Sunday, 4 November 2012

OUGD504 // Design for print // Stock

Paper density (also known as basis weight and grammage) is a term used in the pulp and paper industry and also for fabric industry to denote a measure of mass of the product per unit of area for a type of fabric, paper or paperboard.
The term "density" is not used in its traditional sense of mass per unit volume. "Paper density", rather, is a measure of the area density. Paper products that let little or no light pass through (e.g. poster board) are considered dense or heavy. Paper products that allow some light to pass through (e.g. tissue paper) are considered lightweight. In the pulp and paper industry, it is common to set a commercial paper machine to produce paper to a target paper density. Paper density can also be used to distinguish paper from paperboard as the latter usually has a grammage greater than 134 g/m².
Two ways of expressing paper density are commonly used:
Expressed in grams per square meter (g/m²), paper density is also known as grammage. This is the measure used in most parts of the world.
Expressed in terms of the mass (expressed as weight) per number of sheets, it is known as basis weight. The convention used in the United States and a few other countries using US paper sizes is pounds of a ream of 500 (or in some cases 1000) sheets of a given (raw, still uncut) basis size. Japanese paper is expressed as the weight in kg of 1000 sheets.

In the metric system, the mass per unit area of all types of paper and paperboard is expressed in terms of grams per square meter (g/m²). This quantity is commonly called grammage in both English and French (ISO 536), though printers in most English-speaking countries still refer to the "weight" of paper.
Typical office paper has 80 g/m², therefore a typical A4 sheet (1⁄16 m²) weighs 5 g.
The unofficial unit symbol "gsm" instead of the standard "g/m²" is also widely encountered in English speaking countries.
While paper is measured by weight, card is measured by thickness in micrometres.[citation needed]
Typically grammage is measured in paper mill on-line by Quality Control System (QCS) and verified by laboratory measurement.

Basis Weight
In countries that use United States paper sizes, a less direct measure known as basis weight is used in addition to or instead of grammage. The basis weight of paper is the density of paper expressed in terms of the mass of a ream of given dimensions and a sheet count. In the US system, the weight is specified in avoirdupois pounds and the sheet count of a paper ream is usually 500 sheets. However, the mass specified is not the mass of the ream that is sold to the customer. Instead, it is the mass of the uncut "basis ream" in which the sheets have some larger size. Often, this is a size used during the manufacturing process before the paper was cut to the dimensions in which it is sold. So, to compute the mass per area, one must know
the mass of the basis ream,
the number of sheets in that ream, and
the dimensions of an "uncut" sheet in that ream.
The standard dimensions and sheet count of a ream vary according to the type of paper. These "uncut" basis sizes are not normally labelled on the product, are not formally standardized, and therefore have to be guessed or inferred somehow from trading practice. Historically, this convention is the product of pragmatic considerations such as the size of a sheet mold.
By using the same basis sheet size for the same type of paper, consumers can easily compare papers of differing brands. Twenty pound bond paper is always lighter and thinner than 32 pound bond, no matter what its cut size. And 20 pound bond letter size and 20 pound bond legal size papers are the same weight paper having different cut size.
However, a sheet of common copy paper that has a basis weight of 20 pounds (9.1 kg) does not have the same mass as the same size sheet of coarse paper (newsprint). In the former case, the standard ream is 500 sheets of 17-by-22-inch (432 by 559 mm) paper, and in the latter, 500 sheets of 24-by-36-inch (610 by 914 mm) paper. Here are some basic ream sizes for various types of paper. Units are inches except where noted.

