CN107973953B - Thermoplastic elastomer composition and preparation method thereof, sealing gasket and method for preparing sealing gasket in crown cap - Google Patents
Thermoplastic elastomer composition and preparation method thereof, sealing gasket and method for preparing sealing gasket in crown cap Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
- C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
- C08L23/04—Homopolymers or copolymers of ethene
- C08L23/06—Polyethene
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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
- B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
- B29C48/25—Component parts, details or accessories; Auxiliary operations
- B29C48/92—Measuring, controlling or regulating
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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
- B29C2948/00—Indexing scheme relating to extrusion moulding
- B29C2948/92—Measuring, controlling or regulating
- B29C2948/92504—Controlled parameter
- B29C2948/9258—Velocity
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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
- B29C2948/00—Indexing scheme relating to extrusion moulding
- B29C2948/92—Measuring, controlling or regulating
- B29C2948/92504—Controlled parameter
- B29C2948/92704—Temperature
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L2201/00—Properties
- C08L2201/08—Stabilised against heat, light or radiation or oxydation
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L2205/00—Polymer mixtures characterised by other features
- C08L2205/03—Polymer mixtures characterised by other features containing three or more polymers in a blend
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L2207/00—Properties characterising the ingredient of the composition
- C08L2207/04—Thermoplastic elastomer
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L2207/00—Properties characterising the ingredient of the composition
- C08L2207/06—Properties of polyethylene
- C08L2207/066—LDPE (radical process)
Abstract
The invention relates to the field of packaging, in particular to a thermoplastic elastomer composition, a preparation method and application thereof, and a method for preparing a sealing gasket in a crown cap. The thermoplastic elastomer composition comprises (a) low-density polyethylene, (b) linear low-density polyethylene and/or high-density polyethylene and (c) a styrene elastomer, wherein the thermoplastic elastomer composition has a molecular weight distribution index DPI of 4 to 8, preferably 4.62 to 6.97, and a high molecular tailing index PI in the width of the molecular weight distributionHTGreater than 4.9, preferably greater than 5.7. The thermoplastic elastomer composition has simple components, does not need to add extra auxiliary agents, meets the food safety regulations, has good sealing property, heat resistance and pressure resistance, and is particularly suitable for preparing a sealing gasket in a crown cap.
Description
Technical Field
The invention relates to the field of packaging, in particular to a thermoplastic elastomer composition, a preparation method thereof, a sealing gasket and a method for preparing the sealing gasket in a crown cap.
Background
Nowadays, people have more and more careful and more critical requirements on the taste, smell and the like of drinks such as beer, and sometimes even become a key factor for the success or failure of a drink manufacturer in the market, and the taste and smell of the drinks are directly related to substances such as gas contacting the drinks. For the beverage in the glass bottle, the solution is to place an elastic gasket material between the bottle cap and the bottle neck, thereby sealing and protecting the beverage in the glass bottle. The gasket material must be capable of preventing gas or liquid outside the glass bottle from diffusing into the bottle, such as oxygen, chlorophenol, chloroanisole and the like, or seriously damaging the taste of the beverage; meanwhile, the gasket material also needs to ensure that gas in the bottle cannot diffuse outside the glass bottle, such as carbon dioxide, so that the phenomenon that the taste of the beverage is monotonous due to excessive bubble overflow is avoided, and the gasket material has good sealing performance. The gas in the glass bottle is ensured not to overflow, and the gas is required to be ensured not to leak under the condition of the pressure in the bottle, wherein the pressure in the bottle is 0.5-0.7Mpa under the normal condition. But the pressure resistance of the sealing gasket cannot be too large or even exceed that of the glass bottle. For example, under some extreme conditions, high temperature and violent shaking exist at the same time, high pressure can be generated in the glass bottle instantly, and if the sealing gasket cannot effectively leak air at the moment, the glass bottle can be cracked. For example, according to the specification in GB-4544-. Therefore, the gasket material should be capable of effective air leakage at pressures in excess of 1.2 MPa. In a word, the ideal gasket material at least can bear the pressure of more than 0.7Mpa, thereby ensuring that the gas inside and outside the bottle can be effectively blocked, and simultaneously, the gasket material can leak gas under high pressure, and ensuring the safety of the glass bottle.
The process of manufacturing the crown cap is that granules are extruded into a die head by a single-screw extruder at a certain temperature, materials with fixed quality are accurately cut on the crown cap by a high-speed cutter, and the materials are directly hot-pressed into a whole. After 90 s in the 20 th century, the filling capacity of beer is greatly improved, the production capacity reaches more than 4 ten thousand bottles per hour, and more than 700 bottle caps containing sealing gaskets are required to be provided per minute, so that the bottle caps have high requirements on continuous high-speed conveying of the bottle caps on equipment, the processing performance of gasket materials is also high, and the phenomena of flash, gaps and the like cannot frequently occur, so that the equipment stops running due to the detection of waste caps, and economic loss is caused. In addition, the performance of the gasket material needs to maintain uniform stability, and if the gasket material is composed of two or more components, it is necessary to effectively disperse the components of the gasket material so as to maintain the pressure resistance and heat resistance of the material at the same level.
