avpm guide 1 blister card se… · blister card sealing guidlines interface temperature and...

1 | A S S O C I A T I O N O F V I S U A L P A C K A G I N G M A N U F A C T U R E R S

B L I S T E R C A R d S E A L I N G G U I d L I N E S

Blister CardBlister Card

SEALINGSEALINGGUIDELINE

SGUIDELINE

S

avpm-online.com ©AVPM 2018 4th Edition 2/18



A. Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

B. Objective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

C. Seal Master Machine SM-500 - . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 “If you don’t measure it, you can’t control it.”

D. Common Industry Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

E. Parameters for Heat Sealing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

F. Determining Interface Temperature and Pressure . . . . . . . . . . . . . . . . . . . . . . . . . 10

G. Standard Procedure for Determining the Integrity of the Blister Seal on a Visual Carded Package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11

1. Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11

2. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11

3. Referenced Documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

4. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

5. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

6. Significance & Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

7. Apparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

8. Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

9. Sample Conditioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

10. Procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

11. Failure Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

12. Report. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

13. Recommendation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

14. Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Index



A. Backgound

The Association of Visual Packaging Manufacturers

(AVPM) is a non-profit organization founded in 2003.

Its membership is comprised of manufacturers of skin

and blister cards, thermoformed blisters, blister film,

paperboard, coating, and equipment. The AVPM is

organized exclusively as a business league for the

advancement of the domestic carded packaging industry.

The AVPM membership organized a Blister Sealing

Standards Committee to review, evaluate and recommend

the best practices, guidelines and test procedures for

producing and evaluating quality blister packaging.



This publication, Blister Card Sealing Guidelines, is

intended to document the mutually agreed upon best

practices for producing and evaluating heat seal blister

packaging for the benefit of AVPM members and their

customers. The following guidelines are not exhaustive

and not intended to cover every blister seal application.

However, these guidelines are designed to cover

a majority of the domestic applications and uses.

B. Objective



The validation of the quality of a product or process is paramount in the

manufacturing arena. This is especially true in the production of a blister

card.

There are four components of a blister card: 1) board, 2) ink, 3) coating,

and 4) blister. The quality characteristics of each of these materials must

be measured and controlled in order to ensure the product performs

as required. There are tools and instruments that measure the quality

characteristics of each of these components and validate their suitability

for use. Keep in mind: If you do not measure it you cannot control it.

And yet, even with the current technology and monitoring sophistication,

when it comes to checking the quality of sealed blister cards, an old and

outdated method is still used - cut an “X” on the back of the card and

tear each quadrant. Each person that tears a card using this method tears

at a different rate, and at a different angle of tear. No quantifiable data is

generated, thus there is no repeatability. When a sealing problem occurs

in the field there is no hard proof of a successful seal during the quality

checking procedure at the manufacturing facility.

In order to overcome this antiquated validating system, the Seal Master 500

Machine was developed and available for purchase. The SM-500 Machine

measures the actual force it takes to tear a blister from a card and produces

quantifiable data. Also, by producing charts, the SM-500 Machine gives you

a graphic profile of the actual tear. The SM-500 Machine controls the rate of

tear, the angle of tear, and is consistent from card to card. The human factor

is taken out of the equation and repeatability replaces inconsistency.

The SM-500 Machine is a valuable tool to use in the everyday quality control

procedures in the manufacturing of a blister card. By producing a graphic

profile of a particular card along with quantifiable data you now have

predictability as to the performance of that card in the future. The SM-500

Machine is also a valuable tool to be used in the resolution of sealing

C. Seal Master Machine SM-500



problems in the field. The quantifiable data can be used in a statistical

format producing quality curves and a statistical history of that particular

card.

In a nutshell, The Seal Master SM-500 will:

• Consistently measure and record seal strength to improve your overall

process

• Improve overall productivity and profitability with standardized and quanti-

tative methods that provide a historical record

• Minimize customer complaints, downtime and re-work

Bottom line, would you rather “Pull it and guess” or “Measure it and know”?

