1. Film definition for flexible packaging

In general national packaging terms (GB4122-83) flexible packaging is defined as: flexible packaging refers to packaging in which shape of container can change after contents are filled or removed. Flexible packaging includes various bags, boxes, sleeves, pouches, etc. from paper, aluminum foil, fiber, polyethylene film and their composites. Films are commonly referred to as sheet plastics less than 0.25 mm thick. The plastic film is transparent, flexible, has good water resistance, moisture and gas resistance, good mechanical strength, stable chemical properties, oil resistance, exquisite graphics can be easily printed, and can be sealed into bags. It can meet packaging requirements of a variety of products, and is an ideal packaging material for easy-to-storage and easy-to-pack semi-finished products, daily necessities, and small-pack goods in supermarkets.

The printing of flexible packaging based on plastic film occupies an important place in packaging printing. According to statistics, since 1980, plastic packaging in some developed countries of world has accounted for 32.5% to 44% of all packaging and printing.

Generally speaking, since a single film material is not ideal for protecting contents, a composite film that combines two or more films into a single layer is often used to meet requirements of food preservation technology and aseptic packaging. The outer material of composite film is mainly made of materials that are difficult to scratch and grind, have excellent optical properties and good printing performance, such as: paper, cellophane, stretched PP, polyester, etc.; middle layer is a barrier polymer, such as: aluminum foil, vapor-deposited aluminum, polyethylene inner layer materials, diazepam, mainly use odorless non-toxic polyethylene and other thermoplastic resins.

2. Introduction of plastic barrier technology

1. Is plastic permeable?

Shielding ability of plastic products (containers, films) from small molecular gases, liquids, water vapor and odors.

2. Transfer coefficient?

Indicator of magnitude of barrier ability of plastics.

Definition:

Products made of plastic of a certain thickness (1 mm), under a certain pressure (1 MPa), a certain temperature (23 degrees), a certain humidity (65%), a unit of time (1 day = 24 hours), a unit of area (1 m2 ). ), by volume or weight of low molecular weight particles (O2, CO2, H2O). Expressed as (cm3), (g)

For gas:

Unit cm3, mm/m2, d, MPa;

For liquids:

Unit g, mm/m2, d, MPa;

3. Coefficient prlowering of commonly used medium and high barrier plastics:

Plastic type/factor

O2

CO2

H2O

EVOH (PE29%)

0.1

1.5

20-25

EVOH (PE38%)

0.4

6

40–70

PVDC

0.5–4

1.-2

0.2–6

MXD6

2–5

28

15-30

PAN

8

16

50

FEATHER

12–22

50

5–9

PA666

15-30

50–70

100

PA6

25–40

150–200

150

PET

49–90

180

180–300

PND

2500

PP

3000

LDPE

10000

EVA

18000

4. Explanation of terms

EVOH: (EVAL) ethylene-vinyl alcohol

PA6-666: Polyamide (Nylon)

MXD6: polymer of aromatic nylon, m-xylylenediamine and adipic acid

PVDC: polyvinylidene chloride

PAN: polyacrylonitrile

PEN: polyethylene naphthalate

PET: polyethylene terephthalate

PP: polypropylene

PE: polyethylene

PS: styrene

HDPE: high density polyethylene

Low density polyethylene LDPE

Linear low density polyethylene LLDPE

MLLDPE: Metallocene Linear Low Density Polyethylene

IONOMER：Ionometer

EVA: copolymer of ethylene and vinyl acetate

TIE: titanium, polymer bond

AC: polyethyleneimine AC: ethanol: water = 1:6:3

PU: polyurethane PU: hardener: acetone = 7:1:45

PVA: polyvinyl alcohol

Among them: materials with high barrier properties: EVOH, PVDC, PAN, MXD6;

Medium protection materials: PA, PEN, PET

5. Plastic barrier method?

Multilayer mold barrier and composite mold barrier

Layer blending - BOPA, BOPET, etc.;

The composite forming barrier is divided into:

Dry Composite Barrier and Coextrusion Composite Barrier

The dry compound barrier is usually laminated with paper, CPP, BOPP, PET, aluminum platinum or aluminized film, such as milk packaging roof boxes, pillow bags, etc.

The co-extrusion composite barrier is made from various plastic materials that are melted and co-extrusioned.

6. The formula for barrier properties of multilayer composite materials:

1/P = T1/P1 + T2/P2 +T3/P3. . . . . .

In formula: T1, T2 --- thickness of each composite layer

P1, P2-----Each gain

P: The overall permeability coefficient of composite material, more layers, thicker, better barrier property, and better overall barrier property.

7. Composite multilayer co-extrusion method?

1], composite of ordinary resin and ordinary resin --- suitable for packaging soy sauce, vinegar, etc. with low barrier properties.

Commonly used resins:

LDPE, HDPE, LLDPE, PP, PS, PVC, etc.

2], composite of conventional resin and medium barrier resin ****

The outer layer is a normal resin, inner layer is a medium barrier resin, and barrier layers are combined from 3 to 7 layers.

LLDPE, LDPE, HDPE, PP, PS, PVC, + PA, PET, EVA, etc.

3], composite of medium barrier resin and medium barrier resin*****

MXD6, PA6, PEN, PET, EVA, PA666, good compatibility and no need for adhesive resin, usually composite molding with 2-3 layers structure.

4], Composite molding of conventional resin and high barrier resin********

Common outer layer: LDPE, HDPE, PP, PS, LLDPE, etc.

Inner layer: EVOH, MXD6, PVDC, etc., need to add bonding resin.

5], Forming a composite of medium barrier resin and high barrier resin

Medium resins: PET, PA, EVA, etc.

High barrier resin: EVOH, MXD6, PVDC, PAN, etc. do not require addition of a bonding resin.

8. What is general way of barrier composite at home and abroad?

Abroad: PE//TIE//EVOH//TIE//PE

PE (EVA)//TIE/PA/EVOH/PA/TIE/PE

Internal: PP/TIE/PA/TIE/PP,

LLDPE/TIE/PA/HYD/LDPE,

MLLDPE/tie/EVOH/tie/MLLDPE,

MLLDPE/tie/PA/tie/MLLDPE etc

10. Standards for medium to high barrier composites?

High barrier standard: O2 penetration rateis 5 ml/m2, below d, and moisture permeability is 2 g/m2, below d.

Composite materials with medium and high barrier properties

O2: 5–10 ml/m2, d

H2O: 10 g/m2, d.

