| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | November 1, 1994 |
| PATENT TITLE |
Polyester laminates |
| PATENT ABSTRACT |
Polyester laminates formed by coating by melt-extruding an aliphatic polyester having a melt viscosity of 1.0.times.10.sup.3 -1.0.times.10.sup.5 poises at a temperature of 190.degree. C. and a shear rate of 100 sec.sup.-1, and having a melting point of 70.degree.-200.degree. C. on to paper or cloth. The resin can be coated on paper or cloth at a low temperature with firm adherency, and the sheet thus formed is biodegradable. |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | April 20, 1993 |
| PATENT FOREIGN APPLICATION PRIORITY DATA | This data is not available for free |
| PATENT CLAIMS |
What is claimed is: 1. Polyester laminates formed by melt-extruding an aliphatic polyester having a melt viscosity of 1.0.times.10.sup.3 -1.0.times.10.sup.5 poises at a temperature of 190.degree. C. and a shear rate of 100 sec.sup.-1, and having a melting point of 70.degree.-200.degree. C., wherein said alphatic polyester is obtained by adding from 0.1 to 5 parts by weight of diisocyanate to 100 parts by weight of a prepolymer in a molten state, wherein said prepolymer is obtained from a reaction of at least an aliphatic glycol and an aliphatic dicarboxylic acid, wherein the reaction includes (a) succinic acid, or its anhydride, reacted with 1,4-butanediol, (b) succinic acid, adipic acid, or their anhydride, reacted with 1,4-butanediol, or (c) succinic acid, or its anhydride, reacted with ethylene glycol, and has a number-average molecular weight of at least 10,000, onto a base selected from the group consisting of paper and cloth. 2. The polyester laminates as claimed in claim 1 wherein melt-extrusion is carried out at 150.degree.-290.degree. C. in terms of resin temperature. 3. The polyester laminates as claimed in claim 1 wherein the aliphatic polyester has a repeated chain structure in which a polyester prepolymer having a number-average molecular weight (Mn) of at least 10,000 and consisting of an aliphatic glycol and aliphatic dicarboxylic acid is bonded through urethane bonds. 4. The polyester laminates as claimed in claim 1 wherein the aliphatic polyester has a repeated chain structure in which a polyester prepolymer having a number-average molecular weight (Mn) of 10000 or more and obtained by reacting an aliphatic glycol, aliphatic dicarboxylic acid and, as a third component, at least one polyfunctional component selected from the group consisting of trifunctional or tetrafunctional polyols, oxycarboxylic acids and polybasic carboxylic acids or acid anhydrides thereof, is bonded through urethane bonds. 5. The polyester laminates as claimed in claim 4 wherein the polyester prepolymer contains one or more compounds selected from the group consisting of trimethylol propane, glycerin and pentaerythritol as the trifunctional or tetrafunctional polyol of the third component. 6. The polyester laminates as claimed in claim 4 wherein the polyester prepolymer contains one or more compounds selected from the group consisting of malic acid, citric acid and tartaric acid as the trifunctional or tetrafunctional oxycarboxylic acid of the third component. 7. The polyester laminates as claimed in claim 4 wherein the polyester prepolymer contains one or more compounds selected from the group consisting of trimesic acid, propane tricarboxylic acid, trimellitic anhydride, pyromellitic anhydride, benzophenone tetracarboxylic anhydride and cyclopentane tetracarboxylic anhydride as the trifunctional or tetrafunctional polybasic carboxylic acid of the third component. 8. A release material comprising a polyester laminate formed by melt-extruding an aliphatic polyester having a melt viscosity of 1.0.times.10.sup.3 -1.0.times.10.sup.5 posies at a temperature of 190.degree. C. and a shear rate of 100 sec.sup.-1 and having a melting point of 70.degree.-200.degree. C., wherein said aliphatic polyester is obtained by adding from 0.1 to 5 parts by weight of diisocyanate to 100 parts by weight of a prepolymer in a molten state, wherein said prepolymer is obtained from a reaction of at least an aliphatic glycol and an aliphatic dicarboxylic acid, wherein the reaction includes (a) succinic acid, or its anhydride, reacted with 1,4-butanediol, (b) succinic acid, adipic acid, or their anhydride, reacted with 1,4-butanediol, or (c) succinic acid, or its anhydride, reacted with ethylene glycol, and has a number-average molecular weight of at least 10,000, onto a base selected from the group consisting of paper and cloth, wherein the polyester laminate has thereon an object to be released. 9. A material for containers, comprising a polyester laminate formed by melt-extruding an aliphatic polyester having a melt viscosity of 1.0.times.10.sup.3 -1.0.times.10.sup.5 poises at a temperature of 190.degree. C. and a shear rate of 100 sec.sup.