Key Questions to Ask When Ordering plastic bag production machine

To some people, DFM (design for Manufacturability) might seem a little overkill or an unnecessary step in the already lengthy process of developing a new product. However, it is one that we at Sofeast take seriously and is a step that pays off time and time again resulting in saving time, money, and headaches down the line. Here's why tooling DFM is crucial for successful injection molding.

With competitive price and timely delivery, Bage Machinery sincerely hope to be your supplier and partner.

Let's look at a scenario where you are thinking about skipping tooling DFM: you think you have a great design, and you move straight into mold tool production, however, during mold tool production, unexpected challenges arise. The design needs modifications, leading to delays, rework costs, and a dent in your budget. Tooling DFM would have helped you avoid this nightmare scenario.

By proactively identifying potential issues early on, Tooling DFM saves you from costly fixes later. It analyzes your design through the lens of manufacturability, highlighting areas that could lead to expensive mold modifications or production delays. Addressing these concerns early in the design phase minimizes rework and keeps your project on track, both financially and temporally.

But DFM doesn't stop there. It also helps you choose the right material for your needs, minimizing waste and reducing material costs. Additionally, a DFM-optimized design translates to smoother production with less downtime and potential machine adjustments, further saving you operational costs. In essence, DFM helps you get the most out of your investment, ensuring every penny counts towards a successful outcome.

DFM also plays a key role in ensuring your injection molded parts meet the highest quality standards. It considers critical factors like wall thickness, draft angles, and gating, minimizing the risk of shrinkage, warpage, and other defects that can impact part quality and functionality.

In the image below you can see our own internal feedback during DFM on a product about the size of the gate and the requirement to add some material on the inside of the rim which shows the level of detail the team goes into during a DFM review to ensure that we have the absolute minimum gate mark on the surface of the product.

We get asked about plastic injection molding cost on every project we manage and it is not always that easy to answer. Let's break it down into two parts, first, the cost of the mold tools and second, the cost of the injection molded parts.

A. Injection mold tooling cost

When it comes to injection molding, the tooling itself is the most expensive part, but what factors contribute to all the cost?

The complexity, size, and material of the mold heavily influence its cost. Here's a closer look at each factor:

• Complexity: Simple, single-cavity molds with basic geometries are naturally cheaper than intricate, multi-cavity molds with complex features like undercuts or tight tolerances. The more intricate the design, the more machining and finishing work is required, driving up the cost. Simple, single-cavity molds for small parts might cost around $1,000-$5,000, while complex, multi-cavity molds for high-volume production can soar to $25,000-$80,000 or even more.
• Size: Larger molds require more material and machining time, resulting in a higher price.
• Material: Steel is the most common mold material due to its durability and heat resistance. However, it's also the most expensive. Aluminum offers a cost-effective alternative for simpler molds or low-volume production but with potential limitations in durability and heat tolerance. These days, aluminum tools are not very common in China as most toolmakers prefer to go directly to steel.

Where would the mold tooling usually be fabricated?

Most mold tooling is fabricated in China; mostly around Dongguan and Ningbo, where there is a very dense network of toolmakers and prices are quite competitive. Here's our advice for you when requesting quotes from mold tooling shops in China.

B. Plastic injection molding cost for parts

Several factors will determine the plastic injection molding cost for your parts with the material selection having a significant part in this equation. We have already touched on some of the plastics commonly used, however, it is not the cost of the material that should influence the selection, it has to be the required properties like strength, heat or chemical resistance, etc.

Another factor that will impact the cost is volume. High-volume production benefits from economies of scale, bringing the cost per part down especially if multiple parts can be molded with a single shot (multi-cavity tooling). Conversely, low-volume projects might have a higher per-unit cost due to mold setup and processing costs.

We've written more about the costs of tooling and purchasing process in these blog posts:

• How to avoid paying in full for your tooling
• Buy China Tooling For Plastic Production Abroad? (Benefits & Risks)
  
• Should Tooling Fabrication and Plastic Injection Molding Be Done Together?

As with the question about costs, the answer to how long it takes to make a mold tool is not a straightforward one as no two projects are the same.

