THERMAL PROCESSING 

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Module 18. Flexible/Semi-Rigid 

Containers 

Thermal Processing for Meat and Poultry 

Products Training 

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Semi-Rigid Container 

 Not significantly affected by enclosed product 

at atmospheric temperature/pressure 

 Can be deformed by external pressure less 

than 10 psig 

2 
Examples of Semi-Rigid Plastic Containers 

3 

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Semi-Rigid Plastic 

 Co-extruded, multi-layer body 

 Multi-layer laminated lid fusion sealed to 

body flange 

 Metal lid double seamed to a co-extruded, 

multi-layer body 

 Retortable or aseptic filled 

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Plastic Containers with Double 

Seamed Metal Ends 

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Introduction 

 Container sealed with double seam 

 Seam consists of interlocking layers of metal 

and plastic 

 Plastic container made of multiple layers of 

material 

6 
I 

BODY 

HOOK 

t 

METAL END 

.. THICKNESS____.. 

WIDTH 

OVER 

LAP COVER 

HOOK 

l 

+- PLASTIC CONTAINER 

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7 
 

 

 

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Package Terminology 

 Retortable/microwaveable bowl: Semi-rigid 

container made of plastic and adhesive 

blends 

 Height: Distance from base of bowl to body 

flange 

 Width: Diameter of opening 

8 
 

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Package Terminology 

 EZO end: Scored metal end with pull-tab 

 Stacking ring: Curved area below body 

flange 

 Double seam: Interlocking and compression 

of end curl and body flange 

9 
Score Width 

EZO end 

Double Seam 

r-=-=-==========d-- Stacking Ring 

Height 

Bowl 

_. - - - I 

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10 
 

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Critical Defects – Plastic Containers 

with Double Seamed Metal Ends 

Defects or damage to container and double 

seam must be prevented to ensure container 

integrity. 

 Cuts 

 Damaged flanges 

 Short height 

 Swollen package 

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Major and Minor Defects – Plastic 

Containers with Double Seamed 

Metal Ends 

Major 

 Abrasion 

 Foreign matter inclusion 

 Load damage 

 Malformed 

Minor 

 Abrasion 

 Delamination 

 Foreign matter inclusion 

 Gels 

 Malformed 12 
 

 

 

 

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Inspection of Double Seam 

Two important measurements: 

1 - Overlap 

 Interlock of cover hook and body hook 

 Measured optically 

2 - Tightness 

 Body wall compression of plastic 

components in double seam 

 Different methods for evaluation 

 Package supplier will recommend method 

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20% COMPRESSION 

TOO LOOSE 

OPERATING RANGE 

300/o- 50% 

BODY WALL COMPRESSION 

70% COMPRESSION 

TOO TIGHT 

Tightness 

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Frequency of Testing 

 Inspections must be conducted at 

frequencies sufficient to ensure proper closure 

 Recommend every 30 minutes for visual 

inspections 

 Recommend every 4 hours for tear down 

examinations 

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Paperboard Cartons 

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 Pre-formed/fill/seal 

 Form/fill/seal 

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Flexible Container 

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 Shape is significantly affected by enclosed 

product 

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Retortable Plastic Tray 

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Aseptic Cups, Bowls, and Bottles 

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Container Construction 

 Container body comprised of oxygen 

barrier sandwiched between polypropylene 

layers 

 Flexible container lids comprised of 

oxygen layer sandwiched between 

polypropylene and/or other layers of 

polymer materials 

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Packaging Components in Flexible & SemiRigid Packages for Low Acid Foods 

ETHYLENE VINYL 

ALCOHOL (EVOH) 

Good Oxygen Barrier 

POLYVINYLADINE 

CHLORINE 

(PVDC/SARAN) 

Good Oxygen Barrier 

POLYPROPYLENE Structure; Good Heat 

Sealing; Fair Moisture 

Barrier; Retortable 

ALUMINUM FOIL Good Oxygen and Moisture 

Barrier 

 

 

 

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~= §~ Adhesive 

Eval/Saran .· 

Adhesive · 

pp 

High Barrier Retortabre Container 

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Container Structure (Plastic Container 

with Heat Sealed [Peelable]) Lid 

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Semi-Rigid Containers with Fusion Seals 

 Containers are received pre-formed or formed 

by the food processor in conjunction with 

product filling (form fill and seal) 

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Container Forming Methods 

 Thermoforming - Pressing plastic rollstock into 

die molds 

 Blow Molding - Molten plastic air blown into 

mold to shape of container 

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The Imo lo.rm 

.- ll5i G 

-~ · an (.~-b.o4r ~*1.111..) 

