How Soft Pack Facial Tissue Fiber Ratios Impact Softness and Wet-strength
The production of soft pack facial tissue within the hygiene industry is an intricate process from a technical standpoint. Being an engineer working in the manufacturing plant, one often faces the question, “Can we make it softer but not weak?” Such is the challenge faced by engineers in terms of balancing softness and strength.
For consumers, a tissue may be regarded as just another product. For engineers, it is a complicated web of fibers, where the interaction between long (softwood) and short (hardwood) fibers will decide its fate in the market. Whether you are manufacturing a 2-ply or a 3-ply facial tissue, fiber furnish will prove to be the best weapon you can have.
Understanding the “Skeleton and Skin”: Long Fiber vs. Short Fiber
The foundation of any tissue product lies in its “furnish”—the specific blend of wood pulps. We categorize these into two primary functional groups:
The Long Fiber “Skeleton” (Softwood Kraft Pulp)
Derived from coniferous trees like pine or spruce, softwood fibers typically measure between 2.5 and 3.5 mm. In the papermaking process, these fibers act as the structural framework. Their length allows for extensive hydrogen bonding and physical entanglement. Without a sufficient “skeleton” of long fibers, the tissue web would lack the tensile strength necessary to survive the high-speed converting lines of a soft pack facial tissue plant.
The Short Fiber “Skin” (Hardwood Kraft Pulp)
Hardwood fibers, often sourced from Eucalyptus or Birch, are significantly shorter, ranging from 0.8 to 1.2 mm. These fibers are the secret to “hand-feel.” Because they are finer and more numerous per gram of pulp, they provide a smooth, velvety surface. They act as the “skin” or “filler,” populating the gaps between the long-fiber network to increase opacity and bulk.
Optimizing the Build: 2 Ply vs. 3 Ply Facial Tissue
From an engineering perspective, the number of plies isn’t just about thickness—it changes the physics of the sheet.
Strategies for 2 Ply Facial Tissue
In a 2-ply facial tissue, each individual layer must carry a significant load. Because there are only two layers of defense against tearing, we often have to increase the long-fiber content to roughly 30%–35%.
However, longer fibers usually mean more “stiffness.” To counteract this, we utilize mechanical creping. By adjusting the doctor blade angle on the Yankee Dryer, we can micro-fold the long fibers, breaking some of their rigid bonds to introduce “bulk” and “stretch.” This ensures the 2-ply facial tissue remains strong enough for a heavy sneeze but soft enough for sensitive skin.
Maximizing Performance in 3 Ply Facial Tissue
The 3-ply facial tissue is where we can truly push the boundaries of softness. Since the structural integrity is distributed across three layers, we can lower the long-fiber content in the outer layers to as little as 15%–20%.
A common “pro-tip” in the industry is stratified headbox technology. We can engineer the sheet so that the two outer plies are predominantly short-fiber (for maximum softness), while the center ply is reinforced with long-fiber and wet-strength resins. This “sandwich” effect creates a product that feels like silk but performs like a heavy-duty wiper.
The Technical Impact on Key Performance Metrics
Achieving Elite Softness
Softness is measured in two ways: Surface Softness (the friction felt by the skin) and Bulk Softness (how easily the tissue crumples in the hand).
- To maximize surface softness, we prioritize Eucalyptus hardwood pulp, which has a naturally low coarseness.
- To maximize bulk softness, we minimize the “Refining” (beating) of the fibers. While refining increases strength, it flattens the fibers and makes the tissue feel like parchment paper. For soft pack facial tissue, less refining is almost always better.
Mastering Wet-Strength
The ability to withstand moisture is vital for tissues that are to be used in a moist environment. This can be accomplished through the use of chemicals such as Polyamide-Epichlorohydrin (PAE).
The engineering challenge is that long fibers provide more surface area for these resins to bond. Therefore, if a client demands a “wet-strength guaranteed” 3-ply facial tissue, we must ensure the center layer has a high-purity softwood content to anchor the PAE effectively.
Engineering Checklist for Soft Pack Facial Tissue Production
When auditing a production run for soft pack facial tissue, I follow this technical protocol:
- Slitting Precision: Are the knives sharp? Dull knives cause fiber “fuzz” at the edges of the 2-ply facial tissue, leading to dust buildup in packaging.
- Perforation Tension: For soft packs, the “pull force” to remove the first tissue must be calibrated. If the perforation is too strong, the plastic film tears; if too weak, the tissue rips.
- Moisture Level: We keep the moisture exit level at 5%–7%. Excessively dry, and the fiber will crack; excessively wet, and the softness is gone.
- Bulk Testing: The micrometer helps us make sure the 3 ply tissue meets the caliper requirements since customers consider thickness an important indicator of quality.
In the world of tissue manufacturing, there is no “one-size-fits-all” recipe. A successful soft pack facial tissue is the result of a constant dialogue between the lab and the line. By understanding the microscopic behavior of long and short fibers, we can engineer products that exceed consumer expectations for both luxury and reliability. Whether it’s the cost-effective 2-ply facial tissue or the premium 3-ply facial tissue, the secret is always in the blend.
Frequently Asked Questions
Q1: Why does my tissue feel “scratchy” even though it is 100% virgin pulp?
A1: This is commonly due to making the fibers too fine or using too much softwood (long fiber). Overbeating of fibers at the pulping stage causes them to lose their bulk and become stiff.
Q2: Can 100% bamboo fiber be used for soft pack facial tissue?
A2: Yes, but bamboo is a “medium-to-long” fiber. To get the softness of a 3 ply facial tissue, bamboo often requires specialized enzyme treatments or high-intensity creping to break down the natural stiffness of the bamboo cell wall.
Q3: What is the difference in wet-strength requirements between 2 ply and 3 ply?
A3: Generally speaking, 3 ply facial tissue will have a higher “perceived” wet strength since the air between the three layers will slow down the absorption of water. However, a 2-ply facial tissue actually requires a higher percentage of wet-strength resin per ton of paper to prevent immediate disintegration.
Q4: Why does my soft pack facial tissue leave lint or tear apart when wiping sweat?
A4: This is often caused by an excessively high percentage of short fibres or insufficient wet-strength agents. If insufficient long fiber reinforcement or chemical bonding is present, the tissue structure will not be able to resist moisture and friction, causing “pilling” or disintegration.
Q5: Will increasing the softwood pulp ratio decrease the softness of tissue?
A5: Yes. More softwood (long fibre) generally means more stiffness. But this can be mitigated with layered forming technology. Long fibers are placed in the middle layer for strength, while the outer layers are 100% short fibers for a silky-smooth touch.
