Blown Film Extrusion Introduction

Blown Film Extrusion Introduction
Blown film extrusion is a technology that is the most common method to make plastic films, especially for the packaging industry. The process involves extruding a tube of molten polymer through a die and inflating to several times its initial diameter to form a thin film bubble. This bubble is then collapsed and used as a lay-flat film or can be made into bags. Usually polyethylene is used with this process, and other materials can be used as blends with these polymers. A diagram of a polyethylene chain is shown in Figure 1 to the right.
Background Theory on Polymers

In the cooling step of blown film extrusion, the amorphous, transparent melt crystallizes to form a translucent, hazy, or opaque film. The point where opacity begins in the bubble is known as the frost line. 
Fig 1: Model of polytheylene chain frompolyethylene Wikipedia article.The frost line height is controlled by several parameters: the air flow, film speed, and temperature difference between the film and the surroundings. Properties of the film, such as tensile strength, flexural strength, toughness, and optical properties, drastically change depending on the orientation of the molecules. As the transverse or hoop direction properties increase, the machine or longitudinal direction properties decrease. For instance, if all the molecules were aligned in the machine direction, it would be easy to tear the film in that direction, and very difficult in the transverse direction.

The Film Blowing machine Process

Fig 2: Schematic of set-up from User:J.Chiang.

Typically, blown film extrusion is carried out vertically upwards, however horizontal and downward extrusion processes are now becoming more common. Figure 2 shows a schematic of the set-up for blown film extrusion. This procedure consists of four main steps: The polymer material starts in a pellet form, which are successively compacted and melted to form a continuous, viscous liquid. This molten plastic is then forced, or extruded, through an annular die. Air is injected through a hole in the center of the die, and the pressure causes the extruded melt to expand into a bubble. The air entering the bubble replaces air leaving it, so that even and constant pressure is maintained to ensure uniform thickness of the film. The bubble is pulled continually upwards from the die and a cooling ring blows air onto the film. The film can also be cooled from the inside using internal bubble cooling. This reduces the temperature inside the bubble, while maintaining the bubble diameter. After solidification at the frost line, the film moves into a set of nip rollers which collapse the bubble and flatten it into two flat film layers. The puller rolls pull the film onto windup rollers. The film passes through idler rolls during this process to ensure that there is uniform tension in the film. Between the nip rollers and the windup rollers, the film may pass through a treatment centre, depending on the application. During this stage, the film may be slit to form one or two films, or surface treated. Advantages Blown film generally has a better balance of mechanical properties than cast or extruded films because it is drawn in both the transverse and machine directions. Mechanical properties of the thin film include tensile and flexural strength, and toughness. The nearly uniform properties in both directions allow for maximum toughness in the film.
Blown film extrusion can be used to make one large film, two smaller ones, or tubes that can be made into bags. Also, one die can make many different widths and sizes without significant trimming. This high level of flexibility in the process leads to less scrap material and higher productivity. Blown films also require lower melting temperatures than cast extrusion. Measured at the die opening, the temperature of cast film is about 220 C, where as the temperature of blown film is about 135 C. Furthermore, the cost of the equipment is approximately 50% of a cast line.

Blown Film Extrusion Disadvantages Blown film has a less effective cooling process than flat film. Flat film cooling is done by means of chill rolls or water, which have significantly higher specific heat capacities than the air that is used in the blown film cooling process. The higher specific heat capacity allows the substance to absorb more heat with less change in the substance temperature. Compared to cast film, blown film has a more complicated and less accurate method to control film thickness; cast film has a thickness variation of 1 to 2% versus the 3 to 4% for blown film. The resins used for casting typically have a lower melt flow index, which is the amount of polymer that can be forced through a standard die in 10 minutes according to a standard procedure. The melt flow index for cast film is about 5.0 g/10 min where as for blown film it is about 1.0 g/10 min. Consequently, the production rates for cast film are higher: cast film lines can reach production rates of up to 300m/min where as blown film lines are usually less than half this value. And finally, cast film has better optical properties, including transparency, haze, and gloss.

