Flexo Print Process / 플렉소 인쇄 공정의 이해
플렉소인쇄의 정의 :
유연한 인쇄판을 갖는, 다양한 잉크를 사용하는, 다양한 소재에 인쇄가 되는, 그리고 다양한 후가공과 연결될 수 있는 인쇄기법을 플렉소 인쇄라고 할 수 있다.
위 그림의 간단한 설명 :
위 그림에서 잉크가 모터에 의해서 닥터쳄버에(Doctor chamber) 공급이 되고 공급된 잉크는(Blade)에 의해 깍인다. 애닐록스 로라의(Anillox roller) 셀 속에 남겨진 잉크가 인쇄판(Printing Plate)에 전사가 되고 전사된 잉크는 판통과 압통사이를 통과하는 인쇄용지에 인쇄가 된다.
잉크전사의 원리 :
유연성있는 인쇄판(수지판)은 이미지 부분이 양각으로 돋아나 있으며 이것이 하나의 Dot 이며 이 돗트보다 몇 배 더 작은 크기의 잉크를 담는 애닐록스 로라의 셀 속에 있는 잉크를 퍼간다.
Flexographic printing is the only letterpress process that is still showing growth, mainly in packaging, label, and newspaper printing. The main feature of flexographic printing is the use of flexible printing plates that are relatively soft compared to book printing plates and enable special ink feeding.
플렉소 인쇄는 주로 포장, 라벨, 신문 인쇄 분야에서 계속 성장하고 있는 활판 인쇄 과정입니다. 플렉소 인쇄의 주요 특징은 서적인쇄에 사용되는 프린팅 플레이트에 비해서 비교적 부드럽고 유연한 인쇄판을 사용하는 것이다.
Using the flexible (soft) printing plate and the appropriate ink (low viscosity) for the printing substrate, it is possible to print on a wide range of absorbent and non-absorbent printing substrates. The principle on which a flexographic printing unit works is illustrated in figure 1.3-9.
이것은 인쇄용지에 적합한 유연한(소프트) 인쇄판 및 적합한 잉크(저점도)를 사용함으로써 넓은 범위의 흡수성 및 비 흡수성 인쇄용지에 인쇄를 할 수 있다.
The low-viscosity ink is transferred to the printing plate via a roller that is evenly screened with cells, the so-called screen roller/anilox roller (screen width 200–600 lines/cm, ceramic or hard chromed metal surface). The rubber or plastic plate is attached to the printing plate cylinder. Ink is transferred to the printing substrate by the pressure of the impression cylinder. The use of a blade (together with the ink supply system) on the screen roller has a stabilizing effect on the printing process resulting from even filling of the cells on the screen roller.
저점도 잉크는 소위 이야기하는 스크린 로라 또는 애니록스 로라 (스크린 200-600 선 / cm, 세라믹 또는 하드 크롬 도금 금속 표면) 에 있는 아주 미세한 셀 포켓에 담겨있는 잉크가 닥터브레이드에 의해서 깍이고(Screen) 이것이 수지판(프린팅 프레이트)에 잉크가 전사가 된다.
고무 또는 탄성을 갖는 수지판이 판통에 부착된다. 잉크는 판통과 압통사이에 용지 두께에 의해서 샛팅된 인압이 가해지고 이로 인해서 잉크가 용지에 다시 전사가 된다. 스크린 로라상의 닥터 브레이드(잉크공급 장치)를 사용함으로써 스크린 또는 애니록스 로라의 셀에 잉크를 고루게 공급해주는 역활을 한다.
With the rubber plates in exclusive use earlier, only a low to moderate printing quality of solid motifs and rough line drawings could be achieved. For today’s higher-quality requirements, especially in the printing of packaging, photopolymer wash-off plates are used, such as “Nyloflex” from BASF and “Cyrel” from DuPont. These allow screen resolutions of up to about 60 lines/cm.
초기에 사용된 고무로라 판으로는 할프톤이 아닌 솔리드 모티브나 세밀한 라인이 아닌 거친 라인 밖에 재현 할 수 없었다. 오늘날 높은 품질이 요구되는 페케징 인쇄에 듀폰의 BASF에서 “Nyloflex”와 “Cyrel” 와 같은 포토플리머 판 세척장치를 사용한다. 현재 60 선 / cm까지의 화면 해상도를 재현한다.