11. Physical and mechanical properties of aseptic packaging

1], O2 transmittance ≤1ml

2], tensile strength is ≥30MPa

3], elongation at break ≥40

4], peel strength ≥1

5], heat seal strength ≥40

6], light transmission ≤0.4

7], pressure resistance of bag is shown in table:

Bag capacity

Internal pressure maintenance (2 mm)

Opening pressure

(kPa)

Maintain pressure (kPa)

demand

≤25 l

20

No bleeding, no cracks

≥25

≥25 l

10

No bleeding, no cracks

≥15

8], drop characteristics of bag are shown in the table:

Bag capacity

Drop height H

demand

≤5 l

0.8

No leaks, no failures

≤25 l

0.6

No leaks, no failures

≥25 l

0.4

No leaks, no failures

3. Composite packaging materials

In line with development of packaging industry, product packaging has also been developed. From simple paper packaging to single-layer plastic film packaging and extensive use of composite materials. Composite film can give contents of package properties of moisturizing, aroma preservation, appearance, freshness preservation, light protection, penetration prevention and shelf life extension, so it develops rapidly.

Composite materials are two or more materials that are combined through one or more compositional processes to form composite materials with specific functions. Generally, it can be divided into base layer, functional layer and heat sealable layer. The base layer mainly plays role of aesthetics, printing and moisture resistance. Such as BOPP, BOPET, BOPA, MT, KOP, KPET, etc.; functional layer mainly plays role of barrier and light protection, such as VMPET, AL, EVOH, PVDC, etc.; heat seal layer is in direct contact with packaged items, and floor penetration adaptability and resistance, good heat sealability, transparency, sun exposure and other features such as LDPE, LLDPE, MLLDPE, CPP, VMCPP, EVA, EAA, E-MAA, EMA , EBA etc. The following is a brief introduction to design, development, and current situation of core materials for composite flexible packaging materials.

LDPE, LLDPE resins and films

Composite film in my country started in late 1970s. From early to mid-1980s, my country began to introduce some extruders, blown film machines and printing machines to produce simple two-layer or multi-layer composite materials. For example, extruded BOPP/PE, paper/PE, PP/PE; dry BOPP/PE, PET/PE, BOPP/AL/PE, PET/AL/PE, etc., among which LDPE resin and film, often a certain proportion of LLDPE is mixed to increase its strength and rigidity. It is mainly used for packing instant noodles, biscuits, mustard and other products. General purpose LDPE coating resins include: IC7A, L420, 19N430, 7500, etc.; LDPE resins for blown film include: Q200, Q281, F210-6, 0274, etc.; LLDPE resins include: 218w, 218F, FD21H, etc.

CPP film, CPE filmFrom late 1980s to early 1990s, with advent of a new generation of flexible packaging equipment and foundry equipment, packaging The inclusion scope has been further expanded, and requirements for transparency of some puffed food, oatmeal and other packaging bags are relatively high, while products for cooking and high temperature sterilization have been introduced to market one by one, and requirements for packaging materials have also increased accordingly. materials can no longer meet requirements aboveindicated products. Made by injection molding, has good heat sealability. CPP with oil resistance, transparency, aroma retention and special heat sealing properties in low humidity and high cooking temperature is widely used in packaging. Developed on this basis, aluminum coated CPP is quickly and widely used due to its metallic luster, aesthetics and barrier properties. And cast CPE film finds further applications because of its ease of one-sided tearing, low temperature heat sealing and good transparency.

MLLDPE resin

In connection with continuous development and changes in packaging market, more and more special requirements are placed on packaging. The American company DOW Chemical Company produced metallocene polyethylene MLLDPE by metallocene catalyzed polymerization. Such as APFINITY, POP1880, 1881, 1840, 1450 and other resins. Then Exxon in USA. Mitsui in Japan and Philips in US have also consistently produced MLLDPE. For example, EX-CEED350D60, 350D65 Exxon, E-VOLVE SP0540, SP2520 Mitsui Petrochemical, MPACT D143 and D139 Philips, etc. mixing ratio can be from 20% to 70%. This type of film has good tensile strength, toughness, good transparency, good low temperature heat sealing and anti-pollution properties. The composite material with it as inner layer is widely used in frozen, refrigerated food, shampoo, oil, vinegar. , soy sauce, detergent, etc. It can solve packaging speed, broken packaging, packaging leakage, penetration, etc. of above products in packaging production and transportation process.

Inner protective film material

Packaging cups for jelly, juice, yogurt, fruit milk, soup and other liquids. Bottle, its main material is HDPE. PP, PS, etc. The cover film of this package must take into account not only shelf life, but also strength of heat seal between cover film and cup, as well as consumer convenience - ease of tearing. In order to achieve this feature, material of inner layer can only form adhesion strength of surface with sun of cup, but cannot completely penetrate and fuse together. As a rule, a modified EVA resin is used. For example, DuPont APPEEL53007 in USA. TOPCO L-3388 from Toyo Japan, LOTRYL 20MA 08 from France, WT231 from HIRO.DINE from Japan, etc. Its structure can be: PET/PE/HM, BOPA/PE/HM, PET/VMPET/PE/HM, PET/AL/PE/HM, Paper/PE/AL/PE/HM. The requirement that protective film and bottom cup be tightly closed without tearing usually requires that material of lower cup matches inner material of protective film so that two materials can fullyawn to fuse when heat sealable. For example, for HDPE cups, inner liner is LDPE or EAA; for cups made of polypropylene, inner layer of protective layer is a CPP film; For PET bottles, we found coated modified PET film as heat-sealing layer. Capping PET bottles for pesticides gave satisfactory results.

Co-extruded film

Films made by blending single layer LDPE or LDPE with other resins have separate properties and cannot meet packaging requirements of today's product development. Improved general characteristics. For example, comprehensive characteristics of film, such as mechanical strength, heat sealing characteristics, heat sealing temperature, barrier properties, opening properties, and anti-fouling properties, are improved, and its processing cost is reduced, so it is widely used. For example, H-layer co-extrusion blown film with hot melt adhesive: PE/HM, PE/EAA cable film, MLLDPE low temperature heat sealable film, EVA cover film, anti-static film and smooth film. H-layer co-extruded co-extruded polypropylene, unmodified polypropylene/heat-sealable polypropylene, etc. Three-layer and five-layer nylon co-extruded films, five-layer and seven-layer EVOH and PVDC high barrier films are also being developed and widely used.

Film development for inner layer of composite flexible packaging materials, from LDPE, LLDPE, CPP, MLLDPE to widespread use of coextruded films at present, mainly realizes functionalization and customization of packaging, and meets requirements of quality assurance. and processing of contents of package, performance characteristics, transportation and storage conditions. With continuous introduction of new materials and improvement of inner film production technology and equipment, composite flexible packaging material inner film is sure to develop rapidly and promote food products. Other With development of society, human needs continue to grow, and various functional and environmentally friendly packaging films continue to appear. For example, water-soluble polyvinyl alcohol film, which is environmentally friendly, fully degradable, and has good heat sealing performance, is being developed not only as a single-layer packaging material, but also as an inner layer film.

