CN114907657A - Reactive extrusion method biaxially oriented polyvinyl alcohol film and preparation method thereof - Google Patents
Reactive extrusion method biaxially oriented polyvinyl alcohol film and preparation method thereof Download PDFInfo
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- CN114907657A CN114907657A CN202210607333.5A CN202210607333A CN114907657A CN 114907657 A CN114907657 A CN 114907657A CN 202210607333 A CN202210607333 A CN 202210607333A CN 114907657 A CN114907657 A CN 114907657A
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
- C08J5/18—Manufacture of films or sheets
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C41/00—Shaping by coating a mould, core or other substrate, i.e. by depositing material and stripping-off the shaped article; Apparatus therefor
- B29C41/24—Shaping by coating a mould, core or other substrate, i.e. by depositing material and stripping-off the shaped article; Apparatus therefor for making articles of indefinite length
- B29C41/26—Shaping by coating a mould, core or other substrate, i.e. by depositing material and stripping-off the shaped article; Apparatus therefor for making articles of indefinite length by depositing flowable material on a rotating drum
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C55/00—Shaping by stretching, e.g. drawing through a die; Apparatus therefor
- B29C55/02—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets
- B29C55/10—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets multiaxial
- B29C55/12—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets multiaxial biaxial
- B29C55/14—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets multiaxial biaxial successively
- B29C55/143—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets multiaxial biaxial successively firstly parallel to the direction of feed and then transversely thereto
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2329/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an alcohol, ether, aldehydo, ketonic, acetal, or ketal radical; Hydrolysed polymers of esters of unsaturated alcohols with saturated carboxylic acids; Derivatives of such polymer
- C08J2329/02—Homopolymers or copolymers of unsaturated alcohols
- C08J2329/04—Polyvinyl alcohol; Partially hydrolysed homopolymers or copolymers of esters of unsaturated alcohols with saturated carboxylic acids
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- Shaping By String And By Release Of Stress In Plastics And The Like (AREA)
- Extrusion Moulding Of Plastics Or The Like (AREA)
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Abstract
The invention discloses a film, aiming at providing a reactive extrusion method biaxial stretching polyvinyl alcohol film and a preparation method thereof, the technical scheme main point is that the reactive extrusion method biaxial stretching polyvinyl alcohol film comprises the following steps: polyvinyl alcohol resin with alcoholysis degree of 88% and one or more resin mixtures of PVA2488, PVA2088, PVA1788 and PVA 0588; the components are reaction auxiliary agents of a plasticizer, a lubricant and a stabilizer, the reaction auxiliary agents are liquid mixed liquor, and the liquid mixed liquor is mixed in a polyvinyl alcohol resin mixture after partial primary melting and extrusion are carried out on the polyvinyl alcohol resin, and the process flow is as follows: the method comprises the steps of preparing cleaning equipment → preparing 88% of polyvinyl alcohol resin → feeding (adopting a weight loss scale) → preliminary melting → extruding → reaction auxiliary agent (adopting a liquid pump) → extruding (adopting a back mixing element to control extrusion time for 15min-20min) → melting → filtering → head distribution → tape casting into sheets → longitudinal stretching → transverse stretching → sizing → water solubility testing, and the method is suitable for the technical field of film preparation.
Description
Technical Field
The invention belongs to the technical field of film preparation, and particularly relates to a reactive extrusion method biaxially oriented polyvinyl alcohol film and a preparation method thereof.
Background
With the continuous deepening of the environmental protection concept of people, the requirement on green packaging in the packaging field is higher and higher, the variety of the water-soluble film is also endless, the water-soluble film is used as an important type of green packaging material, and the water-soluble film is more and more emphasized by the packaging industry of various countries due to the characteristics of good water solubility, barrier property, environmental protection property and the like, and the water-soluble film is mainly made of a water-soluble polyvinyl alcohol (PVA) film.
