Abstract:
A process of manufacturing a pulp molded cup lid includes making a pulp slurry; distributing the pulp onto a continuous screen wherein the pulp slurry is converted into a blank; feeding the blank and the continuous screen onto a first blanking die; moving a first blanking punch onto the first blanking die to dry the blank at a temperature of 160-180° C. for 2-5 seconds; causing the first blanking punch to exert pressure of 27-40 N/cm 2  on the blank for 8-20 seconds; conveying the blank onto a second blanking die which is disposed under a second blanking punch; drying the blank, the second blanking punch, and the second blanking die at a temperature of 160-180° C.; moving the second blanking punch onto the second blanking die in 2-8 seconds; and causing the second blanking punch to exert pressure of 80-120 N/cm 2  on the blank for 30-45 seconds.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This present application claims the benefit of PCT application No. PCT/CN2013/070512 filed on Jan. 16, 2013, which claims the benefit of Chinese Patent Application No. 201220410099.9 filed on Aug. 17, 2012; the contents of which are hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention is of pulp moulded cup lid manufactured with improved technology, and particularly, of the process of manufacturing the lid which has fine, smooth, non-reticulated inner and outer surfaces. 
         [0004]    2. Description of Related Art 
         [0005]    Pulp moulding is a three-dimensional papermaking technique in which pulp made from plant fibers is shaped in a mould by pulp moulding machines to produce paper products. 
         [0006]    Below is detailed in a first conventional process including the steps of distributing pulp made from plant fibers into a vacuum forming mould with a filtering screen and being shaped via adsorption moulding, wherein the mould, filtered pulp has a water percentage of 65 to 75 wt %; drying the pulp to reduce water content to 10-15%, and, shaping the pulp in a thermoforming mould at a temperature of 160-180° C. through compression moulding to produce a finish product. In this process, shape of the product has been basically finalized at the stage of drying. The compression moulding leaves clear reticulated surfaces on both sides with coarse texture and a paper density of 0.35-0.40 g/cm 3 . Such process is generally applied to the packing materials which have cushioning and less aesthetic requirements. 
         [0007]    Below is also detailed in a second conventional process including the steps of distributing pulp made from plant fibers into a vacuum forming mould equipped with a filter and being shaped via adsorption moulding, wherein the mould, filtered pulp has a water percentage of 65 to 75 wt %, and, pressing, drying, and moulding the pulp in a thermoforming mould with a metal filter to produce a finish paper product. The final product has a reticulated surface with coarse texture on one side and a smooth non-reticulated surface on the other side. 
         [0008]    It has a paper density of 0.60-0.65 g/cm 3 . Products made in such process are primarily used to pack food or as a cap for a container. However, because the side with reticulated surface has not been calendered. Subtle plant filbers (paper fibers) tend to separate out on the paper package. 
         [0009]    The existing moulding processes of making pulp moulded cup lids also includes the steps of diluting the plant fibers to make pulp slurry, distributing the pulp, vacuum adsorption forming, drying, moulding and pressing under high temperature, cutting, punching, and sealing or forming annular groove on a skirt. The final product has also a reticulated surface with a coarse texture on one side and a smooth non-reticulated surface on the other side. It has a density of 0.60-0.65 g/cm 3 . The smooth non-reticulated side is usually used as outer surface of the lid for aesthetic purpose while the reticulated side with a coarse texture is used as inner surface. However, tiny fibers on the coarse inner surface may fall into the liquid content in the container and it is not acceptable to consumers. If, alternatively, the smooth, non-reticulated side is used as inner surface and the reticulated side as outer surface, its appearance is unaesthetic. High quality printed graphics cannot be printed on top of the coarse outer surface as an advertising medium. Furthermore, the tiny fibers could be in contact with the mouth of a consumer in drinking. This is not desired. Moreover, pulp moulded cup lid manufactured by the existing techniques, because of the process of forming with filtering screen, has a low density of 0.6˜0.65 g/cm 3  which leads to a weak overall strength, weak structure, insufficient fastening force of the skirt of the lid upon the container. This very often leads to a bad sealing effect of the container. When containing hot beverage, the lid and the cup could be separated easily, resulting in a potential leaking of the hot beverage and causing dangerous of burning users. Meanwhile, lids made with the existing designs have low strength around the suction mouth of the lid. When a user taking beverage, the area of the suction mouth is easy to be impregnated by hot beverage, and, then softened and deformed under force of lips of the user. 
