Flat yarn process includes: raw material modification, *** mixing, coloring, filling, preparation, anti-aging, anti-degradation issues, extrusion process of temperature, pressure, flow regulation and control and rheological behavior of the extrusion process, power consumption, yield issues, the drafting process of the haul-off ratio, blowing ratio, draw ratio, crystallization, cooling, orientation, heat treatment and stereotypes, the winding process of the molding and spindles, such as the quality of the inspection. Technical problems.
Flat yarn process, also known as yarn-making process, it is the first process of plastic knitting production, but also the most important process.
Flat wire production process according to the film method, there are two kinds of film, tube film and flat film, according to the film cooling method, air-cooled, water-cooled and intercooled, according to the drafting heating method of hot plate, hot rollers, hot air, according to the spindle winding and molding, centralized oscillating coil, single spindle torque motor coiling, magnetic torque coiling.
3-1. Flat wire production process technical indicators are mainly divided into four categories:
3-1-1. is the physical and chemical modification indicators, mainly *** mixed modification, mixing ratio, functional additives than the mixing ratio of waste recycled materials.
3-1-2. Physical rheology indicators, mainly draw ratio, blowing ratio, draw ratio, shrinkage ratio.
3-1-3. Mechanical properties, mainly tensile strength, relative tensile strength, elongation at break, linear velocity, linear density deviation.
3-1-4. is the tolerance dimension index, mainly flat wire thickness, flat wire width and so on.
3-1-1. Modified blend ratio and percentage:
Flat wire production process according to the film method, there are two kinds of film, tube film and flat film, according to the film cooling mode, air-cooled, water-cooled and intercooled, according to the drafting heating mode of hot plate, hot rollers, hot air, according to the spindle winding molding, centralized oscillating coil, single spindle torque motor winding, magnetic torque winding. Flat wire raw materials often add some modifiers or functional masterbatch and waste recycled materials, available in two indicators.
3-1-1-1. Mixing ratio, the weight ratio of an added component and the main raw material is called mixing weight ratio.
3-1-1-2. Add the percentage, an additive group of the overall weight of each group of the weight of the percentage of added weight.
3-1-2. Rheological traction ratio, blowing ratio, stretching ratio, retraction ratio:
3-1-2-1. The traction ratio is the ratio of the extrusion film traction speed to the speed of extrusion from the mouth of the film, which is not only used for flat film, but also used for tubular film, through the control of the traction ratio, so that the film in the direction of traction with a slight orientation effect. Control of the draw ratio is the only effective means of controlling the thickness of the extruded film after cooling. Because an extruder's die gap is basically fixed, the amount of adjustment is small, in general, the haul-off ratio is maintained at 4-8 is appropriate.
3-1-2-2. Blow-up ratio, blow molding, tube film blown out of the bubble diameter and the original diameter of the die mouth of the ratio, called the blow-up ratio. Obviously, there is no blowing ratio problem for flat film. Theoretically, the larger the blowing ratio, the better the film's transverse tensile orientation, the better the tensile strength, but not too high in the actual production, so as not to cause serpentine swing, uniformity of the degree of decline in the thickness of the film is not equal to the wrinkles and so on. Generally speaking, the blowing ratio is controlled between 2.0-3.5, and the maximum is not more than 8 bits.
3-1-2-3. Drawing ratio, flat wire drawing, unit length of split wire (billet) drawn length times, or described as drawing (two draw) speed and traction (a draw) speed ratio for the drawing ratio. The draft ratio is the most important process indicator in flat wire production. Draw ratio is also known as draw times, stretch ratio. Drawing of flat wires is a unidirectional stretching process below the melting point temperature, and the stretching process is an orientation process in order to obtain high strength and other physical and mechanical properties of the flat wires. In general, the draw ratio is controlled at 4-7 times, and for special needs, the draw ratio is up to 11 times.