Paper type - Paper size - Number of sheets
Bond, writing, ledge - 17 × 22 - 500 sheets
Manuscript cover - 18× 31- 500 sheets
Blotting - 19× 24 - 500 sheets
Box cover - 20 × 24 - 500 sheets
Cover - 20× 26 - 500 or 1000 sheets
Bristol and tag - 22½× 28½ - 500 sheets
Tissue - 24× 36 - 480 sheets
Newsprint - 24 × 36 - 500 sheets
Hanging, waxing, bag, etc. - 24× 36 - 500 sheets
Book, Text, Offset - 25× 38 - 500 sheets
Index bristol - 25½× 30½ - 500 sheets
Paperboard (all types) - 12× 12 - 1000 sheets (1,000 square feet per ream)

Paper thickness, or caliper, is a common measurement specified and required for certain printing applications. Since a paper's density is typically not directly known or specified, the thickness of any sheet of paper cannot be calculated by any method. Instead, it is measured and specified separately as its caliper. However, paper thickness for most typical business papers might be similar across comparable brands. If thickness is not specified for a paper in question, it must be either measured or guessed based on a comparable paper's specification.
Caliper is usually measured in micrometres (1/1000 of a mm), or in the United States also in mils. (1 mil = 0.001 inch = 25.4 ┬Ám)
Typically grammage is measured in paper mill on-line by Quality Control System (QCS) and verified by laboratory measurement.

Paper (or ‘stock’ as printing geeks insist on calling it) takes many forms. So which type should you choose for your project?
Coated vs Uncoated
As the name suggests, coated paper has a coating, usually of china clay, which gives it a smooth finish. Coated papers are available in a gloss, silk (sometimes called satin) or matt finish and are used for projects requiring a fine finish, which is why coated paper is sometimes referred to as ‘art’ paper. Most of the leaflets you get through your letterbox, the glossy brochures you pick up from the travel agent and the fancy programmes you buy at concerts are printed onto coated paper.

Uncoated paper doesn’t have a coating and is therefore not as smooth as coated paper. You will use uncoated paper in your laser printer and photocopier. Premium quality uncoated papers are used for business stationery and are becoming increasingly popular for use in prestigious brochures and catalogues as an alternative to the more commonly used coated papers. Uncoated papers are available in a range of finishes:

Laid paper 
is a premium quality paper with a textured pattern of parallel lines, similar to hand made paper. Commonly used for business stationery.

Wove paper
is a premium quality paper with a uniform surface, not ribbed or textured like laid paper. Again, used mostly for business stationery.

Bond paper
is a term commonly used to describe economical uncoated wove papers. You will probably use bond paper in your photocopier and fax machine.

Paper Thickness
It is normal practice to specify the ‘thickness’ of paper by its weight in grams per square metre (GM or GSM). A low quality photocopier paper is usually around 80gsm; a good quality letterhead around 120gsm; a fast food menu around 130gsm, a flyer around 300gsm; and a business card around 400gsm.

As papers are graded by weight, one manufacturer’s 150gsm paper may seem slightly bulkier or thicker than a competitor’s product. Also uncoated papers tend to be bulkier than their coated counterparts, whilst matt and silk coated papers tend to be bulkier than their gloss coated counterparts. That said, a paper’s GSM rating is a good guide to how ‘thick’ or ‘stiff’ the paper will feel but always ask for paper samples if you’re unsure. Card (or ‘board’ as it is usually called in the industry) is sometimes measured in microns (a micron is 1000th of a millimetre).

Choosing paper - which paper works best for what
If you’re creating a full colour document featuring photographs or colourful illustrations, you’ll get the most vibrant colours if you opt for a coated paper. Whether you choose a gloss, silk or matt finish is mostly down to your personal preference, although gloss paper will produce the most vibrant colour reproduction. Some people think that gloss is classy, others consider it to be a bit tacky. Something to consider if your document is being printed conventionally is that silk and matt papers should normally be machine sealed (a sealant is applied to the printed image to avoid it being smudged). This may add to the cost of printing – check with your print contractor. Uncoated paper can be used for full colour projects but colours tend to be less vibrant and unless you use a low quality bond paper, it could end up costing considerably more than if you’d selected a coated stock.

Due to its glossly finish, you should avoid using coated papers if your document is designed to be written on. You’re probably best opting for an uncoated stock instead.