Mold complexity is probably the single most influencing factor to the time it will take to fabricate your mold tooling. Single-cavity molds with basic geometries are quicker to create, often taking 2-4 weeks. But intricate designs with multiple cavities, tight tolerances, or complex features like undercuts can push the lead time to 6-8 weeks or even longer. The more intricate the design, the more steps and time required.

The second part of this complexity equation is the mold size. The more cavities involved, the larger the mold itself, the larger the mold, the more machining is involved which increases the time.

Another factor to take into consideration is the mold maker's schedule. With a busy workshop, your mold may have to wait its turn which adds to the overall lead time. On top of the mold maker's lead times, you have the supply chain to consider where material shortages or delays in components like cooling systems can add unexpected waiting periods.

Key factors to remember when planning the build of your mold tool are:

• Estimates are your friends: Experienced mold makers can provide an initial estimate based on your design and requirements. Keep in mind, that this might change depending on unforeseen circumstances.
• Communication is key: Stay in touch with your mold maker throughout the process. Understanding potential delays and adjustments helps manage expectations and adapt your timeline accordingly.
• Planning is crucial: Factoring in the mold lead time when planning your overall project timeline is essential. Rushing the mold creation often compromises quality and can lead to costly rework later.

An example of the difference in mold tool fabrication lead times between China and India, and why they're not the same.

China is still the fastest place to have mold tooling fabricated. The same mold might get made in 3 weeks in China (not including DFM, mold design, first trial, etc.), and 7 weeks in India, simply because Chinese toolmakers have automated the processes much more than in India where a lot of the finishing is done by hand (which is a more labor-intensive process).

Prototype plastic injection molding is a must for prototyping your design before mass production for many businesses, as it is crucial for identifying flaws, refining functionality, and ensuring a smooth transition into the tooling phase. While 3D printing has emerged as a popular prototyping tool, various injection molding-specific methods offer distinct advantages and cater to diverse needs. Here we will look at the different prototype tooling methods, exploring their materials, lead times, limitations, and what they can produce:

Rapid Injection Molding (RIM):

This method utilizes simplified, single-cavity molds often crafted from aluminum or epoxy resin. These molds are quicker and cheaper to create compared to their production counterparts, offering faster lead times and lower upfront costs.

• Materials: Aluminum, epoxy, nickel-plated steel (for higher durability)
• Lead Time: 2-4 weeks for simple designs, longer for complex geometries
• Limitations: Limited part size and complexity, lower durability and repeatability compared to production molds, potential dimensional deviation from the final part
• Applications: Functional testing, design validation, low-volume production runs

Prototype Insert Molding (PIM):

PIM leverages inserts made from materials like aluminum or beryllium copper, integrated into a standard production mold base. This offers faster lead times than full production molds while delivering closer quality to the final product.

• Materials: Aluminum, beryllium copper (for higher heat resistance), steel (for complex geometries)
• Lead Time: 4-6 weeks for simple designs, longer for intricate features
• Limitations: Can be more expensive than RIM, limited to mold base configurations, might still not be a replica of the final production part
• Applications: Functional testing, design verification, pilot production runs, pre-production validation

3D Printing for Injection Molding Patterns:

The 3D printing rapid prototype approach utilizes 3D-printed patterns to create sand molds for casting metal molds. It offers a relatively fast and affordable way to produce prototype molds, particularly for simpler geometries.

• Materials: 3D printing materials like ABS, SLA resins, SLS nylon (for better heat resistance)
• Lead Time: 1-2 weeks for simple designs, longer for complex geometries
• Limitations: Limited material options, lower mechanical strength, and heat resistance compared to metal molds, not ideal for complex geometries or high-precision parts
• Applications: Initial design verification, early testing, low-volume prototypes with simple shapes

In many cases, going straight from 3D printing to hard steel tooling makes sense when one considers the overall lead time of the project. One common exception is product designs that rely on technical assumptions that can only be validated by getting parts in the right polymer coming out of a mold.

Read more: We have created a guide to rapid tooling prototyping which discusses other options for rapid tooling.