Modern logistics transportation also puts more strict requirements on the performance of gasket materials, logistics companies often stack bottled drinks together due to large demand in busy seasons, which inevitably causes great pressure on a glass bottle cap at the bottom layer, and under the external force condition, the gasket needs to be capable of stably keeping the sealing property in the bottle so as to ensure the fresh taste of the drinks, and according to the regulation in GB-4544 + 1996, the qualified sealing gasket needs to have a pressure resistance index of 0.8 MPa. Meanwhile, long-distance transportation of partial drinks can be caused by long-distance sale of brands, frequent collision and bouncing are strict in performance requirements of gasket materials, and the gasket materials need to have better elasticity and strength to guarantee that the glass bottles always keep good sealing performance.
At present, more than 95 percent of domestic sealing gaskets are made of polyolefin materials to replace the prior polyvinyl chloride materials, so that the problems of the polyvinyl chloride in the aspects of food safety and the like are solved, but the domestic sealing gasket market mainly depends on import, so that the development of the domestic polyolefin sealing gasket capable of being stably produced is necessary. Chinese patent application CN104250404A discloses a sealing gasket prepared from polypropylene, polyethylene and thermoplastic elastomer, but no specific material performance analysis is available, the key performances such as density and sealing performance are not reflected, and the addition of an auxiliary agent causes the problem of food safety of the material. Chinese patent application CN1465507A discloses a formula composed of EVA, PE, PP, PS, SEBS and the like, but the hardness of the material is higher, the material is not suitable for long-distance transportation in domestic markets, and the heat-resistant problem is not solved, and oil and fine smooth substances are separated out at high temperature.
In the practical application process, the polyolefin sealing gasket is widely applied due to the advantages of environmental protection, easily obtained raw materials and the like, but the domestic formula still does not replace imported materials due to the problems of processing and partial performance, mainly because of strict requirements on the sealing property, the heat resistance and the processing performance of the sealing gasket. Therefore, the sealing gasket provided by the invention has the advantages of good sealing performance, high heat resistance, strong pressure resistance, good processing stability and simple preparation process, and has wide application prospect and important scientific research value.
Disclosure of Invention
The invention aims to overcome the defects of the existing sealing gasket in the crown cap, and provides a thermoplastic elastomer composition, a preparation method thereof, a sealing gasket and a method for preparing the sealing gasket in the crown cap.
In order to achieve the above object, the present invention provides a thermoplastic elastomer composition comprising:
(a) the low-density polyethylene has a melt index of 4-10g/10min, preferably 5-8g/10min, a molecular weight distribution index of 2-10, preferably 2-7, a melting temperature of 100-110 ℃, preferably 100-105 ℃ and a crystallization temperature of 90-100 ℃ which are measured under the action of a 2.16kg load at 190 ℃ according to a method specified in GB/T3682-2000;
(b) the linear low-density polyethylene and/or the high-density polyethylene has a melt index of 10-25g/10min, preferably 15-20g/10min, a molecular weight distribution index of 2-10, preferably 2-5, a melting temperature of 110-130 ℃, preferably 120-125 ℃, and a crystallization temperature of 105-115 ℃ which are measured under the action of a 2.16kg load at 190 ℃ according to a method specified in GB/T3682-2000; and
(c) a styrene-based elastomer;
wherein the thermoplastic elastomer composition has a molecular weight distribution index of 4 to 8, preferably 4.62 to 6.97; high molecular tailing index PI in molecular weight distribution widthHTGreater than 4.9, preferably greater than 5.7.
Secondly, the present invention also provides a method for preparing the above thermoplastic elastomer composition, which comprises: mixing, extruding and granulating, cooling and drying the component (a), the component (b) and the component (c) in sequence.
The present invention also provides a thermoplastic elastomer composition prepared by the above method.
In addition, the invention also provides a sealing gasket which is prepared from the thermoplastic elastomer composition.
Finally, the invention also provides a method for preparing a sealing gasket in a crown cap, which comprises the following steps: the thermoplastic elastomer composition is extruded and then stamped on a crown cap.
The thermoplastic elastomer composition provided by the invention has multi-component polyethylene and styrene elastomer with a certain structure, and has more remarkable macromolecular chain tail end by controlling the specific molecular weight distribution index and the macromolecular tailing index in the molecular weight distribution width, so that the crystallization temperature of the macromolecular weight part in the polyethylene in the thermoplastic elastomer composition is increased, extruded granules are solidified more quickly in the high-speed extrusion process, the knife sticking phenomenon in the high-speed shearing process is reduced, the notch phenomenon in the process of preparing a sealing gasket in a crown cap by the thermoplastic elastomer composition is reduced, the industrial high-speed production can be realized, and the processing stability is improved.