For more information regarding the

Seal Master SM-500, please contact:

Cheminstruments, Inc.

510 Comercial Drive

Fairfield, OH 45014

Phone: 513.869.1598

[email protected]



Adhesive Failure

A failure between bonded layers of materials; specifically paper-board

pigment coating to ink interface, ink to blister coating interface, blister coating to blister interface.

Aqueous Coating

A blister card industry term used to describe a water-soluble, heat seal blister adhesive.

Blister

A thermoformed part made of PVC or other polymer that has been formed through the application of heat, pressure and/or vacuum to create a product cavity.

Blister Card

A pigment coated (typically clay) paperboard card, usually printed, heat seal coated and die cut, designed to seal to a blister for the purpose of display-ing a product.

Blister Flange

The engineered flat sealing area of a thermoformed blister.

Blister Package

A finished package formed by heat sealing a thermoformed blister to a pigment coated paperboard card.

Cold Forming (also known as Stress or Soft Forming)

Caused by forming a blister outside its optimum temperature range.

Durometer Gauge

An instrument used to measure the hardness of rubber compounds.

Dwell (Seal) Time

The amount of time that heat and pressure are applied to the blister card and blister flange area to achieve proper seal.

Face Pressure

The pressure applied to the card and blister flange by the heat seal platen during the heat sealing process.

D. Common Industry Definitions



Fiber Tear

The result of a successfully sealed blister to a paperboard card that can visually be confirmed by the attachment of paper fiber to the blister flange upon separation.

Grain Direction

The orientation of paperboard fibers in a blister card relative to the machine direction of the paperboard manufacturing process.

Heat Tape

A thermally sensitive tape designed to indicate a maximum achieved

temperature at the blister flange/blister card interface within a specific range for a single event.

Interface Temperature

The temperature achieved between the blister flange and the blister card during sealing.

Mayer Rod

A device used to apply a specific thickness of coating to a substrate.

Seal Strength

The degree of bond between the blister card and the blister flange created by the heat sealing process.

Slip Agent

A silicone coating or internal additive applied to the blister film to prevent the blisters from adhering to each other while nested.

Solvent Coating

A blister card industry term used to describe a solvent soluble, heat seal

blister adhesive.

Tear Direction

Fiber tear inline with the board grain (machine direction, MD) or across the board grain (cross direction, CD).



Blisters

a) Gauge - 0.0075” min to 0.0300” max thickness before thermoforming1

b) Flange Width 0.312” recommended minimum flange width

c) Chemical Composition PVC2

d) Sheet or Formed Blister Formed blister1

Coating

a) Application Thickness 0.50 lb/MSF min to 0.75 lb/ MSF max (aqueous); 0.85 lb/MSF min to 1.20 lb/ MSF max (solvent)

b) Coating Type Solvent or aqueous

c) Application Method In-line press coating or off-line coating; Mayer rod for lab testing aqueous coating; Mayer rod for lab testing solvent coating

Board Board formulated for blister application

Ink Ink formulated for blister application

Drying Hot air for aqueous and solvent coatings

Forming Seals

a) Apparatus Commercially available heat seal machine in good operating condition with the rubber on the seal tray surface having a hardness ranging from 50 to 90 durometer

b) Pressure Minimum face pressure of 80 psi on seal area

c) Interface Temperature 200˚F to 220˚F for aqueous coating; 200˚F to 220˚F for aqueous coating

d) Seal Time (Dwell) Optimized to achieve proper interface temperature

E. Parameters for Heat Sealing

1 Flange should be no less than 40% of original thickness after thermoforming. Blisters should be well formed with a tight cavity radius

2 Other Materials such as PET, PETG, and Polystyrene could require different coatings and may have different performance results.

1 0 | A S S O C I A T I O N O F V I S U A L P A C K A G I N G M A N U F A C T U R E R S


Interface temperature and pressure are considered critical metrics in the

heat sealing process. The ultimate objective is to ensure intimate contact

between the components for the purpose of transferring sufficient energy

to effect a good heat seal by activation of the blister card adhesive.