Aluminum seldom makes sense if a mold is fabricated in China (which we cover later). Steel is the most common injection mold material, but choosing the right injection mold steel material is similar to selecting the foundation for a building: it dictates the mold's durability, performance, and ultimately, the quality of your parts. As engineers, we understand the critical nature of this decision.

Let's delve into the three most common types of hard steel and pre-hardened steel utilized in injection molding:

Hard Steels:

1. / / H13: This trio offers a workhorse option. After hardening, they achieve a Rockwell C hardness of 49-53 HRC, making them suitable for ordinary hardening molds. Their versatility allows for applications across various projects.

ESR: This steel takes the performance of the previous group a notch higher. It boasts the same hardness range (49-53 HRC) after hardening but excels in applications demanding both durability and a highly polished finish.

S136 / S136SUP / : Don't be fooled by the 'steel steel' reference ' these are actually high-performance stainless steels. Their strength lies in corrosion resistance, making them ideal for molds processing materials like POM and PVC, which can be corrosive to standard steels. Additionally, they hold their own when it comes to achieving a polished finish.

Lifespan: Mold tooling made from hard steels like 1.#, #, and # will usually last for around 300k-500K shots, but can reach 1 Million if the mold structure is simple.

Pre-Hardened Steels:

S50C / S55C: These steels offer a cost-effective option for mold bases, providing adequate strength and machinability. However, their lower hardness limits their suitability for high-wear applications.

718 / 718H: Renowned for their toughness and ability to achieve a good surface finish with standard polishing techniques, 718 and 718H are popular choices for mold cavities and inserts. Their well-rounded properties make them a versatile option for various applications.

738 / 738H: Offering superior rigidity compared to 718 grades, 738 and 738H excel in core and insert applications. While their polishing capabilities are considered 'ordinary,' their rigidity often outweighs this limitation for specific applications.

A Note on P20: It's important to clarify the perception of P20 steel in China. While technically encompassing a series that might include materials like 718 or 738, the term 'P20' in China often refers to a lower-grade steel with potentially less desirable properties compared to the 718/738 series.

NAK80 / XPM: The champion of pre-hardened steels, NAK80 boasts a hardness of 37-43 HRC. This, coupled with its excellent polishing capabilities, makes it the go-to choice for molds requiring high-precision parts from materials like PC, PA+GF, and PC+GF.

Remember, this is just a starting point. Selecting the optimal steel grade requires careful consideration of factors like part complexity, plastic-type, production volume, and budget. Consulting with experienced mold makers and material suppliers is crucial to ensure you make the best choice for your specific project.

Lifespan: For pre-hardened materials the mold life is usually 100K-300K shots.
In particular:

• 278#; 718#; p20#: 100k-200K;
• NAK80; XPM: 200-300K

Watch these videos on how to test steel's properties which may help you to select the types you require.

When we talk about tonnage or the term 'tonne' in the injection molding process, it means the injection molding press machine capacity regarding the clamping force it can exert. It has nothing to do with the weight of the machine.

So, if you encounter a statement like 'this mold requires a 120 Tonne machine,' it essentially means that the mold needs a press capable of exerting a minimum clamping force of 120 tonnes (metric tons, specifically) to hold the mold halves tightly shut during the injection molding process. This force ensures:

• Proper mold closure: Prevents molten plastic from leaking out under high pressure (known as flash).
• Dimensional accuracy: Maintains the mold cavity shape for precise part formation.
• High-quality parts: Minimizes warpage and other defects caused by insufficient clamping force.

It's important to understand that injection molding machine capacity isn't the only factor to consider when choosing a plastic injection molding press. Here are some additional key parameters:

• Shot size: The volume of molten plastic the machine can inject into the mold. This needs to be compatible with the part size and material selection.
• Injection pressure: The pressure applied to force the molten plastic into the mold cavity.
• Clamping stroke: The maximum distance the mold halves can travel during opening and closing. The size of the injected parts needs to be removed between the two halves of the mold when it is open.
• Platen size: The dimensions of the movable and stationary platens that hold the mold.