3-1-2-4. Retraction ratio, refers to the ratio of flattened wire pull-out speed and traction speed. From the needs of the production process, the pull-out speed should be lower than the traction speed, to the edge of the second heating and shaping of a retraction, so that the flat wire internal stress elimination, to obtain a strong tension and excellent elongation. Retraction ratio, also known as shaping ratio. Generally, the shrinkage ratio is between 0.96 and 0.99.
3-1-3. Flat Wire Density, Relative Tensile Load, Elongation at Break:
3-1-3-1. Flat Wire Density characterizes the mass per unit length of a linear object. The greater the density, the greater the breaking force. In plastic knitting, flat wire density is a measure of the overall strength of the basic elements of plastic knitting. According to GB/T8946 in Appendix A of the provisions of the frame length gauge to 100M flat wire, weighing accurate to 0.1 grams.
3-1-3-2. Relative tensile load, also known as the relative tensile force, refers to the tensile force of each tex of flat wire, for each flat wire, due to its density and thickness varies, and thus different tensile force. However, the relative tensile load is basically similar. Because the relative tensile load is a physical strength index independent of the width and thickness of the wire. Its size depends on the temperature of the raw material, drafting ratio, sizing, cooling, crystallization and other factors. National standard relative breaking force greater than or equal to 0.32N/tex.
3-1-3-3. Elongation at break, refers to the flattened wire stretching part of the effective marking (between the two fixtures) and the initial effective marking part of the length of the increase in length (between the two fixtures) length of the percentage of the flattened wire is a measure of the toughness of the flat wire (elasticity) indicators. Has a large elongation at break, characterizing the flat wire impact resistance has a certain unisex elongation, not immediately brittle. Therefore, the elongation at break is large, in the same conditions of the tensile force, the number of drop test may be more. The national standard requires that the elongation at break is 15-30%.
3-1-4. Flat wire width and thickness:
3-1-4-1. Flat wire width, refers to the width of the split wire after drafting, which determines the density of the woven fabric. For plastic woven bags and composite plastic woven bags, the national standard recommended three commonly used weaving density (diameter density * weft density), that is, 36 * 36, 40 * 40, 48 * 48 roots / 10cm. These three weaving density also applies to other fabrics, according to the three kinds of weaving density, the width of the flat wire theoretically calculated as: 2.78mm, 2.5mm, 2.08mm. In the process of producing flat wire, the width of flat wire should be controlled according to the weaving density required by customers.
3-1-4-2. Thickness of the flat wire is the thickness of the split wire after drawing. The thickness determines the weight of the woven fabric per unit area. At the same time, if the width of the filament has been determined, the thickness of the filament is the determining factor of the density of the filament.
3-2. Woven bag weaving process indicators:
3-2-1. weaving density and weaving density tolerance.
3-2-1-1. Weaving density refers to 100mm × 100mm woven fabric, the number of warp and weft yarns. The national standard GB/T8946-1998, "the bag is flat, in the bag on the two diagonally below the circle of 100mm × 100mm two squares, the outer edge of the square and the bag edge line 100mm apart, visual inspection of the square of the warp, weft roots, take the average value, counting when the end of the last point is less than one, according to a count." The national standard specifies the density of the weave as well as the tolerance of the density. The density of the weave depends mainly on the packaged product and is determined by the user.
Commonly used density of woven fabric is 36 x 36 / 10cm, 40 x 40 / 10cm, 48 x 48 / 10cm.
3-2-1-2.Tolerance of woven density.
Weave density tolerance is the number of more or less flat wires than the given standard weave density.
3-2-2. Mass per unit area of woven fabric.
The weight per unit area of woven fabric is expressed in grams per square meter, which is an important technical index of woven fabric. Square meter weight depends mainly on the warp and weft density and the thickness of the flat wire, square meter weight affects the tensile strength of the woven fabric, load capacity, square meter weight is a major part of the production company to control the cost.
3-2-3. Woven fabric tensile load.
The tensile load is also called tensile strength, tensile strength. For the woven fabric to withstand the warp and weft direction of the tensile load, so called warp, weft tensile load.
3-2-4. Width.
A variety of woven fabric width directly affects the bag-making process. For tube fabric, the width is expressed in terms of the warp fold, which is equal to half of the circumference of the circle.