Achieving a proper seal is dependent on multiple factors such as coating

type, blister card thickness, blister flange thickness, heat seal surface

material composition, face pressure, and seal (dwell) time. Heat and

pressure sensing materials are available.

To measure interface temperature: 1) place thermal sensitive heat tape

between the blister flange and blister card and 2) apply heat and pressure.

The heat tape will indicate the maximum temperature reached.

To measure interface pressure: 1) place pressure sensing materials

between the blister flange and the blister card without heat and

2) apply pressure. The pressure sensing material will indicate the

maximum pressure achieved. This is shown by color; follow the

manufacturer’s supplied documentation.

In the absence of pressure sensing materials, the face pressure can be

calculated by dividing the pressure at the sealing face by the area of the

sealing face.

F. Determining Interface Temperature and Pressure



1. Purpose

1.1. The purpose of this procedure is to establish a method to determine

the integrity of a sealed, thermoformed blister to a blister card by both

a Manual Method and a Machine Method. This will provide a real world

test that can be accepted and used by material suppliers, machine

suppliers, package assemblers, and their quality departments to agree

on acceptance or rejection of a blister package.

2. Scope

2.1. This test method measures the strength of the seal at the pigment

coated paperboard and blister flange juncture.

2.2. This test method covers low-density, solid bleached sulfate board and

recycled board.

2.3. This test method includes Rigid PVC, PETG, Polystyrene, and PET films.

2.4. The Manual Method visually establishes the integrity of a seal by

evaluating the degree of fiber tear achieved.

2.5. The Machine Methods measure the maximum force required to tear a

coated blister card from a thermoformed blister.

2.6. This test method identifies the various modes of system failure.

2.7. This guideline does not cover materials such as foil, plastic, or other

types of impervious stock.

2.8. This standard does not purport to address the cause of the failure.

G. Standard Procedure for Determining the Integrity of the Blister Seal on a Visual Carded Package



3. Referenced Documents

3.1. TAPPI Standard: T 402

Standard Conditioning and Testing Atmospheres for Paper, Board, Pulp

Handsheets, and Related Products.

3.2. ASTM Standard: E 691

Practice for Conducting an Interlaboratory Study to Determine the

Precision of a Test Method.

4. Terminology

4.1. Definition of terms specific to this standard

4.1.1. Blister Package - a finished package formed by heat sealing

a thermoformed blister to a pigment coated paperboard card.

4.1.2. Fiber Tear - the result of a successfully sealed blister to a pa-

perboard card that can visually be confirmed by the attachment

of paper fiber to the blister flange upon separation.

4.1.3. Maximum Seal Strength - the maximum force required to

separate the bond between the blister card and the blister

flange created by the heat sealing process.

4.1.4. Tear Direction - fiber tear inline with the board grain (machine

direction, MD) or across the board grain (cross direction, CD).



5. Discussion

5.1. In both the manual and machine methods, the criteria for a successful

fiber tear is for fiber separation to be present in 85% of the flange seal

area.

5.2. All test samples should be cooled to ambient conditions before manual

or machine tear tests are performed.

5.3. The manual test method provides a qualitative (accept/reject) visual

inspection method. Constraints associated with this method are the

rate of tear, the tear direction, and the repeatability.

5.4. The machine test method provides a quantitative (numerical)

inspection method. In this method, the maximum tear force is

calculated by the testing machine from the digitized plot of force

versus grip travel distance.

6. Significance & Use

6.1. Maximum seal strength is a quantitative measure for use in process

validation, process control, and capability. Seal strength is not only

relevant to opening force and package integrity, but to measuring the

packaging process’ ability to produce consistent seals. Seal strength

at some minimum level is a necessary package requirement. At times

it is desirable to limit the strength of the seal to facilitate opening.

6.2. The test sample will fail at the weakest point. This point may not

necessarily be the seal. Other modes of failure constitute constraints

that can prevent the method from indicating the true strength of the

seal. This methodology is not intended to include the myriad of causes

for the failure modes.