1, - ~l)'dit> · ·· ~ldii :at.HiU;gU,on-wt.!:, 

l - :bil<hi"'.! t. . t iii! 1111 paCU ~ -~Ida . $o:f:tadl ~ wli i:<IH' ~~ -. , 

- f',r;-m!.'1111 (N.:~-" pl.liC, ~ .a/111:' ~•to If .. 14 e.,i;,r-11,,.) 

.. 

.. 

- '6 - !r'lUlJ'I& 

1 - 1W .-;'tede. r-<il 

111-1~- ~'IQ:· 

9 - l'b.t hie:· ~·· :IQI • l.l U - 0..U. hl.i/k ~ L 

Thermoform / Fill / Seal 

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Co-Extruding Plastic Sheets 

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Thermoforming Oven 

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I ~lus-assist ~ ......... -

· ~ Clarnp 

oo 

Mold 

cavity · form 

cavity 

j, 

Pressure 

t 

0 . C· • ·. 0 - . . .• 

Cooling 

Plug Assist Thermoforming 

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Receiving Examinations 

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It is important that 

the food processor 

measures thickness 

of side walls, 

corners, and flange 

upon receipt. 
 

 

 

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Sealing Principles 

 Avoid seal area contamination 

 Avoid wrinkles in seal area 

 Maintain adequate sealing bar temperature, 

pressure and dwell time 

 Assure that sealing materials are compatible 

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Sealing Methods 

 Induction 

 Impulse 

 Hot bar 

 Ultrasonic 

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Heated 

Rounded 

edge -.. 

,' 

· Resi I ient ~~~00-

00-00 -

00 .JV', 00 ,IV\~.JV\oiAJI 

surface 

Rounded 

edge· 

Bar Sealing 

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l.Jd ClCIIIPODl!!Dt:r-----'ill 

Aha1Ban fell 

PD.1~i- l..i.d 

:fUll./P0,l~1- J:x-,,j 

meak:sdY.ring~:lng 

 

 

 

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Adhesive Failure of the Seals 

 Sealant layer (PP) of lid breaks away from foil 

component and remains fused to container 

flange 

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Detachment of the Seal 

 After peeling lid from 

container body, the 

presence of PP 

residues on flange 

indicates a well 

fused seal 

 Good seal 

 Poor seal 

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Cohesive Failure of the Lid Stock 

 Sealant layer (PP) of lid breaks within itself 

and splits 

 Half of sealant layer remains adhered to lid 

 The other half remains adhered to flange 

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Defect Definitions and 

Classification 

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Critical Defects - Semi-Rigid 

Containers with Heat Sealed Lid 

 Channel leaker 

 Cut 

 Fracture 

 Incomplete seal 

 Swollen package 

 Puncture 

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.NNEL LEAKER 

50 

A pathY,tay of nr;r1-b::md1r1g 

across he vi. th of 

the seal creatin. a le· ker. 

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INCOMPLETE SEAL 

A port[ on of the seal hat has a lack of ad hes ion 

between lid and body. 

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Major Defects – Semi-Rigid 

Containers with Heat Sealed Lids 

 Contaminated seal 

 Abrasion 

 Crushed 

 Seal width variation 

 Uneven seal impression 

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CONTAMINATED SEAL 

Foreign matter in the seal area, such as, but not 

limi 1 ed ·to,, water, g rease1 or ood. 

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ABRASION 

A scratch partially through the surface layer(s) of the package 

caused by mechanically rubbing or scuffing. 

48 

CD If pronounced and may affect 

hermeticity. 

If sl ight and does not affect 

hermetic1ty. 

