inje molding

8/8/2019 Inje Molding

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Injection molding process is very versatile molding process. It been used in all around the

world since last century. This molding process is used to manufacture plastic articles.This can be made from either from thermoplastic material or from Thermoset material.

The process starts with a mold, which is clamped under pressure to accommodate theinjection and cooling process. Then, palletized resins are fed into the machine, followed

by the appropriate colorants. The resins then fall into an injection barrel, where they are

heated to a melting point, and then injected into the mold through either a screw orramming device.

These are recent developments has been occurred in Injection Molding Techniques.

Injection molding of thermoplastic bio-composite (wood composite)

Thermoset injection molding process

Side core injection molding process

Double color injection molding process

Electrically operated injection molding machine

In-label injection molding process


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In mold labeling process


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In mold labeling process

Introduction

In-mould labeling (IML) is a high-quality and cost-effective technology where a plastic

label is placed in the mould and bonds with the moulded product during the process. It isan optimal technology to enhance your offer and brand with exclusive, richly coloured

plastic packaging.

Process

In mold labeling process is same as injection molding process with increasing the processstep and decreasing final cost. In this method the molded product is not required further

labeling process this process is been carried out in same mold where it been formed by

using help of robotic arm which applying static charged film inside the mold cavity

which is transferred to the final product by again closing the mold with formed product.

Applying a static charge to hold the label in the injection mold eliminates the need forvacuum ports that add significantly to the cost of making and maintaining the tool.

Applying the label during molding eliminates a secondary step for pad or screen printing

or label application, as well as corona or flame treating. More important, the end result is permanent. This makes it especially attractive for product-liability and instructional

information, as well as UPC codes, logos, and decoration. IML is also cleaner and more

sanitary because theres less handling of the product. And recyclability is enhanced if the

label material is the same as that of the molded part.

Although there are numerous ins and outs of IML technology, one of the most importantconsiderations is how the label is held in place in the injection molding tool. In manyapplications, electrostatics offers a reliable and cost-effective alternative to the use of

vacuum for holding the label in its proper location in the die. This approach can provide

distinct benefits to the molder as well as the molders customer and the end user.

Holding with vacuum

A label can be held in the desired location in the mold by specially designed andmachined vacuum ports. The sequence is as follows: A robot picks up the label from a

magazine, places it in the proper position in the die, the vacuum is turned on, and the

mold is shot.

Designing and machining the die to incorporate vacuum can add significant cost to the

tooling. Next, the label must be substantial enough to prevent it from being sucked intothe vacuum ports, causing a deformed image or pimples on the surface of the finished

product. Vacuum passages in the molding die may also result in non-uniform die

temperatures.


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In addition, it is very important that the robot does not miss the label. Injecting the mold

without a label in place can result in very time-consuming and costly downtime to

remove the die and clean out all the vacuum ports and passages. To prevent this requiresa means of detecting the vacuum and stopping injection of the polymer into the die.

The use of vacuum appears to be most advantageous when the shape of the molded

product requires complex preformed labels or when the molded part and/or label isrequired to have a textured surface.

Holding with electrostatics

Use of electrostatics in the IML process offers cost and reliability benefits by eliminating

the need for vacuum in the die. When a static charge is placed on a label of suitable

material and construction, the label will be attracted electrostatically to the groundedmetal surface of the die and may stick with excellent adhesion for up to several minutes.

In the electrostatic process, the robot picks up the label from the magazine with suction.

A high static charge is placed on the label either as the EOAT with the label approaches

the press or as the label approaches the die surface. The robot positions the label, releasesthe vacuum, and the label is transferred to the surface of the die. No vacuum in the die

nor adhesive on the label is needed.

Fig: Mandrel with suction cups embedded in antistatic foam (left) rotates to pick up label

from magazine while static charge is applied to the label.

Although some injection molders have attempted to charge the label and place it in the

die manually, experience has shown this to be a labor-intensive and unreliable approach

that also slows down the press cycle.