6.3. The intent of this test is to determine the seal strength by measuring

the force required to initiate a separation at the board pigment coating/

substrate interface. Essentially, this is the goal of package design.

This is accomplished by pulling on the ends of a strip of material

containing the seal. However, the pulling process may or may not result

in the desired mode of strip failure. Extension of the sample ends can

cause one or more failure modes within the sample.

6.4. When a seal fails at the pigment coated/substrate interface (fiber tear),

the value of the bond strength measured is recorded. A failure at this

interface is considered to be a successful seal. (See “Fiber Tear” section 4.1.2, Terminology)

6.5. Other failure modes do exist and represent a limiting factor in the

strength of the package. These failure modes should also be recorded.

The value obtained for seal strength can be affected by properties of

the sample other than seal strength. (These failure modes are discussed in section 11, Failure Modes)

7. Apparatus

7.1. Testing Machine

7.1.1. A tensile testing machine of the constant rate-of-grip-separation

type is to be used. The grips must move a sufficient distance

to strip the blister flange area. The rate of separation of the

grips shall be uniform and capable of adjustment from approxi-

mately 50 to 300 mm/min (2 to 12 in/min). The gripping system

shall be capable of minimizing sample slippage and applying an

even stress distribution to the sample.

7.1.2. The calculation of maximum seal strength is required. The

testing machine system shall have the capability to calculate its

value over a specified range of grip travel, programmable by the

operator. Preferably, the machine shall have the capability also

to plot the curve of force versus grip travel distance.



8. Sampling

8.1. The number of test specimens shall be randomly chosen to permit

adequate determination of representative performance. Sealed test

samples should be examined for any defects. Noted defects can provide

an insight into malfunctions in the sealing process. Defective samples

should be excluded from testing.

9. Sample Conditioning

9.1. Before samples are tested they should be conditioned to 50 +/-2% R.H.

at 23.0 +/-1˚C (73.4 +/-1.8˚F), reference TAPPI T 402.

10. Procedure

10.1. Manual Method

10.1.1. This test should be performed on 3 to 5 samples.

10.1.2. To prepare a sample for testing, the blister package should

be cut with a utility knife in a cross cut pattern. These cuts

are to be made through the back of the card into the blister

cavity. They should extend across the blister flange to the

outer edges of the card. (See Figure #1)

10.1.3. At the intersection of the cut lines, the corner of each

quadrant should be folded back slightly to afford an area

to grip that particular quadrant. (See Figure #2)

FIGURE 1

FIGURE 2

FIGURE 3



10.1.4. Each quadrant of the cut card is then torn from the blister

by hand in a direction toward the corner at an approximate

angle of 45˚. (See Figure #3)

10.1.5. Each quadrant should be torn at a moderate rate to ensure

consistency in the test. Care should be taken since fluctuations

in tear rate can result in deviation of fiber tear results.

10.1.6. The entire perimeter of the flange/paperboard interface

should be visually examined to determine the extent of

acceptable fiber tear (AFT). The percentage of acceptable fiber

tear should be caculated around the total flange. For example,

if the total flange circumference (TFC) is 12 inches and the

acceptable fiber tear circumference (AFTC) is 8 inches, then

the percentage of acceptable fiber tear (%FT) equals 67%

(%FT = AFTC/TFC).

10.2. Machine Method – Sample Preparation

This method is suggested for field testing of production runs.

10.2.1. This test should be performed on 3 to 5 samples.

10.2.2. This test method can be used in the field (a production

environment) or in a laboratory environment.

10.2.3. This test method can be used on packaging of various card

and blister sizes.

10.2.4. The one constraint in this test method is that the blister profile

(height) must be tall enough to cut the top off the blister and

still leave an upright blister tab of at least a minimum of

0.5 inch (one half inch) long. This 0.5 inch long blister tab

is required by the upper grip to pull at a 90-degree angle.