Fourth, multilayer composite technology

Multilayer composite technology consists in use of materials with medium and high barrier properties for connection with other inexpensive packaging materials, as well as in combination of high barrier properties of barrier materials with cheap or special mechanical, thermal and other properties of other materials. Different combinations of multilayer composite films can meet different requirements. The multi-layer composite technology mainly includes dry multi-layer composite and co-extrusion multi-layer composite.

(1) Multilayer dry mix

Dry composite multi-layer technology was pioneered in food packaging such as HDPE (PP)/EVOH/HDPE (PP). Its structure is often BOPP, outer layer is BOPET, middle barrier layer can be PA. , PVDC, EVOH or aluminum foil, inner heat sealing layer is usually chlorinated polypropylene (CPP), if high temperature resistance is not required, PE can also be used, and adhesives can be used to bond with each other. Its barrier properties are mainly associated with barrier films and adhesives. Multi-layer dry composite barrier technology is mainly based on development of barrier films. In recent years, many barrier substrates have been recently developed, such as MXD6 special nylon film and silicon oxide film, which have excellent barrier properties and can be reverse printed, printed The quality is exquisite. However, due to need for secondary molding and use of more expensive adhesives, people are gradually moving towards use of multi-layer co-extrusion compounding.

(2) Multilayer co-extrusion composite

A multi-layer co-extrusion composite is a combination of two or more materials in a molten state and welding them together in a die. The main co-extrusion resins are usually HDPE, PP and other resins, and barrier resins are mainly PA, EVOH, PVDC, etc. Since compatibility of barrier materials and heat sealing materials is generally poor, it is necessary to consider choosing a good compatibilizer such as an acrylate copolymer resin. Barrier resins require good processing properties to meet good flow requirement for a co-extrusion mixing head. If flow is too poor, or flow of several resins varies too much, it will cause composite to shrink due to laminar flow. barrier properties of membrane. Co-extrusion composite is usually designed according to symmetry of ABCBA five-layer structure and ABCDCBA seven-layer structure, and its barrier property and composite strength are best.

Compared to dry compoundingm, multi-layer co-extrusion composite technology started late, but its advantages are raw material saving, raw material diversification, adapting to environmental protection requirements, and no use of toxic adhesives. In addition, barrier effect is very ideal, and effect will be better as number of composite layers increases. At present, number of composite layers has been increased to nine or even eleven layers, which have been rapidly developed and applied to manufacture of packaging films and hollow containers. However, co-extrusion composite method imposes very stringent requirements on technology and equipment, requires highly skilled workers and relatively complex machinery and equipment, expensive equipment and low waste disposal rates, which greatly limits its large-scale application.

A. Classified by compound process.

Currently, composite materials for flexible packaging are classified according to processing methods, mainly into following categories:

① Solvent dry-coated composite soft packaging material;

②Wet coated inorganic adhesive composite soft packaging material;

③Composite packaging material laminated with extruded film;

④Multilayer co-extrusion (through two or more extrusion dies) of composite soft packaging material;

⑤Composite hotmelt-coated soft packaging material;

⑥ Solvent-free composite flexible packaging material (i.e. hard adhesive);

⑦ Physical vapor deposition composite soft packaging material;

⑧Physical vapor deposition composite soft packaging material;

⑨Mixed composite flexible packaging material;

⑩The above methods are combined with composite soft packaging materials, etc.

B. Classify according to composite material.

The main material used for flexible packaging compounding is mainly plastic film, followed by paper, metal foil and composite materials.

Use them to make following types of composite packaging materials:

①Paper and paper;

②Paper and metal foil;

③Paper and polyethylene film;

④PE film and PE film;

⑤Plastic film and metal foil;

⑥Plastic film and metal film;

⑦PE film and base material;

⑧Plastic film and inorganic compound film;

⑨Plastic film and organic film;

⑩Amorphous plastic film and plastic film;

(11) Composite substrate and ultrathin nanoparticles;

(12) Special additives for coating or impregnating a substrate;

(13) Multilayercompounding of composite materials, etc.

C. Classify by compound form.

Generally speaking, compounding of material most often occurs evenly over entire surface.

Composite mold packaging materials mainly include following categories:

①Large area composite (homogeneous);

② Partial compounding, such as compounding and reinforcing or giving certain functions to only sealing or reinforcing part of package;

③Composite sheet or composite package that combines special functions in one place and performs a common function;

④ Gradient mixing (or non-uniform mixing), changing concentration, composition or thickness of added material in thickness direction (or length direction) of composite film as needed;

⑤Special blending such as mesh blending.

3rd, 4th and 5th types are green technologies.

D. Classification by composite function.

With regard to packaging industry, since each industry has different product packaging requirements, different systems use different classification methods. Currently, there are no uniform rules and standardized terminology.

According to new packaging system recently advocated by Europe and United States, it can be divided into following 10 categories.

①Advanced composite packaging;

②High impermeability composite packaging (air, water, oil blocking);

③Anti-corrosion (anti-corrosion and anti-corrosion) composite packaging;

④ Electromagnetic shielded composite packaging (dry worry);

⑤ Anti-static composite packaging;

⑥Biological composite packaging (warming fruits, canned fish, insect protection, mold protection);

⑦Composite packaging for fresh storage (for fruits, vegetables and meat products);

⑧Composite packaging for cooking (such as cooking, microwave baking, etc.);

⑨Smart composite packaging;

⑩Ultramicro-nanocomposite packaging.

5. High barrier multilayer co-extrusion composite film

Currently, co-extruded high barrier films composed of layers of PA, EVOH, PVDC and PE, EVA, PP and other resins are popular in functional packaging film market due to their reasonable, economical and reliable performance. In particular, some asymmetrically structured multilayer coextruded blown films are better known for their excellent composite peel strength, outstanding barrier properties, excellent environmental and chemical resistance, low cost processability, and suitable reprocessability. laminating as main body or simplifying dry lamination process, multi-layer co-extrusion laminating film is popular in market due to no residual solvent pollution.

In addition to ever-changing resin development, technological progress in field of multi-layer overlay co-extrusion die and continuous improvement of plastic injection molding process has accelerated continuous development of plastic composite film processing industry to adapt to changing social environment and technological development pace. And push co-extruded composite film to a new stage of development, and provide ample development space to improve quality level of composite packaging film, especially packaging base film.

1. Current status and requirements for multilayer co-extruded composite film

At present, production of multilayer composite films in China generally uses bonding and compounding method of plastic films with various functions. Generally speaking, each additional function requires an additional film substrate layer and two additional manufacturing processes. During this period, it not only increases cost, but also increases contamination (in case of compounding with solvent-based adhesives), and even function of film becomes redundant due to limitation of manufacturing process. Manufacturers have paid dearly for rising production costs, declining profits and weakening competitiveness of products in market.