-1, and having a melting point of 85.degree.-200.degree. C., wherein said aliphatic polyester is obtained by adding from 0.1 to 5 parts by weight of diisocyanate to 100 parts by weight of a prepolymer in a molten state, wherein said prepolymer is obtained from a reaction of at least an aliphatic glycol and an aliphatic dicarboxylic acid, wherein the reaction includes (a) succinic acid, or its anhydride, reacted with 1,4-butanediol, (b) succinic acid, adipic acid, or their anhydride, reacted with 1,4-butanediol, or (c) succinic acid, or its anhydride, reacted with ethylene glycol, and has a number-average molecular weight of at least 10,000, onto paper. -------------------------------------------------------------------------------- |
| PATENT DESCRIPTION |
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to polyester laminates, for example, release base materials and base material for paper containers having excellent heat stability and mechanical strength which are prepared by using aliphatic polyesters with biodegradability and sufficiently high molecular weights and specific melt properties for practical use. 2. Discussion of the Background As a release base material, one comprising a release layer laminated on a filling layer on one or both sides of a paper or a cloth has been well known, wherein said filling layer is a low density polyethylene having a long branched chain obtained by the ordinary high-pressure method, a medium density polyethylene obtained by blending a low density polyethylene with a high density polyethylene, or a composition obtained by blending a low density polyethylene with polypropylene. Further, as for paper cups such as used for foods and drinks, for example, coffee, soup, miso-soup and instant noodles, paper trays for food, for example, pizza, daily dishes and food for microwave ovens and the like, at least inner surface where the content such as liquid contacts, a resin composition as same as aforementioned is conventionally laminated to provide a water-repellent layer. In the current processes for producing the release base materials, it is required to melt-coat the polyolefins used as a filling layer as mentioned above on base materials at a high temperature over 315.degree. C. in order to obtain close-adhesive and bonding properties between the polyolefins and the base materials. Further, in the production of the base material for paper containers used for hot drinks and foods such as paper cups or paper trays, it is required to laminate the above-mentioned polyolefin compositions used as a water-repellent layer on the paper at a high temperature over 300.degree. C. in order to coat the polyolefin composition firm to the paper. Because of this high temperature melt-coating, the oxidative deterioration of the polyolefin themselves occurs, and the generation of a great volume of smoke is unavoidable. Consequently, not only is the condition of the working environment worsened, but also the living environment around the factory becomes polluted by the smoke exhausted from the factory, creating a great community problem. Accordingly, there has been a strong demand for improvement thereof. On the other hand, waste disposal of the used release papers by burying them in the earth is insufficient, since the base materials are laminated with unbiodegradable polyolefins. Furthermore, trying to recycle the paper from the used release papers, by soaking the paper in an alkaline aqueous solution followed by tearing off the polyolefins, is very difficult and required much labor and cost. Accordingly, there has also been a strong demand for development of a release base material which can be biodegraded together with other biodegradable base materials such as paper and cloth. One object of the present invention is to develop a release base material filled with a polymer which can be molded at a low temperature in order to minimize the volume of generated smoke in the melt-coating process, which has good bonding and firm-adhesive properties to the base material such as paper and cloth and which can be decomposed by natural and ordinary microorganisms in the earth. Another object of the present invention is to develop a novel base material for a paper-made container, by which the problems concerning the odor of the oxidatively deteriorated polyolefin remaining on the paper-made container because of the high temperature lamination and the generation of a great volume of smoke can be solved, and which gives the paper-made container biodegradability and is advantageous to the preservation of the natural environment, where undecomposable materials of the used container have been accumulated. SUMMARY OF THE INVENTION In the present invention, the above-mentioned object has been achieved by the development of aliphatic polyester laminates characterized by coating a base material consisting of paper or cloth by melt-extrusion with an aliphatic polyester having a melt viscosity of 1.0.times.10.sup.3 -1.0.times.10.sup.5 poises at a temperature of 190.degree. C. and a shear rate of 100 sec.sup.