FIGURE 1

FIGURE 2

FIGURE 3



10.2.5 To prepare the sample for testing, make a cut in the blister

profile approximately 0.5 inch long. The initial cut can be

made with a razor blade. (See Photo #1) Then insert a scissor

into the cut and proceed to cut around the entire blister cavity.

(See Photo #2)

10.2.6. Cut a 1 inch cross section from sample card. This cut should

extend to the outer perimeter of the card. (See Photo #3)

10.2.7 This method provides a system for checking the tear

direction with the board grain (machine direction MD) or

across the board grain (cross direction CD)

10.3 The Test Procedure

10.3.1 Calibrate the machine according to the manufacturer’s

specifications.

10.3.2 Place the sample horizontally in the lower fixture of the

machine with the blister tab perpendicular to this fixture and

held in position by the upper grip. The card is held to the

lower fixture by a clamp. Allow sufficient slack so that the seal

is not stressed prior to initiation of the test. (See Photo #4)

10.3.4 The seal shall be tested at a grip separation rate of 10mm/mm.

(4in/mib) With this test method, the one inch test strip can be

cut in both the x and Y orientation.

10.3.5 For each tab, record the maximum force encountered as the

seal is stressed to failure and identify the mode of failure.

Photo 1

Photo 2

Photo 3

Photo 4



11. Failure Modes

FT (Fiber Tear) Fiber tear at the board pigment coating/

substrate interface.

PCS Cohesive failure of the board pigment coating

(Pigment Coating Split) (typically clay).

ACIS Fracture or bond failure between the blister

(Adhesive Coating/Ink Split) adhesive coating and the printed ink film.

BAF (Blister/ Fracture or bond failure between the thermo

Adhesive Coating Split) formed blister and the heat reactive, blister

adhesive coating.

BLIS

TER

ADH

ESIV

E C

OAT

ING

FAILURE

BLIS

TER

ADH

ESIV

E C

OAT

ING

INK

FILM

FAILURE

BLIS

TER

ADH

ESIV

E C

OAT

ING

INK

FILM

PIG

MEN

T C

OAT

ING

FAILURE

BLIS

TER

ADH

ESIV

E C

OAT

ING

INK

FILM

PIG

MEN

T C

OAT

ING

SUBS

TRAT

E

FAILURE



INTER

B B B B B NO O O O O Base A

Blister N Blister N Ink N Second N First N Sheet LD Coating D 4 - Color D Clay D Clay D Paperboard

Coating Coating No Coating PE D C B A L

YBOND

Internal Plybond of Paperboard Bond C = Bond of Ink to Second Clay CoatingBond A = First Clay Coating Bond to Paperboard Bond D = Bond of Blister Coating to Ink and Second Clay CoatiBond B = Second Clay Coating Bond to First Clay Coating Bond E = Bond of Blister to Blister Coating

Heat Seal Diagram

BOND E > BOND D > BOND C > BOND B > BOND A > INTERNAL PLYBOND

15

Heat Seal Diagam

12. Report

12.1. Complete identification of material being tested.

12.2. Conditions and equipment used to form seals.

12.3. Blister flange width.

12.4. Grain direction of board in relation to direction of pull.

12.5. Equipment used to test the seals.

12.6. Grip separation rate.

12.7. Report the number of samples tested.

12.8. Report the maximum seal strength for each tab in Newtons

per centimeter of width to three significant places or other

acceptable units to the same degree of accuracy.

12.9. Report the mode of failure for each tab. More than one mode

of failure can occur during testing.

Heat Tapes can be ordered from:

Paper Thermometer Co., Inc.

603.547.2034

web: paperthermometer.com

email: [email protected]

Pressure Film can be ordered from:

Sensor Products, Inc.

973.884.1755

sensorprod.com



Recommendation

The association recommends using the machine method wherever possible.

The use of this method provides a system for monitoring and measuring

the sealing process though the collection of meaningful data. This collection

of historical data can provide confidence and predictability in the future

performance of the process. It is also suggested that statistical process

control tools be used to convert the historical data to sealing process

tolerances and capability.