       SUMMARY OF THE INVENTION 
       [0010]    The object of the patent application is to provide a pulp moulded cup lid which has non-reticulated inner and outer surfaces, and, to provide a method of manufacturing the cup lids. The lids can satisfy the need of covering the cup tightly and achieve a good sealing effect. 
         [0011]    According to one aspect of the patent application, a pulp moulded cup lid includes a lid body; a sealing skirt extending downward the lid body; a plurality of buckling projections disposed evenly and circumferentially on an outer surface of a lower portion of the skirt. The above described lid body has fine, smooth, non-reticulated inner and outer surfaces. 
         [0012]    According to another aspect of the patent application, a method of manufacturing the lids including the following steps: 
         [0013]    (1) diluting plant fibers in water to make pulp slurry; 
         [0014]    (2) filling the pulp slurry into a forming mould with a filtering screen for vacuum adsorption moulding to become a blank, wherein the blank has a water content of 65-75 wt %; 
         [0015]    (3) closing a transfer mould (plank punch) of temperature of 160-180° C. and the forming mould with no pressure applied for 2-5 seconds; then, applying a pressure up to 27-40 N/cm 2  on the blank for 8-20 seconds; when this step is completed, the blank has a total water content of 50-55 wt %, while a side contacting the filtering screen has a water content of 58-65 wt %; and 
         [0016]    (4) moving The blank into a set of heat setting drying moulds with upper and lower moulds at temperature of 160-180° C.; closing the two moulds together with no pressure applied for 2-8 seconds; then, applying a pressure up to 80-120 N/cm 2  on the blank for 30-45 seconds. Cup lids manufactured through the method of this patent application has fine, smooth, non-reticulated inner and outer surfaces. No paper fibers separate from either the surface contacting liquid or the dispensing window contacting with user lips. Paper fibers of the cup lids bind tighter. The cup lids have a thickness of 0.50-0.60 mm, and a high paper density of 0.77˜0.8 g/cm 3 , which reinforce solidarity and strength of product body, especially the strength of bucking projections. The high density pulp moulded cup lids are not to be easily damped and deformed in an environment of high humidity. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a perspective view of a cup lid for a container according to a first embodiment of this invention; 
           [0018]      FIG. 2  is a bottom view of the cup lid of this invention; 
           [0019]      FIG. 3  is a sectional view of the cup lid of this invention; 
           [0020]      FIG. 4  is a perspective view of the cup lid for a container according to a second embodiment of the present invention; and 
           [0021]      FIG. 5  is a schematic drawing of the moulds used in manufacturing the cup lids in this invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    The following is the detailed description of the technique used in this invention. 
         [0023]    Referring to  FIGS. 1 to 3 , a pulp moulded cup lid with non-reticulated inner and outer surfaces in accordance with the invention is shown. Both surfaces are fine and smooth. The cup lid includes the following components as discussed in detail below. 
         [0024]    The cup lid includes lid body  1  which has smooth non-reticulated inner and outer surfaces. There is a sealing skirt  4  formed at one end of the lid body  1  extending along the axial direction. A plurality of buckling projections  5  are formed on the inner surface of the skirt  4  and evenly distributed along the circumference. The projections  5  project inward with a height of 1.5-2.0 mm. When the lid is applied on a cup, the projections  5  clamp together with rim of the cup. An effective result can be achieved with 8 to 16 such projections. The projections  5  makes it easier to apply the lid to cover the opening of the cup and also easy to take the lid off the cup. 
         [0025]    Existing techniques and processes tries to add a clamping function on pulp moulded products by pressing upwards to make a ring of rim and groove to achieve the effect of clamping to the rim at cup edge. This continuous deformation of the material damages combination strength between fibers along the circumference, and, therefore, leads to weak overall strength of the lid skirt. 