Diversification of packaging functions, streamlining packaging structure, and maximizing benefits of packaging are research and development topics of composite film manufacturers, especially composite film substrates, in recent years.

1) Diversification of packing functions

As market demand for packaging functions continues to grow, functions of multilayer composite films are becoming more comprehensive. Asymmetric coextrusion blown multilayer films result from fatal stress deformation and difficult to improve optical properties of film. Thus, this influenced further development ofdevelopment of its diverse functions. The secondary processing equipment on market, especially in China, has special requirements for material asymmetry, so it cannot effectively improve stress warping and optical properties, which hinders rapid development of multilayer co-extrusion. level of blown film development.

2) Rationalizing packaging structure

Because environment and security change and guide development of market in many aspects, at same time to protect earth's resources and ensure safety of people's lives. This requires a more reasonable packaging structure, which is reflected in requirement that structure of composite film be more perfect (protective function), simpler (convenient to use, convenient to transport), safer (hygiene, environmental adaptability) and enhancing social and environmental protection Environmental resilience (waste management and recovery).

3) Making most of packaging

Maximizing benefits of packaging is a goal pursued by composite film manufacturers in close cooperation with customers. Comprehensively improve product quality, maximize benefits by quantifying functions of composite films, reducing production processes, reducing thickness and reducing their cost (high productivity, labor saving, resource saving and energy saving).

If analyzed from a technical point of view, development and application of co-extrusion technology can simultaneously meet above three requirements and formed an industrial production. The development of co-extruded multilayer composite film is inseparable from close cooperation and interaction of equipment, raw materials and processing technology. Only when processing equipment technology, raw material processing and processing technology reach best state through cooperation, most ideal product can be obtained.

Compared with single-layer plastic substrate, multi-layer co-extrusion composite film greatly simplifies production process of dry composite film, expands functionality and can quantify functions by effectively adjusting thickness, and structure combination is convenient and flexible, a wide range of materials can be selected. Comprehensive performance full of functions and flexible to change, low cost and high quality level, high added value and strong market adaptability. Therefore, multilayer co-extruded composite films are widely used in packaging.

2. Structure and development trend of multilayer co-extrusion composite film

Generally speaking, structure of a multilayer co-extruded composite film depends on functional requirements of film. Subject to compliance with technological requirements forThere is no combination of different polymers functional requirements for packaging materials such as barrier, heat sealing, body strength, puncture resistance, environmental suitability, recycling performance, and extended shelf life and shelf life. . Based on analysis of functional requirements, a combination of five polymers is sufficient. However, seven-layer, nine-layer, ten-layer and even more layered co-extrusion composite films are applied in market, making it a trend and developing rapidly. The structural design of co-extruded composite films gradually requires systematic achievement of ideal state of integration of functions, technology, cost, environmental protection, safety and recycling.

1], Barrier

(1) Using multiple layers of same resin in barrier layer instead of a single layer of resin can improve stability of barrier layer. For example, if a polyamide material is used as barrier layer, oxygen barrier coefficient is 40 units. In order to ensure stability of its oxygen barrier performance, its thickness is usually specified as theoretical design value of material + negative value of equipment error + safety factor. And when we use multiple layers of same resin instead, negative value of equipment thickness error is greatly reduced and safety factor is greatly improved.

(2) When we confirm that thickness of barrier layer is sufficient to meet barrier requirement, introduce multiple layers of same resin into barrier layer instead of a single layer of resin, which can reduce high value-added raw material cost of barrier film.

(3) Replacing one polymer with two different polymers in barrier layer can greatly improve barrier properties of film. For example, combining an EVOH layer with a typical PA layer can not only protect puncture resistance of PA, but also improve strength of EVOH and improve crack resistance of EVOH. For five-layer structure, if two different barrier layers are used at same time, one layer can only be on outermost layer, in order to prevent barrier film of outer layer from being easily damaged by external forces and cause barrier effect to decrease, increase in PA is usually used, to compensate for it, thickness method is used, which leads to higher prices.

2], other

(1) Divide heat seal layer and composite layer into two groups, one of which uses cheaper resins instead of more expensive resins to reduce film cost while maintaining film strength. Another group uses functional polymers that fulfill their functional requirements. Use multi-layer concept to make more economical composite films. HFor example, when comparing two 1K films, material cost of a five-layer film is about 19% higher than that of a seven-layer film.

(2) The performance of co-extruded polyamide films containing less than five layers can be improved by using co-extruded films with more layers. For example, use of an additional adhesive layer can improve film's barrier properties by increasing film's water vapor barrier effect. Another advantage obtained in this way is that film can be made softer, pleasant to touch and has good crack resistance.

(3) The use of coextruded films with a large number of layers can improve stress warping resistance of coextruded polyamide films containing less than five layers. At same time, it meets needs of secondary processing such as bag making.

(4) Integrate other functions of dry composite film other than internal printing, so that composite process is simple, composite structure is flexible, functions are diversified, cost is greatly reduced, and it is safer and more hygienic. And requirements of environmental protection, social and economic benefits are more significant.

With continuous improvement of polymer synthesis technology, new polymers with unique physical and mechanical properties can be widely used to meet packaging needs. The function and structure of multi-layer co-extruded composite substrate will have greater flexibility and cost-effectiveness. Through application and improvement of forming equipment and technology, combined with a unique and efficient composite structure design, film manufacturers will revolutionize implementation of concepts such as diversification of packaging functions, streamlining packaging structures, and maximizing benefits and possibilities of packaging. thinking.role.

However, scientific use of raw materials, development of a reasonable product structure, and close cooperation with processing technology are endless challenges for each of our composite film manufacturers. Because only when technical resources of processing equipment, processing raw materials, and design of structure (processing technology) are fully utilized and reach best condition, packaging substrate can be used in final product in most economical, reasonable and most complete way. ., appears in the cheapest form and satisfies market demand.

6. Packaging of various food products

Orange, apple and other natural juices

Cans, bottles and paper containers are sold on market. Among them, natural drinks packed in paper containers have best taste, and waste paper can be recycled after consumption. Juices in aseptic packaging are most popular on market, pH of juice is below 4.5, and sterilization temperature does not exceed 100°C. a few seconds and then quickly cooled to 20°C. The paper container is first sterilized, then sterilized and then aseptically packed. Fruit juice drink packaging material is composed of PE/AL/PE/paper/PES layer, and aluminum foil can insulate oxygen penetration to prevent juice oxidation.

Dairy

There are two types of butter produced in Japan: regular cream and soft cream, and cheese includes fresh cheese and processed cheese, which are classified into hot and cold.

Packaging materials and microbiological control methods for representative butter and cheese are as follows:

Cream packaged in metal cans, sulfuric acid paper and aluminum foil circulate at low temperature to prevent re-microbial contamination.

