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10. (4) General Wrapping Paper Classification
Kraft Paper: This type of paper is characterized by its yellowish-brown color, robust texture, and high tensile strength. It is extensively utilized in commodity packaging, hardware products, automotive components, and other fields. Kraft paper is categorized into pressed and non-pressed varieties, with sulfate chemical wood pulp serving as the primary raw material. Currently, the main types available on the Chinese market include these two categories.
Chicken Skin Paper: This single-sided glossy paper comes in white, pink, or other light colors, resembling kraft paper in texture but slightly inferior in quality. Its grammage typically ranges from 40g to 50g/m².
Corrugated Paper: Widely applied in cartons, inner packaging, crafts, and other domains, corrugated paper features diverse flute patterns such as A, B, C, D, E, F, N, G, etc. Additionally, corrugated cardboard adheres to various standards concerning flute height and flute count, offering flexible solutions for different requirements. Corrugated paper also includes specifications like double-flute, triple-flute, quintuple-flute, and septuple-flute to meet varying packaging needs.
Yellow Paperboard: Primarily composed of rice and wheat straw, this type of file packaging paper is commonly used for making cardboard boxes and thin pads for goods.
Cellophane: Despite being referred to as "paper," cellophane is actually a type of adhesive film or membrane not produced by a paper machine. Its unique properties render it highly suitable for food and pharmaceutical packaging applications.
Rust-Proof Paper: Widely employed in industrial hardware, rust-proof paper incorporates anti-rusting coatings with varying compositions to satisfy diverse protective demands. Its grammage generally falls between 40g/m² and 80g/m².
Greaseproof Paper: Also known as fat-resistant paper, this category includes sulphate paper, translucent paper, and butter paper. Due to its excellent oil resistance, it is predominantly used for food packaging.
Food Wrapping Paper: A broad range of papers specifically designed for food packaging must comply with stringent hygiene standards, including limits on lead (Pb) and arsenic (As) content, decolorization tests, luminescent substance detection, and pathogen testing for Escherichia coli.
11. Paper Size and Specification
Paper sizes and specifications vary significantly depending on specific needs and application areas. Common sizes include A0, A1, A2, A3, A4, etc., which are widely utilized in office work, printing, packaging, and other fields. Special sizes, such as envelope and card dimensions, are often customized according to practical requirements. Understanding the required size and specification is crucial when purchasing or using paper to ensure it meets specific needs.
12. Common Paper Sizes and Specifications
Paper specifications can be divided into flat paper and web paper. Unless otherwise specified, references to paper size usually pertain to flat paper dimensions. These sizes adhere to certain standards but can also be custom-manufactured to meet individual or business-specific needs.
International paper sizes, also known as ISO paper sizes, are prevalent in countries utilizing the metric system. This standard is based on rectangles with a long-to-short side ratio of 1:1.414. Regardless of how the rectangle is divided, the ratio remains constant, and the area is halved after each division. ISO standard paper sizes are categorized into three series: A, B, and C.
A-Series Paper Sizes:
- A0: 840x1189mm
- A1: 594x840mm
- A4: 210x297mm
The largest A0 size has an area of 1 square meter. A-series paper is primarily used for general printed materials such as books and publications. Common letterhead paper is A4 size.
B-Series Paper Sizes:
- B0: 1000x1414mm
- B1: 707x1000mm
- B5: 176x250mm
B-series specifications are mainly used for advertising brochures and wall posters.
C-Series Paper Sizes:
- C0: 917x1297mm
- C1: 640x917mm
- C2: 456x640mm
C-series specifications are predominantly used for envelopes, greeting cards, and documents.
In China, two common paper sizes are 787x1092mm (positive size) and 889x1194mm (generous size). The selection of paper size is closely related to printing and packaging processes and must align with corresponding equipment. Paper specifications are mainly divided into roll and sheet types. Common web paper sizes in China include 635mm, 660mm, 787mm, 889mm, 1000mm, 1092mm, 1194mm, 1230mm, 1280mm, 1400mm, 1562mm, and 1575mm. In addition, millimeters (mm) and centimeters (cm) are commonly used size units in China, while inches (in) are more prevalent internationally. The conversion relationship is 1 mm = 25.4 inches.
