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1

Ji Zhong (季忠） Ph.D., Professor

Packaging Research Institute

Phone: 0531-88392817

Email: jizhong@sdu.edu.cn

Http://www.dplab.sdu.edu.cn

Office: RM908, Main Building (Qianfoshan Campus);

RM510, Xipeilou

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Plastic in Packaging

Lesson 4 c

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Plastic and polymer are often used interchangeably

Smallest repetitive unit in a polymer

Monomer units are joined together to make a a larger polymer molecule

But plastic tends to be used to describe finished partspolymer tends to describe raw materials

Polymers can be grouped into two classes:Thermoplastic and thermoset or commodity and engineering polymers

日用品

Plastics: 1. plastic +s 信用卡,塑料件2. plastics 塑料 整形外科

Derived from petrochemicals

Polymer and Plastic

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1. What elements are in the molecule? (C, H, Cl chlorine)a water molecule has only three atoms

a typical molecule contains hundreds or thousands of atoms

2. What size (molecular weight) is the molecule?• Today there are hundred of identified(识别，认明）species

|| ‘spɪːʃɪːz 种类of synthetic 合成的 polymer.• Any polymer is available in a range of molecular masses, most can

be modified by the addition of other monomers.• In reality, the choice in plastics is almost limitless.• Properties such as melting point, stiffness will change as

molecular weight changes

Polymer Properties Depend On:

[ˈklɔrin]

2

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3. Is the molecule polar or non-polar?It’s depending on the participating参与 含有 atoms [,sɔlju'biliti]

Often influence melting point , COF, solubility 溶性, barrier properties

4. What shape is the molecule?

It will determine how large numbers of them will fit together

Many physical properties are affected by the molecule’s shape

5. What is its thermal history?

Final property depends on it. Changing it changes the plastic’s

performance characteristics

Polymer Properties Depend On:

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6. What is its mechanical history?

A plastic’s final properties also depend on its mechanical history, how it flowed in the molten state and how it was stressed when

cold.

Polymer Properties Depend On:

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Deformation and Thermal History

Room temperature deformation is ‘permanent.

Plastics stretched at about Tg and cooled slowly are heat stable.

Become soft and pliable易曲折的 but do not melt flow

Plastics stretched at about Tg and cooled quicklyhave “memory” and will shrink if reheated.

Of its original dimensions

In general,

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1. Extrusion （profile extrusion, extrusion cast

film, blow film extrusion, co-extrusion)

2. Injection molding

3. Extrusion blow molding 挤出吹塑

4. Injection blow molding (including injection

stretch blow molding) 注射吹塑

5. Other methodsIn all thermoplastic shaping methods, the plastic must first be

heated to a point where the material has a plasticity, or fluidity.

Common thermoplastic forming methods

[flu:'iditi]

3

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Plasticating（塑炼 ）Extruder

Exitport

Gear reducer

Variable speed motor

Feed throatFeed hopper

Hopper throatCooling jacket

Screw

Heater bands

Fig. 7.2

Granules or pellets丸

进料斗

冷却套管

Barrel

The first task is to heat and melt the polymer resin pellets into a flowable form 'rezɪn]

10/43Fig.7.3Extruder Tube die Mandrel 心轴

Tube

Profile Extrusion

A shape of constant cross-section can be extruded

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Adjustable Die Lips

Extrusion Die

Adjustable Pressure (Restrictor) Bar

Extruder

Cast Film 流延薄膜and Sheet Extrusion

限流器

Sheet extrusion is an application of profile extrusion but using a die with a slot orifice

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Extrusion Cast Film Line Layout

Extruder

Extrusion die Chill roll

Edge trimmer

Material roll

Fig.7.4

The film is immediately cooled and solidified on chill rolls

Fig.4 General layout of a cast-film extrusion line

4

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Cast Film 流延薄膜and Sheet Extrusion

• Sheet extrusion is an application of profile extrusion but using a die with a slot orifice

• The dies have a narrow opening between the die lips through which the plastic melt is extruded in a thin film

• The film is immediately cooled and solidified on chill rolls• The dies can be several metres long • Depending on thickness, the end product may be called film or

sheet. There’s no clear division between the two• Film product formed by this process is referred to as cast film

Extruder

Extrusion die Chill roll

Edge trimmer

Material roll

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ExtruderCircular die

Air ringInternal bubble cooling

Plastic film bubble

Collapsing frame

Upper nip rolls

SlitterDual rollwinder

Blown Film 吹塑薄膜Line With Slitter

Fig.7.5

Plastic film can also be manufactured by extruding the polymer through a

circular die into a closed circular bubble and expanding the bubble with air

展平辊

复卷机

收缩

纵切机

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Bubble

Blow-up air inlet

Cooling air Cooling air

Plastic from extruder

Die lip adjusting bolts

Die BodyDie core

Frost line

Bubble constantly pulled up

Blown-film Die Cross-Section

The die is often rotated

霜线

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Blown Film Line with Die & Bubble