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Minor Defects - Semi-Rigid 

Containers with Heat Sealed Lids 

 Abrasion 

 Burnt seal 

 Crushed 

 Delamination 

 Flex cracks 

 Foreign matter 

inclusion 

 Gels 

 Label foldover 

 Malformed 

 Wrinkle 

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M.ALFORME .· 

Pla~rc v,hicl does nol cor~f Drm to contours as spec·fied. 

76 

P3 el bod¥ def er.:I after.tin !J ~ iP P.aramc:e1 bu~ not 

1n~egri ti-;. 

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Critical Defects – Flexible 

Containers with Heat Sealed Lids 

 Channel leaker 

 Cut 

 Fracture 

 Incomplete seal 

 Swollen package 

 Puncture 

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Channel leaker 

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Channel leaker 

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Critical Defect - Contaminated Seal 

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!~ 

' 

I 

TRAINING 

THERMAL PROCESSING 

Examples of Cuts 

Critical—Cuts Major—

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Critical Defect – Incomplete Seal 

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l'fonabc:nded Seal 

,Accept b,Je 'Seail 

Critical Defect - Unbonded Seal 

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Critical -

Wrinkle

Critical Defect - Wrinkle 

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Critical Defect - Swollen 

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Critical Defect - Puncture 

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Major Defect - Abrasion 

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Short Seal Width 

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Major Defect - Blister 

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Minor Defect – Double Seal 

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Minor -

Delaminatio

n

Minor Defect - Delamination 

60 

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Minor Defect - Cosmetic 

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Destructive Test Requirements for 

Fusion Sealed Containers 

 Appropriate and  Test records must be 

detailed inspections maintained. 

and tests must be  Select test 

conducted at containers from 

intervals of sufficient each seaming head frequency by or lane. 

qualified personnel. 

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Destructive Tests 

 Burst test 

 Peel test 

 Dye test 

 Electro-conductivity test 

 Residual gas 

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Preparing Semi-Rigid Trays for Burst Testing 

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Burst Test Under Water 

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Peel Test 

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 The continual and 

even presence of a 

frosty like residue 

(pp residue from lid) 

on the flange 

indicates a well 

fused seal 

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Dye Test 

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Dye test the seal area by adding drops of dye 

to the inside seal area through a hole cut in 

the bottom of the cup 

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Electrolytic Testing 

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2 

3 

1. Power source 

2. - Ammeter 

3. Electrode 

4. NaCl solution 

5. Packagecut In half 

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,-ETORT STAN~ 

RUBBER CONNECTOR 

FUNNEL. 

WATER . 

--· 

PUNCi~f' TO 

TO l.fT AIR 

ESCAPE 

A 

Residual Gas Test 

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Non-destructive Examination 

 Visual test 

 Squeeze test 

 Pressure differential test 

 Vacuum (bubble) test 

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-

·.~ ... ;.:,/ · . . , . . 

< 

I 

..... _ , .i . 

-figure ·.9-.lid deflect.ion wilt· occur in a prol)erly seaied 

piastic ·cup with a heat. sealed lid when the container is 

. subject~ to pressure by squeezing Jhe sjdewall_s .. 

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Squeeze Test 

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DIFFERENTIAL 

PRESSURE SENSOR 

PACKAGE FOOD 

. . . 

. 

'RECORDER 

. 

• • 

INERT GAS 

SUPPLY 

Pressure Differential Test 

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Pressure Differential Test 

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73 
GAUGE 

0~ 

, .. - o ·. WATER r ".:: - O 

r "=- , - 0 

, -

,,,.. ... 0 ,,,,,-----

~ - -------~o 0 -,,,,,._...__ 

' 

PACKAGE 

TO VACUUM 

 

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Vacuum Bubble Test 

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Frequency of Testing 

 Visual Examinations: 

• Seals must be examined from each sealing 

machine 

• Necessary corrective actions must be taken 

and recorded 

• The entire container must be examined 

• Must be performed before and after the 

thermal process operations 

• Must be done at sufficient frequency 

• Should be based on a statistical sampling 

plan 

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Frequency of Testing 

 Physical Tests: 

• Must be conducted with sufficient frequency 

• Must be performed after the thermal 

process and should be made at least every 

2 hours of continuous production 

• Guidelines for test procedures must be on 

file and made available to the CSI 

• Results and corrective actions must be 

recorded. 

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77

Questions 

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Questions?