Using electrostatics to their full advantage requires the following components:

A robot with a suitably designed end-of-arm tool (EOAT). A label magazine.

A high-voltage DC charging power supply with 30-kV adjustable output

capability.

A label of proper material and construction to accept and maintain a static charge.


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Standard charging method

Although incorporating the charging applicator(s) on the EOAT offers a high degree ofreliability and repeatability, it presents somewhat of a challenge for the designer of the

EOAT. The applicator may be a straight static-charging bar of some specified length

having a row of emitter pins, or it may be a series of individual emitter modules. Thestyle and number of applicators required depends upon the size and shape of the label and

contours of the die surface where the label is to be placed. Therefore, each EOAT will

require its own unique charging applicator set-up.

(Fig: electrostatic charge is applied on film)

While the label is being held by the suction cups on the EOAT, the charging applicators

are located directly behind the label. The emitter pins typically face the back of the label

from a distance of about 1 in. When the robot places the label against the die surface, thecharging power supply is turned on for a period of about 0.5 to 2 sec. This places a static

charge on the label and the label instantly adheres to the grounded metal die. The vacuum

is turned off and the robot extracts the EOAT from the press.

When designing the EOAT to incorporate the charging applicator, a few guidelinesshould be considered to assure optimum label charging. For example, if the emitters are

to be placed 1 in. behind the label, any metal parts of the EOAT should be grounded andat least 1.5 in. away from the emitters. Metal any closer than this will attract some of the

electric field from the charging applicator, resulting in less charge on the label. If

individual emitters are to be mounted on a plate that also holds the vacuum suckers, theplate must be made of a nonconductive material such as polyethylene, PTFE, PVC,

UHMW-PE, or acrylic. Any component of the EOAT close to the charging applicator


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should be made of a nonconductive material, if that can be done without sacrificing

strength and structural integrity. Any component that is electrically conductive (metal)

must be grounded.

Two types of charging applicator are available: current-limited and non-current-limited.

Current-limited types come in the straight static-bar style or as individual emittermodules. They contain a resistor that is in series with the high-voltage supply. The

advantage is that this applicator will not hard arc if it gets too close to the metal and

offers a high degree of safety if personnel should accidentally touch it while energized.A hard arc is a high-current arc-over, usually seen as a distinct bright white or yellow

spark from the high-voltage emitter of the charging applicator to a conductive surface,

such as the cavity of the metal mold. This can occur when a non-current-limited

applicator is positioned too close to the mold or when its operating voltage is set too high.The high-voltage energy from the applicators emitter breaks down the insulation

properties of the air between the emitter and the grounded metal surface of the mold,

causing the arc. Such arcs can cause pits in the die surface and radio-frequency

interference (RFI) that may affect microprocessor controls of the robot or the press.In contrast, the current-limited applicators resistor limits the amount of current that can

be drawn from the emitter, thereby preventing a high-voltage arc.

Some of the newer electrostatic power supplies contain arc-sensing circuitry designed to

protect the solid-state components of the power supply when it is used with a non-

current-limited applicator. If excessive current draw is sensed by the power supply, itscontrol circuitry immediately goes into arc-protection shutdown mode, which turns off

the high-voltage output to protect the power supplys sensitive electronics. When this

happens, static charging is interrupted. That can be a common and troublesomeoccurrence when non-current-limited applicators are used.

As another safety precaution, the high-voltage cable from the charging applicators to the

power supply must be supported along the robot arm with sufficient slack to allow for the

required movement with the least physical stress on the cable. These cables should beinspected on a weekly basis and replaced if fracture, abrasion, or weakness of the cable is

detected.

Simple charging method

Use of a remote-mounted charging applicator is a simplified way to apply a charge. It

requires little modification of the EOAT, is relatively easy to set up, and can satisfy therequirements of many different sizes and shapes of labels with the same charging

applicator.This means of charging will work for most film labels that are applied to

relatively flat mold surfaces.


