Adhesive material.

0001The present invention relates generally to materials for use in the manufacture of creped fibrous webs. More particularly, it relates to a formulation which reduces or eliminates blocking.

0002Inventors in the prior art have developed methods for providing strength and abrasion resistance to the surface of a fibrous web while at the same time increasing the softness, absorbency and bulk of the web. US- A- 3 879 257 discloses a unitary or single-ply fibrous web having a laminate-like structure which consists of a soft, absorbent central core region of relatively low fibre concentration sandwiched between two strong, abrasion resistant surface regions. According to US- A- 3 879 257 the surface regions are formed by application of a bonding material, preferably elastomeric. The bonding material in at least one surface region is disposed in a fine, space-apart pattern, and the bonded portions in that surface region are finely creped to soften them. According to US- A- 3 879 257, the bonding material adheres the web in a pattern to a creping surface from which it is removed by a doctor blade to greatly disrupt the fibres within the web where bonding material is not disposed. This "bonding material", which adheres the web to the creping surface in a controlled manner, is variously referred to in the art as "binder", "adhesive" or more particularly "creping adhesive".

0003Where the present invention has its greatest utility in processes derived from the teachings of US- A- 3 879 257, the term "creping adhesive" will be employed herein to describe a bonding material which performs the functions of adhering a fibrous web to a creping surface and imparting strength to the creped sheet by bonding the fibres together. As thus broadly defined it encompasses materials applied to the surface of the web or to the creping surface.

0004The concepts of US- A- 3 879 257 were extended to the formation of laminates of two or more dry webs in US- A- 4 610 743. According to US- A- 4 610 743, as in US- A- 3 879 257, both surface regions of the resulting product have creping adhesive disposed therein. Another variation on patterned creping of fibrous webs is disclosed by US- A- 4 125 659. According to US- A- 4 125 659, a creping adhesive is uniformly applied to just one side of the web and after the web has been adhered to the creping cylinder, a raised pattern is pressed into the web toward the creping cyclinder. While all of these patented process offer substantial improvements in strength and absorbency, the products can suffer from a serious disadvantage, not mentioned in any of the patents, which is "blocking".

0005The term "blocking" refers to the tendency of adhesively bonded webs or sheets to adhere to one another when in contact under pressure such as when wound up on a reel or when packaged in rolls or stacks. This negative characteristic interferes with the conversion of parent rolls and the dispensing and unfolding of the finished product. The tendency of creped web to "block" is proportional to the amount of creping adhesive on the surface of the web and thus is more severe in the case of pattern-creped adhesively bonded materials such as described by US- A- 3 879 257 and the other Specifications mentioned above.

0006The phenomenon of blocking of creped fibrous sheets is specifically addressed in US- A- 4 063 995. The term is defined therein at Column 1, lines 58-66. US- A- 4 063 995 teaches the use of a four component binder and creping adhesive composition comprising, inter alia, a blocking suppressant. US- A- 4 063 995 describes a variety of materials as being suitable blocking suppressants among them being any of the known polymers suitable for use as a binder for fibres "provided it has a glass transition temperature of from about +30°C to about +50°C so that it will function as a blocking suppressant". (See Column 6, lines 17-22).

0007According to the present invention there is provided a new, improved creping adhesive comprising a polymer or copolymer having a Tg of more than 50°C. Preferably, the creping adhesive further comprises a second component which is a soft polyner emulsion having a Tg below 10°C and which cross-links upon drying and heating. The hard polymer component makes up from 10% to 100% and preferably 25% to 40% of the formulation by weight of the total solids content of the formulation. A further characteristic of the hard polymer component is that it does not form a film at ambient (room) temperature. Specifically preferred as the hard polymer is poly(methyl methacrylate). The combination is non-­blocking when used as a creping bonding material. The term "non-blocking" as used herein indicates that the webs separate readily, as will be described in greater detail hereinafter. By following the teachings of the present invention, it is actually possible to attain "zero" blocking wherein the sheets separate under the force of the weight of one web. Other things being equal, blocking tends to be proportional to the concentration of creping adhesive at the surface of the web. Accordingly, the problem the present invention seeks to solve, namely blocking, is primarily associated with creped webs which have relatively high concentrations of creping adhesive at the surface, such as webs made in accordance with the teachings of US- A- 3 879 257 and the other specifications mentioned above, that is to say patterned creping. However, the present invention has applicability to any type of conventional creping process wherein the web is adhered to a creping surface (a heated rotating drum) and removed with a doctor blade (creping blade). The creping adhesive, which also adheres the web to the creping surface, can be applied to the creping surface itself or to the fibrous sheet by any suitable means. It can by sprayed onto the fibrous sheet or onto the creping surface. It can be transferred uniformly over all or printed in a pattern. The pattern may be a continuous one or consist of spaced apart dots or discontinuous lines. Discontinuous patterns result in more pleasing tactile properties, i.e. better "hand feel". Long fibres (longer than wood pulp fibres) may be incorporated in the web to compensate for the lesser strength of a discontinuous pattern.