         [0026]    The lid fails to clamp on the cup tightly. It is impossible to lift a cup of full of beverage by only holding the cup lid covered on the cup. By contrast, in the present invention, elongated projections  5  evenly distributed along the circumference are functioned as buckles to maintain and reinforce the overall strength of the skirt  4 . 
         [0027]    On the outer periphery of the lid body  1 , a convex platform  2  is set along the circumferential direction. A dispensing window  3  is opened on the convex platform  2 . The dispensing window  3  is either open or provided with a clamshell type cover. 
         [0028]    A concave groove  6  is formed on the lid body  1  adjacent to the dispensing window  3 , which helps to expose the dispensing window  3  as a suction mouth. The provision of the concave groove  6  allows a user to easily drink the liquid stored in the container by placing his or her lips on both the dispensing window  3  and the concave groove  6  without relying on a straw. By changing the shape and size of the dispensing window  3 , it can be adapted to suit different usages, i.e. inserting a straw or have user&#39;s mouth contact to the dispensing window directly. 
         [0029]    On the lid body  1  of the above described lid, a plurality of reinforcing ribs  7  are formed on the outer surface of the dispensing window  3 . They are used to increase the overall strength of the lid. Setting on the outer surface of the dispensing window, the ribs make the area around the dispensing window strong and stiff This structure prevents the area from being deformed by impregnation of liquid and force applied by a user&#39;s mouth when the user is drinking the liquid through the dispensing window  3 . The reinforcing ribs are bump in an evenly spaced arrangement. Alternatively, the reinforcing ribs  7  can be in the form of creases or a wavy structure to achieve the same effect. 
         [0030]    The shape of the lid body  1  shown in  FIG. 1  is a disc. Alternatively, shape of the lid body  1  shown in  FIG. 1  can be made rectangular, square, or any of other shapes other than a disc. The lid body  1  shown in  FIG. 1  can also be irregularly shaped. 
         [0031]    Referring to  FIG. 4 , a cup lid for a container in accordance with a second embodiment of the present invention is shown. The characteristics of the second embodiment are substantially the same as that of the first embodiment except the following: 
         [0032]    The concave groove is eliminated. A window  3  is provided on a top. A clamshell  8  is hingedly secured to an edge of the window  3 . A well  9  is provided adjacent to both the clamshell  8  and the window  3 . In a ready to dispense state, the clamshell  8  is pivoted to expose the window  3  and temporarily fastened in the well  9 . To the contrary, in a storage state the clamshell  8  is pivoted in an opposite direction to close the window  3 . 
         [0033]    Referring to  FIG. 5 , a process of manufacturing a pulp moulded cup lid in accordance with the invention is illustrated. The process comprises the following steps: 
         [0034]    (1) Plant fibers are diluted to make pulp slurry, concentration of the pulp can be 4-6% or other appropriate percentage; 
         [0035]    (2) The pulp slurry is filled into a forming mould (blank die)  102  with filtering screen  106  for vacuum adsorption moulding to form a blank  105 . The blank has a water content of 65-75 wt %; 
         [0036]    (3) As illustrated in  FIG. 4 , a transfer mould (blank punch)  101  at temperature of 160-180° C. is brought onto the forming mould (blank die)  102  for 2-5 seconds without exerting pressure. The purpose is to bake the blank  105  to cause slight contraction on the blank surface contacting the transfer mould (blank punch)  101 . This step will enhance the strength of the fiber structure on that surface to prevent the blank from fracturing under an abruptly applied pressure. Then, a pressure up to 27-40 N/cm 2  (calculated from horizontal projected area of the blank) is applied on the closed moulds (blank punch and blank die) for 8-20 seconds to drain water out from the blank. In the meantime, this process let the transfer mould (blank punch)  101  to dry preliminarily the surface of the blank. After this process of pressing and predrying, the blank has a water content of 50-55% while the side of the blanking contacting the filtering screen has a water content of 58-65%. 