13. Paper Cutting Orientation
When determining the direction of paper cutting, factors such as printing machine characteristics, intended paper use, and grain direction must be considered. Theoretically, calculations are performed using either long-side-to-long-side or long-side-to-short-side methods, selecting the scheme that maximizes cutting efficiency and minimizes waste.
The opening number, or paper format, is a critical indicator of paper size. Uncut flat base paper is referred to as full-size open. Under conditions ensuring no paper waste and convenient printing, binding, and production operations, full-size open paper is cut into smaller sheets of comparable area. The number of these smaller sheets constitutes the opening number, and their bound form is called a folio. For example, folding a whole piece of paper in half yields a folio or difolio. Folding folio paper in half again produces quarto paper, and so forth, resulting in octavo and sixteen formats. Dividing the entire paper into three pieces creates three-open paper, which can further be divided into six-open paper, leading to twelve-open formats.
It should be noted that the opening number is closely related to paper size. Practical applications require selecting appropriate opening numbers and sizes based on specific needs and equipment conditions.
14. Paper Measurement
During paper production, sales, and usage, accurate measurement and accounting are essential. Commonly used paper measurement units include grammage, ream weight, and roll weight.
Grammage refers to the weight of paper per square meter, an important indicator reflecting paper thickness and density. In the printing industry, grammage correlates with paper quality and price, influencing crispness, ink absorption, and printing effects.
Ream weight measures paper according to a standardized quantity (e.g., 500 sheets). In sales and accounting, ream weight serves as a unit for easy calculation and statistics.
Roll weight is suitable for mass production and bulk trading scenarios. In the paper and printing industries, rolled paper is typically measured by roll weight, aligning with mass production needs.
Understanding and correctly applying these paper measurement methods ensures the smooth progress of paper production, sales, and usage.
15. Units of Measurement
Grammage, as the fundamental index of paper, represents the weight per square meter, directly reflecting paper thickness and density. In the printing industry, grammage is closely tied to paper quality and price, with variations affecting crispness, ink absorption, and final printing outcomes.
Ling is a unique unit for flat paper measurement. One ream equals 500 sheets of flat paper with identical quantity and format. Note that imported paper reams may vary (e.g., 400, 480, 500, or 1000 sheets), requiring attention in international trade.
Additionally, the ton is a commonly used unit in paper measurement, expressed as T or KG, with 1T equaling 1000KG.
16. Flat Paper Calculation
Based on paper grammage, the weight of a single sheet or the number of sheets per ton can be calculated. For instance, consider a 250g white cardboard sheet measuring 787mm x 960mm. Its weight is calculated by multiplying the grammage (250) by the size factor (length x width): 0.787 x 0.96, yielding a sheet weight of 188.889 grams.
To calculate the number of sheets in 1 ton of paper: Convert 1 ton to kilograms (1000 kg). Using the sheet weight formula (grammage x size factor), divide 1000 kg by the sheet weight (188.889 grams), resulting in approximately 5,294 sheets per ton. Similar calculations apply to other sizes and grammages.
Weight (kg) = Grammage (g/m²) × Length (m) × Width (m) × Number of Sheets / 1000
This formula facilitates calculating the weight of any sized and grammed paper within 1 ton. Simply input the grammage, length, width, and required number of sheets to obtain quick results.
17. Physical Indicators of Paper
Quality assessment encompasses multiple physical properties of paper, including grammage, thickness, moisture content, pH, tensile strength, folding endurance, burst resistance, brightness, smoothness, roughness, and colorfastness. These indicators collectively form a comprehensive evaluation system for paper quality. Grammage refers to the weight per square meter in grams; thickness is typically measured in millimeters or micrometers. Moisture content significantly impacts paper performance. Tensile strength reflects the maximum tension limit in both transverse and longitudinal directions. Folding endurance and burst resistance evaluate paper durability under repeated folding and maximum pressure per unit area, respectively. Brightness and smoothness relate to optical properties and surface texture, while roughness describes surface irregularities. Colorfastness indicates color stability, measured over time.
Application Fields
The physical properties of paper hold significant value across various industries, particularly in printing and packaging, carton manufacturing, clothing, hardware, building materials, electrical appliances, electronics, and food packaging. Each industry relies on specific paper properties to ensure product quality, durability, and functionality.