0008In carrying out the present invention, a fibrous base web is produced as a continuous web from substantially all wood pulp fibres or in combination with long fibre elements. To provide soft, non-blocking fibrous webs, it is preferred to blend a self-cross-­linkable soft binder having a Tg of less than 10 degrees Celsius with a non-film forming hard polymer emulsion having a Tg greater than 50 degrees Celsius. The optimum solids blend may be formulated by selecting the ratio of soft polymer to the hard polymer which provides the non-blocking feature while providing adequate adhesion to the creping surface and the least compromise to tensile strength and hand feel. It is believed that the use of a hard polymer or copolymer having a Tg greater than 50 degrees Celsius either exclusively or at a level greater than 10% with a soft polymer having a Tg of 10 degrees Celsius or less in an aqueous dispersion to provide a non-blocking creping adhesive has not heretofore been employed because the hard polymer components as such are viewed as being non-film-forming at room temperature. It is unobvious to use these hard polymers in a high concentration suggested by the present invention of 10% or more, as one of ordinary skill in the art would expect to achieve a harsh surface which is board-like or disintegrates into powder when touched.

0009In the preferred mode of carrying out the present invention for making heavyweight tissue to be converted into, for example towels or wipers, the creping adhesive comprises cross-linking polymers and is applied to the sheet material at one or more print stations typical in a patterned creping process to provide a fibrous web which remains soft to the hand but does not block. As will be understood by one of ordinary skill in the art to which the present invention pertains, if a lighter weight, flushable sheet is desired, for example for conversion into bathroom tissue or facial tissue, then the creping adhesive consists of non-cross-linking polymers and is applied to the web in a lesser quantity preferably by application to the creping surface.

0010The following Examples taken from actual operating data will serve to more fully illustrate our invention. In the Examples which follow, the bonding material was applied to both sides of a previous formed and dried paper web having a basis weight of 76 grammes per square metre and creped by printing creping adhesive on the first side with a diamond pattern, pressing and adhering the first side to a hot creping cylinder, then removing the web with a doctor blade and pull rolls rotating at the same speed as the creping cylinder. Immediately thereafter, the second side is printed with creping adhesive and adhered to a secod hot creping cylinder, then removed with a doctor blade and pull rolls, rotating slower than the creping cylinder. After creping, the web is passed through a hot through-air curing oven to raise the temperature of the web to 150°C, followed by winding on the reel, where the percentage crepe from the second pull rolls to the reel is 12%.