Soft cream packaged in sterile plastic and distributed at low temperature.

Fresh cheese aseptically packed in aluminum foil and plastic film, aseptically packed in polystyrene containers and circulating at low temperature. Cardboard cheese, packaging material - sulfuric acid paper, plastic packaging material and cardboard, aluminum foil film, heat treatment to prevent re-infection with germs.

Cheese sticks wrapped in PVDC film, heat treated to prevent re-infection with microbes.

PVDC-filled plastic cheese, PET cellophane wrapped, PET/PVDC/PE.COP/PE outer packaging, inflatable packaging can be used to prevent re-microbial contamination.

Meat

Meat products (ham, sausage) require low salt and calorie packaging, aseptic packaging and gas-filled packaging. Microorganisms that grow on raw ham and sausage meat include Streptococcus, Pseudomonas, Pediococcus, Leuconostoc, Lactobacillus and other poor heat tolerance bacteria and high heat resistance bacteria such as Clostridium botulinum.

Packaging, composition of packaging material and characteristics of meat products are as follows:

Aseptic Tank: Mainly used in USA for packaging beef stew, meat pate, stock, etc. that have been sterilized with high temperature steam.

Inflatable packaging: PET/PFOPP/PE packaging materials, cheap gas, packaging of sausages, beef, sausage mixes, etc.

Zclosed inert gas packaging: used for high quality sausages, high quality beef, mixed sausages, etc., packaging materials KM/PE.KOP/CPP, OPP/QS/CPP, with good gas and water vapor. barrier properties.

Surface packing method: used for packing bacon slices (a kind of meat industry name), sausage slices, ham slices, sausages, etc. The packaging materials are composed of IONOMER/E-VAL/EVA, IONOMER/PVDC/EVA, EVAL and PVDC for gas tightness and EVA for thermal adhesion.

Deep pressure vacuum packaging: used to pack ham slices, sausage slices and roast pork. The bottom material of packaging material is Nylon/PE, Nylon/IONOMER and cover material is OPP/PE, PET/PE or ILNOMER-NY/PE or IONOMER.

Serial tight-fitting packaging: packaging of ham slices, sausage slices, sausages, packaging material - soft material PVC / PVDC, pressed film PVC / PVDC / EVA, hard material - PVC film.

Non-standard hermetic packaging: packaging of sliced ​​ham and sliced ​​sausage. Packing material – film pressed from IONOMER/EVAL/E-VA.IONOMER/PVDC/EVA.PVC/PVDC/EVA.

Vacuum shrink packaging: pack a whole or half sausage from whole or half ham, packaging material - EVA / PVDC / EVD, shrink after vacuum packaging.

Inkjet device: packaging of ham, sausages, packaging material PVDC.

Retort packaging bags: packaging of beef cutlets for hamburgers, meatballs, etc. Packaging materials PET/PVDC/CPP, PET/AL/CPP.

Processed meat products are protein products and there are problems with microbial contamination and discoloration of meat. Generally, packaged products are sterilized at 118°C for 35-40 minutes, and products air-packed jet devices are sterilized at 120°C for 10 to 27 minutes, can completely sterilize meat spoilage microorganisms and be stored at room temperature. temperature for 3 months.

In order to preserve hams and sausages for a long time, following packaging bags and antiseptic methods are adopted: to make processed meat products almost frozen before cutting, and to prevent re-contamination of knives. Sealed with 100% nitrogen or carbon dioxide gas, which can lower pH to prevent microbial growth. The packaging material is a multi-layer film made of EVA or polyvinylidene dichloride with good thermal insulation. Gas-filled packaging products sold below 10°C.

Vegetable products

Products based on lettuce (western-style coleslaw) are evolving. The composition of salad includes carrots, cucumbers, onions, potatoes, pasta, vermicelli and so on. Microbial control in processing and packaging of raw materials with an emphasis on lowering pH, most of bacterialHeavy contamination of salads occurs as a result of heat treatment and raw materials in process of cutting with a knife and mixing. To extend shelf life of non-essential plant-based foods, attention should be paid to disinfection and sterilization of raw materials, mechanical devices and containers.

For example, soak cucumbers in a solution of acetic acid with 200-300 ppm available chlorine and pH 4.0, stir for 60 minutes, then rinse with water, run under a water shower for 20-30 seconds, and then skip through hot water. above 90°C with 200-300 ppm available chlorine. Sterile cut of a knife after treatment with 50-100 ppm iodoform.

With development of economy and change of social life, rapid production and large-scale production have become main factors for reducing production costs and surviving in highly competitive market for various products. In food packaging process, except for a few manufacturers who still use bag packaging, most manufacturers have installed large-scale rapid packaging machines in food production line, so rolls of flexible colorful art packaging plastic film are widely used. However, as market consumption emphasizes individuality, specialization and needs of global environmental protection trend, various flexible packaging bags are resurging, and new types of flexible packaging bags are very popular.

In recent years, flourishing of instant noodles has become best explanation and summary of packaging of "high temperature sterilization and normal temperature conditioning bags." Among them, in order to increase variability and variety of instant noodles, traditional flavor foods such as fried pork with shredded bamboo shoots, beef with green onions, lamb angelica, curry chicken and other seasonings are also transformed into delicious packages through advanced food products. processing and packaging technology. Delicious cooking packaging matching with noodles enriches types of instant noodles, activates instant food industry, and adapts to needs of people's rapidly changing life.

Products subjected to high temperature sterilization are prone to discoloration and taste, especially vegetables such as brightly colored green peppers, tomatoes, carrots, etc. After processing at high temperature, in addition to serious loss of vitamins, color will also change. The appearance seems lifeless. To overcome these shortcomings, some food conditioning equipment manufacturers in Japan have started to promote use of modified atmosphere conditioning machines (MAP) for fresh food and meat products conditioning and packaging in domestic and Taiwan markets. Its main working principle is to use soft materials with high barrier gas (nitrogen, carbon dioxide, oxygen) for food packaging, and adjust gas composition in packaging bag to reduce breathing rate of contents and inhibit growth of microorganisms, thereby extending shelf life of food. . Its main material structure is a special polyester film / ONY / R-CPP, using a special polyester film with excellent gas barrier function, to meet need of content gas does not permeate quickly. However, due to high cost of mechanical equipment and limited applications, it is currently not widely used and has yet to be developed.

Add a zipper or add a bottom to opening of a three-sided (three-sided) bag, which has been used for many years to increase capacity of bag and place it on a stand, and can also prevent food in bag from spoiling or weakening. Dropped, but before opening bag can only be tied with an elastic band. The launch of zipper bag is a masterpiece of flexible food packaging manufacturers, material suppliers and equipment manufacturers who use their ingenuity to improve quality of life. It is commonly used for packaging food products that need to be reused many times, such as dried tofu. , beef jerky, dry pork, and other snack foods or pet foods. In afterIn recent years, there has been a breakthrough in consumer market in field of application. For example, tea bags that were originally packed in ordinary cartons are replaced with air chain bags to give them a charming and elegant look. The unique features of this type of packaging.