5

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Machine Direction Orientation

Rotation x 1 x 3x 2 X 4

From extruder casting rolls

Fig.7.8

The properties of cast and blown film can be improved by orienting the polymer molecules

Cast sheet is oriented in the machine direction by being pulled away faster than it is extruded. This is usually accomplished by passing the cast film through a series of rolls

Each roll rotating progressively faster than the previous one

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Extruder

Casting Rolls

Annealing Zone

Extrusion Die

Tenter Clips

Cross Direction Orientation

Fig.7.6

Cross or transverse direction orientationis done in a tenter frame 拉幅机, which stretches the film in the transverse direction

张 夹

流延

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Three-layer Extrusion Blow Mold

Cut-away view

material 1

material 2

material 3

film bubble

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Extruder #1

Extruder #2

Extruder #3

Material #1Material #2

Material #3

Three-Layer Co-extrusion

Fig.7.7

Both cast- and blown-film extrusion dies can be Designed to be fed from more than one extruder,thus producing a sheet composed of 2 or morematerials

A co-extrusion, slot-orifice cast film die

6

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Injection Molding注塑

Fig.7.8

往复的

Uses a powerful extruder with the capability to inject a precise amount of resininto a fully enclosed mold.

移动螺杆式Ram-screw type

ˋrɛzn22/43

Injection Molding Machine

Extruderbarrel

Feed hopper

Mold location

Extruders are sized by their clamping capacity

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Three-Plate Injection Mold

Fig

主流道

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Parts With Attached Runners

9

The distance between the sprue and the gate must beexactly the same for every cavity

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Plastic Shrinkage and Sink Marks

Fig.7.16

Most commonly can be seen opposite closure threads

Sink marks over cup flange can cause sealing problems

Intended design

Shrinkage = fx

Shrinkage = 4fx

Actual part produced

Sink mark

3x 4x

X

缩痕

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Molding Undercuts倒扣 底切

Fig.7.15

Pedestal plug

Main body ring

Pedestal ringhalves

Body plug

Gate

支座

基架, 基础, 座

座圈，封圈|| 'pedɪstl]

•座圈

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Injection Molding Undercuts

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Bottle-Making Terminology

Finish: That part of a bottle or jar that acceptsthe closure

Parison: An initial shape that will be expanded into abottle or jar in a second step

Preform: Describes the parison when using injection blow-molding

Moyle: The pinch-off trim piece from an extrusion blow-molded bottle 十字镐 鹤嘴

掐掉

8

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Neck ring insert

Pinch-off insert

Flash pocket

Mold cavity

Mold guide pins

Coolingchannels

Extrusion Blow Mold挤出吹塑

Fig. 7.20

切断

飞边 毛剌

镶块

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Extrusion Blow Mold

R

1. Neck-ring insert

2. Cooling water ports

3. Cut-off insert

1

2

3

1

3

2

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Extrusion Blow Molding (EBM)挤出吹塑

Fig.7.18 32/43

Untrimmed EBM PP Bottle

R

3. Tail or pinch-off trim

1. Finish trim

2. Handle knock-out移出，敲出

1

2

3

9

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Parison Expansion & Wall Thickness

Initial parison expansion is equal in all directions wall thickness

Expanding parison freezes the moment it touches the chilled mold wall

Parison continues stretching after the parison center freezes

Parison continues stretching after the parison center freezes

As a result, corner wall thickness is significantly reduced

Figure 7.24 34/43

Uniform-Walled Parison Programed Parison

Fig. 7.22

Parisons and Bottle Wall Thickness

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Variable openingcontrols parison-wall

thickness

Programmable Parisons

Fig. 7.23 36/43

Examples of Coextruded Bottles

1 & 2 Reduced pigment(颜料） on inner layer

3 Three layer bottle with U.V. barrier central layer

1 2 3

R

10

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Injection-Blow Molding (IBM)

Fig.7.23

Injection mold

Blow mold open closed

Preform expanded to blow mold

Preform carriedover on core pin

Air

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Injection-Blow Molding Machine

Fig.7.27

Blow position

Stripposition

Preforms

Injection mold

Blow mold

Stripper plate

ExtruderInjectionposition

rotating

tableCore rod

剥离

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Injection-Blow Molding Machine

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IBM Preforms and Container

R

11

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Injection-Stretch Blow Molding (ISBM)

Fig.7.28

Preform and core pinclamped in blow mold

Core pin moves down,stretching preform

Preform blown tocontainer shape

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ISBM Preforms and Soda Bottles

R

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Properties Imposed施加 by Molding

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EBM and IBM Compared

tooling one mold set two mold setsmold cavities commonly 2 or 3 12 and more possiblesecondary operations trim and regrind no trim or regrindfinish tolerances acceptable precisionunique finish designs limited possiblehandleware common complexthin-wall containers yes nocomplex multi-layers yes difficultlarge containers yes (e.g. drums) limitedbase design requires pinch-off no pinch-off

Feature Extrusion B.M. Injection B.M.

Table7.2