Width retraction, the width of all woven fabrics after weaving and rolling, in the roll cutting, printing, sewing, the width of the bag made of slightly less than the width of the roll, we call the width retraction.
3-2-5. Hand feel.
PP flat silk braid feel thicker, broader, thicker and harder.
HDPE flat silk fabrics feel softer, lubricated, not dense.
Add calcium masterbatch in PP flat silk material, feel broad, PP less HDPE will make it softer.
Flat yarn is narrow, the weaving is flat and soft, flat yarn is wide, the weaving is folded and rough.
3. Plastic weaving process indicators:
3-3. Woven bag coating process indicators.
GB/T8947-98 and GB10803-89 respectively, the provisions of the coated bags and coated fabric technical quality standards. They have the same, there are differences, the reason is that the application of woven bags and woven fabrics of different requirements, indicators are slightly different. 1998 revised to recommended standards, more scientific than the original GB8947-88, more perfect.
3-3-1. Size series and tolerance.
3-3-1-1. Composite plastic woven bags.
The effective width of composite plastic woven bag is 450-700mm, every 50mm is a grade, the tolerance of width is ±15 to -10mm. The effective length of the bag is for the decision of both sides, the tolerance is ±15 to -10mm, and the thickness of the film tolerance is ±0.005mm.
3-3-1-2.Composite Plastic Woven Fabric.
The width of the woven fabric is 100m or 200m for each piece of fabric below 2m, the tolerance of width is 0 to +10mm, the tolerance of length is not allowed to be negative deviation. The width of the woven fabric above 2m is 50m or 100m per piece, the tolerance of width is 0-20mm, the tolerance of length is not allowed to have negative deviation.
3-3-1-3. Mass per unit area and mechanical strength.
The mass per unit area and tensile load of woven fabric after coating, peeling strength. Woven bag peeling strength of 3.0N/3cm, woven fabric peeling strength of 2.5N/3cm. There is a method of experimental peeling force, that is, with adhesive tape on the coated film, and then tear the tape, can not be separated from the woven fabric and film as qualified, that is, to achieve the peeling strength. This method is not valid for non-statutory testing.
3-4. Woven bag making process index:
Woven bag making process is the last process of plastic weaving, which includes printing, cutting, sewing, packing and other major links.
3-4-1. Sewing process indicators.
3-4-1-1. Sewing strength index.
This index is the most important and critical index of bag making. In the plastic woven bag GB/T8946 and composite plastic woven bag GB/T8947 national standards, clear sewing side to the bottom of the sewing to the tensile load. The main factors affecting the strength of the seam is the type and model of the sewing thread, stitch size, stitching, rolled or folded edge seam to the bag edge size, hot and cold cutting methods. Plastic knitting enterprises should develop internal control indicators for these factors. For the container bag, the national standard stipulates that the tensile strength of the main connecting part must reach more than 67% of the basic strength, and the tensile strength of the bottom connecting part must reach more than 42% of the basic strength. For the top seal of the socket cement bag, it is recommended to treat it as the strength of the bottom of the seam, the strength of the bottom of the seam of the paper bag is generally not up to the target, so it is recommended to change to the bottom of the paste bag. For laminating cold-cutting bags, it is recommended to use the rolled edge treatment, because the cold-cutting edge of the seam may be torn out from the warp wire together with the weft wire. For non-strength requirements of the woven bag top lock edge one week, stitch can be dense, fine thread.
3-4-1-2. Dimensional tolerances.
For plastic woven bags and composite plastic woven bags length and width tolerance is the same +15mm and -10mm. For the width tolerance does not meet the cylinder cloth, in the bag-making process, sieve out, waiting for processing. For sticky center-sewn bags, the length tolerance refers to the effective length of the sewn seam, which is left as a seam when cutting. The amount of seam allowance is determined by the specifics of the rolled edge, the folded edge, and the inside fold of the top opening. The size tolerance of the container bag is: 20mm for 1m or less, 30mm for 1m or more.