In addition, the thermoplastic elastomer composition provided by the invention has simple components, does not need to add additional auxiliary agents, meets the food safety regulations, has good sealing property, heat resistance and pressure resistance, and is particularly suitable for preparing a sealing gasket in a crown cap.
Additional features and advantages of the invention will be set forth in the detailed description which follows.
Detailed Description
The following describes in detail specific embodiments of the present invention. It should be understood that the detailed description and specific examples, while indicating the present invention, are given by way of illustration and explanation only, not limitation.
The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.
The present invention provides a thermoplastic elastomer composition comprising:
(a) low density polyethylene;
(b) linear low density polyethylene and/or high density polyethylene; and
(c) a styrene-based elastomer;
wherein the thermoplastic elastomer composition has a molecular weight distribution index of 4 to 8, preferably 4.62 to 6.97; high molecular tailing index PI in molecular weight distribution widthHTGreater than 4.9, preferably greater than 5.7, and may be, for example, from 5.7 to 10.
According to the invention, the polymer tailing index PI of the thermoplastic elastomer compositionHTCalculated according to the formula (I),
PIHT＝10^5×(Mz/Mp)/Mw (I)
wherein Mp is peak molecular weight, Mw is weight average molecular weight, Mz is Z average molecular weight, and Mp, Mw, Mz and molecular weight distribution index can be measured by gel permeation chromatography.
According to the invention, a thermoplastic bulletPolymer tailing index PI of body compositionHTThe higher the content of the thermoplastic elastomer composition, the more obvious macromolecule chain tail end exists in the composition, so that the crystallization temperature of a high-molecular-weight part in polyethylene in the thermoplastic elastomer composition can be increased, and extruded granules are cured more quickly in the high-speed extrusion process, so that the knife sticking phenomenon in the high-speed shearing process is reduced, the notch phenomenon in the process of preparing a sealing gasket in a crown cap from the thermoplastic elastomer composition is reduced, the high-speed production in the industry can be realized, and the processing stability is improved.
In the thermoplastic elastomer composition provided by the invention, the low-density polyethylene has a melt index of 4-10g/10min, preferably 5-8g/10min, a molecular weight distribution index of 2-10, preferably 2-7, a melting temperature of 100-110 ℃, preferably 100-105 ℃ and a crystallization temperature of 90-100 ℃ which are measured under the action of a 2.16kg load at 190 ℃ according to the method specified in GB/T3682-2000.
In the thermoplastic elastomer composition provided by the invention, the linear low-density polyethylene and/or the high-density polyethylene has a melt index of 10-25g/10min, preferably 15-20g/10min, a molecular weight distribution index of 2-10, preferably 2-5, a melting temperature of 110-130 ℃, preferably 120-125 ℃ and a crystallization temperature of 105-115 ℃ which are measured under the action of a 2.16kg load at 190 ℃ according to a method specified in GB/T3682-2000. Wherein the low density polyethylene and the linear low density polyethylene both have a density of 0.91-0.925g/cm3The density of the high-density polyethylene is 0.94-0.976g/cm3Linear low density polyethylene differs from high density polyethylene mainly in the number of short chain branches, high density polyethylene has a smaller number of short chain branches, both linear low density polyethylene and high density polyethylene have higher crystallinity and melting point, and lower density polyethylene has higher tensile strength, penetration resistance, tear resistance and elongation.
In the thermoplastic elastomer composition provided by the present invention, the content of the component (a) may be 35 to 60 parts by weight, for example, 35 parts by weight, 40 parts by weight, 45 parts by weight, 50 parts by weight, 55 parts by weight, 60 parts by weight, and any content between any two content ranges, the content of the component (b) may be 15 to 25 parts by weight, for example, 15 parts by weight, 16 parts by weight, 17 parts by weight, 18 parts by weight, 19 parts by weight, 20 parts by weight, 21 parts by weight, 22 parts by weight, 23 parts by weight, 24 parts by weight, 25 parts by weight, and any content between any two content ranges, and the content of the component (c) may be 20 to 50 parts by weight, for example, 20 parts by weight, 25 parts by weight, 30 parts by weight, 35 parts by weight, 40 parts by weight, 45 parts by weight, 50 parts by weight, and any content between any two of the ranges.
In the thermoplastic elastomer composition provided by the present invention, in order to reduce the size of the phase region of the thermoplastic elastomer composition, reduce light scattering, and thereby improve the optical properties thereof, the styrene-based elastomer may contain a styrene segment in an amount of 20 to 40% by weight, preferably 24 to 30% by weight.
