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Stone Paper

“Stone Paper” Process and Development

 

By Xu Tongkao 

1. Foreword

The invention of papermaking is a major contribution from China to human. The paper is extremely important to people’s work, study and life. The over-exploitation of trees from the traditional papermaking caused the lack of world forest reserves .The papermaking process has leaded to the serious pollution and negative effects to the ecology entironment, Which has been focused by the whole human.

Based on the raw material of inorganic powder (mainly for CaCO3) , added with a little synthetic resin and chemical additives, adopting the advanced technology to produce the new type environmental protection paper, this is the newest type in paper’s field. It can be used in the fields of printing、packing、snap-gauge and sorts of labels. It has the excellent paper performance and environmental protection performance.

The synthetic paper is also named as “non-torn” paper. At present, it is normally named as “stone paper”, but named as “synthetic paper ”in this article.

2 Producing process

The percentage of the inorganic fillers (CaCO3,talcum powder, wollastonite, titanium dioxide etc) in the synthetic paper is about 60%~80%,according to the different useage, it is added with PP,PE etc resin and sorts of chemical additives to be produced to the special application master batch by the process of compound,modification and extrusion.

At present,at home and abroad, the methods of synthetic paper are mainly for rolling process, curtain coating process ,film blowing process, two-way stretch and non-woven paper etc. The different constructions contain single- layer, three -layer, five -layer and multi -layer etc.


 

2.1 Rolling process

Process flow :Dosing – compound-- banburying – extrusion – special master batch,then through the process :extrusion – rolling—stretching – cooling – surface treatment –cutting – coating -- synthetic paper. The separated producing of the master batch and the rolling process is adopted sometimes, the complete process line for the whole forming at the same time is also adopted mostly by the developed equipments from abroad.

The feature of rolling process:

Advantage:High producing efficacy, good quality for products, smooth surface for paper, it is suitable to print the top grade painting albums and books’ cover etc.    

Weakness:complex process,high proportion for products, more expensive for the equipments.

2.2 Curtain coating process:

The curtain coating process is similar with the rolling process. the feature of the curtain coating process is :there is a curtain speed difference between the speed of die extruding and the rotation of the curtain coating rollers. The stretch comes into being between the die extruding meniscus and cooling rollers. According to the different products’ demands, the width of synthetic paper can be adjusted . The products are mainly based on PP resin  to reach the advantage of good rigidness、strong tenacity and good tensile strength. Because of the producing process, the products’ molecular structure distribution has the unipolarity,and a curtain difference between the lengthways and crosswise of the synthetic paper.

 

2.3 Film blowing process:

The raw material of this process mainly for PE, and most for three-layer extrusion and forming. Also some for single-layer、five-layer、muti-layer producing process. According to the different usage, the resin content in the outside layer can be proprerly improved,and high inorganic powder content for inside layer. The lengthways and crosswise stretch can be adjusted in a certain scope to make the synthetic paper thickness uniform and physical performance stable. But because of the high content of inorganic powder in the film blowing process, it affects the film mouldability and restricts the adding amount of inorganic powder, so it leads to the higher manufacturing cost.

2.4 Two-way stretch:

This kind of process adopts the similar extrusion process as the rolling process and curtain coating process. Installing the added two-way stretch system,through the lengthways and crosswise stretch, the resin molecular chain uniformly distributes, also similar for the lengthways and crosswise physical performance. During the course of stretch, because of the different performance for raw materials and the interface compatibility etc reasons, the very small gap may appear in the synthetic resin and inorganic powder, the small gap is commonly named of ”Island phenomenon”. This phenomenon may reduce the content and manufacturing cost of the synthetic paper, also can improve the paper’s phsical performance , appearance, dyeing property and hygroscopicity, especially for the pearl effect appearance after stretch, it can make the gorgeous and delicate effect for the paper print . it can be applied in advertisement inkjet、exquisite painting album etc fields.

3 The application teature of the synthetic paper

3.1 The advantage and the feature:

(1)Save resourse:the raw materials of synthetic paper are mainly Calcium carbonate etc inorganic powder and synthetic resin, saving large woods and water resource.

(2)Outstanding environmental conservation。It doesn’t use water ,wood pulp and steam, no poison gas, no waste water , no waste residue, no waste gas, and the leftover material can be recycling used.

(3)Excellent application performance. It adopts the plastic to instead of the paper

and wood, so it owns the double function of the plastic and paper.

(4)Good hygiene: Non-poisonous, non smell, non-pollution for the raw material ;  

(5)Good chemical stability. Can be applied in most chemicals’ packing ;

(6)Excellent processability, can be applied in triming、die cutting、stamping、Gilding etc.

3.2 The application field:

(1)Print;

(2)Decoration;

(3)Packing ;

(4)Hand bag .

4 The development foreground of the synthetic paper

The spread and application of the synthetic paper will lead to a sustainable development foreground to our national low carbon economic and building friendly enviroment society .

(1)There are many producing methods of the synthetic paper at home and abroad.Atpresent, the suitable producing process is to adopt the producing of compound modification material ,then curtain coating / rolling process, surface treatment to get the synthetic paper.

In the synthetic paper which produced by this process, the percentage of inorganic powder is about 60%~80% of the whole . High producing effective、functional reasonable. The types of the products can be adjusted following the market’s needs.

(2)The new research of PLA/CaCO3 synthetic paper,is adopting the PLA which is produced based on the sweet potato、corn etc crops, as its carrier, instead of the synthetic resin produced by the oil resources. This kind of synthetic paper is normally used for the packing of food、life chemical、medicine etc,the products can be nature degradable after be used. It is really a kind of low-carbon energy conservation product supported by the national development recycling economic.

(3)The synthetic paper is a kind of plastic modification paper gathering the synthetic resin、inorganic powder、chemical additives, the resin and the additives are the key important roles.

(4)The appearance of the synthetic paper is not so early. It also has many weaknesss on the material choice、mechanical equipment 、producing process、products’s performance、application spread etc. so the further research is needed for its modification、perfection and improvement .

(5)The synthetic paper is applied as an interdisciplinary technology project focusing on the plastic 、papermaking、machinery、technical process、application etc .