0011The adhesive components in these Examples are aqueous emulsions of polymers or copolymers as identified below. Each is cross-linkable, except where noted to the contrary. Because the Examples were selected to be illustrative, polymer identification numbers are not inclusive. <tables id="tabl0001" num="0001"><table frame="all"><tgroup cols="3" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="52.50mm" /><colspec colnum="2" colname="col2" colwidth="52.50mm" /><colspec colnum="3" colname="col3" colwidth="52.50mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" align="center"><u style="single">Polymer/Copolymer</u></entry><entry namest="col3" nameend="col3" align="center"><u style="single">Tg, °C</u></entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="right">1.</entry><entry namest="col2" nameend="col2" align="left">acrylic copolymer</entry><entry namest="col3" nameend="col3" align="right">-33</entry></row><row><entry namest="col1" nameend="col1" align="right">3.</entry><entry namest="col2" nameend="col2" align="left">ethylene/vinylacetate copolymer</entry><entry namest="col3" nameend="col3" align="right">0</entry></row><row><entry namest="col1" nameend="col1" align="right">4.</entry><entry namest="col2" nameend="col2" align="left">poly(methyl methacrylate)</entry><entry namest="col3" nameend="col3" align="right">+100</entry></row><row><entry namest="col1" nameend="col1" align="right">5.</entry><entry namest="col2" nameend="col2" align="left">styrene/butadiene</entry><entry namest="col3" nameend="col3" align="right">0</entry></row><row><entry namest="col1" nameend="col1" align="right">6.</entry><entry namest="col2" nameend="col2" align="left">ethylene/vinylacetate</entry><entry namest="col3" nameend="col3" align="right">0</entry></row><row><entry namest="col1" nameend="col1" align="right">7.</entry><entry namest="col2" nameend="col2" align="left">vinylacetate/acrylate</entry><entry namest="col3" nameend="col3" align="right">0</entry></row><row><entry namest="col1" nameend="col1" align="right">8.</entry><entry namest="col2" nameend="col2" align="left">styrene/acrylic</entry><entry namest="col3" nameend="col3" align="right">56</entry></row><row><entry namest="col1" nameend="col1" align="right">9.</entry><entry namest="col2" nameend="col2" align="left">acrylic</entry><entry namest="col3" nameend="col3" align="right">-33</entry></row><row><entry namest="col1" nameend="col1" align="right">10.</entry><entry namest="col2" nameend="col2" align="left">styrene, non-crosslinking</entry><entry namest="col3" nameend="col3" align="right">+100</entry></row><row><entry namest="col1" nameend="col1" align="right">11.</entry><entry namest="col2" nameend="col2" align="left">styrene/butadiene</entry><entry namest="col3" nameend="col3" align="right">- 3</entry></row><row><entry namest="col1" nameend="col1" align="right">13.</entry><entry namest="col2" nameend="col2" align="left">styrene, non-crosslinking</entry><entry namest="col3" nameend="col3" align="right">100</entry></row><row><entry namest="col1" nameend="col1" align="right">14.</entry><entry namest="col2" nameend="col2" align="left">vinylacetate/ethylene</entry><entry namest="col3" nameend="col3" align="right">-2</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="right">15.</entry><entry namest="col2" nameend="col2" align="left">acrylic terpolymer</entry><entry namest="col3" nameend="col3" align="right">-30</entry></row></tbody></tgroup></table></tables><tables id="tabl0002" num="0002"><img file="EP0340020A2_D0001.tif" /></tables><tables id="tabl0003" num="0003"><img file="EP0340020A2_D0002.tif" /></tables>

0012The blocking values are obtained by placing together a strip 10.2 cm wide x 15.2 cm, long smooth side to smooth side, the smooth side being defined as the less undulated of the two surfaces, (compare US- A- 3 879 257, column 16, lines 27-41), the strips are maintained under a pressure of 18 grammes per square centimetre and a temperature of 60 degrees C for 12 hours followed by cooling to room temperature for 12 hours. This cycle of heating and cooling was repeated up to 4 times, the number of iterations being held constant for any series of creping adhesive compositions. After the final cooling period to room temperature, the blocking level is measured as the number of grammes in excess of the weight of the two strips, pulling on the top sheet lying in a horizontal plane with a hand held scale. Zero blocking is the condition where the weight of the bottom sheet is great enough to separate the two sheets. When the blocking is great enough to lift the top sheet, the scale is used, hooked to the top sheet while thre adjacent edge of the bottom sheet is clamped to the supporting surface during pulling with the scale to obtain the reading in grammes.

0013In the following Examples, the creping adhesive was applied to a single side of the web; and the creping step was performed as above described but on one side only.