For more information regarding

the Seal Master Machine SM-500,

please contact:

Cheminstruments, Inc.

510 Comercial Drive

Fairfield, OH 45014

Phone: 513.869.1598

[email protected]



Troubleshooting

The purpose of this procedure is to assist you in the resolution of a

customer-sealing problem.

Determine which blister coating is being used and the type of blister

material - PVC or RPET. If the customer is using a blister coating and either

of these blister types, you can be pretty sure that the problem is the sealing

process. Most sealing compounds are very forgiving and will seal on most

plastics if proper sealing protocols are followed. In most cases, you will find

that the problem is not card related.

You can determine if the blister is PVC or PET/RPET material by several

simple tests as follows: 1) crease a PVC blister and it will turn white at the

crease, or 2) burn it and it will smoke and char (blacken) badly. The PET

or RPET material will not char and will turn white in the heated area. It will

also drip. Blister gauge should be at 0.0075’’ min to 0.0300” max thickness

before thermoforming. Flange width should be 0.312” minimum.

If there is a question regarding the type of coating, you can conduct a simple

test. Put a few drops of ammonia on the blister coating and let it remain

there five or ten minutes, and then wipe it off. If it “eats” into the coating,

the coating is an aqueous coating. If it does not destroy the coating, the

coating is a solvent coating.

Your investigation should begin with the sealing process trilogy: 1) time,

2) temperature, and 3) pressure. The one element that must be maintained

in the sealing of a blister card is the interface temperature. Blister coatings

are designed to be reactivated at very specific temperatures. The blister

coating will reactive at 180-190 °F and the AquaSeal will reactive at

190-205°F.

This reactivation of the coating creates a hot sticky mass known as “hot

tack” wherein this hot mass sticks to the plastic blister and as the coating

cools the bonding of the blister and card takes place.



If too much heat is applied, or the dwell time is excessive, the blister coating

viscosity will be reduced and the coating will penetrate into the card leaving

insufficient coating on the card surface to adhere to the blister. Of course

the dwell time must be long enough to reactivate the coating.

Heat tapes are used to determine the interface temperature. See the

photographs on left:

The card is then turned over and placed in the tray face down. The

sealing process commences. The last square on the tape that turns black

determines the interface temperature. Occasionally, the placement of the

tapes will not be in line with the flange area. The result is that you will not

get a reading. The tape must have pressure on it to work.

The next step is to take your pyrometer and check the heat platen. Usually,

the temperature on the machine-reading indicator varies from the true

reading of the heat platen. Also, check the platen in different areas. The

platen could have a burned element that causes a fluctuation in sealing

around the flange area. If the situation allows, the heat platen can be taken

off the sealing machine, laid on a flat surface, and checked for warping with

a straight edge placed diagonally on the platen.

Look at the unsealed area of the blister flange that is not sealing. If it’s

“glossy” like the unsealed areas of the entire card, you can assume that

there is no pressure or heat being applied in the flange area. If the configu-

ration of the blister allows it, turn a new blister around in the tray and see if

it fails in the same area. If the failure moves to a different area, it could be a

blister problem. Also, note how many cavities are being sealed at one time.

Now is the time to check the platen pressure with your pressure film.



The photographs to the left demonstrate the process of measuring heat

platen pressure using pressure film. The process flows top to bottom.

The first two photographs show two pieces of pressure film. Both have a

glossy and dull side; one piece is opaque, the other is translucent.

The second two photographs show the two pieces put together: 1) film put

together dull side to dull side and 2) film put into the tray on top of a blister

with opaque piece on the bottom, dull side facing up with translucent piece

on top and dull side facing down. To register a reading, the film must be

placed dull side to dull side.

The last two photographs show the card placed face down over the two

pieces of pressure film. The sealing machine is put in motion and the results

are shown in the last photograph on the right. The translucent top piece of

pressure film usually sticks to the face of the card and resulting pressure

shows up on the bottom opaque piece. A minimum face pressure of 80psi

is required in the face area.