In past, when consumers bought traditional canned foods such as juices, wines and other beverages or salad dressings, condiments, etc., they typically poured contents into stationary containers and discarded original packaging, making cleaning difficult. industry and bring significant environmental pollution problems. At present, many Taiwanese manufacturers have launched environmentally friendly riser bags that can replace blown bottles. Using characteristics of riser bags can also achieve effect of standing upright and reduce costs. In addition to use of beverages and food, share of packaged goods in this form is increasing on shelves of some shopping centers. Some manufacturers have also invented stand-up bags for organic supplements, that is, a swivel stopper is added to corner of stand-up bag, which allows consumers to verify integrity of product before consumption, and also whether someone has opened it in advance. In addition, in such a package, you can conveniently pour contents into a container bottle, and after use, body of bag can be rolled up into a tube and thrown into a trash can, which takes up very little space. Generally, stand-up bags or environmental supplement stand-up bags are mainly made of thick material to meet special requirements of product and achieve display effect, which can stand upright.

According to forecast of experts of international packaging market, development trend of food packaging is as follows:

1. Aseptic packaging will use high technology and new materials.

2. Non-toxic packaging materials are safer.

3. Large plastic containers and plastic bottles of small and medium size will gradually replace glass products.

4. Composite flexible packaging made of paper, aluminum foil, polyethylene film, etc. will be of higher quality and multifunctional.

5. Apply petrochemical products to produce auxiliary packaging materials for new packaging raw materials.

6. Great potential for development of special baking trays for microwave ovens.

7. The development of fast food packaging will continue.

8. Rationalization of packaging design and overall ease of packaging.

9. Improve performance and functionality of packaging materials, reduce amount of packaging materials and reduce packaging costs.

10. The advertising of packaging for "churning" stuffing will be continued.

Food packaging (2)

Food packagingoccupies a very important place in packaging industry of my country and is one of pillars of packaging industry. Competition in food market this century will largely depend on competition in packaging. According to information provided by World Packaging Organization, turnover of global packaging industry has exceeded 500 billion US dollars, which is 1-2% of global GDP, and its composition is: paper and cardboard 32%, plastic 28%. , metal 24%, glass 6%, packaging equipment 5%, other 5%. This article will discuss current situation and development trends of food packaging in my country in four main areas of food packaging: plastic and composite packaging, metal packaging, glass packaging and paper packaging.

Plastic and composite packaging

Plastic and composite materials are light in weight, beautiful to look at, inexpensive, and an empty bag of flexible packaging takes up little space. Low energy consumption in processing, flexible and diversified production methods make it possible to produce various forms of packaging and containers, such as packaging bags, bottles, cans, hoses, casings, shrink films, stretch films, special functional films, foam containers, sheet thermoformed cups, trays, cans and skin packaging containers, blister packaging containers, etc.

Because plastics have advantages that other packaging plastics do not have, plastics and composites containing plastics are advancing rapidly. From mid-1990s to 2000, average annual growth rate of synthetic resins for packaging worldwide was more than double that of packaging industry. The growth rate of plastic packaging materials has been significantly higher than that of other packaging materials. In US flexible packaging market, plastic accounts for about 3/4 with a CAGR of 6%, doubling GDP growth rate, while paper and metal foil growth is only 1.0%. and 1.5%, respectively, over same period.

Seven Commonly Used Barrier Materials

Over past 10 years, range of plastic packaging materials in my country has continued to increase, and annual production of packaging materials has increased by more than 10%. The plastic packaging market is expected to grow by 7%-9% in 21st century. The plastic used for flexible packaging is mainly polyethylene, which accounts for about 80% of plastic used in flexible packaging market; HDPE accounts for largest share of rigid plastic packaging market, accounting for about 45% of resin used in rigid packaging. , and has maintained an annual growth rate of about 7.3% in recent years. Average growth rate; PET is packaging material with fastest growing demand, which is mainly due to a decrease in price and an increase in demand.PET bottles have entered a new generation of beverages, hot fill bottles (canning at 90°C), juice and drinking water, as well as in spirits and beer markets.

However, plastics also have big drawbacks such as environmental pollution, and their heat resistance and barrier properties are generally inferior to metal and glass containers. High Barrier Polymers Internationally, polymers with an oxygen transmission rate of less than 3.8 cm3 mm/24 bar m2 MPa are referred to as barrier polymers. High barrier plastic materials have characteristics of oxygen barrier, water vapor barrier, oil barrier and transparency, which can effectively maintain original taste and smell of foods in containers and packages, prevent deterioration, and extend shelf life and shelf life of foods. ; at same time, packaging for same amount of food, barrier plastic can also reduce amount of plastic used, and even can be reused, which is beneficial to environmental protection. In international food packaging industry, increasing attention is being paid to use of barrier plastics in packaging. The consumption of barrier plastic packaging in United States increased from 1.04 million tons in 1995 to 1.99 million tons in 2000, an annual increase of 13.6%, while development of barrier plastic packaging materials in my country is still in progress. in its infancy.

At present, industrial barrier plastic packaging materials mainly include EVOH, nitrile resin, PVDC and PEN. Various plastics can further improve their barrier properties through blending, surface coating, surface coating, multi-layer compounding, tensile orientation, and other methods depending on specific conditions. 1.1.EVOH It is an ethylene-vinyl alcohol copolymer, its most remarkable feature is its excellent gas-tight property, which can effectively block penetration of oxygen, carbon dioxide and other gases, at same time, it also has good transparency and gloss. , properties, mechanical strength and thermal stability. It can be made into a film and used as middle layer of a composite film to make a rigid or flexible container that can be used to package sauce, tomato juice, fruit juice, meat, cheese and fruit.

1.2 PVDC (polyvinylidene chloride) PVDC has a high degree of crystallinity, and its main feature is that it has excellent all-round barrier properties, but due to its hard texture, high softening point and thermal instability, it is quite difficult to process and shape .If its VDC (vinylidene dichloride) monomer is copolymerized with other monomers such as vinyl chloride, methyl acrylate, acrylonitrile, etc., copolymer can better solve above problems, so products usually appear as copolymers. Currently, PVDC copolymers are widely used in food packaging. For example, single-layer PVDC film is produced by double stretch stretch blow molding, which has shrink and barrier properties and does not

Decomposition widely used in household preservation. Co-extruded composite films of PVDC and resins such as polystyrene, high-impact polystyrene and polypropylene can be used for vacuum packaging of dairy products, jams, etc. 1,3 PEN (polyethylene naphthalate) ring in PET molecule is replaced by naphthalene, and initial polymer monomer is replaced by 2,6-naphthalenedicarboxylic acid Terephthalic acid, similar in composition to PET. Thus, PEN is leader among polyester materials, which is superior to PET in almost all respects, having excellent barrier properties, UV absorption, heat resistance and chemical stability. We can foresee development of PEN based on development potential of polyester bottles. Regardless of heat resistance, barrier properties, or other aspects, PEN-blended polyester bottle undoubtedly plays a leading role in beverage packaging.