You may also like to read: How To Check The First Production From A New Plastic Injection Mold?

The allure of speed and affordability often leads to the question of soft tooling, particularly aluminum molds. While this approach might seem appealing at first glance, let's delve deeper to understand why, in many cases, hard steel molds remain the preferred choice for the average plastic injection molding process:

Cost Considerations in China

In China, the cost differential between hard steel and aluminum molds is often surprisingly minimal. This eliminates the initial cost advantage that aluminum might seem to offer elsewhere.

Automated Process

Modern injection molding facilities leverage automation extensively.  While machining hard steel does take slightly longer due to its inherent hardness, the difference is typically measured in days, not weeks. This automation advantage significantly diminishes the time-saving argument for soft tooling.

Durability and Production Efficiency

Aluminum molds, by their nature, are less durable than their hard steel counterparts. This translates to shorter lifespans, more frequent replacements, and ultimately, higher overall costs, especially for high-volume production runs. Hard steel molds provide significantly more cycles, maximizing production efficiency and minimizing downtime for mold changes.

Part Quality and Precision

Soft tools can struggle to maintain the same level of dimensional accuracy and surface finish as hard steel molds over extended use. This can lead to part quality issues, increased scrap rates, and the need for additional finishing steps. Hard steel molds ensure consistent part quality throughout their lifespan, minimizing rework and maximizing yield.

Our Experience

We've been approached about soft tooling in the past, and after careful analysis, we've consistently concluded that hard steel molds offer the best overall value. Their durability, efficiency, and ability to deliver superior part quality make them the smarter long-term investment, even when considering the slightly longer machining times.

The Takeaway about Aluminum Molds

In China, the combination of readily available steel, efficient machining practices, and economies of scale often shrink the cost gap between hard steel and aluminum molds.  When you factor in the superior durability, longer lifespan, and higher production efficiency of hard steel molds, they often become the more cost-effective choice in the long run, even for initial production runs.

The world around us is shaped by injection molding, a technology that transforms concepts into tangible realities. This guide has hopefully answered some of your key plastic injection molding questions and equipped you with the knowledge to use this intricate process with confidence.

We've covered critical factors like material selection, steel options, runner systems, and gate design, allowing you to optimize production efficiency and achieve superior part quality.  We've also explored important considerations often overlooked, such as quality control and environmental impact.

But the journey doesn't end here.  Our expertise extends far beyond this guide. 

Ready to transform your innovative ideas into real-world products?

First, delve into how Sofeast can help organize and look after your mold tooling in China: Tooling management for plastic injection molds in China.

Second, get help from our China-based injection molding subsidiary to design and fabricate your tooling and produce your injection molded parts in China.

Third, contact us today! Our team of injection molding specialists in China is here to answer your questions, discuss your project requirements, and help you leverage the immense potential of injection molding to achieve manufacturing success.  Together, we can turn your vision into reality.

The short answer is no, we can't provide custom film color matches. We do offer nearly 30 different standard colors of film, in both HDPE and LDPE, so most customers can find a color that works for their bags.

We do not provide custom film matches due to the complexity of color matching. Colored films are made by adding color concentrate (in pellet form) to white or natural resins. All our color concentrates are supplied to us ready to add to the resin. Mixing these concentrates may seem like a simple solution for making custom colors, but formulating the right mix is very time consuming and involves a lot of trial and error - and waste. Custom colors also create issues with reorders, even when we know the formula. From time to time dye-lots change, and even a slight change when mixing colors based on a formula can throw off the color of the match. 

Visit our Film Colors page to see all the colors we offer, downlonad our line card (PDF), or contact us to request film color samples. 

Bags measurements are expressed as the entire width x height (9x12, 15x18, etc) of the flattened bag. If bag has side gussets, the measurement is written as Width x Gusset x Height (12x7x22 is a standard T-shirt bag). If bag has a bottom gusset, the measurement is written as Width x Height + Gusset Width (15x18+4"BG for instance).

If you want to learn more, please visit our website plastic bag production machine.

It's important to understand that bags with side gussets always have a bottom seal, and bags with bottom gussets will have a side seal. 