Polyvinyl alcohol (PVA) is an environment-friendly water-soluble polymer, and due to the fact that the PVA is regular in structure, strong hydrogen bonds exist in molecules, the crystallinity is high, the melting temperature of the PVA is higher than the decomposition temperature, and thermoplastic forming is difficult, therefore, a solution casting coating method is mainly adopted for the PVA film sold in the market at present, but the wet casting method is low in production efficiency, long in production period, unstable in product quality, difficult to control the film thickness, and high in cost, so that popularization and application of the PVA water-soluble film are limited.
For example, chinese patent application No. (CN201510232932.3) discloses a biaxially oriented polyvinyl alcohol film and a method for preparing the same, wherein polyvinyl alcohol with alcoholysis degree of 95 (mol)% -99.9 (mol)% is used as a raw material, and a plasticizer, soft water and a processing aid are added, the process of the application is simple and the pollution is less, but the application has low adjustability (the water solubility is usually water solubility at room temperature, for example, in water with 25 ℃, the dissolution time of a water soluble film should not exceed 3 min) by adding the plasticizer, the soft water and the processing aid and the polyvinyl alcohol together from the beginning of an extruder, and the application uses polyvinyl alcohol with alcoholysis degree of 95% -99.9% as a raw material, which has high cost and low applicability and needs to be improved.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a reactive extrusion method biaxially oriented polyvinyl alcohol film and a preparation method thereof.
In order to achieve the purpose, the invention provides the following technical scheme: a reactive extrusion biaxially oriented polyvinyl alcohol film comprising:
the polyvinyl alcohol is polyvinyl alcohol resin with alcoholysis degree of 88%, and is one or a mixture of more of PVA2488, PVA2088, PVA1788 and PVA 0588;
the reaction auxiliary agent is mixed in the polyvinyl alcohol resin mixture after partial primary melting and extrusion of the polyvinyl alcohol resin;
wherein the reaction auxiliary agent is liquid mixed liquor and comprises 50-80% of PVA resin, 20-50% of plasticizer, 0-3% of lubricant and 0-2% of stabilizer.
In the technical scheme, 88% of polyvinyl alcohol resin is adopted, and a plasticizer, a lubricant and a stabilizer are supplemented, so that the processing cost is reduced, the processability, the water-solubility adjustment property and the thermal stability of the polyvinyl alcohol resin are effectively improved, meanwhile, a reaction auxiliary agent is added after partial preliminary melting and extrusion of the polyvinyl alcohol resin is carried out, the mixing effect and the mixing efficiency of the reaction auxiliary agent and a polyvinyl alcohol melt are improved, the influence of high temperature on the reaction auxiliary agent is reduced, and the controllability of the reaction auxiliary agent is good, so that the water-solubility adjustability of the polyvinyl alcohol film is higher.
The invention further provides that the plasticizer comprises:
one or more liquid mixed liquid of sorbitol, mannitol, glycerol, diethanolamine, triethanolamine, diglycerol, triglycerol, decapolypropylene triol and diethylene glycol.
In the technical scheme, because PVA molecules contain a large amount of hydrogen bonds and crystal structures, and the melting point is far higher than the decomposition temperature, the hydrogen bonds among the molecular chains are weakened through the plasticizer, the crystal structures are broken, the melting temperature of the PVA molecules is reduced, the PVA molecules are prevented from being decomposed along with the PVA molecules in the processing process, and the plasticizer composed of liquid is adopted, so that the PVA molecules are convenient to measure uniformly, and the mixing effect and the mixing efficiency between the plasticizer and the polyvinyl alcohol melt are convenient to realize
The invention further provides that the lubricant comprises:
erucamide, oleamide, myristic acid, hardened oil, glycerol monostearate and pentaerythritol stearate.
In the technical scheme, the lubricant is favorable for lubricating during extrusion and extrusion molding, and the lubricant formed by liquid is convenient for uniform metering and is convenient for the mixing effect and mixing efficiency between the plasticizer and the polyvinyl alcohol melt.
The invention further provides that the stabiliser comprises:
one or more liquid mixed liquids of organotin stabilizing agent, rare earth stabilizing agent, zinc stearate, cerium stearate, barium stearate, aluminum distearate and calcium stearate.