Common Problems Air entrapment between film layers and rollers – this may cause film scratching or wrinkling, or processing problems when winding up the film due to reduced friction. Possible solutions to this is using a vacuum to remove entrapped air or by using winding rolls with a diamond shaped groove in the rubber cover to increase surface area and decrease amount of entrapped air in the film. Large output fluctuations from the die – this causes thickness variations, and can be prevented by keeping the extruder clean and by using more consistently shaped pellets in the extruder. Melt fractures – these appear as roughness or wavy lines on the film surface, and can be eliminated by lowering the viscosity of the polymer melt. This can be done by increasing the melting temperature or by adding an internal lubricant to the material composition. Thickness variations in the film – this can be avoided by centering the die in the extrusion line before every run, adjusting the air speed of the cooling system, or by using heated die lips. Die lines on the surface of the film – this defect reduces the aesthetic appeal of the film, reduces optical properties, and weakens mechanical properties such as tear strength. This can usually be avoided by routinely cleaning the inner surfaces of the die and by refinishing scratched or roughened flow surfaces. Gels – these defects are small, hard globules encapsulated in the film or stuck on the film surface and reduce the aesthetic appeal of the film and cause stress concentration points which may result in premature failure. These are caused by overheating to the point of polymer degradation in the die, and can therefore be avoided by cleaning the inner surfaces of the die on a regular basis. Optimization of the Process Coextrusion One way to improve the line efficiency of blown film extrusion is to implement coextrusion. This is the process of extruding two or more materials simultaneously through a single die. The orifices in the die are arranged such that the layers merge together before cooling. This process saves time because it extrudes two or more layers at the same time, and it provides a method with fewer steps to produce multilayer films. The production rate for a coextruded multilayer film of three layers is about 65m/min, and the production rate for a single layer of blown film is about 130m/min. Thus, in order to produce 10 000m of a three layer multilayer film, it would take almost 4 hours using a single layer blown film process, and only 2 and a half hours using the coextrusion process. Furthermore, the film produced from the single layer process would require an extra step to glue the layers together using some sort of adhesive. Coextrusion is the least expensive means of producing layered films and the coextrusion system is capable of quick changeovers to minimize production line down time.

Minimizing the Melt Temperature
The efficiency of blown film extrusion can be improved by minimizing the temperature of the polymer melt. Reduction of the melt temperature causes the melt to require less heating in the extruder. Normal extrusion conditions have a melting temperature at about 190 C despite the fact that the temperature of the melt only needs to be about 135 C. However, it is not always practical to decrease the melting temperature by that much. By decreasing the melt temperature 2 to 20 C, the motor load can be decreased by about 1 to 10%. Furthermore, reduction of the melt temperature causes less need for cooling, so there is a reduced use of the cooling system. Moreover, removing heat from the bubble is usually the rate-limiting factor in this extrusion process, so by having less heat in the polymer to remove, the rate of the process can be increased, thus yielding higher productivity. A way to maintain the melt temperature at a minimum is to choose an extruder that is matched to the specific processing conditions, such as the material of the melt, pressure, and throughput.

Heated Extrusion Die Lips
Typically, solutions to melt fractures involve decreasing the output or increasing the melt temperature to decrease the shear stress in the extruder. Both of these methods are not ideal because they both reduce the efficiency of the blown film line. Heated extrusion die lips can solve this problem. This targeted heating method allows for film extruders to be run at higher production rates with narrower die gaps while eliminating melt fractures. Direct heat is applied to the surface of the polymer melt as it exits the die so that viscosity is reduced. Therefore, melt fractures, which are caused when trying to extrude too much of the polymer at one time, will no longer act as a limiting factor to increasing the production rate. Furthermore, heated die lips use less energy than increasing the melting temperature because only the surface of the melt is heated and not the bulk of the liquid. Another benefit of using heated die lips is that thickness variations can be controlled by adding heat to certain areas along the die circumference to make the film at that position thinner. This would ensure that no excess material is used.
Determine how much energy each of these processes can save per given volume of material. 