Bottom Seal bags are sealed between 1/4" and 1/2" from the very bottom of the bag, while side sealed bags are sealed at the very side edges. 

The height of the bag is measured from the very bottom of bag to the very top, except for Soft Loop Handle bags where the handle is attached and not included in the height measurement. 

ALL DIMENSIONS ARE APPROXIMATE.

If your bag needs to hold a specific sized item, please let us know so that we can make sure the bag is sized correctly

TOLERANCES

• All Dimensions are approximate. Length and width of bag vary within 1/2" ±. Larger bags can vary by as much as 1"
• Gauge (mil) can vary by up to 10% ± from order to order and/or within the same order.
• Film and Ink colors may vary from order to order and/or within the same order.
• For multiple color prints, ideal trapping is 1/16" or greater. Image will shift slightly from bag to bag. 
• Two sided print alignment can vary by up to 1" front to back.
• Artwork with screens will be printed at 35 LPI. Uneven ink coverage may result due to dot gain. 
• Colors on proofs are approximate and may not display accurately on monitors or desktop printers. Inks are matched to Pantone PMS colors. 

Overruns and underruns are one of the most misunderstood part of the manufacturing process. It's tempting to look at it similarly to printing copies on your desktop printer. If you need 200 copies, you print 200 copies. Manufacturing isn't quite as simple, and adds some unknowns into the equation. 

In a manufacturing environment, overruns and underruns are quite common. There are three main steps in making bags - blowing the film, printing the film, and converting it into individual bags. All three of those steps require setup which creates waste. For instance, to produce 20,000 bags, we need to have enough printed film to cut those bags, plus some extra to set up the job, and in case of misprints that are discarded at this step. So we need to print quite a few more than 20,000 impressions. To print enough film for any given job, we need extra blank film in order to set up the printing press. So we need to blow enough extra film to account for printing setup, converting setup, and possible misprints. The raw material for the film is in pellets of plastic resin that are weighed out in an amount that is approximately enough to make enough bags, plus a little bit. Extruding the film can also result in small variances in bag width and thickness, which also affects overruns. 

So making an exact number of bags is nearly impossible, and the over/under run percentage is not predictable. 

Information about our overrun policy is on our terms and conditions page. https://www.apmbags.com/terms-and-conditions

American Plastic takes pride in being able to offer minimums as low as 3,000 bags, but depending on the specs of the bag, that minimum can end up being as high as 20,000.  The reasons for this mainly have to do with setup times, labor, and waste. 

Setup for all jobs takes about the same amount of time, regardless of the size of the bag. There are three basic steps involved in making bags: extruding film, printing, and converting individual bags. 

Extruding Film - This involves loading an extruder with raw resin, melting it, and blowing it into a tube of the specified width and thickness. Before being wound on a roller, the blown film needs to be threaded through a set of rollers, and adjustments made to width and gauge of the film. This process is the same no matter how much material we are making. So for smaller orders, the percentage of setup time compared to the whole run is much higher. On larger runs, the setup time is a very small percentage of the time it takes to run a job.

Printing - Printing setup is also time consuming, and that multiples for each ink color added. Many one color jobs can be printed inline, as the film comes off the extruder, but for bags printed offline, or with more than one color, the film is transferred to a separate printing press. Each color requires its own printing plate, attached to a printing cylinder. Usually workers need to change out the print cylinders to match the bag size being made. The only way to register multiple colors so that they line up correctly is to print some film and make final adjustments as it runs through the press. Running a six color job can require hours of setup time, which makes smaller runs very impractical. 

Converting - The final step in making bags is moving the printed (or unprinted) film to a machine that cuts, seals, and stacks the bags. There is setup time required to wind the film through the converter, adjust digital print sensors, and ensure seals line up properly. 

General rules of thumb on minium orders: 

• Total weight needs to be at least 100 lbs to justify the setup processes involved.
• Printing multiple colors will increase minimums
• Larger, thicker bags have lower minimums than small, thin bags

Because of the complexity of the manufacturing process, we may refuse to quote some jobs if we are unable to offer a competitive price. 

