Technical Papers

Lining Tank（Application）

1. Introduction

attachment of the sheet to the head reduces theamount of scraping to the sheet surface when

Following on from the previous article on“Lining Tank”

attaching the sheet, and drastically reduces（Basic version）, this article will overview thescratches on the surface and contamination of the“Application”.

sheet.

In the basic version, we have described the types and・‌The sheet before reformation is processed into acharacteristics of fluoropolymers, the fluoropolymer

square, and there are few welding lines. This

sheet lining process, and the basic points to note in

reduces the risk of problems such as broken

the design of fluoropolymer lining tanks, etc. Thiswelds.
・‌The reformation temperature is higher than thelining process and the sheets for lining that we handle.

vulcanization temperature of the adhesive, so
there is less residual stress in the sheet.

2. Characteristics‌of our lining
processing method

This reduces the risk of adhesive peeling problems.
The above three effects could be expected.

This article describes the manufacturing process ofNo.36

our high-purity fluoropolymer lining tanks,
characteristics of our processing technology.
2-1）Reformation‌and attachment offluoropolymer lining sheet to the head part
Fluoropolymer lining tanks generally have a

Winter 2019

time, we will introduce the characteristics of our sheet

Figure1

 anks made byTother manufacturers

Figure2

Our liner

fluoropolymer sheet attached to the metal can of the

Figure1 shows a lining tank constructed by anotherouter shell. The sheets are rolled up and cut into

company. There are many weld lines on the head at

strips for use. Strips of the sheet can be attached as is

the bottom.

to the body part of the can, but the head part has a

Figure2 shows the liner of the head part with our

curved surface and it is difficult to attach strips ofheating reformation and there are no weld lines.

sheet, so the sheet is attached in several equal parts.

The liner of a tank with an internal diameter of more

In our attachment method, the lining sheet of the headthan 1200 mm will have one or two welding lines as

shape is heated and molded before use.

shown in Figure3.

By processing the lining sheet for the head in advance,
it is possible to：・‌The combination of the vacuum attachment
method described below and the reforming
20Lining Tank（Application）

In the conventional method of attaching the sheet, ascraping jig press the liner against the tank. This
causes abrasion scratches on the entire surface of theliner.
In vacuum bonding, it was realized that the sheet ispressed against the tank at atmospheric pressure, so
Figure3

The liner in the head part of a large tank

The maximum internal diameter for head part

only a small portion of the sheet, such as the edge ofthe sheet, is scraped, and the scraped area is greatly
reduced.

reformation is φ2800. Three sheets are connected by
2 automatic welding lines and reformed. The

Figure6 shows a photograph of the head part attachedconnection between the head liner and the body liner

by the vacuum attachment method, and Figure7 is a

is also welded automatically because the head liner

magnified photograph.

reaches the body.
2-2）Vacuum attachment method with fewer
scratches on the sheet surface
The vacuum attachment method is a method in which

Winter 2019a flat sheet or a head molded sheet is placed along the
body of a can, and the air between the back of the
sheet and the body of the can is removed to create avacuum, so that the lining sheet is pressed against the
body of the can at atmospheric pressure and could bebonded without scraping.

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In this attachment method：・‌Reduces the scratches on the surface of the sheet

Figure6 ead of a tank with liner attached by vacuumHbondingand contamination of the sheet.
・‌Makes it possible to bond evenly and the bonding
strength is stable.
The above two effects could be expected.
2-2-1）‌Appearance of head part attached by
vacuum attachment method

Figure4 shows an image of the scraping attachment
method used by other companies.
Figure5 shows an image of the vacuum bonding
method which our company developed.

Figure7

Enlargement of the surface of our liner

2-2-2）Surface roughness after lining

The following are the results of comparing the liner
surface of a tank head when“attachment by scraping”
is used and“head reforming + vacuum bonding”isFigure4 Rubbing Attachment
21

Figure5 Vacuum Attachment

used to attach using M－PTFE sheets.

Technical Papers

Figure9 shows the surface roughness of the liningtank processed by the vacuum bonding method, and it
was Ra 0.25μm.
Figure10 shows a graph of measurements of thesurface of a sheet with conventional attachment, and it
was Ra 0.34μm.
2-3）Stable quality by mechanized welding
Figure11 shows the cross-section of the welded part ofthe liner.
The liner of the lining tank is joined by PFA welding.
Figure8

Electron micrograph of the scraped area

There are two stages of welding: beveling at the endof the liner, followed by priming welding with PFA
rods, and then band welding（reinforcement welding）
using PFA strips.
liner

Figure11

Figure9Liner surface of our company（Ra 0.25μm）

Winter 2019priming welding

band welding

liner

Cross-sectional shape of band weld

We use self-propelled welders（automatic welders）for
welding strips to stabilize“temperature”“speed”,
and“pressure”, which are important conditions for welding.
As a result, compared to manual welding by operators,
the welding conditions were more stable and thestrength variation significantly reduced.
In addition, it is now possible to weld strips with lessundulation, meandering, and deformation of thewelding line.
Furthermore, while other companies use a 14 mm
width for manual strip welding, we have increased thestrip width to 17 mm through mechanization to
improve the welding strength and increase thewelding part’s reliability.

