1 mm according to the formula;

[0031] S2: The additives and resin particles are weighed according to the ratio and mixed in the first mixing chamber 5, and the resulting new material is injected into the second mixing chamber 6;

[0032] S3: The second mixing chamber 6 mixes all the materials therein, and the resulting mixture is injected into the extruder 7 to melt and form a melt;

[0033] S4: The die head connected to the extruder 7 extrude the melt onto the casting roller 8 to form a film blank 1, and then guides the film blank 1 to pass through the traction roller 9 and the edge roller 10 in sequence. When the film blank 1 passes through the edge roller 10, the two sides are cut, and two ear materials 2 are separated from the film blank 1;

[0034] S4.1: The ear material 2 cut from the film blank 1 is cut into a plurality of waste strips 3 at equal intervals;

[0035] S4.2: The waste strips 3 are twisted and gathered to form a waste rope 4. During the twisting process, the waste strips 3 are twisted to form a spiral structure.

[0036] S4.3: Heating the waste rope 4 causes the outer surfaces of the waste strips 3 in contact with each other in the waste rope 4 to form a melt bond to form a primary material. Finally, the primary material is cut into equal intervals to form waste sheets.

[0037] S5: After the ear material 2 is cut, the film blank 1 is cooled to form a cast film, and the cast film is wound by the winding roller 11;

[0038] The mixed material includes new material and waste flakes. In order to better mix the resin particles and the waste flakes during mixing, the resin particles are non-spherical, that is, the resin particles can have a special-shaped structure with multiple edges or corners on the surface. Since the resin particles produced by the granulator are mostly cylindrical, the larger diameter resin particles are usually crushed twice to form non-spherical resin particles with a diameter that meets the requirements. The waste flakes are formed with multi-level gaps separated by their spiral structures. The new materials filled in the gaps can be constrained by each other in the waste flakes through the support structure abutting the side of the gap. Since the mixing of new materials in the waste sheets and the mixing in the second mixing chamber 6 are strongly related, in order to allow more waste sheets to enter the waste sheets, this embodiment causes the waste sheets and new materials to be stirred by a paddle mixer when mixed, and the stirring direction of the paddle mixer is unidirectional stirring. The gap between each waste strip 3 in any cross-section of the waste sheet and its circumscribed circle area accounts for 80%±5%, and this proportion is positively correlated with the number of turns of the spiral structure formed by twisting the waste strip 3. However, in most cases, the gap needs to be large enough to accommodate the entry of new materials, so the number of turns of the spiral structure can be 3 to 6.

[0039] like Figure 2as well as Figure 3 As shown, pipeline a connects the first mixing chamber 5 and the second mixing chamber 6 to transfer new material to the second mixing chamber 6, pipeline b connects the second mixing chamber 6 and the extruder 7 to transfer the mixed material to the extruder 7, and pipeline c transfers waste sheets to the second mixing chamber 6.

[0040] like Figures 1 to 3 As shown, when the thin waste strip 3 is twisted, it will be deformed into a structure with a single spiral line or a double spiral line with one end closed. The cross-sections of the two cross-sectional shapes have gaps that can accommodate new materials to be filled. Similarly, the setting of the gaps also allows the melt D formed by the melting of the new material and the melt E formed by the waste sheet composed of the waste strip 3 to form a multi-layer mixed state before the waste sheet is completely melted. After the waste strips 3 with the two cross-sections are bonded to each other, the supporting structure on the inner side of each waste strip 3 retains the characteristic of being deformable toward the gap because a stable bond is not formed, so that the supporting structure on the inner side can be deformed under the abutment of several new materials, so that the waste sheet can temporarily store new materials. Moreover, since the spiral structure of the waste strip 3 after twisting forms multiple levels of gaps separated by the supporting structure, the gaps in the waste strip 3 can change in space as the waste strip 3 is squeezed, thereby temporarily storing more new materials.

[0041] In this embodiment, the mechanism for twisting the waste strips 3 continuously rubs the circumference of the waste rope 4 back and forth during the production line of cast film. Because the stroke of each reciprocating friction is large enough, after the mechanism for twisting the waste rope 4 gathers a number of waste strips 3 into a rope-like structure, the twisted waste strips 3 are sufficiently stably deformed into a double helix structure with one end closed in cross section, and the helical direction changes alternately along the length of the waste strip 3.

[0042] In order to make the structure of the waste strips 3 uniform after twisting and deformation, and ensure the consistency of the structure of the waste strips 3 constituting the waste rope 4, the several waste strips 3 cut from one ear material 2 are all in the same plane before twisting, so as to facilitate the same twisting action.

[0043] like Figures 1 to 3 As shown, when heated, the scrap rope 4 can be pulled in a specific direction to transmit the scrap rope 4 in a twisted state around its axis, so that the outer contour of the scrap rope 4 is closer to a circular shape, and a single scrap strip 3 can be connected with three or four adjacent scrap strips 3 in most cases, and a stable surface bonding is achieved in the process of heating the scrap rope 4. Considering that the contours of the scrap rope 4 and the scrap strips 3 after twisting are both approximately circular structures, in order to make the outer surfaces of the adjacent scrap strips 3 after twisting fully melt-bonded and improve the heat distribution, the heat source for heating the scrap rope 4 evenly heats the circumference of the scrap rope 4.