In the technical scheme, the stabilizer can prevent thermal degradation in the processing process and avoid skid resistance of the film, and the stabilizer formed by liquid is convenient for uniform metering and mixing effect and mixing efficiency between the plasticizer and the polyvinyl alcohol melt.
A method for preparing a biaxially oriented polyvinyl alcohol film by a reactive extrusion method comprises the following steps:
s1: feeding polyvinyl alcohol resin with alcoholysis degree of 88% into a reactive extruder from a main feeding port by a weight loss scale, and uniformly metering and pumping pre-mixed reaction auxiliary agents by a liquid pump after partial primary melting and extrusion of the polyvinyl alcohol resin;
s2: extruding the polyvinyl alcohol resin by a reactive extruder, and controlling the extrusion time to be 15-20 min to obtain a melt after the reaction is finished;
s3: conveying the melt after reaction to a metering pump, a special melt filter and a special fluidly-arranged grope, performing good attachment and cooling with a cooling roller through the fluidly-arranged grope, and then drawing to prepare a casting sheet;
s4: biaxially stretching and shaping the obtained cast sheet, and then obtaining a reactive extrusion method biaxially stretched polyvinyl alcohol film;
s5: and (4) water solubility test.
In the technical scheme, the weightlessness metering scale is adopted for feeding, the feeding accuracy and the control precision are improved, the control and the regulation are convenient, meanwhile, the reaction auxiliary agent is uniformly metered and fed by the liquid pump, the processing effect of reactive extrusion on the polyvinyl alcohol film is ensured, the extrusion time is controlled, the melt quality and the melt flowing stability are ensured, meanwhile, the bidirectional stretching setting is adopted, the film thickness is convenient to control, the process is simple, the production efficiency is high, the production period is short, and the popularization value is high.
The invention is further arranged that in the step of S4:
firstly, stretching in the longitudinal direction, wherein the preheating and stretching temperature is 60-100 ℃, the stretching ratio is 2-6 times, and the stretching control mode is the speed difference of a roller;
stretching in the transverse direction at 60-100 deg.c and 2-6 times of stretching ratio, and controlling the width of the track chain.
In this technical scheme, can improve tensile strength, the optics of film, control heat shrinkage, thickness uniformity also can promote simultaneously through biaxial stretching, and the efficiency of manufacturing also can promote in addition.
The invention is further configured such that the water solubility test is:
the membrane sample was cut into a size of 40mm × 40mm, fixed by being placed between frame clips, and then purified water (1 liter) was poured into a1 liter beaker while keeping the water temperature at 25 ℃, and the membrane fixed by the frame clips was immersed in the purified water in the beaker while stirring to measure the time required for the membrane to dissolve.
In the technical scheme, the water solubility of the polyvinyl alcohol film is tested, so that the quality of the product is ensured, and meanwhile, the reaction auxiliary agent is adjusted through the test structure, so that the adjustability is improved.
The invention further provides that the reactive extruder comprises:
heating zones, wherein the number of the heating zones is 12, the 1 st heating zone and the 4 th heating zone carry out partial preliminary melting and extrusion on the polyvinyl alcohol resin, and the 5 th heating zone is added with a pre-mixed reaction auxiliary agent;
the screw is arranged in the reactive extruder and is used for pushing the internal mixture to move;
the back mixing element is sleeved on a screw rod in the reactive extruder and is used for increasing the residence time of the melt and ensuring the sufficiency and uniformity of the reaction;
wherein the length of the reactive extruder is more than 5m, and the length-diameter ratio is more than 50; the temperature for melt kneading in the extruder is preferably 80 to 160 ℃ and if the temperature is less than the lower limit, the poor plasticization of the film surface is caused, and if the temperature is more than the upper limit, the foaming is caused.