The first method of plate development uses light-sensitive polymer. A film negative is placed over the plate, which is exposed to ultra-violet light. The polymer hardens where light passes through the film. The remaining polymer has the consistency of chewed gum. It is washed away in a tank of either water or solvent. Brushes scrub the plate to facilitate the “washout” process. The process can differ depending on whether solid sheets of photopolymer or liquid photopolymer are used, but the principle is still the same. The plate to be washed out is fixed in the orbital washout unit on a sticky base plate. The plate is washed out in a mixture of water and 1% dishwasher soap, at a temperature of approximately 40°C. The unit is equipped with a dual membrane filter. With this the environmental burdening is kept to an absolute minimum. The membrane unit separates photopolymer from the washout water. After addition of absorb gelatine for example, the photopolymer residue can be disposed of as standard solid waste together with household refuse. The recycled water is re-used without adding any detergent.
플레이트를 만드는 첫 번째 방법은 빛에 민감한 폴리머를 사용하는 것이다. 플레이트에 네가티브 필림을 올려놓고 자외선에 노출 시킨다. 자외선 빛이 필림을 통과하게 되고 이 빛에 쪼인 폴리머는 경화된다. 빛에 쬐이지 않는 즉 굳지 않은 연성의 부분을 물이나 솔밴트에 담긴 통에 넣어서 씻겨낸다. 세척을 촉진시키기 위해서 브러쉬를 사용하여 플레이트를 비벼준다.
이 과정은 액체 포토폴리머 이냐 아니면 고체 시트의 포토풀리머이냐에 따라서 다를 수 있다. 하지만 원리는 동일하다. 세척해야 할 프레이트는 끈적거리는 베이스판위에 궤도모양의 세척 유니트에 고정되게 된다. 플레이트는 약 40도 정도를 유지하는 물과 1%의 식기 세척기 비누와 혼합된 통에서 세척이 된다. 이 세척 유니트는 두개의 막을 가지고 있는 필터로 구성되여 있다. 이렇게 하여 환경 부담을 최소화 시킬 수 있다.
멜브레인 유니트는 세척된 물로 부터 포토폴리머를 분리해 낸다. 예를 들어 항고형체 젤라틴을 첨가하면 포토폴리머의 찌꺼기를 가정용 쓰레기와 함께 표준 고형 페기물로 처분 할 수 있다. 재생된 물은 어떤 세제를 추가하지 않고도 재 사용할 수 있다.
수지판 제조 공정도
The second method used a computer-guided laser to etch the image onto the printing plate. Such a direct laser engraving process is called digital platemaking. Companies such as AV Flexologic, Esko, Polymount and Screen from The Netherlands are market leaders in manufacturing this type of equipment.
두 번째 방법은 인쇄 판에 이미지를 에칭하기 위해서 컴퓨터로 제어되는 레이저를 사용하는 것이다. 이렇게 직접적으로 레이저를 이용해서 조각하는 과정을 디지털 제판이라고 한다. AV Flexologic, 에스코, 네덜란드의 Polymount와 스크린이 이러한 장비를 만드는데 시장의 리더들이다.
For every colour to be printed, a plate is made and eventually put on a cylinder which is placed in the printing press. To make a complete picture, regardless of printing on flexible film or corrugated paper, the image transferred from each plate has to register exactly with the images transferred from the other colors. To ensure an accurate picture is made, mounting marks are made on the flexographic plates. These mounting marks can be microdots (down to 0.3 mm) and/or crosses. Special machinery is made for mounting these plates on the printing cylinders to maintain registration.
A flexographic print is made by creating a positive mirrored master of the required image as a 3Drelief in a rubber or polymer material. Flexographic plates can be created with analog and digital platemaking processes. The image areas are raised above the non image areas on the rubber or polymer plate. The ink is transferred from the ink roll which is partially immersed in the ink tank. Then it transfers to the anilox or ceramic roll (or meter roll) whose texture holds a specific amount of ink since it is covered with thousands of small wells or cups that enable it to meter ink to the printing plate in a uniform thickness evenly and quickly (the number of cells per linear inch can vary according to the type of print job and the quality required). To avoid getting a final product with a smudgy or lumpy look, it must be ensured that the amount of ink on the printing plate is not excessive. This is achieved by using a scraper, called a doctor blade. The doctor blade removes excess ink from the anilox roller before inking the printing plate. The substrate is finally sandwiched between the plate and the impression cylinder to transfer the image. The sheet is then fed through a dryer, which allows the inks to dry before the surface is touched again. If a UV-curing ink is used, the sheet does not have to be dried, but the ink is cured by UV rays instead.