0014The adhesive components in these Examples are aqueous emulsions of polymers or copolymers as identified below. Each is cross-linkable, except where noted to the contrary. Because the Examples were selected to be illustrative, polymer identification numbers are not inclusive. <tables id="tabl0004" num="0004"><table frame="all"><tgroup cols="3" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="52.50mm" /><colspec colnum="2" colname="col2" colwidth="52.50mm" /><colspec colnum="3" colname="col3" colwidth="52.50mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" align="center"><u style="single">Polymer/Copolymer</u></entry><entry namest="col3" nameend="col3" align="center"><u style="single">Tg, °C</u></entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="right">1.</entry><entry namest="col2" nameend="col2" align="left">carboxylated styrene/butadiene</entry><entry namest="col3" nameend="col3" align="right">-33</entry></row><row><entry namest="col1" nameend="col1" align="right">2.</entry><entry namest="col2" nameend="col2" align="left">poly(methyl methacrylate) non-cross-linking</entry><entry namest="col3" nameend="col3" align="right">+100</entry></row><row><entry namest="col1" nameend="col1" align="right">3.</entry><entry namest="col2" nameend="col2" align="left">ethylene/vinyl acetate</entry><entry namest="col3" nameend="col3" align="right">0</entry></row></tbody></tgroup><tgroup cols="3" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="52.50mm" /><colspec colnum="2" colname="col2" colwidth="52.50mm" /><colspec colnum="3" colname="col3" colwidth="52.50mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" align="center"><u style="single">Polymer/Copolymer</u></entry><entry namest="col3" nameend="col3" align="center"><u style="single">Tg, °C</u></entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="right">4.</entry><entry namest="col2" nameend="col2" align="left">poly(methyl methacrylate)</entry><entry namest="col3" nameend="col3" align="right">+100</entry></row><row><entry namest="col1" nameend="col1" align="right">6.</entry><entry namest="col2" nameend="col2" align="left">ethylene/vinyl acetate</entry><entry namest="col3" nameend="col3" align="right">0</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="right">7.</entry><entry namest="col2" nameend="col2" align="left">vinyl acetate/acrylate</entry><entry namest="col3" nameend="col3" align="right">0</entry></row></tbody></tgroup></table></tables><tables id="tabl0005" num="0005"><table frame="all"><tgroup cols="8" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="19.68mm" /><colspec colnum="2" colname="col2" colwidth="19.68mm" /><colspec colnum="3" colname="col3" colwidth="19.68mm" /><colspec colnum="4" colname="col4" colwidth="19.68mm" /><colspec colnum="5" colname="col5" colwidth="19.68mm" /><colspec colnum="6" colname="col6" colwidth="19.68mm" /><colspec colnum="7" colname="col7" colwidth="19.68mm" /><colspec colnum="8" colname="col8" colwidth="19.68mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" align="center">Component Nos.</entry><entry namest="col2" nameend="col2" align="center">% Soft Comp</entry><entry namest="col3" nameend="col3" align="center">% Hard Comp</entry><entry namest="col4" nameend="col4" align="center">Basis Weight g/m²</entry><entry namest="col5" nameend="col5" align="center">Bulk mm</entry><entry namest="col6" nameend="col6" align="center">Bulk to Basis Weight</entry><entry namest="col7" nameend="col7" align="center">Geometric Mean Dry Tensile Kg/cm</entry><entry namest="col8" nameend="col8" align="center">Blocking* (grams)</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="right">1</entry><entry namest="col2" nameend="col2" align="right">100</entry><entry namest="col3" nameend="col3" align="right">0</entry><entry namest="col4" nameend="col4" align="char" char=".">77.83</entry><entry namest="col5" nameend="col5" align="char" char=".">11.0</entry><entry namest="col6" nameend="col6" align="char" char=".">.141</entry><entry namest="col7" nameend="col7" align="char" char=".">4.89</entry><entry namest="col8" nameend="col8" align="right">18</entry></row><row><entry namest="col1" nameend="col1" align="right">1/2</entry><entry namest="col2" nameend="col2" align="right">50</entry><entry namest="col3" nameend="col3" align="right">50</entry><entry namest="col4" nameend="col4" align="char" char=".">83.19</entry><entry namest="col5" nameend="col5" align="char" char=".">11.7</entry><entry namest="col6" nameend="col6" align="char" char=".">.141</entry><entry namest="col7" nameend="col7" align="char" char=".">5.60</entry><entry namest="col8" nameend="col8" align="right">1</entry></row><row><entry namest="col1" nameend="col1" align="right">2</entry><entry