1, 4 Aromatic Nylon MXD6 In my country, among 4 typical barrier materials, development of EVOH, PEN and nitrile resin is still empty. PVDC has started to be applied in household food packaging, but it still does not meet requirements of international standards, competitive demand in domestic food packaging market, barrier plastic materials have broad development prospects in food packaging market in my country.

VIII. Sample Applications

It is generally recommended to use 5-layer and 7-layer co-extrusion equipment, of which 5-layer structure is most widely used, such as ABCBD and ABCBA. For example: The structure of 3-layer co-extrusion layer is PA/Ad/PE (PP), and nylon is on outer layer, which cannot be protected. Nylon has poor impact resistance, is easy to scratch and leak, is hydrophilic, absorbs moisture easily, and has poor oxygen barrier properties. If it is 5-layer structure, PP(PET)/PE, outside PA/Ad/PA/Ad/PP(PE). In this way, nylon is protected on both sides and can prevent nylon from absorbing moisture. After experiments on 7th and 9th layers, with correct arrangement of various resins, shelf life can reach more than one year, almost reaching effect of cans. For example, PET/Ad/PA/EVOH/PA/Ad/PE(PP).

In a multilayer film, functions and roles of each layer are different.

Oxygen barrier layer: Depending on shelf life of package, determine appropriate barrier material (PVDC, EVOH) and layer thickness. The thickness of nylon is usually 20%, EVOH is usually 10-15%, deviation should not exceed 10%, in this range, it has little effect on safety of package.

Adhesive layer (AD): Although nylon and EVOH have good moldability during extrusion, they are not able to bond with other layers (LDPE, PP, EVA) during co-extrusion, and a special bonding resin must be used as a bonding layer, for achieve higher peel strength between layers. Therefore, choice of layer material is a very important factor. The suitable grade should be selected according to structure, and thickness is usually 5-15 g/m2.

Inner and outer layers: Nylon and EVOH have a small oxygen transmission rate but a large water vapor transmission rate, so when determining materials of inner and outer layers, problem of vapor barrier properties should be fully considered, and material of inner layer should also be taken into account. Heat sealing characteristics and heat sealing strength, such as use of LDPE, mLDPE, EVA, PPO, etc., can be modified by Surlyn, PRIMCOR, POP if necessary. When used as a composite substrate, strength of outer surface during corona should reach 38-42 dynes. Nine, multi-layer co-extruded composite film compared with single-layer plastic film

Compared with single-layer plastic substrate, multi-layer co-extrusion composite film greatly simplifies production process of dry composite film, expands functionality and can quantify functions by effectively adjusting thickness, and structure combination is convenient and flexible, a wide range of materials can be selected. Comprehensive performance is full of functions and flexible to change, low cost and high efficiencyquality, high added value and strong adaptability to market. Therefore, multilayer co-extruded composite films are widely used in packaging.

Structure and development trends of multilayer co-extruded composite film

Generally speaking, structure of a multilayer co-extruded composite film depends on functional requirements of film. Provided that process requirements are met through a combination of different polymers, functional requirements for packaging materials such as barrier, heat sealing, body strength, puncture resistance, environmental suitability, recycling characteristics, and extended shelf life and shelf life. . Based on analysis of functional requirements, a combination of five polymers is sufficient. However, seven-layer, nine-layer, ten-layer and even more layered co-extrusion composite films are applied in market, making it a trend and developing rapidly. The structural design of co-extruded composite films gradually requires systematic achievement of ideal state of integration of functions, technology, cost, environmental protection, safety and recycling.

1. Barrier property

(1) Using multiple layers of same resin in barrier layer instead of a single layer of resin can improve stability of barrier layer. For example, if a polyamide material is used as barrier layer, oxygen barrier coefficient is 40 units. In order to ensure stability of its oxygen barrier performance, its thickness is usually specified as theoretical design value of material + negative value of equipment error + safety factor. And when we use multiple layers of same resin instead, negative value of equipment thickness error is greatly reduced and safety factor is greatly improved. (2) When we confirm that thickness of barrier layer is sufficient to meet barrier requirement, introduce multiple layers of same resin into barrier layer instead of a single layer of resin, which can reduce cost of high value-added products. raw material for barrier film. (3) Replacing one polymer with two different polymers in barrier layer can greatly improve barrier properties of film. For example, combining an EVOH layer with a typical PA layer can not only protect puncture resistance of PA, but also improve strength of EVOH and improve crack resistance of EVOH. For five-layer structure, if two different barrier layers are used at same time, one layer can only be on outermost layer, in order to prevent barrier film of outer layer from being easily damaged by external forces and cause barrier effect to decrease, increase in PA is usually used, to compensate for it, thickness method is used, which leads to higher prices.

2. Other

(1) Divide heat seal layer and composite layer into two groups, one of which uses cheaper resins instead of more expensive resins to reduce film cost while maintaining film strength. Another group uses functional polymers that fulfill their functional requirements. Use multi-layer concept to make more economical composite films. For example, when comparing two films weighing 1 kg, material cost of a five-layer film is about 19% higher than that of a seven-layer film.

(2) The performance of co-extruded polyamide films containing less than five layers can be improved by using co-extruded films with more layers. For example, use of an additional adhesive layer can improve film's barrier properties by increasing film's water vapor barrier effect. Another advantage obtained in this way is that film can be made softer, pleasant to touch and has good crack resistance.

(3) The use of coextruded films with a large number of layers can improve stress warping resistance of coextruded polyamide films containing less than five layers. At same time, it meets needs of secondary processing such as bag making.

(4) Integrate other functions of dry composite film other than internal printing, so that composite process is simple, composite structure is flexible, functions are diversified, cost is greatly reduced, and it is safer and more hygienic. And requirements of environmental protection, social and economic benefits are more significant.