If unsure of the size of bag you need, feel free to contact us for help.

To calculate the size of bag needed, start by measuring the items going into the bag.

Here's some basic math: 

• Bags can have gussets either in the side or bottom, but not both.
• For a bag without side gussets, the circumference twice the width. A 12" wide bag has a 24" circumference. (12+12)
• Bags WITH side gussets have a circumference twice the width, plus twice the gusset. A 12" wide bag with 7" gussets has a 38" circumference. (12+12+7+7)

The circumference of the bag should be larger than the circumference of the items going in the bag.  This is generally only a concern when there is a specific size object needing to be bagged. 

A box that is 9" long and 6" wide has a circumference of 30". (9+9+6+6=30). Half of 30 is 15, so a 15" wide bag would fit perfectly, but best to get a slightly larger bag, around 16", to make sure the item fits. This same box would fit in a side gusseted bag, like a 10x6x22 (10+10+6+6 = 32" circumference) 

Bottom gussets in bags will help the bag sit flat when expanded, but do not increase the circumference of the bag. for that same 9x6 box, a 16" wide bag with a bottom gusset of 6" will hold the boxes nicely. 

Yes, we are happy to provide individual samples of our products.

However, because everything we make is a custom job, and that we offer a large variety of sizes, film colors, bag styles, and thicknesses, we only provide samples for specific orders.

Distributors often ask for "sample packs" containing general samples of all styles in different sizes, colors, and mils, but those are simply not practical for us to assemble, since what would be included would be a limited selection of what we can make. Our line card and website shows all the different handle sizes and film colors offered. Film swatch books that contain all of our film color options are also available to distributors. 

It may seem counterintuitive, but of all options for retail checkout bags, traditional HDPE and LDPE plastic bags come out on top. 

Plastic bags are 100% recyclable and most people reuse checkout bags for a wide number of things. From garbage bags for small trash cans, to picking up pet waste, using as travel laundry bags, or even reusing when shopping.  Studies show that "green" alternatives such as paper bags and popular reusable bag options, can actually be worse for the environment because they require more resources to produce and transport. These replacements simply have a larger carbon footprint when the entire product lifecycle is considered. Studies also show that bag bans and taxes haven't meaningfully reduced overall litter or waste anywhere they've been tried. 

Every bag ordinance allows for, or even encourages, paper bag usage. But compared to plastic bags, paper can't compete environmentally. Making plastic bags requires 70% less energy and 96% less water than paper, and creates far less air pollution. Most store-bought "reusable" bags are made in other countries and shipped across the world to the US, while the vast majority of plastic checkout bags are made domestically. And those imported reusable bags may not be recyclable. Cotton bags would need to be used for over 7 years before they become a better choice than plastic. Cotton bag manufacture is also a very intense process, that involves vast amounts of water to grow and process the cotton, and potentially dangerous fertilizers and pesticides.  

The most talked about impact of plastic bags is litter, especially in marine environments. Obviously, this is a large problem, but it isn't likely to be solved by bans and restrictions on plastic bags. Studies have shown that bag restrictions have not resulted in any waste or litter reduction.  As a matter of fact, due to the heavier materials used in paper and reusable bags, landfill waste has increased. Without the availability of lightweight carryout bags, people instead purchase new, packaged bags for garbage, pet waste, and other uses. And reusable bags simply can't hold up to the usage required to be a better choice. 

Simply put, bans and restrictions on plastic carryout bags result in higher levels carbon entering the atmosphere, more waste going to landfills, and have no impact on litter. 

If you need bags in areas that have restrictions, our reusable bag options can be made to specifications that meet the requirements of most ordinances

For more detailed information about the impact of bag regulations, and links to studies, please visit the Bag the Ban website 

Vector images are shapes and lines drawn in an illustration program (like Adobe Illustrator or CorelDraw) that have mathematical dimensions. This allows unlimited scalability without compromising the image quality. Images have smooth edges at all sizes, and file sizes much smaller than bitmap (raster) images. Common vector formats are PDF, Adobe Illustrator - AI, EPS, and Corel Draw (CDR).  