[0044] like Figures 1 to 3As shown, the temperature of the heat source for heating the scrap rope 4 is controlled between 100 and 140 degrees Celsius, specifically depending on the melting point of the film being produced. In order to make it easier for new material entering the scrap sheet to be temporarily stored in the scrap sheet, the scrap rope 4 is not fully cooled before being cut. The surface temperature of the incompletely cooled scrap rope 4 is controlled so that after cooling, the scrap rope 4 and the scrap sheet near the cross-section to be cut retain the indentations formed by the surface extrusion during cutting. Taking the ear material 2 cut from the cast film produced by casting low-density polyethylene resin material as an example, its melting point is about 110 degrees Celsius. Incomplete cooling means that the surface temperature of the scrap rope 4 is reduced by 20 to 30 degrees Celsius. Generally, air cooling at room temperature can reduce the surface temperature of the scrap rope 4 in a short time.

[0045] The indentation is set to form a constriction structure at both ends of the waste sheet, so that when the new material tends to leave the waste sheet from the constriction structure position, it is difficult to separate from the waste sheet due to accumulation, which plays a role in preventing the new material from escaping. In particular, when the waste sheet and the new material are mixed and subjected to the unidirectional stirring force, the new material entering the waste sheet tends to accumulate in the gap near one of the constriction structures of the waste sheet, so that the new materials entering the gap of the waste sheet are constrained and not easy to pass out of the waste sheet, and make way for the gap of the other constriction structure to allow more new material to enter the waste sheet. At the same time, because the plastic deformation of the two ends of the waste sheet is performed when it is not fully cooled, the waste sheet can maintain the support structure around the gap near the cross-sectional position, effectively reducing the brittle deformation of the waste sheet at the cutting cross-sectional position during the process of cutting the waste sheet;

[0046] Since the waste sheet is provided with a necking structure, in order to make the waste sheet easier to cut, the length of the waste sheet is not less than the diameter of the waste rope 4. In this embodiment, the width of the waste strip 3 is 1.5 cm to 2.5 cm, the number of waste strips 3 in each waste rope 4 is 10 to 14, and the diameter of the waste rope 4 is 0.8 cm to 1.2 cm. The relationship between these three data is positively correlated. The diameter of the waste rope 4 is also positively correlated with the thickness of the ear material 2.

[0047] Taking the production of low-density polyethylene cast film for packaging bags as an example, its thickness range is usually 0.025 mm to 0.15 mm. The ear material 2 cut from it is used to produce waste sheets. The diameter of the waste sheet is 1 cm, and it is composed of 12 waste strips 3. The waste strip 3 is a double helix structure with a cross-section closed at one end. The number of turns of a single helix is ​​close to 4. The gap of each waste strip 3 in any cross-section of the waste sheet and its circumscribed circle area account for nearly 80%.

[0048] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

[0049] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A single-layer cast film production process, characterized in that: The following steps are involved: S1: Prepare additives and resin particles according to the formula; S2: The additive and the resin particles are weighed according to a ratio and mixed in the first mixing chamber (5), and the resulting new material is injected into the second mixing chamber (6); S3: The second mixing chamber (6) mixes all the materials therein, and the resulting mixed material is injected into the extruder (7) to melt and form a melt; S4: The die head connected to the extruder (7) extrude the melt onto the casting roller (8) to form a film blank (1), and then guides the film blank (1) to pass through the traction roller (9) and the edge trimming roller (10) in sequence. When the film blank (1) passes through the edge trimming roller (10), the two sides are cut, and two ear materials (2) are cut from the film blank (1); S4.1: The ear material (2) cut from the film blank (1) is cut into a plurality of waste strips (3) at equal intervals; S4.2: The plurality of waste strips (3) are twisted and gathered to form a waste rope (4), wherein the plurality of waste strips (3) are twisted to form a spiral structure during the twisting process; S4.3: heating the waste rope (4) so ​​that the outer surfaces of the waste strips (3) that are attached to each other in the waste rope (4) are melt-bonded to each other to form a primary material, and finally cutting the primary material into pieces at equal intervals to form waste sheets; S5: After the ear material (2) is cut, the film blank (1) is cooled to form a cast film, and the cast film is wound by a winding roller (11); The mixed material includes new material and waste sheets, the resin particles are non-spherical in structure, and the waste sheets are formed with multi-level gaps separated by their spiral structures. The new materials filled in the gaps can be mutually constrained in the waste sheets by the support structure abutting against the peripheral side of the gaps. The heat source for heating the waste rope (4) uniformly heats the peripheral side of the waste rope (4). When heated, the waste rope (4) twists around its axis. The gaps in the spiral structure section of the waste sheet can accommodate the new materials. The gaps in any section of the waste sheet account for 80%±5% of the area of ​​the gap and its circumscribed circle of each waste strip (3).

2. A single-layer cast film production process according to claim 1, characterized in that: The scrap rope (4) is not fully cooled before being cut, so that the scrap rope (4) and the scrap sheet near the cross-section position to be cut retain indentations formed by the surface being squeezed during cutting after cooling, and maintain the supporting structure around the gap near the cross-section position.

3. A single-layer cast film production process according to claim 1, characterized in that: The plurality of waste strips (3) cut from one ear material (2) are all in the same plane before being twisted.

4. A single-layer cast film production process according to any one of claims 1-2, characterized in that: The length of the waste pieces is not less than the diameter of the waste rope (4).

5. A single-layer cast film production process according to claim 4, characterized in that: The width of the waste strip (3) is 1.5 cm to 2.5 cm.

6. A single-layer cast film production process according to claim 5, characterized in that: The number of waste strips (3) in each waste rope (4) is 10 to 14, and the diameter of the waste rope (4) is 0.8 cm to 1.2 cm.

7. A single-layer cast film production process according to claim 6, characterized in that: The number of turns of the spiral structure is 3 to 6, and the diameter of the resin particles is 0.5 mm to 1 mm.

8. A single-layer cast film production process according to claim 1, characterized in that: The second mixing chamber (6) uses a paddle-type stirrer to stir the materials inside the chamber, and the stirring direction of the paddle-type stirrer is unidirectional stirring.

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