In the technical scheme, 12 heating zones are arranged, and the 1-4 heating zones are used for carrying out preliminary melting and extrusion on polyvinyl alcohol resin, so that a polyvinyl alcohol melt is convenient to generate, meanwhile, a pre-mixed reaction auxiliary agent is added in the 5 th heating zone, so that the mixing effect and the mixing efficiency of the reaction auxiliary agent and the polyvinyl alcohol melt are convenient, the using effect of the reaction auxiliary agent is ensured, meanwhile, a back mixing element is convenient to control the whole extrusion time, and the whole extrusion time is controlled and kept within 15min-20min, so that the requirement on the residence time of the melt is met, and the sufficiency and uniformity of the reaction are ensured; the PVA needs to be extruded for finishing the reaction, the extrusion reaction time is enough, if the reaction time cannot be reached, a good plasticizing effect cannot be obtained, so that the PVA needs to have requirements on equipment, and the PVA has a large length-diameter ratio and is suitable for the production process; meanwhile, the PVA is degraded in a longer time, and the reaction is not complete in a shorter time.
The invention further provides that the screw comprises:
the primary reaction section is positioned in the 1 st to 4 th heating zones;
the first spiral piece is arranged on the surface of the screw rod positioned at the initial reaction section;
the mixing section is positioned in the heating zones from 5 th to 12 th, and the back mixing element is positioned in the mixing section;
the second spiral piece is arranged on the surface of the screw rod positioned on the mixing section and positioned on two sides of the back mixing element along the axial direction;
the convex strip is arranged on one surface of the second spiral piece along the rotation direction and is positioned at one end of the second spiral piece far away from the axis;
the third spiral slice is arranged on the surface of the screw rod positioned on the back mixing element;
the spiral directions of the second spiral sheet and the third spiral sheet are opposite, and the pitch of the first spiral sheet is larger than that of the second spiral sheet.
In the technical scheme, the effect and efficiency of conveying polyvinyl alcohol resin by the screw are improved through the first spiral sheet, the second spiral sheet and the third spiral sheet, wherein the third spiral sheet improves the back mixing effect and the back mixing efficiency of the back mixing element, has the shearing effect when being matched with the second spiral sheet, improves the rolling effect of the polyvinyl alcohol resin, improves the mixing effect with the reaction auxiliary agent, and the screw pitch of the first screw plate is larger than that of the second screw plate, so that the relative speed of the polyvinyl alcohol resin in the 1 st to 4 th heating areas is lower, the heating effect on the polyvinyl alcohol resin is improved, and the relative speed is higher in the heating zones of 5 th to 12 th, the mixing efficiency and the mixing effect can be improved, meanwhile, the convex strips improve the rolling effect of the polyvinyl alcohol resin and the reaction auxiliary agent in the 5 th to 12 th heating areas, and ensure the mixing efficiency and the mixing effect.
The invention is further configured such that the back mixing element comprises:
the back mixing surface is positioned on one surface of the back mixing element close to the primary reaction section, is in an inwards concave arc shape, and has one end vertical to the axial direction and the other end parallel to the axial direction;
notches are arranged at the end of the back mixing element far away from the axis at equal intervals.
In this technical scheme, through the backmixing face, do benefit to polyvinyl alcohol resin's the countercurrent that rolls, guarantee the efficiency and the effect of backmixing to the setting of breach makes the backmixing face be difficult to appear the condition emergence of long-pending material, and can also improve the shearing effect to polyvinyl alcohol resin, further improves mixed effect and mixing efficiency.
The beneficial effects of the invention are as follows: by adopting 88% of polyvinyl alcohol resin and assisting with a plasticizer, a lubricant and a stabilizer, the processing cost is reduced, the processability, the water-solubility adjustment property and the thermal stability of the polyvinyl alcohol resin are effectively improved, meanwhile, a reaction auxiliary agent is added after partial primary melting and extrusion of the polyvinyl alcohol resin, the mixing effect and the mixing efficiency of the reaction auxiliary agent and a polyvinyl alcohol melt are improved, the influence of high temperature on the reaction auxiliary agent is reduced, and the controllability of the reaction auxiliary agent is better, so that the water-solubility adjustability of the polyvinyl alcohol film is higher.