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(Fig: robotic mechanism for labeling process )

In this charging process, the robot picks up the label at the magazine, orients the label,and passes it by the charging bar. The ground reference surface behind the label attracts

the electric field from the charging bar and the label becomes charged. The robot places

the label in position against the surface of the molding die, releases the vacuum to the

suction cups, and the label stays in place on the surface of the die.

With this approach, a charging applicator bar is mounted on a permanent fixture between

the molding press and the label magazine. The charging power supply can be turned onmanually and left on during the duration of the run, or it can be turned on and off

remotely by the robots PLC.

In some cases, the label may not release readily from the suction cups and may skew

slightly due to mutual electrostatic attraction caused by static charges building on the

surfaces of the suction cups. If this occurs, a static neutralizer bar can be mounted in therobots path between the charging bar and the label magazine. Each time the robot returns

to pick up a new label, the suction cups will be neutralized. Smaller diameter suction

cups will decrease the charged surface area, which may help minimize the problem.

The fixture on the EOAT requires a grounded conductor such as a metal plate. The

conductive surface should be at least as large as the label and mounted 0.25 to 0.5 in.

directly behind the label. The suction cups should have the minimum diameter necessaryto provide sufficient holding power to prevent the label from slipping and attracting to the

grounded conductive surface of the fixture.

All conductive components of the robot fixture must be grounded and should have

radiused edges and corners. There should be no sharp edges or corners within 1 in. of the

label.


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Another version of the simplified method provides even better physical support and

uniform transfer of the label from the EOAT to the die. This process functions the same

as described above but requires the addition of a piece of antistatic foam mat bonded tothe metal ground reference plate on the EOAT. This material should have a thickness of

approximately 0.375 in. and should have an electrical surface and volume resistivity of

approximately 109 to 1010 ohms. This type of material is available from most static-control distributors who service the circuit-board assembly industry. Most of these

materials are manufactured with an embossed textured surface and may require sanding

to achieve a smooth, uniform surface. Sanding the surface also enhances charging of thelabel.

(Fig: plastic film or label used for aesthetic look)

The suction cups are incorporated into the foam material and should be flush with the

surface. Since the foam pad has a high electrical resistance compared with the grounded

metal mold surface, the charged label has a greater affinity for the mold and transfersfrom the foam pad to the mold when the vacuum is switched off. Here is an example of

how this may be accomplished for 360 labels on round containers.

(Fig: container used for Appling label inside the mold )

Key label properties

The physical and electrical characteristics of the label are extremely important to the

reliability of using static charges to adhere the label to the mold. The surface of the label

that is to contact the mold cavity must be a good insulator to accept and maintain thestatic charge. This surface should have a resistivity of 1012 ohms/sq or greater. The

higher the resistivity, the better the label will accept the charge without bleeding the

charge to ground when it contacts the metal mold cavity. If the charge is not maintainedwhen in contact with the die, adhesion is lost and the label slips from the intended


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position. Measurement of the labels resistivity can be performed using a commercially

available surface resistivity meter.

If conductive inks, coatings, or foil laminations are used, they must be on the back side of

the label, opposite the surface that is to contact the mold. In such a case, the best method

for charging the label is with the charging applicator external to the press (the simplifiedcharging method) and the conductive surface of the label against the vacuum ports on the

EOAT. If the charging applicator is mounted on the EOAT behind the label, the high-

voltage field cannot penetrate the conductive layer and sufficient charge will not beapplied to the surface that is to contact the mold cavity.

For considering safety factor a charged foil or conductive layer will most likely discharge

in the form of an arc as it approaches the mold surface. A result of this arcing is RFI,which may cause problems with microprocessor controls, especially if unshielded sensors

or cables are nearby. Ongoing arcing over a long period of time may also produce pits on

the die cavity.