-1 and having a melting point of 70.degree.-200.degree. C. In the present invention, the above-mentioned object has been achieved by developing a release base material using an aliphatic polyester laminate. Further the present invention provides a paper container laminated with an aliphatic polyester having a melting point of 85.degree.-200.degree. C. DETAILED DESCRIPTION OF THE INVENTION The present invention will be described below in further detail. The aliphatic polyester of the present invention mainly consists of a polyester obtained by reacting two components of glycols and dicarboxylic acid (or acid anhydrides thereof), and if necessary as a third component, with at least one polyfunctional componment selected from the group consisting of trifunctional or tetrafunctional polyols, oxycarboxylic acids, and polybasic carboxylic acids (or acid anhydrides thereof). The aliphatic polyesters are prepared by reacting relatively high molecular weight polyester prepolymers which have hydroxyl groups at both ends with a coupling agent so as to make them even higher molecular weight polymer. It has been known to obtain polyurethane by reacting a low molecular weight polyester prepolymer having a number-average molecular weight of 2,000-2,500, which have hydroxyl groups as the terminal groups, with diisocyanate as a coupling agent in the preparation of rubbers, foams, coatings and adhesives. However, the polyester prepolymers used in these polyurethane foams, coatings and adhesives are prepolymers having a low molecular weight and a number-average molecular weight of 2,000-2,500 which is the maximum that can be prepared by non-catalytic reaction. To obtain practical physical properties as the polyurethane, it is necessary that the content of diisocyanate should be as much as 10-20 parts by weight in relation to 100 parts by weight of this low molecular weight prepolymer. When such a large amount of diisocyanate is added to the low molecular weight polyester melted at 150.degree. C. or higher, gelation occurs so that no normal resins which can be molded in the form of a melt can be obtained. Therefore, polyesters which are obtained by reacting a large amount of diisocyanate with a low molecular weight polyester prepolymers as a raw material cannot be used as the plastic raw material for the base materials of the present invention. Also, as shown in the case of polyurethane rubbers, although a method is coceivable in which hydroxyl groups are converted into isocyanate groups by the addition of diisocyanate, and then the number-average molecular weight thereof is further increased by using glycols, the same problem as mentioned above arises because 10 parts by weight of diisocyanate relative to 100 parts by weight of the prepolymer should be used in order to obtain practical physical properties. When a relatively high molecular weight polyester prepolymer is to be used, heavy metal catalysts required to prepare the prepolymer would promote the reactivity of the above-mentioned isocyanate groups to undesirably cause poor preservativity, generation of crosslinking and branching; hence, a number-average molecular weight of not more than around 2,500 of polyester prepolymers would be the limit if they were to be prepared without catalysts. The polyester prepolymers to obtain the aliphatic polyesters used in the present invention are relatively high molecular weight saturated aliphatic polyesters having substantially hydroxyl groups at the ends thereof, number-average molecular weights of at least 5,000, preferably at least 10,000, and a melting point of 60 .degree. C. or higher, which are obtained by reacting glycols and dibasic carboxylic acids (or acid anhydrides thereof) in the presence of catalysts. When a prepolymer having a number-average molecular weight of lower than 5,000 is used, the small amounts of 0.1-5 parts by weight of coupling agents used in the present invention cannot provide polyesters for extrusion coating having good physical properties. When polyester prepolymers having number-average molecular weights of 5,000 or higher are used, with hydroxyl values of 30 or less, the use of small amounts of coupling agents even under severe conditions such as a molten state and the like can produce high molecular weight polyesters without gelation as the reaction is not affected by the remaining catalyst. Therefore, the polymer for the base materials of the present invention has a repeated chain structure in which a polyester prepolymer having a number-average molecular weight of 5,000 or more, preferably 10,000 