Drawings
FIG. 1 is a schematic view of a partial structure of a reactive extruder of the present invention;
FIG. 2 is a process flow diagram of the present invention;
FIG. 3 is a schematic view of the screw of the present invention;
FIG. 4 is an enlarged view of the invention at A in FIG. 3;
in the drawings: 1. a weightlessness measuring scale; 2. a liquid pump; 3. a heating zone; 4. a screw; 40. a primary reaction section; 41. a first helical flight; 42. a mixing section; 43. a second flight; 44. a convex strip; 45. a third flight; 5. a back mixing element; 50. back mixing the dough; 51. and (4) a notch.
Detailed Description
The invention is further described in the following with reference to fig. 1 to 4 in a specific embodiment:
example 1:
this example provides a reactive extrusion biaxially oriented polyvinyl alcohol film comprising: 60% PVA1788, 37% glycerol, 2% oleamide, and 1% organotin stabilizer;
wherein the extrusion temperature is 150 ℃ and the retention time is 15 min.
The reactive extrusion biaxially oriented polyvinyl alcohol film produced according to the above composition had the following data:
thickness 25 μm, tensile strength MD: 106Mpa, tensile strength TD: 90MPa, stretch ratio MD × TD: 2 × 2, time to dissolve in water at 25 ℃: 15 s.
Example 2:
this example provides a reactive extrusion biaxially oriented polyvinyl alcohol film comprising: 70% PVA1788, 27% glycerol, 2% oleamide, and 1% organotin stabilizer;
wherein the extrusion temperature is 140 ℃ and the retention time is 18 min.
The reactive extrusion biaxially oriented polyvinyl alcohol film produced according to the above composition had the following data:
thickness 30 μm, tensile strength MD: 120Mpa, tensile strength TD: 120MPa, stretch ratio MD × TD: 3 × 3, time to dissolve in water at 25 ℃: 38 s.
Example 3:
this example provides a reactive extrusion biaxially oriented polyvinyl alcohol film comprising: 61% PVA1788, 18% glycerol, 18% diethanolamine, 2% oleamide, and 1% organotin stabilizer;
wherein the extrusion temperature is 142 ℃, and the retention time is 16 min.
The reactive extrusion biaxially oriented polyvinyl alcohol film produced according to the above composition has the following data:
thickness 25 μm, tensile strength MD: 118Mpa, tensile strength TD: 125Mpa, stretch ratio MD × TD: 3 × 4, time to dissolve in water at 25 ℃: 34 s.
Example 4:
this example provides a reactive extrusion biaxially oriented polyvinyl alcohol film comprising: 57% PVA2088, 40% triethanolamine, 2% oleamide, and 1% organotin stabilizer;
wherein the extrusion temperature is 145 ℃ and the retention time is 18 min.
The reactive extrusion biaxially oriented polyvinyl alcohol film produced according to the above composition had the following data:
thickness 20 μm, tensile strength MD: 140Mpa, tensile strength TD: 135Mpa, stretch ratio MD × TD: 4 × 4, time to dissolve in water at 25 ℃: 23 s.
Example 5:
this example provides a reactive extrusion biaxially oriented polyvinyl alcohol film comprising: 70% PVA0588, 27% decapolyglycerol, 2% oleamide, and 1% organotin stabilizer;
wherein the extrusion temperature is 145 ℃ and the retention time is 16 min.
The reactive extrusion biaxially oriented polyvinyl alcohol film produced according to the above composition has the following data:
thickness 20 μm, tensile strength MD: 120Mpa, tensile strength TD: 146Mpa, stretch ratio MD × TD: 3 × 5, time to dissolve in water at 25 ℃: 23 s.
Example 6:
this example provides a reactive extrusion biaxially oriented polyvinyl alcohol film comprising: 62% of PVA1788, 35% of glycerol trimer, 2% of oleamide and 1% of organic tin stabilizer;
wherein the extrusion temperature is 145 ℃ and the retention time is 20 min.
The reactive extrusion biaxially oriented polyvinyl alcohol film produced according to the above composition had the following data:
thickness 12 μm, tensile strength MD: 120Mpa, tensile strength TD: 157MPa, stretch ratio MD × TD: 3 × 5, time to dissolve in water at 25 ℃: 15 s.