3-4-1-3.Printing of graphics.
Plastic printing is mainly letterpress printing, printing graphic position tolerance, printing graphic clarity, printing graphic color. The national standards for plastic products are not clearly defined, and some standards only require clear printing. Therefore, plastic knitting enterprises should be based on user requirements for the development of enterprise printing standards. The development of enterprise standards, take into account the type of printing equipment, printing ink type, printing capacity, etc. BOPP gravure printing to be standardized.
3-4-1-4. Appearance quality.
Plastic woven bags, composite plastic woven bags, container bags, cement bags, all the appearance of the lack of quality is not always caused by the bag-making process. However, the bag-making process is the last process, but also the last process of quality control.
3-4-2. Bonding process index.
3-4-2-1. Bonding strength index.
The national standard of plastic knitting products does not specify the bonding strength index. Therefore, plastic knitting enterprises can formulate enterprise standards according to user requirements and related standards. We recommend that the national standard GB/T8947 in the bonding to the tensile strength to develop enterprise standards. It is not only applicable to all kinds of adhesive, but also applicable to all kinds of adhesive bonding seams. The main factors affecting the adhesive strength are the adhesive force of the adhesive, the lap width, the affinity of the substrate to the adhesive and so on.
3-4-2-2. Lap width.
When bonding with molten resin, the strength of the bond should be about 80% of the strength of the base material if the temperature of the raw material is selected appropriately.
3-4-2-3. Selection of Melt Resin.
For polyethylene-based coated fabrics can be used for coating grade polyethylene, because they are more compatible. For polypropylene-based coated fabrics, you can use coated polypropylene or special polypropylene seaming material, their melt index is: 16-20g/10min. We hope that the melting temperature of the seaming bonded PP material is about 10 ℃ lower than the melting temperature of the PP material of the flat wire to prevent the woven fabric from aging of the heat and oxygen.
3-4-2-4. When applying PP center seam bonding material. Extruder extrusion temperature can be controlled between 260-280 ℃, for PE center seam bonding material. Extruder extrusion temperature can be controlled at 255-265 ℃, different resins, different equipment, can be adjusted appropriately. Extrusion flow control depends on the bonding speed, extrusion film thickness of 0.05-0.12mm can be.
3-4-2-5. Preparation of binder.
Bonding agent for the middle seam is less, mainly used for gluing the bottom. Adhesive formula, preparation process, preparation equipment. Application methods all affect its quality and adhesion. The main agent and curing agent of the formula are provided to the user separately and are prepared by the user on site. The main agent and curing agent are mixed to produce cross-linking and curing, this chemical reaction process is slow at room temperature, and cures quickly at elevated temperatures. Therefore, the preparation quantity should not exceed the dosage too much, low temperature storage after preparation, storage time should not be too long, storage sealed. For example, a formula: 200L ethyl acetate and 25kg Ulite3076 particles stirring 8h, formulated into a mother liquor, and then add solidifying agent and thickening agent, and then stirring for 5min, formulated into a bonding agent, used to bond the middle seam or paste the bottom.
3-4-3. Heat sealing welding and square valve bottom port process indicators.
Currently, the world's most advanced bag-making process is not sewing, not gluing, but heat-seal welding.
3-4-3-1. Heat seal welding process.
Heat sealing welding equipment is similar to the bottom of the paper bag gluing machine, only the bottom of the gluing part of the change to heat sealing welding, heat sealing equipment, first of all, the film coated cylinder cloth printing and cutting, and then its upper and lower mouth folding. With about 400 ℃ hot air welding valves and reinforcement sheet. The key to this technology is to weld the reinforcement piece.
3-4-3-2. Factors affecting heat sealability.
Sufficient adhesion of the coating film and the substrate is a prerequisite, if the peel strength is not enough, heat sealing and welding, will produce the phenomenon of cloth film separation. This requires that the surface of the film must be moderately oxidized to improve the peel strength. Excessive oxidization can also have undesirable effects. Heated and pressurized resin surfaces are not as compatible with each other as they could be.