or more and consisting of an aliphatic glycol and aliphatic dicarboxylic acid is combined through the urethane bonds derived from, for example, diisocyanate as a coupling agent. Further, the polymer for the base materials sheets of the present invention has a repeated chain structure in which the above-mentioned polyester prepolymer provided with branched long chains derived from polyfunctional components is combined through the urethane bonds derived from, for example, diisocyanate as a coupling agent. When oxazoline, diepoxy compounds, and acid anhydrides are used as a coupling agent, the polyester prepolymer has a repeated chain structure through ester bonds. According to the present invention, there can be obtained a release base material which essentially comprises an aliphatic polyester having a melt viscosity of 1.0.times.10.sup.3 -1.0.times.10.sup.5 poises at a temperature of 190.degree. C. and a shear rate of 100 sec.sup.-1 and having a melting point of 70.degree.-200.degree. C. as a filling layer of, for example, adhesive sheets, binding tapes and the like. Further, by using aliphatic polyesters having a melting point of 85.degree.-200.degree. C. and melt viscosity of 1.0.times.10.sup.3 -1.0.times.10.sup.5 poises at 190.degree. C. and a shear rate of 100 sec.sup.-1 for sealing material for a base material having good adherence, heat resistance can be made with small amount of smell of oxidative deterioration. In particular, according to the present invention, since melt-coating is proceeded at a low temperature, very little smoke, which has been a cause of community problems, is generated if at all, and concomitant problems such as worsening of the working environment and environmental pollution around the factory by exhausted smoke, can be solved. Furthermore, since the resin used in the present invention is biodegradable by microorganisms, they can be disposed of by waste disposal means being buried in the earth. Examples of glycols which can be used as a reaction component include aliphatic glycols. Among them, those having a straight chain alkylene group with even number carbon atoms of 2, 4, 6, 8 and 10 such as: ethylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, and mixtures thereof are preferable. Of these glycols, those having a smaller number of carbon atoms, such as ethylene glycol, 1,4-butanediol and 1,6-hexanediol, are preferable because they can produce an aliphatic polyester having a high crystallinity and a high melting point. In particular, ethylene glycol and 1,4-butanediol are most suitable because they produce good results. Examples of aliphatic dicarboxylic acids or anhydrides thereof which provide aliphatic polyester by reacting with glycols include aliphatic dicarboxylic acids. Among them those having a straight chain alkylene group with even number carbon atoms of 2, 4, 6, 8 and 10 such as: succinic acid, adipic acid, suberic acid, sebacic acid, 1,10-decanedicarboxylic acid, succinic anhydride and mixtures thereof are preferable. Of these dicarboxylic acids, those having a smaller number of carbon atoms, such as succinic acid, adipic acid and succinic anhydride, are preferable because they can produce an aliphatic polyester having high crystallinity and high melting points. In particular, succinic acid, succinic anhydride and an acid mixture of succinic acid or succinic anhydride and another dicarboxylic acid such as adipic acid, suberic acid, sebacic acid or 1,10-decanedicarboxylic acid are preferable. In the system of an acid mixture containing two or more acid components, for example, succinic acid and other dicarboxylic acids, the mixing ratio of succinic acid is at least 70 mol %, preferably at least 90 mol %, and the mixing ratio of the other carboxylic acids is 30 mol % or less, preferably 10 mol % or less. A combination of 1,4-butanediol and succinic acid or succinic anhydride and a combination of ethylene glycol and succinic acid or succinic anhydride are particularly preferable for the present invention because the combinations exhibit melting points close to that of polyethylene. (Third component) To these glycols and dicarboxylic acid, if necessary, may be added as a third component at least one polyfunctional component selected from the group consisting of trifunctional or tetrafunctional polyols, oxycarboxylic acid, and polybasic carboxylic acids (or acid anhydrides thereof). The addition of this third component, which causes the branching of long chains, can impart desirable properties in molten state to the polyester prepolymer, because the ratio of weight-average molecular weight (MW)/number-average molecular weight (Mn), i.e., the molecular weight distribution, increases with increases in its molecular weight. In terms of the amount of polyfunctional components to be added without fear of gelation, a trifunctional component