Example 7:
this example is a comparative example, which comprises: 61% PVA1788, 12% diethylene glycol, 24% glycerol, 2% oleamide and 1% organotin stabilizer;
wherein the extrusion temperature is 148 ℃, the retention time is 17min, and the film is not stretched.
The reactive extrusion biaxially oriented polyvinyl alcohol film produced according to the above composition had the following data:
In the above examples 1 to 6, the method for preparing the reactive extrusion biaxially oriented polyvinyl alcohol film comprises the following steps:
s1: feeding polyvinyl alcohol resin with alcoholysis degree of 88% into a reactive extruder from a main feeding port by adopting a weight loss scale 1, and uniformly metering and pumping pre-mixed reaction auxiliary agents by adopting a liquid pump 2 after partial primary melting and extrusion of the polyvinyl alcohol resin;
s2: extruding the polyvinyl alcohol resin by a reactive extruder, and controlling the extrusion time to be 15-20 min to obtain a melt after the reaction is finished;
s3: conveying the melt after reaction to a metering pump, a special melt filter and a special casting die head, casting through the casting die head, well attaching and cooling with a cooling roller, and then drawing to prepare a casting sheet;
s4: biaxially stretching and shaping the obtained cast sheet, and then obtaining a reactive extrusion method biaxially stretched polyvinyl alcohol film;
s5: and (4) water solubility test.
Wherein, the water solubility test is as follows: the membrane sample was cut into a size of 40mm × 40mm, fixed by placing it between frame clips, and then purified water (1 liter) was poured into a1 liter beaker while keeping the water temperature at 25 ℃, and the membrane fixed by the frame clips was immersed in the purified water in the beaker while stirring, and the time required for the membrane to dissolve was measured.
Wherein the reactive extruder comprises:
heating zones 3, wherein the number of the heating zones 3 is 12, the heating zones 3 from 1 st to 4 th carry out partial preliminary melting and extrusion on the polyvinyl alcohol resin, and the heating zone 3 from 5 th adds a pre-mixed reaction auxiliary agent;
the screw 4 is installed in the reactive extruder and is used for pushing the internal mixture to move;
the back mixing element 5 is sleeved on the screw 4 in the reactive extruder, and is used for increasing the residence time of the melt and ensuring the sufficiency and uniformity of the reaction;
wherein the length of the reactive extruder is more than 5m, and the length-diameter ratio is more than 50.
And the screw 4 comprises:
the primary reaction section 40, the primary reaction section 40 locates in 1 st-4 heating zone 3;
the first spiral sheet 41, the first spiral sheet 41 is installed on the surface of the screw 4 located at the initial reaction section 40;
a mixing section 42, the mixing section 42 being located in the heating zone 3 of the 5 th to 12 th, the back mixing element 5 being located in the mixing section 42;
the second spiral plates 43 are arranged on the surfaces of the screw rods 4, positioned on the mixing section 42, and positioned on two sides of the back mixing element 5 along the axial direction;
the convex strip 44 is arranged on one surface of the second spiral sheet 43 along the rotation direction and is positioned at one end of the second spiral sheet 43 away from the axis;
a third screw flight 45, wherein the third screw flight 45 is arranged on the surface of the screw 4, which is positioned on the back mixing element 5;
the second spiral sheet 43 and the third spiral sheet 45 have opposite spiral directions, and the pitch of the first spiral sheet 41 is greater than that of the second spiral sheet 43.
And the back mixing element 5 comprises:
the back mixing surface 50 is positioned on one surface of the back mixing element 5 close to the primary reaction section 40, is in an inward concave arc shape, and has one end vertical to the axial direction and the other end parallel to the axial direction;
notches 51, the notches 51 being circumferentially equally spaced apart at an end of the back mixing element 5 remote from the axial center.