         [0037]    Because this process heating the blank from one single side, the water content varies in different paper layers of the blank. If water content of the side of the blank contacting the filtering screen is too low, the network pattern left by the screen cannot be removed and will be left on the surface of that side. However, if water content is too high on the side of contacting the filtering screen, the subsequent high temperature pressing process applied on the blank can cause a large amount of water vapor, and therefore, a big pressure between the blank and the mould. This will result in separation of paper layers in the final product and even a blank explosion. Advantageously, the above drawbacks have been eliminated in the above described step in this invention; 
         [0038]    (4) The blank is moved into a thermoforming drying mould with the upper mould (blank punch)  103  and lower mould (blank die)  104  at a temperature between 160° C. and 180° C. The set is closed without exerting pressure for 2-8 seconds. Then, pressure up to 80-120 N/cm 2  is applied for 30-45 seconds. Thereby, a finished pulp moulded cup lid is produced. 
         [0039]    After predried through the step 3, plant fibres in the blank have been adsorbed strongly onto the blank. A large amount of water has been removed under pressure and predrying. It is therefore in the thermoforming process of the step 4 unnecessary to use filtering screen to drain out the water, which avoids leaving a network pattern on the surfaces of the pulp moulded cup lids. In the step 4 above, the moulding pressure applied is 80-120 N/cm 2 . 
         [0040]    As a marked contract to this process, the maximum moulding pressure applied in the other existing techniques and processes of manufacturing pulp moulded food packaging products is not higher than 50 N/cm 2 . The reason for this difference is that in the other existing processes thickness of products is normally between 0.55 mm and 0.65 mm. Because metal filtering screen is used in those processes, higher mould pressure will not only leave reticulated surface on the side of the products contacting the filtering screen, but also the opposite side can be marked with black network pattern in the process of heating and pressing. Meanwhile, the filtering screen can also sink deep to the blanks and cause weakening of the strength of the blanks. This defect can cause leakage when containers made in such process containing liquid. As no filtering screen used in the above step 4, mould pressure can be increased to 80-120 N/cm 2 , which increased greatly density of the blank. Therefore, the overall strength and stiffness of cup lid has been improved remarkably, which makes it easier to set the bump-like reinforcing ribs and the clamshell style cover over the dispensing window. 
         [0041]    The existing techniques and processes uses filtering screen in the stage of high pressure forming. Under high pressure, the filtering screen (usually stainless steel screen) could break at small angles or concave corners of products. This drawback limited design of shape of cup lids. Because in this invention no filtering screen used in the stage of high pressure forming, there is no such limit on product design. The designs of cup lids can meet more functional and aesthetic requirements. 
       EXAMPLE I 
       [0042]    In the above described step (2), the blank has a water content of weight percentage of 70 wt % after the filtering and vacuum forming. In the step (3), the transfer mould (blank punch) is at the temperature of 170° C. the transfer mould (blanking punch)  101  closes onto the forming mould (blanking die)  102  for 3 seconds with no pressure exerted. Pressure is then exerted on the blank  105  up to 33N/cm 2  for 15 seconds. The blank  105  has a water percentage of 52 wt % and the surface of the blank  105  contacting the filtering screen  106  has a water percentage of 59 wt %. In the step (4), the temperature of both upper and lower moulds is 170° C. The upper mould (blanking punch)  103  closes onto the lower mould (blanking die)  104  without exerting pressure for 3 seconds. Then, pressure exerted on the blank  105  is 97 N/cm 2  and lasts for 38 seconds. The finished cup lid has a thickness of 0.55 mm and a paper density of 0.78 g/cm 3 . 
       EXAMPLE II 
       [0043]    In the above described step (2) the blank has a water content of 68 wt % after the filtering vacuum forming. In the step (3), the transfer mould (blanking punch) is at temperature of 168° C. and the blanking punch  101  closes onto the blanking die  102  for 2 seconds with no pressure exerted. Then, pressure up to 40N/cm 2  is exerted on the blank  105  for 10 seconds. The blank  105  has a water percentage of 50 wt % and the surface of the blank  105  contacting the filtering screen  106  has a water percentage of 58 wt %. In the step (4), the temperature of upper and lower moulds is 168° C. The upper mould (blanking punch)  103  closes onto the lower mould (blanking die)  104  without exerting pressure for 2 seconds. Pressure up to 92 N/cm 2  is then exerted on the blank  105  and lasts for 30 seconds. The finished cup lid has a thickness of 0.52 mm and a paper density of 0.79 g/cm 3 . 