Any light colored areas on the opaque piece indicate a lack of heat platen

pressure on that area of the card. Incidentally, wooden trays are noted

for this problem because they warp badly with the fluctuation of relative

humidity in the atmosphere. If the problem is on a carousel sealing machine,

check the rails and tray fixtures for the degree of vertical fluctuation.

Heat platens can either be milled tooling or flat head platens. The milled

tooling does not put as much heat into the blister card as a flat head platen.

Flat head platens without a Teflon cover can easily burn the back of a blister

card. The rubber or cork used on trays should be checked for damage and

compression caused by too much platen pressure. The rubber on the seal

tray surface should range from 50 to 90 durometer.

Keep in mind that the thickness of the blister card can have a bearing on

the heat transmission through the back of the card. Old blister cards have

a tendency to dry out, therefore temperatures and dwell times will have to

be increased to attain a successful seal.



The board generally used is known as “low density board”, which means it

has a “fluffy” surface so the blister coating can easily bind with the surface

layer of clay coating. Carton board has a hard smooth finish.

See the diagram below and note the various interfaces of a sealed blister

card.

The weakest interface, and the one that should fail, is Bond A to the base

sheet. The fracture at this juncture results in fiber tear (a successful seal).

A failure at any other juncture would be considered a failed seal. If the

bond between Bond A and the base sheet is too strong, it would be a board

problem. The split between Bond B and Bond A (clay split) is often a result of

this situation. With clay spit you will have white coating on the blister flange,

but there will be no board fiber attached.

This is why conducting various lab tests is recommended on all incoming

board before the board goes into production.

One of the most prevalent sealing problems today is the sealing of RPET

blisters (oriented). The plastics used, and the quantities used in the film,

varies greatly. As a result, film properties change from batch to batch. In

addition to this situation, the heat history of the film that the thermoformer

receives has a significant bearing on the thermoforming process used.

INTER

B B B B B NO O O O O Base A

Blister N Blister N Ink N Second N First N Sheet LD Coating D 4 - Color D Clay D Clay D Paperboard

Coating Coating No Coating PE D C B A L

YBOND

Internal Plybond of Paperboard Bond C = Bond of Ink to Second Clay CoatingBond A = First Clay Coating Bond to Paperboard Bond D = Bond of Blister Coating to Ink and Second Clay CoatiBond B = Second Clay Coating Bond to First Clay Coating Bond E = Bond of Blister to Blister Coating

Heat Seal Diagram

BOND E > BOND D > BOND C > BOND B > BOND A > INTERNAL PLYBOND

15



When the thermoformer processes PVC film, a temperature can be used that

is high enough to reach the Glass Transition point. Once past this point, the

film reaches the “Optimum Forming Temperature,” which allows the film to

be stretched and formed without creating orientation or stress.

When processing RPET film, the thermoformer cannot achieve the

“Optimum Forming Temperature” because the film surface will become

crystallized and will not seal. Therefore, the film is processed at a lower

temperature. The result is a formed blister that contains stress, a Cold

Formed blister. Memory remains in the film: during the sealing process,

when heat is applied, the blister flange softens and the stressed film tries

to return to its original shape.

As a result of this stress, the blister flange will 1) ripple and pull away

the card, 2) it will pick off ink from the inside of the blister wall, and

3) the flange will curl back up towards the vertical blister wall.

When dealing with RPET blisters and a sealing problem, you can save time

and effort if you have two pieces of Polarized Film. By placing the blister

between the two pieces of film, one piece at held at 45° angle, you will

immediately see the stress areas in the blister. The stress will show up as

colored rings or areas. The more purple rings that show, the more stress is

present in the blister. Check the flange area in particular. This method, in

many cases, will direct you to the source of the problem immediately. It also

gives you something definite you can show a customer. The technical term

for the purple rings is Birefringence.

Several other points to consider in trouble shooting a sealing problem:

1) the number of cavities on a sealing tray, 2) the shape of the blister (long

narrow flanges can create sealing problems), and 3) thin and narrow flanges

will ripple if too much heat is applied.

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