Figure10Liner surface of another company（Ra 0.34μm）

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Lining Tank（Application）

stress relief
structure

Figure15

Our nozzle construction method

2-4-2）Liquid collection cup structure

The structure of the liquid collection cup at the bottom
Figure12  Welding with an automatic welding machineof the tank is the same as that of the nozzle.

Figure13 Our product - Automatic welding（M－PTFE－ET）

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Figure13 shows a strip weld done by automatic welding,which is wider and has less meandering.
2-4）Safety design of the component structure
2-4-1）Nozzle structure

No.36

 he cause is damage to
Figure16 ‌L ining around the Figure17 ‌T
the weld between theliquid collection cup
collecting cup and sheet
is detachedliningsheet band welding

The tube part of the nozzle is a part that has many
problems with welding because it is difficult to adhere
it tightly to the body of the can.
Other companies use a structure where the expansion
and contraction stresses of the liner due toliquid collection cup
the bodyof the canFigure18 E‌ xamples of construction Figure19
by other companies‌Our construction
methodtemperature changes are directly applied to the weld,
as shown in Figure14. As shown in Figure15, theinside of the tank is also flare processed, and this

3. Selection of lining material

flared part receives the stress, so the welding part is

We use three types of materials of fluoropolymer

not subjected to expansion and contraction stress.

lining sheets, PTFE, PFA, and M－PTFE. Two typesof sheets are used for the adhesion method: chemicaletched sheets with fluoropolymer surface that is
chemically processed and glass-backed sheets
laminated with glass cloth sheet.

delamination

3-1）Functionality evaluation of our lining sheetsNozzle activity and loss examples due totemperature change

The following table shows an in-house evaluation of

expansion andcontraction

Figure14

the five functionalities of our lining sheets on a 5-point
scale.

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Technical Papers

Evaluated sheets

3-1-1）Surface smoothness

PTFE-ET：PTFE chemical-etched sheet

The following is a photograph of the surface of three

M-PTFE-ET：‌Modified PTFE chemical-etched

types of lining sheets made of different materials andsheet（PLP Sheet）
M-PTFE-GB

surface roughness：‌Modified PTFE glass-backed
sheet

PTFE-GB：PTFE glass-backed sheet

PFA（NEW）-GB：PFA glass-backed seat
PFA（HP-PLUS）-GB：PFA glass-backed sheet
Evaluation details
Surface smoothness

Figure20

PTFE－ET×100

Figure21 Ra 0.29μm：‌Indicates the quality of dirt
removal during washing.

Adhesion performance：‌Indicates the quality of theadhesive strength between
the sheet and the adhesive.
Welding performance ：‌I n d i c a t e s t h e w e l d i n greliability of the sheet’s

Figure22 M－PTFE－ET×100

Figure23

Ra 0.24μm

Figure24 NEW PFA×100

Figure25

Ra 0.03μｍ

Winter 2019connecting parts.
Permeation resistance ：‌Permeation resistance tochemical solutions.
Affects‌
the life expectancy
of chemical solution permeation.
Price：‌‌Indicates the quality of thecost of the sheet.

Table1lining sheet

Functional evaluation of sheets for lining
evaluation: (excellent) 5・4・3・2・1 (poor)
surfaceadhesion
weldingpermeation
pricesmoothness performance performance resistance

PTFE-ET

3

3

3

4

5

M-PTFE-ET

4

3

4

5

4

PTFE-GB

3

3

3

2

3

M-PTFE-GB

4

3

4

4

2

PTFE-GB

5

3

5

3

2

PFA（HP-Plus）-GB

5

3

5

4

1

Note 1 ET: Etched sheet, GB: Glass Backing, M: Modified.
Note 2 Values are rated on a 5-point scale to indicate the quality.

PTFE：Highest surface roughness.

M-PTFE：‌Surface roughness is slightly lower thanPTFE.

NEW PFA ：The surface is the smoothest.
This measurement is at the stage of the sheets, andthe surface roughness Ra after lining varies greatly
due to the difference in lining construction methods
described above.
3-1-2）Adhesion performance

Fluoropolymers are non-adhesive, so even if anadhesive is applied to a fluoropolymer sheet, it will not
stick and peel off.
To add adhesiveness to fluoropolymer sheets in our
etching processed sheets, chemical etching is
conducted to add adhesiveness after the sheets are
24

No.36

Lining Tank（Application）

manufactured.

same as the welding rod and strip material, could

On the other hand, glass-backed sheets are made bytheoretically be said to have better fusion during

anchoring fluoropolymer sheets and glass cloth sheets

welding and higher welding stability.

by melting PFA between them to make them

Guessing from the fluoropolymer material（molecularadhesive.

structure）, the welding stability would be PFA>
M－PTFE>PTFE.
3-1-4）Permeation resistance
There is no difference inbonding strength between
the etching sheet and theglass-backed sheet.