In the thermoplastic elastomer composition provided by the invention, the styrene-based elastomer has a melt index of 0.25-4g/10min, preferably 2-4g/10min, measured at 200 ℃ under a load of 5kg according to the method specified in GB/T3682-2000.
In a preferred embodiment, the thermoplastic elastomer composition has a melt index, measured according to the method specified in GB/T3682-2000 at 200 ℃ under a load of 5kg, of preferably 4-8g/10 min. According to the preferred embodiment, the occurrence of flash or the like in the high-speed stamping process of an article produced from the thermoplastic elastomer composition can be avoided.
In the thermoplastic elastomer composition provided by the invention, in order to ensure that the thermoplastic elastomer composition has good mechanical properties, the shore a hardness of the styrene-based elastomer can be 60-85, and preferably 60-70.
In the thermoplastic elastomer composition provided by the invention, in order to ensure that the thermoplastic elastomer composition has good tensile strength, the styrene-based elastomer is preferably a styrene-butadiene-styrene block copolymer and/or a styrene-ethylene-butylene-styrene block copolymer.
The present invention also provides a method for preparing the above thermoplastic elastomer composition, which comprises: mixing, extruding and granulating, cooling and drying the component (a), the component (b) and the component (c) in sequence.
According to the method provided by the present invention, in the mixing process, the mixing conditions are not particularly limited as long as the components can be uniformly mixed, for example, the mixing can be performed under stirring, and the mixing time can be not more than 5min, preferably not more than 2 min.
According to the method provided by the present invention, in the extrusion granulation process, conditions of extrusion granulation are not particularly limited as long as the prepared thermoplastic elastomer composition can be extruded into granules, and for example, the conditions of extrusion granulation include: the motor rotation speed is 250-300rpm, the extrusion temperature is 160-230 ℃, and preferably 160-170 ℃.
According to the method provided by the invention, in the extrusion granulation process, the extrusion granulation equipment can be at least one of a double-screw extruder, a single-screw extruder, an open mill and an internal mixer, and is preferably a double-screw extruder.
According to the method provided by the present invention, in the cooling process, the cooling conditions are not particularly limited as long as the prepared pellets can be cooled and shaped, and for example, the cooling conditions include: the cooling temperature may be 40 to 60 ℃ and preferably 50 to 60 ℃.
According to the method provided by the present invention, in the drying process, the drying conditions are not particularly limited as long as the prepared pellets can be dried, and for example, the drying conditions include: the drying temperature can be 70-90 deg.C, and the drying time is 24-48 h.
The invention also provides a thermoplastic elastomer composition prepared by the method.
The invention also provides a sealing gasket which is prepared from the thermoplastic elastomer composition provided by the invention.
The invention also provides a method for preparing a sealing gasket in a crown cap, which comprises the following steps: the thermoplastic elastomer composition is extruded and then stamped on a crown cap.
According to the method for preparing a sealing gasket in a crown cap provided by the invention, in the extrusion process, the extrusion conditions are not particularly limited, for example, the extrusion conditions may include: the motor speed is 200-400rpm, the extrusion temperature is 85-120 ℃, and the preferred temperature is 85-115 ℃.
According to the method provided by the invention, in the stamping process, the stability in the processing process is not ensured, the stamping speed cannot be too high, and the stamping temperature cannot be too high for rapidly cooling and forming the sealing gasket, for example, the stamping conditions may include: the stamping speed is 2000-8000/min, preferably 5000/min, and the stamping temperature is 5-10 deg.C.
The present invention will be described in detail below by way of examples.
In the following examples and comparative examples, the density of low density polyethylene was measured according to the method specified in GB 1033-1986.
In the following examples and comparative examples, the melt index of the thermoplastic elastomer composition was measured at 200 ℃ under a load of 5kg according to the method specified in GB/T3682.
In the following examples and comparative examples, the melt indices of low density polyethylene, linear low density polyethylene and high density polyethylene were measured at 190 ℃ under a load of 2.16kg according to the method specified in GB/T3682-2000.
In the following examples and comparative examples, the melt index of the styrenic elastomer was measured at 200 ℃ under a load of 5kg according to the method specified in GB/T3682-2000.
In the following examples and comparative examples, the Shore A hardness of the thermoplastic elastomer compositions was measured according to the method specified in GB/T2411.