of 0.1-5 mole %, or a tetrafunctional component of 0.1-3 mole % is added relative to 100 mole % of the total of aliphatic dicarboxylic acid (or acid anhydride thereof) components. (Polyfunctional components) Examples of polyfunctional components as the third component include trifunctional or tetrafunctional polyols, oxycarboxylic acids, and polybasic-carboxylic acids. The trifunctional polyols representatively include trimethylol propane, glycerin or anhydrides thereof. The tetrafunctional polyols representatively include pentaerythritol. The trifunctional oxycarboxylic acid components are divided into the two types of (i) a component which has two carboxyl groups and one hydroxyl group in one molecule, and (ii) another component which has one carboxyl group and two hydroxyl groups in one molecule. Malic acid which has two carboxyl groups and one hydroxyl group in one molecule becomes practical and sufficient to the purposes of the present invention in view of commercial availability at low cost. The tetrafunctional oxycarboxylic acid components are the following three types of components: (i) A component which has three carboxyl groups and one hydroxyl group in one molecule; (ii) Another component which has two carboxyl groups and two hydroxyl groups in one molecule; and (iii) The remaining component which has three hydroxyl groups and one carboxyl group in one molecule. Any type can be used, though in view of commercial availability at low cost, citric acid and tartaric acid are practical and sufficient to the purposes of the present invention. As a trifunctional polybasic carboxylic acid (or acid anhydride thereof) component trimesic acid, propane tricarboxylic acid and the like can be used. Among them, trimesic anhydride is practical for the purposes of the present invention. As a tetrafunctional polybasic carboxylic acid (or anhydride thereof) various types of aliphatic compounds, cycloaliphatic compounds, aromatic compounds and the like, described in certain literatures, can be used. In view of commercial availability, for example, pyromellitic anhydride, benzophenone tetracarboxylic anhydride and cyclopentane tetracarboxylic anhydride are practical and sufficient to the purposes of the present invention. These glycols and dibasic acids are mainly consisted of aliphatic series, while small amounts of other components, for example, aromatic series may be concomitantly used. These other components may be blended and copolymerized in amounts up to 20% by weight, preferably up to 10% by weight, and more preferably up to 5% by weight because using these compounds degrades biodegradability. The polyester prepolymer for aliphatic polyesters to be used in the present invention has hydroxyl groups at the terminals. To introduce the hydroxyl groups, it is necessary that glycols are used somewhat excessively. For preparation of the polyester prepolymer having a relatively high molecular weight, it is necessary to use deglycol-reaction catalysts in the deglycol reaction subsequent to the esterification. Examples of the deglycol-reaction catalysts include titanium compounds such as acetoacetoyl type titanium chelate compounds and organic alkoxy titanium compounds and the like. These titanium compounds can be used in combination. Examples of compounds used in combination include diacetoacetoxy oxytitanium (Nippon Chemical Industry Co., Ltd.; Nursem Titanium) tetraethoxy titanium, tetrapropoxy titanium, tetrabutoxy titanium and the like. The amount of the titanium compound used is 0.001-1 part by weight, and preferably 0.01-0.1 part by weight relative to 100 parts by weight of the polyester prepolymer. These titanium compounds may be blended before the esterification, or may be blended immediately before the deglycol-reaction. As a result, polyester prepolymers having an acid-average molecular weight of at least 5,000, and preferably at least 20,000 and a melting point of 60.degree. C. or higher, can be generally obtained easily. It is even more preferable if these polyester prepolymers have crystallization. To the polyester prepolymer which has a number-average molecular weight of at least 5,000, preferably at least 10,000, and whose terminal groups are substantially hydroxyl groups are added coupling agents in order to increase its number-average molecular weight. Examples of the coupling agents include diisocyanate, oxazoline, diepoxy compounds, acid anhydrides and the like. Diisocyanate is particularly preferred. In the cases of oxazoline and diepoxy compounds, It is necessary that the terminal hydroxyl groups are reacted with acid anhydrides and the like to convert them into carboxyl groups, then coupling agents are used. Although not limited, examples of diisocyanate include 2,4-tolylene diisocyanate, a mixture of 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate, diphenylmethane