The steps and the requirements on the reactive extruder are known, 12 heating zones 3 are arranged, and the 1-4 heating zones 3 are used for carrying out primary melting and extrusion on polyvinyl alcohol resin, so that a polyvinyl alcohol melt is convenient to generate, and meanwhile, a pre-mixed reaction auxiliary agent is added in the 5 th heating zone 3, so that the mixing effect and the mixing efficiency of the reaction auxiliary agent and the polyvinyl alcohol melt are convenient, the using effect of the reaction auxiliary agent is ensured, and meanwhile, the back mixing element 5 is convenient to control the whole extrusion time and control and keep the whole extrusion time within 15-20 min so as to meet the requirements on the residence time of the melt and ensure the sufficiency and uniformity of the reaction; the PVA needs to be extruded for finishing the reaction, the extrusion reaction time is enough, if the reaction time cannot be reached, a good plasticizing effect cannot be obtained, so that the PVA needs to have requirements on equipment, and the PVA has a large length-diameter ratio and is suitable for the production process; meanwhile, the PVA is degraded in a longer time, and the reaction is not complete in a shorter time.
Meanwhile, the effect and efficiency of conveying polyvinyl alcohol resin by the screw rod 4 are improved through the first spiral sheet 41, the second spiral sheet 43 and the third spiral sheet 45, wherein the third spiral sheet 45 improves the back mixing effect and the back mixing efficiency of the back mixing element 5, and has a shearing effect in cooperation with the second spiral sheet 43, the rolling effect of the polyvinyl alcohol resin is improved, the mixing effect with a reaction auxiliary agent is improved, the screw pitch of the first spiral sheet 41 is larger than that of the second spiral sheet 43, so that the relative speed of the polyvinyl alcohol resin in the 1 st to 4 th heating zones 3 is slower, the heating effect on the polyvinyl alcohol resin is improved, the relative speed in the 5 th to 12 th heating zones 3 is faster, the mixing efficiency and the mixing effect can be improved, meanwhile, the rolling effect of the polyvinyl alcohol resin and the reaction auxiliary agent in the 5 th to 12 th heating zones 3 is improved through the convex strips 44, guarantee mixing efficiency and mixed effect to back mixing face 50 does benefit to polyvinyl alcohol resin's the countercurrent of rolling, guarantees back mixing's efficiency and effect, and breach 51's setting makes back mixing face 50 be difficult to the condition emergence of long-pending material, and can also improve the shearing effect to polyvinyl alcohol resin, further improves mixed effect and mixing efficiency.
While the present embodiments have been described with reference to the accompanying drawings, it is to be understood that the invention is not limited to the precise embodiments described above, which are meant to be illustrative and not restrictive, and that various changes may be made therein by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (10)
1. A reactive extrusion biaxially oriented polyvinyl alcohol film, comprising:
the polyvinyl alcohol is polyvinyl alcohol resin with alcoholysis degree of 88%, and is one or a mixture of more of PVA2488, PVA2088, PVA1788 and PVA 0588;
the reaction auxiliary agent is mixed in the polyvinyl alcohol resin mixture after partial preliminary melting and extrusion of the polyvinyl alcohol resin;
wherein the reaction auxiliary agent is liquid mixed liquid and comprises a plasticizer, a lubricant and a stabilizer.
2. The reactive extrusion biaxially oriented polyvinyl alcohol film of claim 1, wherein the plasticizer comprises:
one or more liquid mixed liquid of sorbitol, mannitol, glycerol, diethanolamine, triethanolamine, diglycerol, triglycerol, decapolypropylene triol and diethylene glycol.
3. The reactive extrusion biaxially oriented polyvinyl alcohol film of claim 2, wherein the lubricant comprises:
erucamide, oleamide, myristic acid, hardened oil, glycerol monostearate and pentaerythritol stearate.
4. The reactive extrusion biaxially oriented polyvinyl alcohol film of claim 3, wherein the stabilizer comprises:
one or more liquid mixed liquid of organic tin stabilizer, rare earth stabilizer, zinc stearate, cerium stearate, barium stearate, aluminum distearate and calcium stearate.