Above article from www.appropedia.org

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Media Addiction Quiz for Teens: Do TV, Video Games and Computers Run Your Life?

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Welcome to “The Media Generation”

Teens are spending so much time watching TV and playing with their computer and video games that the Kaiser Family Foundation has dubbed this generation “The Media Generation.”

The recent study found that children aged 8-18 were watching TV, playing video games, on their computers, and listening to music for a total of 6 hours and 23 minutes EVERY DAY! Many kids were doing two or more activities at once. Most of this time is still spent watching TV. Kids spent almost four hours every day watching TV. With so much time in front of   TV  and other  media , perhaps Kaiser should have labeled it “The Media-Addicted Generation.”

What excess TV, video game, and computer use may be doing to you

How much time you spend in front of a TV, video, and computer screen is important, because these activities have been linked to obesity, attention problems (like ADHD), and poor grades. Violent content may condition you to accept violence in your life. The sexual content of many popular shows and games may encourage you to experiment before you are ready. The TV can act as a depressant, stifle your creativity, encourage conformity, and simply waste your valuable time.

Find out if you are part of “The Media-Addicted Generation”:

1. Does your family have more than one TV set? Yes [] No []

2. Are you in front of a screen for more than 2 hours per day?Yes [] No []

3. Do you sometimes have trouble getting TV or video game

jingles “out of your head”? Yes [] No []

4. Is there a TV/video game/computer playing in your

home much or all of the time? Yes [] No []

5. Do you have a TV, video game, and/or computer in your

bedroom? Yes [] No []

6. Is it easy for you to turn off the TV/video game in the

middle of a favorite show/game? Yes [] No []

7. Do you ever rush home, ditching friends and family, to

catch a favorite TV show, play video games, or go on the

computer? Yes [] No []

8. Do you frequently eat meals while in front of the TV,

video games, or computer? Yes [] No []

9. Have you ever caught yourself unintentionally mimicking

a TV or video game character? Yes [] No []

10. Do you talk to and play with your friends more than you

watch TV, play games, and play with computers? Yes [] No []

11. Can you turn off the TV, computer, and video games OFF

right now and leave them off for three days? Yes [] No []

12. Do you ever mindlessly surf through TV channels or

the internet? Yes [] No []

13. Do you need TV, video game, or a computer to relax after

a rough day? Yes [] No []

14. Do you feel edgy, anxious, or “not right” if there is no TV,

video game, or a computer playing? Yes [] No []

15. Do you watch TV, play video games, and/or play on the

computer more than spend time with your family? Yes [] No []

16. Do you ever watch the TV, play video games, or surf

the internet longer than you intend to? Yes [] No []

17. Do you feel spend too much time with TV, video games,

or computer? Yes [] No []

18. Have you missed a special event with friends or family

because you were watching a TV program? Yes [] No []

19. Have you ever tried to quit watching TV, playing video

games, or going on computer, but were unsuccessful? Yes [] No []

20. Do you have difficulty limiting the time you watch TV,

play video games, or go on the computer? Yes [] No []

*Note: Time spent on the computer for homework purposes does not count:

To calculate your score:

For all questions, except for #6, #10, and #11, give yourself 1 point for every “Yes” answer and 0 points for every “No”. For questions #6, #10, and #11 give yourself 0 points for every “Yes”, answer and 1 point for every “No”. Add your total.

Your total: ____________

Scoring:

0-6: Great! Your TV, computer, and video games are not in control of your life. You are. But keep an eye on how much time you spend with these activities to make sure an addiction does not sneak up on you.

7-14: You are moderately addicted to your TV, video games, or computer. Maybe all of them. The good news is that with a little effort, a list of fun non-screen activities, and a reasonable schedule you should be able to keep your addiction under control. “The TV-FREE System” also helps you create a schedule that keeps you busy with fun, goal-centered activities. Follow your dreams instead of staring at a screen..