diisocyanate, 1,5-naphthylene diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate and the like. Particularly, hexamethylene diisocyanate is preferably used in terms of hue of prepared resins, reactivity at the time of blending polyesters, and the like. The adding amounts of these coupling agents are 0.1-5 parts by weight, and preferably 0.5-3 parts by weight relative to 100 parts by weight of polyester prepolymer. Addition of less than 0.1 part by weight causes insufficient coupling reaction, whereas with more than 5 parts by weight gelation tends to occur. The addition is preferably performed when the polyester is in a uniformly melted state under easily stirrable conditions. Although it is not impossible for the coupling agents to be added to the polyester prepolymer in the form of a solid and melted and mixed through an extruder, adding the agents in a polyester preparation unit, or adding them to polyester prepolymer in a melt state (for example, in a kneader) is more practical. When urethane bonds are contained in the aliphatic polyester to be used in the present invention, the amount of urethane bonds is 0.03-3.0% by weight, preferably 0.05-2.0% by weight, and more preferably 0.1-1.0% by weight. The amount of urethane bonds is measured by .sup.13 C NMR, showing good correlation with the charged amount. Less than 0.03% by weight of urethane has a little effect on polymerization and leads to poor molding properties, whereas more than 3% by weight causes gelation. The aliphatic polyester to be used in the present invention is required to have selected melt properties for base materials. That is, in release base materials or base materials for paper containers, the aliphatic polyester resin to be used in the present invention preferably has a melt viscosity of 1.0.times.10.sup.3 -1.0.times.10.sup.5 poises at 190.degree. C. at a shear rate of 100 sec.sup.-1. Those having a melt viscosity of lower than 1.0.times.10.sup.3 poises have defects in that surging and non-uniformity of the resin temperature easily occur and extruding stability is lost in the extrusion-molding process. Also, this results in the neck-in of the melt film becoming large making it difficult to lamination-mold in the lamination-molding process, resulting in thickness variations of the obtained laminate film, because of its melt viscosity being too low. On the other hand, those having a melt viscosity of higher than 1.0.times.10.sup.5 poises also have some defects in that the motor load becomes large and the productivity decreases in the extrusion-molding process, and in that it becomes difficult to make a thin melt film in the lamination-molding process, because of its melt viscosity being too high. For these reasons, melt viscosity is preferably within the range of 2.0.times.10.sup.3 -2.0.times.10.sup.4 poise, and more preferably 2.5.times.10.sup.3 -1.2.times.10.sup.4 poise. The melting point of the aliphatic polyester to be used in the present invention is preferably 70.degree. C.-200.degree. C. A melting point of lower than 70.degree. C. gives poor heat resistance in the silicone coating process and in the adhesive agent coating process. Such an aliphatic polyester must be treated at low temperature, and requires a long time to dry and remove the solvents of silicone or adhesive agent. Accordingly, an aliphatic polyester having such a melting point is not preferable. On the other hand, although an aliphatic polyester having a melting point of higher than 200.degree. C. shows an sufficient heat resistance, its rate of biodegradation slows down, and consequently, such an aliphatic polyester is also not preferable. For these reasons, the melting point of the aliphatic polyester is preferably 60.degree. C.-200.degree. C., and more preferably 80.degree. C.-150.degree. C. The melt temperature of the aliphatic polyester to be used for the base material for paper container in the present invention is preferably 85.degree. C.-200.degree. C. A melting point of lower than 85.degree. C. is not preferable, since it will give paper cups and trays poor heat resistance to hot drinks, etc. resulting in release and melting of the laminated aliphatic polyester composition and release of the joint. On the other hand, a melting point higher than 200.degree. C. of melting point is also not preferable, since it makes the biodegradation rate of the paper cups or trays slow down when decomposed by microorganisms in the earth. Therefore, the melt temperature is preferably 90.degree. C.-150.degree. C., and more preferably 100.degree. C.-140.degree. C. In the present invention, the base material for a paper-made container can be prepared by laminating the aliphatic polyester resin obtained by the above-mentioned process on a base paper by T-die method. In this process, the temperature of the resin to be extruded is 150.degree.