3-4-3-3. Quality standards for square valve pockets.
Square bottom valve bag quality requirements than the general composite bags, it is an internationally popular high-strength bags. At present, there is no uniform, applicable to a variety of materials packaging national standards. GB9774-1998, only for the cement packaging of paper bags or paper/plastic bag paste bottom of some of the quality indicators.
3-4-3-4. Comparison of various sealing strength.
Woven fabric/paper composite sewing pockets, whether folded edge, rolled edge, wrapped edge, its strength is the lowest, its tensile strength is only 50N-150N/5cm.
Woven fabric/film sewing pockets, which wrapped edge bag strength is the lowest, followed by folded edge bag, rolled edge bag is the best. GB/T8946/8947 requirements of the sewing bottom to the strength of the TA-type bag 200N/5cm, A-type bag 200N/5cm, the bottom of the bag is the best. GB/T8946/8947 requires the sewing of the bottom to the strength of the TA type bag 200N/5cm, A type bag 350N/5cm, B type bag 300N/5cm, C type bag 350N/5cm. its strength is higher than the woven fabric/paper composite sewing bag.
Square bottom valve mouth folder, its strength can be in accordance with the GB/T8947 adhesive strength to the implementation of the TA-type bag 300N/5cm, A-type bag 350N/5cm, B-type bag 400N/5cm, C-type bag 400N/5cm. its strength is slightly higher than the woven fabric, woven fabric / film sewing bag.
Square bottom valve mouth heat seal welded bags, it has the highest strength. With enough overlap, its strength can be the same as the base material. It is the most popular and strongest bag type in the world.
3-4-4. Technical specifications of sewing thread.
3-4-4-1. Technical specifications of cotton and polyester threads for plastic knitting.
Cotton sewing thread for plastic knitting sewing according to the national standard GB/T6835-1997 and polyester sewing thread national standard GB/T6834-1997.
3-4-4-2. Selection of thread density (tex) and imperial count (Ne).
Thread density is a measure of quality per unit length of a slender object. In the case of sewing thread, it is the thickness of the thread. In the case of polyester and cotton threads, since polyester is heavier than cotton, the thread density is equal. Polyester thread is thinner than cotton thread for the same strand and viscosity. When choosing a polyester thread of 29.9 tex (20Ne) and switching to cotton, it is best to start with 18 tex (32Ne), which has a smaller thread density, to prevent the thread from passing through the needle hole.
Measurement of thread density:
Tex: the number of grams of mass of 1000 meters of yarn at a given rate of dampness.
Denier (D): grams of mass of 9000 meters of yarn at a nominal rate of dampness.
Metric count (Nm): the number of meters of length of one gram of yarn at the metric rate of return.
Number of imperial counts (Ne): the number of meters of length of one pound of yarn at the metric return rate. (Each strand equals 840 yards).
Moisture retention is the percentage ratio of yarn: (weight before drying - weight after drying)/weight after drying. It is dried at a temperature of 105-110°C or less until constant weight.
At present, some sewing thread suppliers still use the imperial index Ne to express the thread density, such as: 20s/2*3, which means imperial 20 count yarn ****6 strands.
3-4-4-3. Number of strands, breaking strength, twist, twist direction.
The number of strands: how many strands are twisted in each strand, generally 2-12 strands are twisted.
Single line breaking strength: according to GB2543-81 test single line breaking force, expressed in Newton N.
Twist: the number of twisting turns of a single strand of 10cm long wire.
Initial twist: the twist of a single strand before it is joined.
Returning twist: the twist of the combined strands.
Twisting direction: the direction of thread twisting, clockwise is S, anti-clockwise is Z.
3-4-4-4. Appearance quality and length tolerance of the thread:
The appearance quality and tolerance of the thread are stipulated in the national standards GB/T6835-1997 and GB/T6834-1997 for cotton and polyester thread for plastic knitting.
The sewing threads produced by plastic knitting enterprises with edge yarn or split film yarn have a thread density of 150 tex or more, no burr in appearance, and no shedding of spindles.