In the following examples and comparative examples, the procedure for testing the chronic air leakage rate included: (1) preparing 3000ml of 0.15mol/l hydrochloric acid solution, respectively injecting the prepared hydrochloric acid solution into 12 glass bottles, injecting 250ml of hydrochloric acid solution into each glass bottle, weighing 12 parts of 3.15g of sodium bicarbonate by using filter paper, placing each paper mass containing the sodium bicarbonate at a bottle opening, immediately sealing the bottle opening by using 12 pieces of bottle caps containing gaskets to be detected, measuring the diameter of the bottle caps by using a caliper, and shaking the bottles for 5 times after the diameter of the bottle caps meets the standard (the inner diameter is 26.75mm) so as to ensure that the chemical reaction is sufficient and is to be detected; (2) then placing the sealed glass bottle on a base of a carbon dioxide determinator, adjusting the height of the puncture head (higher than the flat height by 3mm), screwing down knobs on the left side and the right side, and fixing a puncture head bracket; closing the exhaust valve, and pulling the handle forward to a proper position; repeatedly shaking the sealed glass bottle and the carbon dioxide tester for several times to make the pressure reading reach the maximum value, and reading the pressure value when the pressure is not increased any more; opening an exhaust valve, reading bottleneck gas, and immediately closing the exhaust valve when the pressure is reduced to 0 bar; pulling the handle backwards to a proper position, taking down the sample bottle, opening the bottle cap, and measuring the temperature of the sample by using a standard thermometer (accurate to 0.1 ℃); (3) according to GB10792 'carbon dioxide absorption coefficient table', the volume V1 of carbon dioxide can be measured; (4) and (3) directly pasteurizing the sealed glass bottle and a carbon dioxide determinator for 24 hours, and measuring the carbon dioxide volume V2, wherein the carbon dioxide air leakage rate is (V1-V2)/V1 x 100%, and the processing stability of the sealing gasket is qualified when the carbon dioxide air leakage rate is less than 20%.
In the following examples and comparative examples, the procedure of the test method for instantaneous pressure resistance after pasteurization included: injecting water into the coca cola glass bottle, sealing, treating in a pasteurizing pot at 68 deg.C for 24 hr, taking out, cooling for 24 hr, and performing instantaneous pressure resistance test according to the method specified in GBT13521-92, section 5.3.3. When the pressure resistance value exceeds 0.8Mpa, the sealing gasket is a qualified product.
Example 1
1000g of low-density polyethylene, 500g of linear low-density polyethylene and 500g of styrene-butadiene-styrene block copolymer were accurately weighed, mixed in a high-speed mixer for 2min, extruded and pelletized by a twin-screw extruder at a motor speed of 300rpm and a screw length-diameter ratio of 25, the temperature of the screw zone was set to 160 ℃ in the conveying section, 165 ℃ in the melting section, 170 ℃ in the kneading section, 170 ℃ in the exhaust section and 160 ℃ in the homogenizing section, and the mixture was cooled in a 20 ℃ cold water tank and cut. The resulting mixed ion was dried at 70 ℃ for 24 h. The obtained granules are extruded again by a double screw, the temperature of the screw interval is set to be 85 ℃ in the conveying section, 90 ℃ in the melting section, 100 ℃ in the mixing section, 105 ℃ in the exhaust section and 115 ℃ in the homogenizing section, and the granules are directly punched on a crown cover, the processing speed is 5000 pieces/min, and the punching temperature is 10 ℃.
Wherein component (a) is a low density polyethylene having a density ρA＝0.920g/cm3The molecular weight distribution index DPI is 6.32, the melt index MFR is 7.5g/10min, the melting temperature Tm is 108.2 ℃, and the crystallization temperature Tc is 92.7 ℃;
wherein component (b) is a linear low density polyethylene having a density ρB＝0.926g/cm3The molecular weight distribution index DPI is 3.61, the melt index MFR is 20g/10min, the melting temperature Tm is 123.5 ℃, and the crystallization temperature Tc is 108.1 ℃;
wherein the styrene-butadiene-styrene block copolymer of the component (c) has a styrene segment content of 30 wt%, a Shore A hardness of 62, and a melt index MFR of 3g/10 min.
Testing the density, melt index MFR, Shore A hardness, molecular weight distribution index DPI and trailing index PI of the obtained sealing gasket in the crown cap at normal temperatureHTNormal temperature instantaneous pressure resistance, chronic air leakage rate, instantaneous pressure resistance after pasteurization and processing stability, and the test results are shown in table 1.
Example 2
Accurately weighing 700g of low-density polyethylene, 300g of linear low-density polyethylene and 1000g of styrene-butadiene-styrene block copolymer, mixing for 1min in a high-speed mixer, extruding and granulating by using a double-screw extruder, wherein the rotating speed of a motor is 250rpm, the length-diameter ratio of a screw is 25, the temperature of a screw interval is set to be 160 ℃ of a conveying section, 165 ℃ of a melting section, 170 ℃ of a mixing section, 170 ℃ of an exhaust section and 160 ℃ of a homogenizing section, cooling the mixture by using a 25 ℃ cold water tank, and cutting. The resulting mixed ion was dried at 70 ℃ for 36 h. The obtained granules are extruded again by a double screw, the temperature of the screw interval is set to be 85 ℃ in the conveying section, 90 ℃ in the melting section, 100 ℃ in the mixing section, 105 ℃ in the exhaust section and 115 ℃ in the homogenizing section, and the granules are directly punched on a crown cover, the processing speed is 5000 pieces/min, and the punching temperature is 5 ℃.