15-20: Oh dear. You probably have a serious addiction problem. You may need to take extreme steps, including getting rid of your TV or video games, to get in control of your time. Start with the device which squanders the most of your time. The good news is “The TV-FREE System” was designed to help even the most serious addict, and can be used for video game, or computer addiction as well.

Life is too short to “watch” it go by.

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Television and Children – How TV Affects Your Child

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There is an ongoing debate about the effects of television on children. Some believe that TV has a lot to offer. It can educate, stimulate and entertain. If parents are discerning about what their child watches and how much they watch, there is nothing too harmful about TV. On the other hand, some experts say that any children under two should not watch any television. They feel that it hinders a child’s growth and development in many ways.

So before you sit your kids down in front of your huge plasma TV, have a think about what they are watching and how long they are watching.To get a look at both sides of the debate, lets break this discussion down in to the positive and negative effects of television on young viewers.

Positive:

  • Children can learn about numbers, letters, colours and shapes by watching quality educational programmes.
  • Children can learn about social interaction and manners on good quality dramatic and educational programmes.
  • For many parents of young children, a day at home is many hours to fill. Sometimes a familiar or appropriate movie or programme can provide a relaxing moment both child and parent.
  • Children enjoy the familiarity of a movie or show they have watched many times as much as they love to read the same book again and again.
  • Many movies and shows have a moral tale, and this can sometimes provide a helpful way for parents to introduce moral themes and ideas into their children’s lives.
  • Quite often a movie or show can provide the inspiration for games and creative play away from the TV. A child might enjoy re-enacting a favourite scene or character from a movie and carry on with this scene in their playtime.
  • TV and media is a way of life in this day and age. Children can benefit from being conditioned and familiarised with media concepts. It will help them participate in social and cultural events and discussions in their developing social and educational lives.

Negative:

  • Children under two can be negatively affected by television. It can stunt their social and mental development.
  • Too many hours in front of a TV can prevent children from interacting with their family and siblings.
  • Too much TV can become a problem for some children who engage in less physical activity because they prefer to watch TV.
  • Too much exposure to TV and screen media can make a child’s mind lazy in terms of using their imagination and brainpower in other areas of their lives.
  • When children watch TV they are being exposed to advertising. A lot of advertising is aimed specifically at young children. Ads target young ones and condition them to become loyal brand consumers as adults. Exposure to some ads could encourage poor eating habits and food choices.
  • Injudicious TV watching can expose children to bad habits such as smoking and drinking. It can expose them to violence and create a mindset of fear and aggression.
  • Watching TV can also instil in your children social stereotypes of race, gender and class.

With so many reasons for and against TV watching, it seems that the decision is best left up to the parent. A parent knows their own child and how best to manage their TV watching habits. Undoubtedly a discerning and vigilant attitude is essential when exposing young children to TV, so think twice before you sit you child in front of your beloved flat screen, HD TV.

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Western Digital WD TV Live Review

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Okay! Here goes my first gadget review. I am going to tell about a very cool bit of technology innovation called Western Digital WD TV Live player. A small cute device that is going to change the way you viewed connected media before!

Honestly speaking I didn’t appreciate this amazing piece of work when my husband bought it. Well he is a gadget freak or more rightly an electronics-shopaholic. But just like any shopaholics he has his own way of convincing why that was a ‘can’t live without’ stuff. I was really skeptical if any of his reasoning was going to even convince me on this. But this time, it was the product that convinced me! I’d not say that it’s a gadget you can’t live without, but I’d definitely say its worth every penny for its versatility.

Features:

Full-HD 1080p video playback.

Plays almost all types of media

Audio – MP3, WMA, OGG, WAV/PCM/LPCM, AAC, FLAC, Dolby Digital, AIF/AIFF, MKA

Photo – JPEG, GIF, TIF/TIFF, BMP, PNG

Video – MPEG1/2/4, WMV9, AVI (MPEG4, Xvid, AVC), H.264, MKV, MOV (MPEG4, H.264),MTS, TP, TS

Playlist PLS, M3U, WPL Subtitle -SRT (UTF-8), SMI, SUB, ASS, SSA

Doesn’t require a Western Digital networked device to be able to play the media in it.