Letterheads, compliment slips etc are almost always printed onto uncoated paper – 100gsm is normal, 120gsm adds prestige. There are literally hundreds of different brands of paper to choose from and individual printing contractors will tend to stock and promote a handful of their favourite ranges. If you plan to overprint your stationery using a desktop printer, make sure the paper is inkjet and/or laser compatible. It’s also worth noting at this point that some printing and finishing processes are not inkjet/laser compatible. Ensure you double check before placing your order.

If you’re simply after something cheap and cheerful most people think that a low quality uncoated paper is going to be the most economical option. Not always the case! Printing companies tend to buy coated stock by the truck load and therefore get very good rates. If you’re after the lowest possible price, ask your printer to use his cheapest stock but ask to see a sample first to avoid any nasty surprises.

Finally, be aware that colour reproduction will differ depending upon the type of paper the ink is printed on. If you need accurate colour reproduction across a range of different documents, you may wish to use the same type of stock throughout. For instance, if your letterheads and compliment slips are printed onto an uncoated paper, you will probably want to choose an uncoated board for your business cards.

A paper which has received a special coating to give it a smooth gloss finish. It's meaning is often confused but it is more easily termed as a gloss coated paper.

Coated paper
A term used to describe plain paper which has received a special coating to give an enhanced surface for detail and colour reproduction.

Gloss coated paper
Gloss coated papers have a high shine and a very smooth surface, ideal for producing printed items for promotional work. The finish of the paper gives the ink a high degree of “lift”, giving vibrant colour and definition to printed images in particular. Ink dries well on gloss coated paper, making a seal varnish (to protect the ink from rubbing and marking) less likely to be needed.

Matt coated paper
Plain paper which has received a special coating to give a smooth, matt finish. Matt coated papers have no surface shine, and a slightly “toothy” feel, rougher than a gloss coated paper. The images will not have quite such a lift as when printing onto gloss coated paper, however, applying a gloss seal varnish can often improve this. In addition, printing inks do not dry and harden as well on matt coated stocks as on gloss, meaning that use of a seal varnish is recommended to prevent ink rubbing. However, seal varnish is relatively inexpensive.

Silk coated paper
Plain paper which has received a special coating to give a smooth, silk finish. Silk coated papers have a low surface shine, and are not as toothy feeling as matt coated papers, or as smooth a feel as gloss coated paper – a good compromise between matt and gloss coated paper. Again, inks do not dry or harden as well as on gloss coated papers, and the use of seal varnish is recommended.

Cast coated papers
This paper has a very high gloss finish achieved by using a special coating and the surface is then polished by stainless steel drying cylinders. It is often used for packaging requirements.

Uncoated paper
Plain paper which is not coated. Uncoated paper is typically rougher feeling than any of the coated stocks. This can be used as an effect when considering a print project. Ink lift is not as strong from uncoated papers as any of the coated ones which means images will not appear as defined as when they are printed onto a coated stock. Using uncoated stock is a good idea if you need to write onto the printed item you are producing (e.g. a form, business reply card etc). It is much easier to write on this type of paper.

Paper with a pattern of parallel lines at equal distances giving a ribbed effect.

A paper which shows an even texture rather than a parallel line pattern.

Watermarked paper
An impression is pressed into the top of the sheet on manufacture. This is normally used in high quality writing papers eg Conqueror. Clients can have their own watermark put into a sheet if required.

Carbonless - self copy paper
Paper specially coated to produce an image in black when pressure is applied. Used extensively in sets. There is a top, middle and bottom sheet with the coatings applied accordingly.

Matt uncoated boards in white or tinted ranging from 200 micron thickness to 750 micron.

Bank and bond
Bank paper is under 63g/m2. Both are essentially stationery papers supplied in a variety of colours with a matt uncoated finish.

Mechanical pulp print paper containing a small percentage of chemical wood pulp. Grammage 45 - 50 g/m2. Mechanical pulp is produced by grinding wood mechanically and is used in cheaper papers.

Recycled paper
New paper which is made entirely or in part from old paper

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