-290.degree. C. When the resin temperature is lower than 150.degree. C., the melt viscosity is too high, and hence the motor load becomes large and the productivity decreases in the extrusion-molding process, and it becomes difficult to make a thin melt film in the lamination-molding process as well. On the other hand, when the resin temperature is higher than 290.degree. C., the resin composition deteriorates and loses extrusion stability because of the occurrence of surging, and it is difficult to lamination-mold since the neck-in [a phenomenon in which during the lamination-molding process the width of the melt film discharged from T-die becomes narrow in the space between the melt film and a base material, where the melt film has not yet contacted with the base material, and it is expressed by the difference of widths between the melt film at the T-die outlet and the laminated film laminated on the base material] of the melt film is large and not stable in the lamination-molding process. Furthermore, a great volume of smoke is generated in the molding process, and not only the condition of the working environment but also the odor of the obtained laminated paper gets worse. For these reasons, the resin temperature is preferably 160.degree.-285.degree. C., and more preferably 170.degree.-275.degree. C. In the process for making a base material for a paper container of the present invention, in which an aliphatic polyester resin is extruded and then laminated on a base paper, a general screw-type extruder and laminator can be used. An example of a molding process is one in which a melt resin comprising an aliphatic polyester resin is extruded on one side of the base paper supplied at a speed of 20-200 m/min, and seal-joined by press with the base paper at the position between the cooling roll and the press roll. After cooling and hardening the melt resin by contact with the surface of the cooling roll, this is rolled up or piled up on the cutting stand through the continuous cutter. The cooling roll to be used in the present invention may be any one used for surface-finishing such as a mat finishing type, semi-mat finishing type, mirror finishing type and the like. Among these, a mat finishing type of cooling roll is preferable in view of the stacking property of the resulting paper cups and trays (that is, paper cups, etc. are pulled out one by one from their stacks, that is required when used for vending machines) and releasability of resultants from the roll in the lamination-molding process. Furthermore, according to the present invention, in the space between a melt film extruded from T-die and a board paper where the melt film is not yet contacted with the paper, i.e., an air gap, the surface of the melt film to be contacted with the plate paper may be sprayed with ozone gas and the like in order to strengthen the firm-adhesiveness and bonding property to the board paper. In order to enhance the adhesiveness to the plate paper, adhesive-applying agents such as terpene-based resins and adhesive resins such as ionomers, ethylene-acrylate ester copolymer and acid-modified polyolefines may be added to the aliphatic polyester composition so that the functions of the laminated paper of the present invention would not be lost. In addition, the method in which the board paper is previously treated by, for example, anchor-coat treatment, corona treatment, flame treatment, and the like, may be employed in order to strengthen the firm-adhesiveness and the bonding property to the laminated film. In the present invention, an alphatic polyester prepared by using additionally a small amount (0.2-1.0 mol %) of polyols which has more than 3 of hydroxyl group (--OH) or polybasic carboxylic acid monomer which has more than 3 of carboxyl group (--COOH) in one molecule, has a widened molecular weight distribution and long chain branches, as molding pressure becomes lower resulting in smaller necking-in and surging, thus improving film farmability. As the above-mentioned aliphatic polyester to be laminated according to the present invention, the polyester having no long chain branch alone can be naturally employed; alternatively, a polyester which have long chain branch may be used, or mixture thereof may also be used. However, when smaller necking-in is desired, a polyester having long chain branch may preferably be blended. It is needless to say when the polyester resin of the present invention is used, lubricants, waxes, coloring agents, fillers and the like can be used concomitantly, necessary. Among these, lubricants such as VITON, are especially very effective in improving the smoothness of the surface. |
| PATENT EXAMPLES | available on request |
| PATENT PHOTOCOPY | available on request |
|
Want more information ? Interested in the hidden information ? Click here and do your request. |