Wherein component (a) is a low density polyethylene having a density ρA＝0.916g/cm3The molecular weight distribution index DPI is 2.76, the melt index MFR is 8g/10min, the melting temperature Tm is 98.1 ℃, and the crystallization temperature Tc is 96.8 ℃;
wherein component (b) is a linear low density polyethylene having a density ρB＝0.954g/cm3The molecular weight distribution index DPI is 4.2, the melt index MFR is 20g/10min, the melting temperature Tm is 130 ℃, and the crystallization temperature Tc is 117 ℃;
wherein the styrene-butadiene-styrene block copolymer of the component (c) has a styrene segment content of 24 wt%, a Shore A hardness of 60, and a melt index MFR of 2g/10 min.
Testing the density, melt index MFR, Shore A hardness, molecular weight distribution index DPI and trailing index PI of the obtained sealing gasket in the crown cap at normal temperatureHTNormal temperature instantaneous pressure resistance, chronic air leakage rate, instantaneous pressure resistance after pasteurization and processing stability, and the test results are shown in table 1.
Example 3
Accurately weighing 800g of low-density polyethylene, 400g of linear low-density polyethylene and 800g of styrene-butadiene-styrene block copolymer, mixing for 1.5min in a high-speed mixer, extruding and granulating by using a double-screw extruder, wherein the rotating speed of a motor is 275rpm, the length-diameter ratio of a screw is 25, the temperature of a screw interval is set to be 160 ℃ in a conveying section, 165 ℃ in a melting section, 170 ℃ in a mixing section, 170 ℃ in an exhaust section and 160 ℃ in a homogenizing section, and cutting after cooling through a 30 ℃ cold water tank. The resulting mixed ion was dried at 70 ℃ for 48 h. The obtained granules are extruded again by a double screw, the temperature of the screw interval is set to be 85 ℃ in the conveying section, 90 ℃ in the melting section, 100 ℃ in the mixing section, 105 ℃ in the exhaust section and 115 ℃ in the homogenizing section, and the granules are directly punched on a crown cover, the processing speed is 5000 pieces/min, and the punching temperature is 8 ℃.
Wherein component (a) is a low density polyethylene having a density ρA＝0.920g/cm3The molecular weight distribution index DPI is 7.25, the melt index MFR is 6g/10min, the melting temperature Tm is 106 ℃, and the crystallization temperature Tc is 91.5 ℃;
wherein component (b) is a linear low density polyethylene having a density ρB＝0.92g/cm3The molecular weight distribution index DPI is 2.87,melt index MFR 17g/10min, melting temperature Tm 121.1 ℃, crystallization temperature Tc 107.7 ℃;
wherein the styrene-butadiene-styrene block copolymer of the component (c) has a styrene segment content of 29 wt%, a Shore A hardness of 70, and a melt index MFR of 2.5g/10 min.
Testing the density, melt index MFR, Shore A hardness, molecular weight distribution index DPI and trailing index PI of the obtained sealing gasket in the crown cap at normal temperatureHTNormal temperature instantaneous pressure resistance, chronic air leakage rate, instantaneous pressure resistance after pasteurization and processing stability, and the test results are shown in table 1.
Example 4
The procedure is as in example 1, except that the styrene-butadiene-styrene block copolymer charged has a melt index of 5g/10min, measured at 200 ℃ under a load of 5kg according to the procedure specified in GB/T3682-2000.
Testing the density, melt index MFR, Shore A hardness, molecular weight distribution index DPI and trailing index PI of the obtained sealing gasket in the crown cap at normal temperatureHTNormal temperature instantaneous pressure resistance, chronic air leakage rate, instantaneous pressure resistance after pasteurization and processing stability, and the test results are shown in table 1.
Example 5
The procedure of example 1 was followed except that the added styrene-butadiene-styrene block copolymer had a Shore A hardness of 50.
Testing the density, melt index MFR, Shore A hardness, molecular weight distribution index DPI and trailing index PI of the obtained sealing gasket in the crown cap at normal temperatureHTNormal temperature instantaneous pressure resistance, chronic air leakage rate, instantaneous pressure resistance after pasteurization and processing stability, and the test results are shown in table 1.
Comparative example 1
The procedure is as in example 1, except that the low-density polyethylene added thereto has a molecular weight distribution index DPI of 3.67 and a melt index MFR of 20g/10 min.
Testing the density, the melt index MFR and the like of the sealing gasket in the crown cap at normal temperature,Shore A hardness, molecular weight distribution index DPI and tailing index PIHTNormal temperature instantaneous pressure resistance, chronic air leakage rate, instantaneous pressure resistance after pasteurization and processing stability, and the test results are shown in table 1.
