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Composition of Paper
Paper is a manufactured material composed primarily of cellulose fibers derived from plants, processed with additives such as fillers, sizing agents, and colorants to achieve desired physical and aesthetic properties.
Raw Materials
The primary raw materials used in paper production include straw, bamboo, wood, cotton, linen, and recycled waste paper. These sources provide the essential plant fibers that form the structural basis of paper. The choice of raw material significantly influences the final characteristics of the paper, including strength, texture, and durability. In addition to fibers, chemical components such as fillers, sizing agents, and colorants are incorporated during manufacturing to modify specific attributes.
Fillers
Fillers are added to enhance paper flexibility, reduce transparency and elasticity, and produce a smooth, uniform surface. Common examples include talc for standard printing papers, and kaolin or barium sulfate for higher-grade papers. The filler content should be carefully controlled-typically constituting approximately 20% of the total composition. Excessive use may compromise paper strength and flexibility, impair ink absorption, and lead to issues such as powdering during the printing process.
Sizing Agents
Sizing agents serve to seal microscopic pores within the paper structure, thereby improving water resistance, surface gloss, and mechanical strength. They also help prevent surface linting or fuzzing. Widely used sizing agents include rosin, alum, and starch.
Colorants
Colorants are employed to adjust or enhance the visual appearance and whiteness of paper. Both inorganic pigments and organic dyes are commonly utilized depending on the required hue and stability.
Paper Formats
Paper can be categorized into two main types based on application: sheet-fed paper and web (roll) paper. Sheet-fed paper is typically used in conventional printing presses for products such as books and photo albums, while web paper is designed for high-speed rotary printing machines, particularly in newspaper production.
Paper Size Standards (K Format)
"K" denotes a standard unit for measuring paper size, widely used in the printing and advertising industries. It refers to the number of times a full-size base sheet is divided. For example, 16K indicates that one full sheet is divided into 16 equal parts; each part is referred to as 16K. Similarly, 8K means the base sheet is divided into eight equal portions.
Common Paper Sizes:
Full-Size Basis A (Magnanimity Standard): 889 × 1194 mm
- Full Sheet (1K): 840 × 1140 mm
- Double Size (2K): 570 × 840 mm
- 4K: 420 × 570 mm
- 8K: 285 × 420 mm
- 16K: 210 × 285 mm
- 32K: 143 × 210 mm
Full-Size Basis B ("Zhengdu" Standard): 787 × 1092 mm
- Full Sheet (1K): 740 × 1040 mm
- Double Size (2K): 520 × 740 mm
- 4K: 370 × 520 mm
- 8K: 260 × 370 mm
- 16K: 185 × 260 mm
- 32K: 130 × 185 mm
Paper Grammage
In addition to the distinction between coated and uncoated paper, grammage (measured in grams per square meter, g/m²) is a critical parameter indicating paper thickness and weight. Labels such as "80g" or "157g" denote the mass of one square meter of paper. Higher grammage corresponds to thicker, more rigid paper, while lower values indicate thinner sheets.
Offset Paper
Offset paper, an uncoated type, is commonly used for text-heavy or monochrome printing applications:
- 70g and 80g: Suitable for general-purpose documents, instruction manuals, and book interiors.
- 100g: Ideal for higher-quality manuals, premium book pages, and envelopes.
- 110g and 120g: Frequently used for file folders and envelopes.
- 140g: Rarely used due to its proximity to the upper limit of offset paper usability; occasionally applied for specialized envelopes and folders.
Note: Kraft paper, often appearing in earthy tones, shares similar cost and print characteristics with standard offset paper and is typically printed in single-color formats (e.g., red or blue). It is included here for comparative reference.
Coated Paper
Coated paper is predominantly used in color printing applications such as magazines, posters, brochures, and folding leaflets, offering superior image reproduction and surface finish. It is broadly classified into two categories:
- Glossy Coated Paper: Features a smooth, reflective surface ideal for fashion, technology, and high-impact visual media.