namest="col2" nameend="col2" align="right">0</entry><entry namest="col3" nameend="col3" align="right">100</entry><entry namest="col4" nameend="col4" align="char" char=".">79.68</entry><entry namest="col5" nameend="col5" align="char" char=".">9.7</entry><entry namest="col6" nameend="col6" align="char" char=".">.122</entry><entry namest="col7" nameend="col7" align="char" char=".">6.91</entry><entry namest="col8" nameend="col8" align="right">0</entry></row><row><entry namest="col1" nameend="col1" align="right">3</entry><entry namest="col2" nameend="col2" align="right">100</entry><entry namest="col3" nameend="col3" align="right">0</entry><entry namest="col4" nameend="col4" align="char" char=".">80.56</entry><entry namest="col5" nameend="col5" align="char" char=".">15.8</entry><entry namest="col6" nameend="col6" align="char" char=".">.196</entry><entry namest="col7" nameend="col7" align="char" char=".">2.15</entry><entry namest="col8" nameend="col8" align="right">20</entry></row><row><entry namest="col1" nameend="col1" align="right">4</entry><entry namest="col2" nameend="col2" align="right">0</entry><entry namest="col3" nameend="col3" align="right">100</entry><entry namest="col4" nameend="col4" align="char" char=".">79.00</entry><entry namest="col5" nameend="col5" align="char" char=".">9.5</entry><entry namest="col6" nameend="col6" align="char" char=".">.120</entry><entry namest="col7" nameend="col7" align="char" char=".">6.36</entry><entry namest="col8" nameend="col8" align="right">0</entry></row><row><entry namest="col1" nameend="col1" align="right">6/2</entry><entry namest="col2" nameend="col2" align="right">50</entry><entry namest="col3" nameend="col3" align="right">50</entry><entry namest="col4" nameend="col4" align="char" char=".">82.27</entry><entry namest="col5" nameend="col5" align="char" char=".">16.5</entry><entry namest="col6" nameend="col6" align="char" char=".">.201</entry><entry namest="col7" nameend="col7" align="char" char=".">2.69</entry><entry namest="col8" nameend="col8" align="right">2</entry></row><row><entry namest="col1" nameend="col1" align="right">6</entry><entry namest="col2" nameend="col2" align="right">100</entry><entry namest="col3" nameend="col3" align="right">0</entry><entry namest="col4" nameend="col4" align="char" char=".">80.93</entry><entry namest="col5" nameend="col5" align="char" char=".">17.1</entry><entry namest="col6" nameend="col6" align="char" char=".">.211</entry><entry namest="col7" nameend="col7" align="char" char=".">1.55</entry><entry namest="col8" nameend="col8" align="right">14</entry></row><row><entry namest="col1" nameend="col1" align="right">7</entry><entry namest="col2" nameend="col2" align="right">100</entry><entry namest="col3" nameend="col3" align="right">0</entry><entry namest="col4" nameend="col4" align="char" char=".">82.27</entry><entry namest="col5" nameend="col5" align="char" char=".">16.7</entry><entry namest="col6" nameend="col6" align="char" char=".">.203</entry><entry namest="col7" nameend="col7" align="char" char=".">4.44</entry><entry namest="col8" nameend="col8" align="right">8</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="right">7/2</entry><entry namest="col2" nameend="col2" align="right">50</entry><entry namest="col3" nameend="col3" align="right">50</entry><entry namest="col4" nameend="col4" align="char" char=".">83.14</entry><entry namest="col5" nameend="col5" align="char" char=".">14.0</entry><entry namest="col6" nameend="col6" align="char" char=".">.168</entry><entry namest="col7" nameend="col7" align="char" char=".">4.25</entry><entry namest="col8" nameend="col8" align="right">1</entry></row></tbody></tgroup><tgroup cols="8" colsep="0" rowsep="0"><colspec colnum="1" colname="col1" colwidth="19.68mm" /><colspec colnum="2" colname="col2" colwidth="19.68mm" /><colspec colnum="3" colname="col3" colwidth="19.68mm" /><colspec colnum="4" colname="col4" colwidth="19.68mm" /><colspec colnum="5" colname="col5" colwidth="19.68mm" /><colspec colnum="6" colname="col6" colwidth="19.68mm" /><colspec colnum="7" colname="col7" colwidth="19.68mm" /><colspec colnum="8" colname="col8" colwidth="19.68mm" /><tbody valign="top"><row><entry namest="col1" nameend="col8" align="justify">NOTE: The blocking values were obtained as described above with respect to sheets creped on both sides except that the sheets were placed together printed side to printed side, i.e., the sides to which the adhesive had been applied were adjacent and touching.</entry></row></tbody></tgroup></table></tables>

0015The hand feel, i.e, the tactile perception of the surface, of the sheet obtained using the creping adhesive of the present invention is typical of the hand feel of conventional products made by the patterned creping process.