Plastic and nonmetallic article shaping or treating: processes – Direct application of electrical or wave energy to work – Producing or treating porous product
Reexamination Certificate
1999-09-13
2002-04-09
Eashoo, Mark (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Direct application of electrical or wave energy to work
Producing or treating porous product
C264S415000, C264S423000, C264S469000, C264S045900, C264S173140, C264S173150, C264S288800
Reexamination Certificate
active
06368543
ABSTRACT:
BACK GROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an improvement of a process for producing a three layer co-extrusion biaxially polypropylene (hereinafter as BOPP) synthetic paper a thickness of from 25~250 &mgr;m. More particularly, the invention relates to a process for producing a three layer BOPP synthetic paper by means of a three layer co-extrusion process wherein two different polypropylene (PP) resin compositions are first separately extruded by one primary single screw extruder with venting device and two secondary single screw extruders with venting device and then are co-flowed by the same T-die to form a three layer coating sheet, and through cooling biaxial orientation, corona treatment and winding to form a three layer co-extrusion synthetic paper of thickness 25~250 &mgr;m. The three layer structure of said three layer co-extrusion synthetic paper of thickness 25~250 &mgr;m can be made into three kinds, such as: paper sheet layer/foamed intermediate layer/paper sheet layer with double side paper sheet layer, paper sheet layer/foamed intermediate layer/resin layer with single side paper sheet layer and resin layer/foamed intermediate layer/resin with double side high gloss resin layer, to use as a coating substrate for coating grade synthetic paper.
2. Description of the Related Art
Nowadays the three layer co-extrusion BOPP synthetic paper differs with the polyolefin synthetic paper mainly comprising the basic substrate layer in the intermediate layer, whereon the back surface is laminated with the uniaxially oriented polypropylene (UOPP) containing inorganic fine powder as the paper surface layer(such as disclosed in the Japanese Patent Publication No. 40794/71, Japanese Laid-open Patent Publication No. 41339,81, Japanese Laid-open Patent Publication No. 118437/81 and Japanese Laid-open Patent Publication No, 87225/91, and Taiwan Patent Publication No 72218). The high strength of the paper sheet of the three layer co-extrusion BOPP synthetic paper obtained by these patent processes the problem caused by paper powder formation during printing process, and owing to the fact that the thermal dimensional stability of the paper sheet layer is good enough and cost is very low, so these synthetic papers can be sold widely sold.
However it must be improved in some aspects, such as hiding power, heat resistance, total thickness and cost of BOPP synthetic paper to replace natural pulp in wide applications. These applications can be industrialized package usage such as packaging paper, kraft paper and releasing paper etc.
Although the above mentioned patent publications have been granted, there are still some problems to make use of BOPP synthetic paper in wide applications.
However, BOPP synthetic paper can be used in various applications if the hiding power, heat resistance, total thickness of BOPP synthetic paper product could be enhanced. This, however requires improvement from the viewpoint of, for example depending on the total amount of inorganic powder added.
Upon consideration of the dispersion problem of inorganic powder used in the single screw extruder, only masterbatch ready made by dispersing the inorganic powder with resin can be used. The masterbatch mixes with the polypropylene resin in the inlet of the extruder, then enters into the extruder to melt and extrude. To obtain the dispersion of the inorganic powder in the production of the masterbatch, it is usual to use a dispersing agent such as coupling agent, calcium stearate to enhance surface treatment of the inorganic powder, to obtain much better productivity (to avoid film break in the drawing zone)and product appearance, evenness of BOPP synthetic paper. But the masterbatch containing the inorganic powder with dispersing agent incurred and moisture adsorbed may volatilize its dispersing agent and moisture into gas under high temperature kneading by the screw in the extruder. This will cause voids to be formed in the sheet during cooling after extrusion. The existing voids also form gas bubble in the product of latter zone drawing. It is necessary to control the formulation condition and processing condition.
SUMMARY OF THE INVENTION
It is a primary object of the present invention to provide an improvement of a process for producing a three layer co-extrusion biaxially polypropylene (hereinafter as BOPP) synthetic paper of thickness 25~250 &mgr;m.
It is another object of the present invention to provide a process for producing a three layer BOPP synthetic paper by means of three layer co-extrusion wherein two different PP resin compositions are separately extruded by one primary single screw extruder with a venting device and two secondary single screw extruders with a venting device first, and then are co-flowed by the same T-die to form a three layer coating sheet, and through cooling, biaxial orientation, corona treatment and winding to form a three layer co-extrusion synthetic paper of thickness 25~250 &mgr;m.
It is a further object of the present invention to provide three kinds of three layer co-extrusion synthetic paper of thickness 25~250 &mgr;m, such as: paper sheet layer/foamed intermediate layer/paper sheet layer with double side paper sheet layer, paper sheet layer/foamed intermediate layer/resin layer with single side paper sheet layer and resin layer/foamed intermediate layer/resin with double side high gloss resin layer, to use as coating substrate for coating grade synthetic paper.
The inorganic powder may be added as needed to meet the need of the product application and quality, the applicant adopt the following two ways to reach this aim, namely to vent away the dispersing agent and moisture in the masterbatch to avoid the abnormality occurs during processing.
(1) First, each ingredients used in the extruder should be pelletized into masterbatch by pelletizer. The pelletizer adopts natural venting means to expel the remaining dispersing agent or moisture, and volatile ingredient. Then the masterbatch prepared is transferred into extruder for succeeding step.
(2) The three single screw extruders used in this process should be changed in screw structure (to make reducing zone) and install new venting device to expel the remained dispersing agent and moisture or volatilable gas. In spite of adding any amount of inorganic powder, there is no hollow void may be found in the sheet obtained after cooling.
The above described improvement ways can reach the aim of obtaining quality elevation in hiding power, heat resistance, total thickness of product and cost reduction. It is preferably to adopt the (2) means under the consideration of production cost, raw materials used and storage management.
The BOPP synthetic paper obtained by the venting process of single screw extruder which was manufactured without limitation in adding inorganic powder has much more advantages in increasing quality and cost reduction. This technical feature has not been disclosed in the prior art. The advantageous effects of this invention will be described as follows:
(1) Increasing Hiding Power
The hiding power of BOPP synthetic paper obtained by the biaxial drawing process depends on the amount of masterbatch and quantity inorganic powder. If inorganic powder can be added in large amounts, the foaming formation of product in the drawing zone is satisfactory, and hiding power from light is also good. Consequently, high hiding power can be reached without adding masterbatch or with reducing masterbatch amount used.
(2) Increasing Heat Resistance
The thermal barrier of inorganic powder is better than that of polypropylene resin, preferably used inorganic powder are calcium silicate and talc. The addition of larger amounts of inorganic powder will increase heat resistance and increase high foam formation.
(3) Increasing Total Thickness
The amount of inorganic powder added and the specific gravity of product have good correlation, and the specific gravity of product is the dominating factor of product thickness determination. If the specific gravity of product can be effectively decrea
Bacon & Thomas
Eashoo Mark
Nan Ya Plastics Corporation
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