- Matte Coated Paper (also known as dull or silk finish): Exhibits a textured surface with minimal reflectivity, producing diffuse light scattering that conveys a sophisticated, premium appearance. Preferred by corporate brands and high-end publishers.
Common Grammages and Applications:
- 105g and 128g: Minimum recommended weights for double-sided four-color printing. Thinner stocks may result in show-through and poor opacity. Typically used for magazine inserts and low-cost promotional materials.
- 157g: The most widely adopted weight for commercial single-sheet printing, including flyers, brochures, album pages, and posters. Essential knowledge for industry professionals.
- 200g and 250g: Higher-cost options favored by quality-conscious clients and large enterprises. Used for premium brochures, covers, cards, packaging, and presentation materials.
- 300g and 350g: Comparable in thickness and rigidity to cardstock; applications include album covers, business cards, invitations, and packaging. Usage is limited due to cost and functional overlap.
- 400g: Rarely used in practice; reserved for specialty items such as luxury invitations and rigid packaging. Often substituted with alternative materials like paperboard.
Note: Mastery of the differences between offset and coated papers-including key grammages such as 157g coated, 70g, and 80g offset-is essential and frequently assessed in professional interviews.
White Board Paper
White board paper is a coated cardboard with a smooth front surface, available in two variants:
- White Base White Board: Uniform white on both sides, suitable for full-color printing on either side.
- Gray Base White Board: Smooth white front with gray reverse; typically printed in full color on the front and single-color (often red) on the back.
Applications: Primarily used for packaging boxes in pharmaceuticals, food, and medical products, with pharmaceutical packaging being the most prevalent.
Cardstock
Cardstock is a single-sided, high-gloss coated paper produced by treating base papers of varying weights or white board paper. It offers superior flatness and luster compared to standard coated paper and is commonly used for high-end product labels, artisanal crafts, postcards, greeting cards, business cards, and invitations.
Classification: Market varieties include Dutch White and Super White cardstock, with "Super White" denoting enhanced brightness. While white cardstock is most common (especially for business cards), colored variants such as black, red, and others are also available.
Typical grammage ranges around 300g. Despite higher costs compared to equivalent-weight coated paper, cardstock is preferred for premium applications requiring greater stiffness and visual impact.
Corrugated Paper
Corrugated paperboard is constructed by fluting a central layer of paper and bonding it between two flat linerboards. This structure provides excellent strength-to-weight ratio, rigidity, elasticity, and shock absorption, making it ideal for protective packaging.
Applications:
- Three-layer corrugated board: Used for small appliances and consumer electronics; capable of full-color printing.
- Five-layer corrugated board: Designed for heavy-duty packaging of large appliances and industrial goods.
Specialty Papers
Specialty papers play a crucial role in modern printing, supporting creative differentiation and brand individuality. With the growth of the advertising and design sectors, materials such as tracing paper (sulfate paper), sand-textured paper, and patterned decorative papers are increasingly utilized. Due to the vast diversity of specialty papers, comprehensive coverage is impractical; therefore, hands-on examination of physical samples is recommended for accurate identification and application.
Selection Guidance: The appropriate specialty paper should be chosen based on client profile, design intent, and functional requirements.
Paper Measurement Units
- Ream: One ream consists of 500 sheets of full-size paper. Pricing and quotations are typically calculated per ream.
- Ton: The standard bulk purchasing unit for paper.
- Degree Calculation:
- For Magnanimity Standard: 1884 ÷ grammage = number of sheets per ton
- For Zhengdu Standard: 2320 ÷ grammage = number of sheets per ton
Conclusion
Understanding the technical specifications and appropriate applications of various paper types is fundamental for professionals in design, printing, and packaging. Mastery of these concepts enhances both project execution and client communication.
We welcome your input-please share additional paper types or insights for discussion.