While vector files are always saved in these formats, they can contain bitmap images as well. Saving a JPG image as AI or EPS or PDF does not change the image to vector. 

Bitmap images are made up of a series of individually defined pixels and have a fixed resolution. A 1' x 1' bitmap, at 300dpi, is 300 pixels wide and 300 high. Bitmap images CAN'T be made larger without losing quality. For printing, the higher the resolution of bitmap files, the better the image quality. Common bitmap formats are TIFF, JPG, GIF, PNG, BMP.

Why Vector? 

• Vector art provides much smoother lines and edges to the art. Most bitmap images have smoothing (anti-aliasing) on the edges of the art (a slight gradient around curves to make them look smoother.)  
• All gradients are printed at 35 lpi, which when applied to shapes with smoothing, will result in blurred/jagged edges.  

Both digital bitmap images and printed images are made up of a series of dots. The terms DPI and PPI are usually confused these days. 

• DPI ' Dots Per Inch 'the resolution of a printed image, how many tiny dots of ink printed per inch. The more dots, the finer the print. 
• PPI ' Pixels Per Inch ' Most times when people refer to DPI, they really mean PPI.  Simply the number of pixels per inch (vertically and horizontally) in a digital image
• LPI ' Lines Per Inch ' refers to the lines of in a halftone or screen - the higher the number, the smaller the screen. These dots are not the same as those defined by in DPI. 

DPI and PPI when referring to a digital image are fairly meaningless without knowing how many inches an image is. The image resolution is determined by the number of pixels in an image. An image that is 10" wide at 300dpi is pixels wide, could also be defined as 100" at 30dpi, or 1" at dpi. 

In printing, DPI is the number of dots of ink per inch, and is generally a higher number than the image PPI, and the PPI is a higher number than the LPI.

For most commercial printing applications, digital images need to be a minimum of 300 PPI at full size. If there are image areas that will be printed as halftones (not a solid color), the LPI indicates the number of lines of dots per inch. For many print applications, LPI is approximately half the number of the PPI. For the process that we use for plastic bags 35 is the maximum LPI that prints well. This produces fairly large dots compared to offset printing. As an example, most newspapers print images at around 80 LPI, and most magazines at around 150 lpi or higher.  

Below is an image of 50% gray approximating the difference between 35, 80, and 150 LPI

A font is a collection of letter defined as a specific typeface. The font file contains mathematical descriptions of the shape of each letter. Fonts can only be edited on computers where the font file is installed. PDF files can have embedded fonts, which will display and print properly, but cannot be edited by computers that don't have the font file installed. When opening the document on a machine that doesn't have the proper font installed, programs usually substitute another font. Obviously, this can cause problems. Converting fonts to outlines disconnects the font descriptions from the letters, and prevents the shape from changing. The downside of this is that once the type is converted to outlines, it can no longer be edited as text.

To convert text to outlines, an illustration program like Adobe Illustrator or CorelDraw is required. Adobe InDesign is also capable of converting type to outlines. In Illustrator or InDesign, chose 'create outlines' from the Type menu. In CorelDraw, select 'Convert to Curves' from the Arrange menu. 

Plastic bags are printed using a process called flexography, which uses a flexible relief plate to make imprints. Each color of the print job requires its own plate. We can print a total of up to six colors, combined between both sides of the bag. 6 colors on one side, or 3 colors on each side. 

Flexographic plates can usually be used for many years without any degradation. However, after long use, the plate surface can develop cracks which will affect print quality. When plates do develop cracks, we recommend replacing the plates. When ordering plates through us, we will replace any cracked plates free of charge. 

Our manufacturing process is fairly simple. Film is extruded by heating small resin pellets and blowing the film into a tube, which is then wound onto a large roll. The roll of film is then wound through rollers on the press where it is printed, and then rolled up again as it comes off the machine. The next step is converting the film into bags. Different converting machines make different types of bags. 