It is known that the permeation of chemicals occurs
mainly in the amorphous part inside the polymer.
Figure28 schematically depicts the crystal structure of
a fluoropolymer sheet in the cross section.
▪ Permeation model

crystalline part

amorphous part

Figure26 Bonding strength (shear) of ET sheets and GB sheets
C-F bond

Figure26 shows the shear strength test results of ET
sheet and GB sheet bonded to metal using rubber

Winter 2019No.36

adhesive.
The peeled areas are all metal surfaces and have thesame adhesive strength.
3-1-3）Welding performancepolymer conformation of
PTFE in the cross-section

Figure28

Image of chemical permeation into fluoropolymer

Figure27 shows a comparison of the weld strength of

The part where molecules are lined up orderly fashion

the lining sheets.

is the crystalline part, and the part where molecules
are intricately intertwined is the amorphous part.

Weldability

The crystalline part is densely packed with molecules
and has a high density.
The amorphous part has a low density due to theentanglement and random arrangement of molecules.
Therefore, the more crystalline the sheet, the greater
the specific gravity.
The chemical permeates through the amorphous partand gradually diffuses through the sheet. Eventually,
it reaches the body side of the can, which is the backFigure27

Results of weld strength measurement

side of the sheet with the adhesive surface.

（PLP：this is a sheet of M－PTFE, but a sheet manu-

Figure29 shows the specific gravity of fluoropolymer

factured by our company with improved permeationand the amount of hydrochloric acid permeation. The

resistance.）graph also shows the specific gravity of fluoropolymer

There is no significant difference in the weld strength

sheets available on the market.

of all sheets in the temperature range where they are
generally used. However, the PFA sheet, which is the25Technical Papers

the difficulty of slow cooling.
The translucent part on the GB side is shown in thephoto where the specific gravity has become low.
Figure31 shows a cross-section of our PLP sheet.
high specific gravity（SG 2.19）

Figure29

Permeability against the specific gravity offluoropolymers

This figure shows that the amount of chemical
permeation decreases with the specific gravity.
PTFE gelate can retain its shape even if it exceeds

Figure31

the melting point. So it is possible to control the

Cross-section of PLP sheet

PLP sheet is a polymer that could be denser thancharacteristic can be used to control the degree of

PTFE, and since the etching process that does not

crystallization.

require heat treatment that could gelate the sheet,

The specific gravity of PTFE generally available on

without lowering the specific gravity.

Winter 2019

cooling conditions that affect crystallization. This

the market, considering productivity is about 2.14 to
2.16. However the specific gravity of our sheets forlining is finished to about 2.18 to improve
permeability. PFA is a molten polymer, and it isdifficult to control the cooling conditions due to its
molding method, so the specific gravity is generally in

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the range of 2.14 to 2.15.
Figure30 shows a cross-section of M－PTFE－GB
sheet.
high specific gravity（SG 2.19）

Figure32

  low specific gravity（SG 2.15）

Figure30

Cross-section of M－PTFE－GB sheet.

 pecific gravity, thickness and permeability ofS
fluoropolymers

This figure shows that the thickness of the sheet isalso an important factor in permeation resistance.
3-1-5）Price

It is necessary to gelate the sheet when laminating

Figure33 shows the relationship between the surface

the glass cloth to the sheet to produce PTFE－GB andsmoothness of the lining sheet and the market price of

M－PTFE－GB sheets. Cooling is conducted after

the lining sheet, and Figure34 shows a schema of thegelation, but the specific gravity decreases because of

relationship between surface smoothness and26

Lining Tank（Application）

permeation resistance.
The right side of the horizontal axis indicates higher

4. Conclusion

functionality, and the upper side of the vertical axis
indicates higher cost.

Since the start of lining tank production, our company
has responded with any queries from our customers
regarding our product defects. We always inform ourcustomers if there is any update regarding our
production method. Although the causes ofabnormalities differ, they could be roughly classified

Cost

into three categories.
These are“chemical permeation,”“unexpected structuraldefects,”and“inexperienced construction techniques”.
We have been investigating the causes of each problem
Surface smoothness

Figure33

Surface Smoothness：Costand making improvements.
For example, for chemical permeation, we have beenworking on selecting materials for lining sheets andincreasing the density of the sheets. For structuralof the body of the can and improvement of the nozzle

Cost

Winter 2019problems, we have been working on design methods
structure as described in the previous article. For
construction technology, we have been working on theautomation of welding strips.
With the rise of the semiconductor industry,
resistancecleanliness, which was not a requirement for chemical

Permeation Resistance：Cost

plants, has become more important, and the

The cost of fluoropolymer raw materials is：development of vacuum bonding and head liner

PFA＞ M－PTFE＞ PTFE

molding technologies enabled us to reduce scratches

The cost of providing adhesion is ET＞ GB.

to the liner surface as much as possible.

The surface smoothness of the base sheet is PFA＞

We will continue to strive to develop new technologies

M－PTFE＞ PTFE.

to meet the demands of the market.

This is due to the different characteristics of the raw

Our next article will introduce an overview of thematerials and the processing methods used to maketechnologies we are currently working on and ourthe sheets. However, the method of lining attachment

future goals.

Permeation

No.36

Figure34also needs to be considered.

Takeshi Yokoyama
Assistant To High Performance Plastics
Product Manager
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