       EXAMPLE III 
       [0044]    In the above described step (2), the blank has a water content of 72 wt after the filtering and vacuum forming. In the step (3), the temperature of the transfer mould (blanking punch) is 172° C., and the blanking punch  101  closes onto the blanking die  102  for 4 seconds with no pressure applied. Pressure up to 27 N/cm 2  is then exerted on the blank  105  for 18 seconds. The blank  105  has a water percentage of 53 wt % and the surface of the blank  105  contacting the filtering screen  106  has a water percentage of 63 wt %. In the step (4), the temperature of both upper and lower moulds is 180° C. The upper mould (blanking punch)  103  closes onto the lower mould (blanking die)  104  without exerting pressure for 4 seconds. Pressure up to 90 N/cm 2  is then exerted on the blank  105  and lasts for 45 seconds. The finished cup lid has a thickness of 0.60 mm and a paper density of 0.775 g/cm 3 . 
       EXAMPLE IV 
       [0045]    In the above described step (2), the blank has a water content of 75 wt % after the filtering and vacuum forming In the step (3), the temperature of the transfer mould (blanking punch) is 180° C. and the blanking punch  101  closes onto the blanking die  102  for 5 seconds with no pressure applied. Pressure up to 35 N/cm is then exerted on the blank  105  for 20 seconds. The blank  105  has a water percentage of 55 wt % and the surface of the blank  105  contacting the filtering screen  106  has a water percentage of 65 wt %. In the step (4), the temperature of both upper and lower moulds is 175° C. The upper mould (blanking punch)  103  closes onto the lower mould (blanking die)  104  without exerting pressure for 8 seconds. Pressure up to 88 N/cm 2  is then exerted on the blank  105  and lasts for 42 seconds. The finished cup lid has a thickness of 0.58 mm and a paper density of 0.785 g/cm 3 . 
       EXAMPLE V 
       [0046]    In the above described step (2), the blank has a water content of 65 wt % after the filtering and vacuum forming In the step (3), the temperature of the transfer mould (blanking punch) is 160° C. and the blanking punch  101  closes onto the blanking die  102  for 3 seconds with no pressure applied. Pressure up to 33 N/cm 2  is exerted on the blank  105  for 8 seconds. The blank  105  has a water percentage of 50 wt % and the surface of the blank  105  contacting the filtering screen  106  has a water percentage of 60 wt %. In the step (4), the temperature of both upper and lower moulds is 164° C. The upper mould (blanking punch)  103  closes onto the lower mould (blanking die)  104  without exerting pressure for 2 seconds. Pressure up to 100 N/cm 2  is then exerted on the blank  105  and lasts for 35 seconds. The finished cup lid has a thickness of 0.56 mm and a paper density of 0.80 g/cm 3 . 
         [0047]    Cup lids manufactured through the method of this patent application has fine, smooth, non-reticulated inner and outer surfaces. No paper fiber separates from either the surface contacting liquid or the dispensing window contacting with user lips. Because appropriate techniques, equipments and mould matching are adopted during the manufacturing process, the blank of the pulp moulded cup lid is guaranteed to possess reasonable water content in its various paper layers during each stage of pressing, draining, drying, and forming. In this patent application, adoption of higher pressure in pulp moulding process than the generally used processes makes final product of pulp moulded cup lids having non-reticulated surfaces, tighter binding between paper fibers, and a high paper density of 0.77-0.8 g/cm 3 , which reinforce solidarity and strength of product body, especially the strength of bucking projections. The high density pulp moulded cup lids are not to be easily damped and deformed in an environment of high humidity. 
         [0048]    While the patent application has been described in terms of preferred embodiments, those skilled in the art will recognize that the patent application can be practiced with modifications within the spirit and scope of the appended claims.