Yes, if you prefer to provide your own printing plates, we can usually use them with no problem. However, we highly recommend having your plates made through us. This streamlines the production process and creates far fewer headaches for you and your customers. Using third party plate makers can result in delays, and cost savings are usually minimal. Especially if plates are made to incorrect specifications, contain errors, or become unusable due to cracking.   

Advantages to having us make your plates :

• TIME SAVINGS ' Our local plate maker delivers daily, and turnaround is usually overnight. Customer provided plates can spend several days in shipping, and if plates arrive damaged, or incorrect, more delays can occur. 
• PLATE PREPARATION ' Plates are attached to printing cylinders with double sided sticky-back tape. The cost for tape and labor is included in our plate cost. If plates arrive without sticky-back tape,  there will be an additional charge for adding it to the plates. 
• GUARANTEE ' Plates made through us are guaranteed to match the art. Customer provided plates are used as-is, and while we will compare to your art, we are not responsible for plate quality or replacement if there are problems.
• DAMAGE REPLACEMENT ' Over time, plates wear out and crack, requiring replacement for future orders. If made through us, there is no charge for replacement. For customer provided plates, the customer bears costs for plate replacement.
• QUALITY ' Our art department makes sure that all art files sent to the plate maker are correctly formatted. Incorrect art files can result in text shifts, fonts changing, incorrect line screens, and trapping issues.

TO PROVIDE YOUR OWN PLATES

Plates must match the specifications listed below. If plates are made differently, we may still be able to use them, but cannot guarantee they will work on our presses.

• 3M Cyrel .107 plate media
• Backed with  3M 411DL sticky-back tape
• Between .050 and .060 relief
• 1" dead space around perimeter of image area
• Any raised crop marks (tick marks) must be removed
• Etched center scribe lines
• Beveled edges
• Halftones printed at 35 LPI
• Provide an art proof (PDF) showing proper art positioning on bag

PLATES WILL BE USED AS RECEIVED

Customer bears responsibility for making sure plates are made correctly. American Plastic assumes no responsibility for print quality due to plate abnormalities, damage, or errors. Additional charges will apply if plates require backing or other adjustments.

Digital proof showing art position on bag MUST be submitted.

COMMON PROBLEMS WITH PLATES 

Improperly made plates can result in poor print quality or incur extra charges. Here's some common issues to be aware of.

• Plates made from bitmapped images ' may result in jagged edges on art.
• Plates made to incorrect specifications ' may result in poor print quality, or may be unusable
• Plates made with inadequate trapping ' may result in poor image quality 
• Crop marks not trimmed off of plates '  marks will print on bag. Additional charges will apply to remove crop marks.
• Double sided backing not attached ' Backing has to be added. Additional charges will apply
• Registration marks not included ' Multiple color jobs must have centerlines on plates to avoide additional setup charges. 

Halftone screens help to achieve the look of a lighter shade, or shades, of whatever color ink is being printed. However, there are some limitations of printing art like this. 

We print halftones at 35 LPI (lines per inch), which is the maximum LPI that prints well. This produces fairly large dots compared to offset printing. As an example, most newspapers print images at around 80 LPI, and most magazines at around 150 lpi or higher

See images below for samples of how screens look when printed. 

SCREEN AT DIFFERENT TINTS

Because of the large size of the dots used, we do not recommend printing small text or thin lines as screens. 

TEXT at 50% tint, 35 LPI

LINES - 1pt, 2pt, and 4pt - at 50% tint, 35 LPI

When using screens in your designs, it is best to use them for larger, solid areas. Screens also will look better on larger art. Just as the 4pt line above looks much cleaner than the 1pt line. 

Yes. Printing plates can generally be reused many times. It's not uncommon for plates to last for ten years or longer, and through millions of impressions. 

If the time between orders using a set of plates is longer than about 4 years, we archive the plates. After ten years past the last order date, plates are disposed of. 

We recommend ordering plates through us, although we can usually use plates made elsewhere. There are lots of advantages to order plates through us, as explained in our post about providing your own plates. Flexographic printing plates can get expensive, but will usually last for years. Eventually, plates will begin to develop cracks. If the plate was purchased through American Plastic, the replacement plate will be made at no charge. 

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