(Fig: moulds used for in label molding process)

Label properties such as thickness, curl, and surface texture also affect adhesion. For

example, a relatively thick label that may have some curl due to an asymmetrical

laminated structure or improper storage may break loose from a flat die surface if theelectrostatic forces are unable to overcome the physical forces causing the label to curl.

Similarly, preformed labels may be required for compatibility with contoured diesurfaces.

A textured label or die surface can also result in poor adhesion due to the reduction in

intimate surface contact between the label and die surface.

A relatively thin, non-textured label with good dielectric properties on a non-textured die

surface will produce the best adhesion. However, there are still other important adhesion


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factors to consider, such as molding temperature, polymer compatibility with the label,

gate location, and material flow when the die is injected. For all these reasons, much time

and frustration can be eliminated by consulting a label supplier with IML experience.

Products of in label molding

Advantages of Film for using in labeling purpose

Most commonly used resins but film substrate must match resin being molded. Some films will distort parts

Some films are so conformable they will conform to embossing

Geometrieso Flat

o Round

o Tapered

o Special shapes

Compound curves

Three sided Five sided

Scrounds


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Label considerations

o Material type

Solid or cavitated

Film thickness-thinner films are less costly but can add cost to a project because they can be hard to handle in the automation

process Inks and varnishes A majority of IML labels printed in Europe

use water based inks and coatings

o UV Inks and varnishes

Less than 5% market share

Are very prone to curling which is highly undesirable

Have an undesirable odor Are not FDA compliant

Are glossier

Contaminate molds more maintenanceo Static charging The label will be static charged in most cases and the

inks and coatings used must be specifically designed to hold a charge.

Die Cutting

o No edge welding

o No blocking

o No curling

The injection IML market is comprised of two distinct areas

1. Thin wall polypropylene Packaging Applications which are high volume in

nature and very price driven.2. Other This product area includes applications on a wider variety of substrates

that require durability and unique printing that can include:

1. Screen Printing for a high degree of durability and opacity2. Hot Stamping for the high end cosmetic market

3. Sequential bar codes for tracking required by the FDA

Examples include:

Artic Cat and John Deere fenders and shrouds

Cosmetic cases (P&G) molded of polystyrene that require Hot Stamping

Heavy wall polypropylene containers that undergo 800 washes in a commercialdishwasher.

Cell phones


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Advantages of IML

Improved Quality Visual Advantage Superior Aesthetics

Reduced Part Cost

Increase Image Durability Increased Design Options

Better Quality

Base films used in the IML process offer a preferred surface for the application ofinks compared to pressure sensitive face stocks or direct printing on a container

surface.

Better detail via the offset or gravure process

Ability to offer very opaque colors on a pigmented container

Labels become a permanent part of the container rather than being glued on

Visually Appealing

Multiple print technologies

Off Set

Rotogravure

UV Flexo Conventional Flexo

Screen Printing

Billboard or label area opportunities are much greater with IML compared to

other processes. Visual advantages leads to market advantages which lead toincreased market share.

Reduced Part Costs

Reduction in label cost compared to Pressure Sensitive is at least 50%

Reduction in label cost compared to Heat Transfer is at least 25%

Reduced Scrap rate compared to other labeling methods

Reduction in wall thickness results in reduced resin costs

Increased Durability

IML label affinity for the resin being molded is much greater than Pressure

Sensitive Labels, Heat Transfer Labels, Direct Offset. IML also has better

resistance to abrasion, chemicals and wash cycles than alternative methods oflabeling.


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Design Options

Outstanding metallics via rotogravure Use of non-traditional shapes and forms

5-Sided label coverage on square containers

Use of hot stamping on screen printed labels Sequential bar coding possible on screen printed labels

Lenticular applications

IML is much more difficult to counterfeit

800 cycles through a commercial dishwasher with screen printed IML

Labels available in short, medium or long run volumes

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