Comparative example 2
The procedure is as in example 1, except that the linear low density polyethylene added therein has a molecular weight distribution index DPI of 12 and a melt index MFR of 40g/10 min.
Testing the density, melt index MFR, Shore A hardness, molecular weight distribution index DPI and trailing index PI of the obtained sealing gasket in the crown cap at normal temperatureHTNormal temperature instantaneous pressure resistance, chronic air leakage rate, instantaneous pressure resistance after pasteurization and processing stability, and the test results are shown in table 1.
Comparative example 3
The process of example 1 was followed except that no linear low density polyethylene was added.
Testing the density, melt index MFR, Shore A hardness, molecular weight distribution index DPI and trailing index PI of the obtained sealing gasket in the crown cap at normal temperatureHTNormal temperature instantaneous pressure resistance, chronic air leakage rate, instantaneous pressure resistance after pasteurization and processing stability, and the test results are shown in table 1.
TABLE 1
Comparing the results of example 1 with comparative example 1, it can be seen that the low density polyethylene added in comparative example 1 has a lower molecular weight distribution index DPI and a higher melt index MFR, resulting in a lower molecular weight distribution index DPI and a lower tailing index PI for the sealing gasket in the crown cap made from itHTThe low-density polyethylene added in the embodiment 1 has proper molecular weight distribution index and melt index, the crystallization temperature of the high molecular weight part is higher, the crystallization is fast, and the high molecular weight part is easy to solidify in the high-speed extrusion process, so that the knife sticking phenomenon formed in the high-speed shearing process is avoided, the notch phenomenon of the sealing gasket is further reduced, and the sealing performance is improvedThe normal temperature instantaneous pressure resistance, the chronic air leakage rate, the instantaneous pressure resistance after pasteurization and the improvement processing stability of the high sealing gasket all have technical effects obviously higher than the results of the comparative example 1.
Comparing the results of example 1 and comparative example 2, it can be seen that the linear low density polyethylene added in comparative example 2 has a larger molecular weight distribution index DPI and a larger melt index MFR, which results in a lower molecular weight distribution index DPI and a lower tailing index PI of the sealing gasket in the crown cap prepared from the linear low density polyethyleneHTThe linear low density polyethylene added in the example 1 has proper molecular weight distribution index and melt index, and can effectively control the melt flow rate of the thermoplastic elastomer composition, thereby avoiding the phenomenon of flash during the high-speed stamping process of the sealing gasket prepared by the linear low density polyethylene, improving the normal-temperature instantaneous pressure resistance, the chronic air leakage rate, the instantaneous pressure resistance after pasteurization and the processing stability of the sealing gasket, and having various technical effects which are obviously higher than the results of the comparative example 2.
Comparing the results of example 1 and comparative example 3, it can be seen that the linear low density polyethylene is not added in comparative example 3, and the sealing gasket in the crown cap prepared by the linear low density polyethylene has a low molecular weight distribution index DPI and a low tailing index PIHTThe molecular weight distribution index DPI of the sealing gasket in the crown cap prepared by the method is higher and the tailing index PI is higher in the sealing gasket prepared by the method in example 1 added with linear low density polyethyleneHTHigher, which indicates that more significant macromolecule chain tail end exists in the thermoplastic elastomer composition, so that the crystallization temperature of the high molecular weight part in the polyethylene in the composition is increased, the crystallization is faster, and the high molecular weight part is easier to solidify in the high-speed extrusion process, thereby reducing the knife sticking phenomenon formed in the high-speed shearing process, further reducing the notch phenomenon of the sealing gasket, improving the normal-temperature instantaneous pressure resistance, the chronic air leakage rate, the instantaneous pressure resistance after pasteurization and the processing stability, and each technical effect is obviously higher than that of the result of the comparative example 3.
Comparing the results of examples 1 and 4, it can be seen that when the melt index of the added styrene-butadiene-styrene block copolymer is within the preferred range, the melt flow rate of the thermoplastic elastomer composition can be more effectively controlled, thereby further avoiding the flash phenomenon of the gasket prepared from the thermoplastic elastomer composition during the high-speed stamping process, more effectively improving the normal temperature instantaneous pressure resistance, the chronic air leakage rate, the instantaneous pressure resistance after pasteurization and the processing stability of the gasket, and having better technical effects.
Comparing the results of example 1 and example 5, it can be seen that when the shore a hardness of the added styrene-butadiene-styrene block copolymer is within the preferred range, the elasticity of the thermoplastic elastomer composition can be more effectively improved, thereby further improving the normal temperature instantaneous pressure resistance of the sealing gasket and the instantaneous pressure resistance after pasteurization, and the technical effects are all better.