Basic parts of the press
- Unwind and infeed section – The roll of stock must be held under control so the web can unwind as needed.
- Printing section – Single color station including the fountain, anilox, plate and impression rolls.
- Drying station – High velocity heated air, specially formulated inks and an after-dryer can be used.
- Outfeed and rewind section – Similar to the unwind segment, keeps web tension controlled.
1. Fountain roller
The fountain roller transfers the ink that is located in the ink pan to the second roller, which is theanilox or ceramic roller.
2. Plate cylinder
The plate cylinder holds the printing plate, which is soft flexible rubber. Sticky 2-way tape is used to mount the plate to the plate cylinder.
3. Doctor Blade
The doctor blade scrapes the anilox roll to insure that the predetermined ink amount delivered is only what is contained within the engraved cells. Doctor blades have predominantly been made of steel but advanced doctor blades are now made of polymer materials.
4. Impression Cylinder
The impression cylinder applies pressure to the plate cylinder, where the image is transferred to the substrate.
5. Anilox (old) or Ceramic (modern) roller
This is what makes flexography unique. The anilox or ceramic roller meters the predetermined ink that is transferred for uniform thickness. It has engraved cells that carry a certain capacity of inks that can only be seen with a microscope. These rollers are responsible to transfer the inks to the flexible-plates that are already mounted on the Plate Cylinders
Flexographic printing inks
The nature and demands of the printing process and the application of the printed product determine the fundamental properties required of flexographic inks. Measuring the physical properties of inks and understanding how these are affected by the choice of ingredients is a large part of ink technology. Formulation of inks requires a detailed knowledge of the physical and chemical properties of the raw materials composing the inks, and how these ingredients affect or react with each other as well as with the environment. Flexographic printing inks are primarily formulated to remain compatible with the wide variety of substrates used in the process. Each formulation component individually fulfills a special function and the proportion and composition will vary according to the substrate.
There are five types of inks that can be used in flexography: solvent-based inks, water-based inks, electron beam (EB) curing inks, ultraviolet (UV) curing inks and two-part chemically-curing inks (usually based on polyurethane isocyanate reactions), although these are uncommon at the moment. Water based flexo inks with particle sizes below 5 µm may cause problems whendeinking recycled paper.
The ink is controlled in the flexographic printing process by the inking unit. The inking unit can be either of fountain roll system or doctor blade system. The fountain roll system is a simple old system yet if there is too much or too little ink this system would likely not control in a good way. The doctor blade inside the anilox/ceramic roller uses cell geometry and distribution. These blades insure that the cells are filled with enough ink.
Color stations stack up vertically, which makes it easy to access. This press is able to print on both sides of the substrate.
Central Impression press
All color stations are located in a circle around the impression cylinder. This press can only print on one side. Advantage: excellent registry
Color stations are placed horizontally. This press prints on both sides, via a turnbar. Advantages: Can print on heavier substrates, such as corrugated boards.
Flexo has an advantage over lithography in that it can use a wider range of inks, water based rather than oil based inks, and is good at printing on a variety of different materials like plastic, foil, acetate film, brown paper, and other materials used in packaging. Typical products printed using flexography include brown corrugated boxes, flexible packaging including retail and shopping bags, food and hygiene bags and sacks, milk and beverage cartons, flexible plastics, self-adhesive labels, disposable cups and containers, envelopes and wallpaper. In recent years there has also been a move towards laminates, where two or more materials are bonded together to produce new material with different properties than either of the originals. A number of newspapers now eschew the more common offset lithography process in favour of flexo. Flexographic inks, like those used in gravureand unlike those used in lithography, generally have a low viscosity. This enables faster drying and, as a result, faster production, which results in lower costs.
Printing press speeds of up to 600 meters per minute (2000 feet per minute) are achievable now with modern technology high-end printers. Flexo printing is widely used in the converting industry for printing plastic materials for packaging and other end uses. For maximum efficiency, the flexo presses produce large rolls of material that are then slit down to their finished size on slittingmachines.