Live streaming from YouTube, Flickr, Pandora, and Live365. What’s more here?? You can login to your personal accounts in these internet media sites and play just your favorites! (Unfortunately Netflix and Picasa are missing.)

Comes with a good remote control.

Hitches:

Yeah it does have few hitches.

1. Though the network setup is really simple (just have to plug-in the cable from router), a small mistake in setting up file sharing in connected PCs can take ages to resolve. I personally had this problem (I had one Win7 laptop and one Win XP laptop – WD in fact offered to take the device back as they couldn’t say why I couldn’t connect to the networked laptops. Thankfully I had sense enough to Google for the solution and we were able to do the network media sharing!)

2. No inbuilt wireless connectivity. But this can be excused as streaming media over the network is better when its wired rather than wireless. (We did try the Wireless-N adapter, but it works pretty good as our router is also 802.11 draft2 N class – but definitely not as good as having it hard connected). So what’s the hitch? The extra bucks that you’ll have to throw in for the wireless adapter (and a N router).

Final Word:

This all in one wonder box is sure enough worth the money and will have you hooked on to it. Its a real piece of entertainment – Go for it! Its time for you to experience the good things that come in this small package.

Read more: http://mymindstalk.blogspot.com/2010/09/western-digital-wd-tv-live-review.html

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Go Much Longer With One Of These Profitable Tips

Traveling the world will not really need to require conserving money for years and after that constraining yourself to precisely what your financial allowance can afford. There are several really effective approaches to generate profits whilst you vacation that will allow you to get pleasure from your stay and just go home when you’re all set — definitely not if you exhaust your funds. When you find yourself within a overseas nation in which you really don’t communicate the native language on a conversational level, it really is much easier to make money on the internet and there are several techniques this can be done. Vacation creating is a entertaining way to gain large sums of money every write-up. You may make a lot more if you are a qualified wedding photographer. You might also make money by purchasing securities if you your research before you decide to set off. Read Full Report to find out the most effective varieties of assets for folks who need to get an incredible gain without lots of risk. Home and rare metal are some purchases which may have proved helpful just for travelers and you may see here now precisely how these can easily do the job. If you commence to exhaust your funds so you will not be ready to go back home, consider marketing a number of your stuff. While you might think your stuff is common, the natives may possibly look at them as luxurious items and become happy to pay out significantly more than they will be really worth.

How you can use your conrer sofa bed and corner sofa

There are many space efficient solutions now a day that most home owners can use for their homes or condominiums given the limited space that they have and with the use of a small corner sofa bed, they can achieve this kind of solution. There are many kinds of corner sofa bed that are being sold in the market and this kind of furniture has a double feature that can function well in a bedroom or in a guest room as well.

The corner sofa bed has many uses when it is placed properly in your home and when you learn to decorate it so that it can also be used in your living room when it has a feature of storages. There are many kinds and sizes of corner sofa bed and with this, you must first measure the size of the room so that you would know how big the sofa bed you are going to purchase and you would also define the dimensions of the room.

You must learn to also rearrange the other furniture in the room when you place your corner sofa bed together with other kinds of furniture and by doing this, you can really optimize the space of your room and making it more efficient in terms of the style. There are many kinds of materials for a corner sofa bed and if you want to buy one, you may choose a cheap corner sofa bed made up of a genuine leather because this is more classy as compared to other kinds of materials.

If you are tight on a budget and you are unable to afford a genuine leather of a corner sofa bed then you can purchase a sofa bed with a fabric material which is very affordable and it also blends with other kind of furniture. You can always buy additional storage with fabric textiles as its cover so that it will be more decorative and colorful when you place it under the sofa bed and this is very functional for small space in your room along with other furniture.

What matters most in choosing the kind of corner sofa bed with storage bed that you want is the kind of base that it got because the base will be the basis for the durability of the sofa bed. The use of bright colored pillows or cushions is a big help for you corner sofa bed to become more attractive and these will also serve as additional decorations inside you room.