The preferred embodiments of the present invention have been described in detail, however, the present invention is not limited to the specific details of the above embodiments, and various simple modifications may be made to the technical solution of the present invention within the technical idea of the present invention, and these simple modifications are within the protective scope of the present invention.
It should be noted that the various features described in the above embodiments may be combined in any suitable manner without departing from the scope of the invention. The invention is not described in detail in order to avoid unnecessary repetition.
In addition, any combination of the various embodiments of the present invention is also possible, and the same should be considered as the disclosure of the present invention as long as it does not depart from the spirit of the present invention.
Claims (16)
1. A thermoplastic elastomer composition, characterized in that it comprises:
(a) the low-density polyethylene has a melt index of 4-10g/10min, a molecular weight distribution index of 2-10, a melting temperature of 100-110 ℃ and a crystallization temperature of 90-100 ℃ which are measured under the action of a 2.16kg load at 190 ℃ according to a method specified in GB/T3682-2000;
(b) the linear low-density polyethylene and/or the high-density polyethylene has a melt index of 10-25g/10min, a molecular weight distribution index of 2-10, a melting temperature of 110-130 ℃ and a crystallization temperature of 105-115 ℃ which are measured under the load action of 2.16kg at 190 ℃ according to a method specified in GB/T3682-2000; and
(c) a styrene elastomer, the melt index of which is 0.25-4g/10min and the Shore A hardness of which is 60-85, which are measured under the action of a 5kg load at 200 ℃ according to the method specified in GB/T3682-2000;
wherein the styrene elastomer contains 20-40 wt% of styrene segment;
wherein the thermoplastic elastomer composition has a molecular weight distribution index DPI of 4 to 8 and a high molecular tailing index PI in the width of the molecular weight distributionHTGreater than 4.9;
wherein the content of the component (a) is 35 to 60 parts by weight, the content of the component (b) is 15 to 25 parts by weight, and the content of the component (c) is 20 to 50 parts by weight, relative to 100 parts by weight of the thermoplastic elastomer composition.
2. The thermoplastic elastomer composition of claim 1, wherein (a) the low density polyethylene has a melt index of 5 to 8g/10min, a molecular weight distribution index of 2 to 7, and a melting temperature of 100-;
(b) the melt index of the linear low-density polyethylene and/or the high-density polyethylene is 15-20g/10min, the molecular weight distribution index is 2-5, and the melting temperature is 120-; and
(c) a styrene-based elastomer;
wherein the thermoplastic elastomer composition has a molecular weight distribution index, DPI, of 4.62 to 6.97; high molecular tailing index PI in molecular weight distribution widthHTGreater than 5.7.
3. The thermoplastic elastomer composition of claim 1, wherein the styrenic elastomer has a styrene block content of 24 to 30 wt.%.
4. The thermoplastic elastomer composition of claim 1, wherein the styrenic elastomer has a melt index of 2-4g/10min and a shore a hardness of 60-70.
5. The thermoplastic elastomer composition according to any one of claims 1 to 4, wherein the styrenic elastomer is a styrene-butadiene-styrene block copolymer and/or a styrene-ethylene-butylene-styrene block copolymer.
6. A process for preparing the thermoplastic elastomer composition of any one of claims 1 to 5, comprising: mixing, extruding and granulating, cooling and drying the component (a), the component (b) and the component (c) in sequence.
7. The process according to claim 6, wherein the mixing is carried out under stirring for a mixing time not exceeding 5 min.
8. The process according to claim 7, wherein the mixing is carried out under stirring for a mixing time not exceeding 2 min.
9. The method of claim 6, wherein the extrusion temperature of the extrusion granulation is: 160 ℃ and 170 ℃.
10. The method of claim 6, wherein the cooling conditions comprise: the cooling temperature is 40-60 ℃.
11. The method of claim 10, wherein the cooling temperature is 50-60 ℃.
12. The method of claim 6, wherein the drying conditions comprise: the drying temperature is 70-90 deg.C, and the drying time is 24-48 h.
13. A thermoplastic elastomer composition prepared by the process of any one of claims 6-12.
14. A sealing gasket made from the thermoplastic elastomer composition of any one of claims 1-5 and 13.
15. A method of preparing a sealing gasket in a crown cap, the method comprising: the thermoplastic elastomer composition of any one of claims 1-5 and 13 is extruded and then stamped onto crown caps.
16. The method of claim 15, wherein the temperature of the extrusion is 85-120 ℃; the stamping conditions include: the stamping speed is 2000-.
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| WO2003040199A1 (en) * | 2001-11-06 | 2003-05-15 | Cryovac, Inc. | Heat-sealed easy-open packaging article containing highly branched homogeneous polyolefin |
| EP1861441A2 (en) * | 2005-03-17 | 2007-12-05 | Dow Global Technologies Inc. | Interpolymers of ethylene/alpha-olefins blends and profiles and gaskets made therefrom |
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