5. A method for preparing a biaxially oriented polyvinyl alcohol film by the reactive extrusion method according to claim 4, which comprises the steps of:
s1: feeding polyvinyl alcohol resin with alcoholysis degree of 88% into a reactive extruder from a main feeding port by adopting a weight loss metering scale (1), and uniformly metering and pumping premixed reaction auxiliary agents by adopting a liquid pump (2) after partial preliminary melting and extrusion of the polyvinyl alcohol resin;
s2: extruding the polyvinyl alcohol resin by a reactive extruder, and controlling the extrusion time to be 15-20 min to obtain a melt after the reaction is finished;
s3: conveying the melt after reaction to a metering pump, a special melt filter and a special fluidly-arranged grope, performing good attachment and cooling with a cooling roller through the fluidly-arranged grope, and then drawing to prepare a casting sheet;
s4: carrying out biaxial tension and sizing on the obtained cast sheet, and then obtaining the biaxial tension polyvinyl alcohol film by the reactive extrusion method;
s5: and (4) water solubility test.
6. The method of preparing a biaxially oriented polyvinyl alcohol film by reactive extrusion process according to claim 5, wherein in the step S4:
firstly, stretching in the longitudinal direction, wherein the preheating and stretching temperature is 60-100 ℃, the stretching ratio is 2-6 times, and the stretching control mode is the speed ratio of a roller;
stretching in the transverse direction at 60-100 deg.c and 2-6 times of stretching ratio in chain mode.
7. The method of claim 5, wherein the water solubility test is as follows:
the membrane sample was cut into a size of 40mm × 40mm, fixed by placing it between frame clips, and then purified water (1 liter) was poured into a1 liter beaker while keeping the water temperature at 25 ℃, and the membrane fixed by the frame clips was immersed in the purified water in the beaker while stirring, and the time required for the membrane to dissolve was measured.
8. The method of claim 5, wherein the reactive extruder comprises:
12 heating zones (3), wherein the number of the heating zones (3) is 1-4, the heating zones (3) partially melt and extrude polyvinyl alcohol resin preliminarily, and a reaction auxiliary agent which is mixed in advance is added into the heating zone (3) of the 5 th;
a screw (4), the screw (4) being mounted within the reactive extruder and being for urging the internal mix to move;
the back mixing element (5) is sleeved on the screw (4) in the reactive extruder, and is used for increasing the residence time of the melt and ensuring the sufficiency and uniformity of the reaction;
wherein the reactive extruder has a length greater than 5m and an aspect ratio greater than 50.
9. The method for preparing a biaxially oriented polyvinyl alcohol film by reactive extrusion process according to claim 8, wherein the screw (4) comprises:
a primary reaction section (40), said primary reaction section (40) being located in the 1 st to 4 th heating zone (3);
the first spiral sheet (41), the first spiral sheet (41) is arranged on the surface of the screw (4) positioned at the primary reaction section (40);
a mixing section (42), said mixing section (42) being located in said heating zone of the 5 th to 12 th, said back mixing element (5) being located in the mixing section (42);
the second spiral slice (43) is arranged on the surface of the screw (4) positioned on the mixing section (42) and positioned on two sides of the back mixing element (5) along the axial direction;
the convex strip (44) is installed on one surface of the second spiral sheet (43) along the rotating direction and is positioned at one end, far away from the axis, of the second spiral sheet (43);
a third screw plate (45), wherein the third screw plate (45) is arranged on the surface of the screw (4) positioned on the back mixing element (5);
wherein the second spiral sheet (43) and the third spiral sheet (45) have opposite spiral directions, and the pitch of the first spiral sheet (41) is larger than that of the second spiral sheet (43).
10. The method for preparing a reactive extrusion biaxially oriented polyvinyl alcohol film according to claim 8, wherein the back mixing element (5) comprises:
the back mixing surface (50) is positioned on one surface of the back mixing element (5) close to the primary reaction section (40), is in an inwards concave arc shape, and has one end vertical to the axial direction and the other end parallel to the axial direction;
the notches (51) are arranged at the end, far away from the axis, of the back mixing element (5) at equal intervals on the circumference of each notch (51).
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