With continuous improvement of polymer synthesis technology, new polymers with unique physical and mechanical properties can be widely used to meet packaging needs. The function and structure of multi-layer co-extruded composite substrate will have greater flexibility and cost-effectiveness. Through application and improvement of forming equipment and technology, combined with a unique and efficient composite structure design, film manufacturers will revolutionize implementation of concepts such as diversification of packaging functions, streamlining packaging structures, and maximizing benefits and possibilities of packaging. thinking.role. However, scientific use of raw materials, development of a reasonable product structure, and close cooperation with processing technology are endless challenges for each of our composite film manufacturers. Because only when technical resources of processing equipment, processing raw materials, and design of structure (processing technology) are fully utilized and reach best condition, packaging substrate can be used in final product in most economical, reasonable and most complete way. , cheapesta form that meets needs of market.

10. Film printing technology 1. Plastic film prepress

Plastic films are usually processed by gravure printing, flexographic printing and screen printing, and are usually compounded after printing to achieve a good use effect. The surface properties of various plastics vary greatly depending on their molecular structure, polar groups, degree of crystallization, and chemical stability. These factors have a great influence on adhesive strength of printing inks and adhesive strength of composite films. Therefore, before printing or composite processing, surface must be treated appropriately according to surface properties of various plastics in order to obtain excellent workability. 1. Improve film printability

Theoretically, to ensure good printability on a substrate, surface tension of substrate should be higher than that of printing ink. Polypropylene and polyethylene films are non-polar polymeric materials with stable chemical properties and low surface tension. with ink.

In order to increase surface tension of plastic film, improve its wetting and adhesion characteristics, thereby improving ink fastness, following surface treatment methods are commonly used.

① Corona treatment.

When a high-frequency (intermediate frequency) high-voltage power supply is used, a corona ejection phenomenon is generated in gap between discharge knife holder and blade, and surface treatment of plastic film is performed. This method is called corona treatment, also known as electric shock or electric spark. Its processing function:

a. When discharging, oxygen between two electrodes is ionized to form ozone. Ozone is a strong oxidizing agent that can immediately oxidize surface molecules of plastic film, causing it to change from non-polar to polar, and surface tension increases.

b. After electron impact, pits and dense holes are formed on surface of film, which make plastic surface rough and increase surface activity.

②Chemical treatment method.

Potassium dichromate-sulfuric acid and solutions of other oxidizing agents are used to treat surface of polyolefin film to create polar groups such as hydroxyl and carbonyl, and at same time to obtain a certain degree of roughness.

③ Photochemical processing. Select appropriate wavelength of ultraviolet light to irradiate polymer surface to induce chemical changes such as cracking, crosslinking, and oxidation.

At present, corona treatment is mainly used in manufacturing. Chemical treatment takes a long time and treatment solution is chemically aggressive.veins, so it is used only when other processing methods are inconvenient, photochemical processing is not ideal, time consuming and expensive.

2. Anti-static treatment

Electrostatic film formation is due to excellent dielectric properties of polyethylene and polypropylene, high resistance and poor conductivity. The static electricity generated by friction during film extrusion and winding process will further generate and accumulate static electricity during printing process, and it is not easy to remove, resulting in a large amount of static electricity accumulating on film surface. . Static electricity in film printing will create a number of difficulties in operation and directly affect quality of printed products. Due to electrostatic adhesion, film is in an oxygen-deficient state, which will prevent curing process of inner layer of plastic surface; if it encounters high temperature and high humidity, ink layer adhesion is easier to form, resulting in ink transfer and staining, increased printing and cutting. , Finishing and other processes are complex, and films are bonded to each other and cannot be broken, resulting in recycling of printed products.

Eleven, heat sealable plastic

The heat sealability of plastic is a very important performance requirement for soft plastic packaging materials because any soft plastic packaging product must be made into a pocket; it must be welded to pocket type A2 by thermal fusion. For packaging of various goods, pockets behind packed goods must also be heat sealed. It can be said that heat sealing is main requirement for flexible packaging. Without plastic heat sealing, there will be no flexible packaging.

According to provisions of Japanese Industrial Standard ISZ1526-1976, standard heat sealability of coating by LDPE extrusion at a temperature of 130-140°C, a pressing force of 1 kgf/cm2, and a heat sealing time of 2-3 seconds. The peel strength of heat seal layer is heat seal strength of resin.

The following requirements apply to heat sealability of resin:

(1) Standard heat seal strength

This is strength of a heat sealable resin under optimal sealing conditions. Standard heat seal strength, for same base film substrate such as BOPA6, standard heat seal strength mainly depends on extrusion thickness of extrusion coating heat seal resin and type of resin. For example: main base film is BOPA6 15 µm thick, extruded and compounded with LDPE, heat-sealed at a temperature of 130-140°C, a pressure of 2 kgf/cm2 and a time of 1 s. sealing strength kgf/15mm width and thickness as follows: LDPE thickness µm20, 30, 40, 50, 60, 70 sealing strength, kgf/15mm 1.0, 1.5, 2.5, 3.5, 4.2, 5 .5 sealing strength ingenerally increases in direct proportion to thickness of heat-sealed resin.

For same LDPE, standard heat seal strength depends on MI and resin density, for example: for PT300#/extrusion coated LDPE 20um, 150℃, 2kgF/cm2 and heat seal 0.5s, MI=3, 7g/10m ND=0.923g/cm, heat seal strength 1.25kg F/15mm, heatseal strength MI=3.0D=0.921 is 1.4kg T/15mm, MI=7.0D= 0.917, thermal seal strength 1.75 kgf/15 mm, MI=9.5, D=0.917. The strength of heat seal is 2.0 kgf/15 mm. It can be seen that strength of heat sealing increases significantly with increasing MI. Japanese company Mitsui Petrochemical Co., Ltd. launched new grades of heat sealable resin, specialty VL-LDPE and CS-C polyolefins with improved heat seal levels that can reach 5-6kgF/15mm at 150°C.

(2) Low temperature heat sealability (strength)

The so-called low temperature heat sealing means that resin has a lower heat sealing temperature, and reliable heat sealing can be obtained at a lower heat sealing temperature, which meets requirements of high-speed automatic filling and molding equipment. This resin has a low heat seal start temperature. For LDPE, its ability to heat seal at low temperatures is mainly dependent on MI and density. LDPE with high MI and low density has good low temperature heat sealability. The low heat sealability of resin copolymerized in -5 ethylene phase is closely related to composition and comonomer content. For example: EVA resin, with VA content Density increases, softening point and melting point decrease, heat sealability EVA resin at low temperatures becomes better, and crystallinity of EVA decreases with increasing VA content. When VA content exceeds 25%, EVA becomes an amorphous polymer.

(3) Heat sealability of inclusions

The inclusion of heat sealing characteristics refers to characteristics that still have good heat sealing performance when heat sealing surface of heat sealing resin is contaminated with dust, grease, dirt, powdered substances, etc., heat sealing. Inclusions and heat sealing properties are especially important when filling liquids, rice powder or pesticides. Resins with best heat sealing properties for inclusions are SurlYN (ionic resin), LLDPE, EMAA, EEA and other resins.